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diff --git a/doc/rfc/rfc2246.txt b/doc/rfc/rfc2246.txt new file mode 100644 index 0000000..2e838cf --- /dev/null +++ b/doc/rfc/rfc2246.txt @@ -0,0 +1,4483 @@ + + + + + + +Network Working Group T. Dierks +Request for Comments: 2246 Certicom +Category: Standards Track C. Allen + Certicom + January 1999 + + + The TLS Protocol + Version 1.0 + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (1999). All Rights Reserved. + +Abstract + + This document specifies Version 1.0 of the Transport Layer Security + (TLS) protocol. The TLS protocol provides communications privacy over + the Internet. The protocol allows client/server applications to + communicate in a way that is designed to prevent eavesdropping, + tampering, or message forgery. + +Table of Contents + + 1. Introduction 3 + 2. Goals 4 + 3. Goals of this document 5 + 4. Presentation language 5 + 4.1. Basic block size 6 + 4.2. Miscellaneous 6 + 4.3. Vectors 6 + 4.4. Numbers 7 + 4.5. Enumerateds 7 + 4.6. Constructed types 8 + 4.6.1. Variants 9 + 4.7. Cryptographic attributes 10 + 4.8. Constants 11 + 5. HMAC and the pseudorandom function 11 + 6. The TLS Record Protocol 13 + 6.1. Connection states 14 + + + +Dierks & Allen Standards Track [Page 1] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + 6.2. Record layer 16 + 6.2.1. Fragmentation 16 + 6.2.2. Record compression and decompression 17 + 6.2.3. Record payload protection 18 + 6.2.3.1. Null or standard stream cipher 19 + 6.2.3.2. CBC block cipher 19 + 6.3. Key calculation 21 + 6.3.1. Export key generation example 22 + 7. The TLS Handshake Protocol 23 + 7.1. Change cipher spec protocol 24 + 7.2. Alert protocol 24 + 7.2.1. Closure alerts 25 + 7.2.2. Error alerts 26 + 7.3. Handshake Protocol overview 29 + 7.4. Handshake protocol 32 + 7.4.1. Hello messages 33 + 7.4.1.1. Hello request 33 + 7.4.1.2. Client hello 34 + 7.4.1.3. Server hello 36 + 7.4.2. Server certificate 37 + 7.4.3. Server key exchange message 39 + 7.4.4. Certificate request 41 + 7.4.5. Server hello done 42 + 7.4.6. Client certificate 43 + 7.4.7. Client key exchange message 43 + 7.4.7.1. RSA encrypted premaster secret message 44 + 7.4.7.2. Client Diffie-Hellman public value 45 + 7.4.8. Certificate verify 45 + 7.4.9. Finished 46 + 8. Cryptographic computations 47 + 8.1. Computing the master secret 47 + 8.1.1. RSA 48 + 8.1.2. Diffie-Hellman 48 + 9. Mandatory Cipher Suites 48 + 10. Application data protocol 48 + A. Protocol constant values 49 + A.1. Record layer 49 + A.2. Change cipher specs message 50 + A.3. Alert messages 50 + A.4. Handshake protocol 51 + A.4.1. Hello messages 51 + A.4.2. Server authentication and key exchange messages 52 + A.4.3. Client authentication and key exchange messages 53 + A.4.4. Handshake finalization message 54 + A.5. The CipherSuite 54 + A.6. The Security Parameters 56 + B. Glossary 57 + C. CipherSuite definitions 61 + + + +Dierks & Allen Standards Track [Page 2] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + D. Implementation Notes 64 + D.1. Temporary RSA keys 64 + D.2. Random Number Generation and Seeding 64 + D.3. Certificates and authentication 65 + D.4. CipherSuites 65 + E. Backward Compatibility With SSL 66 + E.1. Version 2 client hello 67 + E.2. Avoiding man-in-the-middle version rollback 68 + F. Security analysis 69 + F.1. Handshake protocol 69 + F.1.1. Authentication and key exchange 69 + F.1.1.1. Anonymous key exchange 69 + F.1.1.2. RSA key exchange and authentication 70 + F.1.1.3. Diffie-Hellman key exchange with authentication 71 + F.1.2. Version rollback attacks 71 + F.1.3. Detecting attacks against the handshake protocol 72 + F.1.4. Resuming sessions 72 + F.1.5. MD5 and SHA 72 + F.2. Protecting application data 72 + F.3. Final notes 73 + G. Patent Statement 74 + Security Considerations 75 + References 75 + Credits 77 + Comments 78 + Full Copyright Statement 80 + +1. Introduction + + The primary goal of the TLS Protocol is to provide privacy and data + integrity between two communicating applications. The protocol is + composed of two layers: the TLS Record Protocol and the TLS Handshake + Protocol. At the lowest level, layered on top of some reliable + transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The + TLS Record Protocol provides connection security that has two basic + properties: + + - The connection is private. Symmetric cryptography is used for + data encryption (e.g., DES [DES], RC4 [RC4], etc.) The keys for + this symmetric encryption are generated uniquely for each + connection and are based on a secret negotiated by another + protocol (such as the TLS Handshake Protocol). The Record + Protocol can also be used without encryption. + + - The connection is reliable. Message transport includes a message + integrity check using a keyed MAC. Secure hash functions (e.g., + SHA, MD5, etc.) are used for MAC computations. The Record + Protocol can operate without a MAC, but is generally only used in + + + +Dierks & Allen Standards Track [Page 3] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + this mode while another protocol is using the Record Protocol as + a transport for negotiating security parameters. + + The TLS Record Protocol is used for encapsulation of various higher + level protocols. One such encapsulated protocol, the TLS Handshake + Protocol, allows the server and client to authenticate each other and + to negotiate an encryption algorithm and cryptographic keys before + the application protocol transmits or receives its first byte of + data. The TLS Handshake Protocol provides connection security that + has three basic properties: + + - The peer's identity can be authenticated using asymmetric, or + public key, cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This + authentication can be made optional, but is generally required + for at least one of the peers. + + - The negotiation of a shared secret is secure: the negotiated + secret is unavailable to eavesdroppers, and for any authenticated + connection the secret cannot be obtained, even by an attacker who + can place himself in the middle of the connection. + + - The negotiation is reliable: no attacker can modify the + negotiation communication without being detected by the parties + to the communication. + + One advantage of TLS is that it is application protocol independent. + Higher level protocols can layer on top of the TLS Protocol + transparently. The TLS standard, however, does not specify how + protocols add security with TLS; the decisions on how to initiate TLS + handshaking and how to interpret the authentication certificates + exchanged are left up to the judgment of the designers and + implementors of protocols which run on top of TLS. + +2. Goals + + The goals of TLS Protocol, in order of their priority, are: + + 1. Cryptographic security: TLS should be used to establish a secure + connection between two parties. + + 2. Interoperability: Independent programmers should be able to + develop applications utilizing TLS that will then be able to + successfully exchange cryptographic parameters without knowledge + of one another's code. + + 3. Extensibility: TLS seeks to provide a framework into which new + public key and bulk encryption methods can be incorporated as + necessary. This will also accomplish two sub-goals: to prevent + + + +Dierks & Allen Standards Track [Page 4] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + the need to create a new protocol (and risking the introduction + of possible new weaknesses) and to avoid the need to implement an + entire new security library. + + 4. Relative efficiency: Cryptographic operations tend to be highly + CPU intensive, particularly public key operations. For this + reason, the TLS protocol has incorporated an optional session + caching scheme to reduce the number of connections that need to + be established from scratch. Additionally, care has been taken to + reduce network activity. + +3. Goals of this document + + This document and the TLS protocol itself are based on the SSL 3.0 + Protocol Specification as published by Netscape. The differences + between this protocol and SSL 3.0 are not dramatic, but they are + significant enough that TLS 1.0 and SSL 3.0 do not interoperate + (although TLS 1.0 does incorporate a mechanism by which a TLS + implementation can back down to SSL 3.0). This document is intended + primarily for readers who will be implementing the protocol and those + doing cryptographic analysis of it. The specification has been + written with this in mind, and it is intended to reflect the needs of + those two groups. For that reason, many of the algorithm-dependent + data structures and rules are included in the body of the text (as + opposed to in an appendix), providing easier access to them. + + This document is not intended to supply any details of service + definition nor interface definition, although it does cover select + areas of policy as they are required for the maintenance of solid + security. + +4. Presentation language + + This document deals with the formatting of data in an external + representation. The following very basic and somewhat casually + defined presentation syntax will be used. The syntax draws from + several sources in its structure. Although it resembles the + programming language "C" in its syntax and XDR [XDR] in both its + syntax and intent, it would be risky to draw too many parallels. The + purpose of this presentation language is to document TLS only, not to + have general application beyond that particular goal. + + + + + + + + + + +Dierks & Allen Standards Track [Page 5] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +4.1. Basic block size + + The representation of all data items is explicitly specified. The + basic data block size is one byte (i.e. 8 bits). Multiple byte data + items are concatenations of bytes, from left to right, from top to + bottom. From the bytestream a multi-byte item (a numeric in the + example) is formed (using C notation) by: + + value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | + ... | byte[n-1]; + + This byte ordering for multi-byte values is the commonplace network + byte order or big endian format. + +4.2. Miscellaneous + + Comments begin with "/*" and end with "*/". + + Optional components are denoted by enclosing them in "[[ ]]" double + brackets. + + Single byte entities containing uninterpreted data are of type + opaque. + +4.3. Vectors + + A vector (single dimensioned array) is a stream of homogeneous data + elements. The size of the vector may be specified at documentation + time or left unspecified until runtime. In either case the length + declares the number of bytes, not the number of elements, in the + vector. The syntax for specifying a new type T' that is a fixed + length vector of type T is + + T T'[n]; + + Here T' occupies n bytes in the data stream, where n is a multiple of + the size of T. The length of the vector is not included in the + encoded stream. + + In the following example, Datum is defined to be three consecutive + bytes that the protocol does not interpret, while Data is three + consecutive Datum, consuming a total of nine bytes. + + opaque Datum[3]; /* three uninterpreted bytes */ + Datum Data[9]; /* 3 consecutive 3 byte vectors */ + + + + + + +Dierks & Allen Standards Track [Page 6] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Variable length vectors are defined by specifying a subrange of legal + lengths, inclusively, using the notation <floor..ceiling>. When + encoded, the actual length precedes the vector's contents in the byte + stream. The length will be in the form of a number consuming as many + bytes as required to hold the vector's specified maximum (ceiling) + length. A variable length vector with an actual length field of zero + is referred to as an empty vector. + + T T'<floor..ceiling>; + + In the following example, mandatory is a vector that must contain + between 300 and 400 bytes of type opaque. It can never be empty. The + actual length field consumes two bytes, a uint16, sufficient to + represent the value 400 (see Section 4.4). On the other hand, longer + can represent up to 800 bytes of data, or 400 uint16 elements, and it + may be empty. Its encoding will include a two byte actual length + field prepended to the vector. The length of an encoded vector must + be an even multiple of the length of a single element (for example, a + 17 byte vector of uint16 would be illegal). + + opaque mandatory<300..400>; + /* length field is 2 bytes, cannot be empty */ + uint16 longer<0..800>; + /* zero to 400 16-bit unsigned integers */ + +4.4. Numbers + + The basic numeric data type is an unsigned byte (uint8). All larger + numeric data types are formed from fixed length series of bytes + concatenated as described in Section 4.1 and are also unsigned. The + following numeric types are predefined. + + uint8 uint16[2]; + uint8 uint24[3]; + uint8 uint32[4]; + uint8 uint64[8]; + + All values, here and elsewhere in the specification, are stored in + "network" or "big-endian" order; the uint32 represented by the hex + bytes 01 02 03 04 is equivalent to the decimal value 16909060. + +4.5. Enumerateds + + An additional sparse data type is available called enum. A field of + type enum can only assume the values declared in the definition. + Each definition is a different type. Only enumerateds of the same + type may be assigned or compared. Every element of an enumerated must + + + + +Dierks & Allen Standards Track [Page 7] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + be assigned a value, as demonstrated in the following example. Since + the elements of the enumerated are not ordered, they can be assigned + any unique value, in any order. + + enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te; + + Enumerateds occupy as much space in the byte stream as would its + maximal defined ordinal value. The following definition would cause + one byte to be used to carry fields of type Color. + + enum { red(3), blue(5), white(7) } Color; + + One may optionally specify a value without its associated tag to + force the width definition without defining a superfluous element. + In the following example, Taste will consume two bytes in the data + stream but can only assume the values 1, 2 or 4. + + enum { sweet(1), sour(2), bitter(4), (32000) } Taste; + + The names of the elements of an enumeration are scoped within the + defined type. In the first example, a fully qualified reference to + the second element of the enumeration would be Color.blue. Such + qualification is not required if the target of the assignment is well + specified. + + Color color = Color.blue; /* overspecified, legal */ + Color color = blue; /* correct, type implicit */ + + For enumerateds that are never converted to external representation, + the numerical information may be omitted. + + enum { low, medium, high } Amount; + +4.6. Constructed types + + Structure types may be constructed from primitive types for + convenience. Each specification declares a new, unique type. The + syntax for definition is much like that of C. + + struct { + T1 f1; + T2 f2; + ... + Tn fn; + } [[T]]; + + + + + + +Dierks & Allen Standards Track [Page 8] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + The fields within a structure may be qualified using the type's name + using a syntax much like that available for enumerateds. For example, + T.f2 refers to the second field of the previous declaration. + Structure definitions may be embedded. + +4.6.1. Variants + + Defined structures may have variants based on some knowledge that is + available within the environment. The selector must be an enumerated + type that defines the possible variants the structure defines. There + must be a case arm for every element of the enumeration declared in + the select. The body of the variant structure may be given a label + for reference. The mechanism by which the variant is selected at + runtime is not prescribed by the presentation language. + + struct { + T1 f1; + T2 f2; + .... + Tn fn; + select (E) { + case e1: Te1; + case e2: Te2; + .... + case en: Ten; + } [[fv]]; + } [[Tv]]; + + For example: + + enum { apple, orange } VariantTag; + struct { + uint16 number; + opaque string<0..10>; /* variable length */ + } V1; + struct { + uint32 number; + opaque string[10]; /* fixed length */ + } V2; + struct { + select (VariantTag) { /* value of selector is implicit */ + case apple: V1; /* VariantBody, tag = apple */ + case orange: V2; /* VariantBody, tag = orange */ + } variant_body; /* optional label on variant */ + } VariantRecord; + + Variant structures may be qualified (narrowed) by specifying a value + for the selector prior to the type. For example, a + + + +Dierks & Allen Standards Track [Page 9] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + orange VariantRecord + + is a narrowed type of a VariantRecord containing a variant_body of + type V2. + +4.7. Cryptographic attributes + + The four cryptographic operations digital signing, stream cipher + encryption, block cipher encryption, and public key encryption are + designated digitally-signed, stream-ciphered, block-ciphered, and + public-key-encrypted, respectively. A field's cryptographic + processing is specified by prepending an appropriate key word + designation before the field's type specification. Cryptographic keys + are implied by the current session state (see Section 6.1). + + In digital signing, one-way hash functions are used as input for a + signing algorithm. A digitally-signed element is encoded as an opaque + vector <0..2^16-1>, where the length is specified by the signing + algorithm and key. + + In RSA signing, a 36-byte structure of two hashes (one SHA and one + MD5) is signed (encrypted with the private key). It is encoded with + PKCS #1 block type 0 or type 1 as described in [PKCS1]. + + In DSS, the 20 bytes of the SHA hash are run directly through the + Digital Signing Algorithm with no additional hashing. This produces + two values, r and s. The DSS signature is an opaque vector, as above, + the contents of which are the DER encoding of: + + Dss-Sig-Value ::= SEQUENCE { + r INTEGER, + s INTEGER + } + + In stream cipher encryption, the plaintext is exclusive-ORed with an + identical amount of output generated from a cryptographically-secure + keyed pseudorandom number generator. + + In block cipher encryption, every block of plaintext encrypts to a + block of ciphertext. All block cipher encryption is done in CBC + (Cipher Block Chaining) mode, and all items which are block-ciphered + will be an exact multiple of the cipher block length. + + In public key encryption, a public key algorithm is used to encrypt + data in such a way that it can be decrypted only with the matching + private key. A public-key-encrypted element is encoded as an opaque + vector <0..2^16-1>, where the length is specified by the signing + algorithm and key. + + + +Dierks & Allen Standards Track [Page 10] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + An RSA encrypted value is encoded with PKCS #1 block type 2 as + described in [PKCS1]. + + In the following example: + + stream-ciphered struct { + uint8 field1; + uint8 field2; + digitally-signed opaque hash[20]; + } UserType; + + The contents of hash are used as input for the signing algorithm, + then the entire structure is encrypted with a stream cipher. The + length of this structure, in bytes would be equal to 2 bytes for + field1 and field2, plus two bytes for the length of the signature, + plus the length of the output of the signing algorithm. This is known + due to the fact that the algorithm and key used for the signing are + known prior to encoding or decoding this structure. + +4.8. Constants + + Typed constants can be defined for purposes of specification by + declaring a symbol of the desired type and assigning values to it. + Under-specified types (opaque, variable length vectors, and + structures that contain opaque) cannot be assigned values. No fields + of a multi-element structure or vector may be elided. + + For example, + + struct { + uint8 f1; + uint8 f2; + } Example1; + + Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */ + +5. HMAC and the pseudorandom function + + A number of operations in the TLS record and handshake layer required + a keyed MAC; this is a secure digest of some data protected by a + secret. Forging the MAC is infeasible without knowledge of the MAC + secret. The construction we use for this operation is known as HMAC, + described in [HMAC]. + + HMAC can be used with a variety of different hash algorithms. TLS + uses it in the handshake with two different algorithms: MD5 and SHA- + 1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret, + + + + +Dierks & Allen Standards Track [Page 11] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + data). Additional hash algorithms can be defined by cipher suites and + used to protect record data, but MD5 and SHA-1 are hard coded into + the description of the handshaking for this version of the protocol. + + In addition, a construction is required to do expansion of secrets + into blocks of data for the purposes of key generation or validation. + This pseudo-random function (PRF) takes as input a secret, a seed, + and an identifying label and produces an output of arbitrary length. + + In order to make the PRF as secure as possible, it uses two hash + algorithms in a way which should guarantee its security if either + algorithm remains secure. + + First, we define a data expansion function, P_hash(secret, data) + which uses a single hash function to expand a secret and seed into an + arbitrary quantity of output: + + P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) + + HMAC_hash(secret, A(2) + seed) + + HMAC_hash(secret, A(3) + seed) + ... + + Where + indicates concatenation. + + A() is defined as: + A(0) = seed + A(i) = HMAC_hash(secret, A(i-1)) + + P_hash can be iterated as many times as is necessary to produce the + required quantity of data. For example, if P_SHA-1 was being used to + create 64 bytes of data, it would have to be iterated 4 times + (through A(4)), creating 80 bytes of output data; the last 16 bytes + of the final iteration would then be discarded, leaving 64 bytes of + output data. + + TLS's PRF is created by splitting the secret into two halves and + using one half to generate data with P_MD5 and the other half to + generate data with P_SHA-1, then exclusive-or'ing the outputs of + these two expansion functions together. + + S1 and S2 are the two halves of the secret and each is the same + length. S1 is taken from the first half of the secret, S2 from the + second half. Their length is created by rounding up the length of the + overall secret divided by two; thus, if the original secret is an odd + number of bytes long, the last byte of S1 will be the same as the + first byte of S2. + + L_S = length in bytes of secret; + L_S1 = L_S2 = ceil(L_S / 2); + + + +Dierks & Allen Standards Track [Page 12] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + The secret is partitioned into two halves (with the possibility of + one shared byte) as described above, S1 taking the first L_S1 bytes + and S2 the last L_S2 bytes. + + The PRF is then defined as the result of mixing the two pseudorandom + streams by exclusive-or'ing them together. + + PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR + P_SHA-1(S2, label + seed); + + The label is an ASCII string. It should be included in the exact form + it is given without a length byte or trailing null character. For + example, the label "slithy toves" would be processed by hashing the + following bytes: + + 73 6C 69 74 68 79 20 74 6F 76 65 73 + + Note that because MD5 produces 16 byte outputs and SHA-1 produces 20 + byte outputs, the boundaries of their internal iterations will not be + aligned; to generate a 80 byte output will involve P_MD5 being + iterated through A(5), while P_SHA-1 will only iterate through A(4). + +6. The TLS Record Protocol + + The TLS Record Protocol is a layered protocol. At each layer, + messages may include fields for length, description, and content. + The Record Protocol takes messages to be transmitted, fragments the + data into manageable blocks, optionally compresses the data, applies + a MAC, encrypts, and transmits the result. Received data is + decrypted, verified, decompressed, and reassembled, then delivered to + higher level clients. + + Four record protocol clients are described in this document: the + handshake protocol, the alert protocol, the change cipher spec + protocol, and the application data protocol. In order to allow + extension of the TLS protocol, additional record types can be + supported by the record protocol. Any new record types should + allocate type values immediately beyond the ContentType values for + the four record types described here (see Appendix A.2). If a TLS + implementation receives a record type it does not understand, it + should just ignore it. Any protocol designed for use over TLS must be + carefully designed to deal with all possible attacks against it. + Note that because the type and length of a record are not protected + by encryption, care should be take to minimize the value of traffic + analysis of these values. + + + + + + +Dierks & Allen Standards Track [Page 13] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +6.1. Connection states + + A TLS connection state is the operating environment of the TLS Record + Protocol. It specifies a compression algorithm, encryption algorithm, + and MAC algorithm. In addition, the parameters for these algorithms + are known: the MAC secret and the bulk encryption keys and IVs for + the connection in both the read and the write directions. Logically, + there are always four connection states outstanding: the current read + and write states, and the pending read and write states. All records + are processed under the current read and write states. The security + parameters for the pending states can be set by the TLS Handshake + Protocol, and the Handshake Protocol can selectively make either of + the pending states current, in which case the appropriate current + state is disposed of and replaced with the pending state; the pending + state is then reinitialized to an empty state. It is illegal to make + a state which has not been initialized with security parameters a + current state. The initial current state always specifies that no + encryption, compression, or MAC will be used. + + The security parameters for a TLS Connection read and write state are + set by providing the following values: + + connection end + Whether this entity is considered the "client" or the "server" in + this connection. + + bulk encryption algorithm + An algorithm to be used for bulk encryption. This specification + includes the key size of this algorithm, how much of that key is + secret, whether it is a block or stream cipher, the block size of + the cipher (if appropriate), and whether it is considered an + "export" cipher. + + MAC algorithm + An algorithm to be used for message authentication. This + specification includes the size of the hash which is returned by + the MAC algorithm. + + compression algorithm + An algorithm to be used for data compression. This specification + must include all information the algorithm requires to do + compression. + + master secret + A 48 byte secret shared between the two peers in the connection. + + client random + A 32 byte value provided by the client. + + + +Dierks & Allen Standards Track [Page 14] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + server random + A 32 byte value provided by the server. + + These parameters are defined in the presentation language as: + + enum { server, client } ConnectionEnd; + + enum { null, rc4, rc2, des, 3des, des40 } BulkCipherAlgorithm; + + enum { stream, block } CipherType; + + enum { true, false } IsExportable; + + enum { null, md5, sha } MACAlgorithm; + + enum { null(0), (255) } CompressionMethod; + + /* The algorithms specified in CompressionMethod, + BulkCipherAlgorithm, and MACAlgorithm may be added to. */ + + struct { + ConnectionEnd entity; + BulkCipherAlgorithm bulk_cipher_algorithm; + CipherType cipher_type; + uint8 key_size; + uint8 key_material_length; + IsExportable is_exportable; + MACAlgorithm mac_algorithm; + uint8 hash_size; + CompressionMethod compression_algorithm; + opaque master_secret[48]; + opaque client_random[32]; + opaque server_random[32]; + } SecurityParameters; + + The record layer will use the security parameters to generate the + following six items: + + client write MAC secret + server write MAC secret + client write key + server write key + client write IV (for block ciphers only) + server write IV (for block ciphers only) + + The client write parameters are used by the server when receiving and + processing records and vice-versa. The algorithm used for generating + these items from the security parameters is described in section 6.3. + + + +Dierks & Allen Standards Track [Page 15] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Once the security parameters have been set and the keys have been + generated, the connection states can be instantiated by making them + the current states. These current states must be updated for each + record processed. Each connection state includes the following + elements: + + compression state + The current state of the compression algorithm. + + cipher state + The current state of the encryption algorithm. This will consist + of the scheduled key for that connection. In addition, for block + ciphers running in CBC mode (the only mode specified for TLS), + this will initially contain the IV for that connection state and + be updated to contain the ciphertext of the last block encrypted + or decrypted as records are processed. For stream ciphers, this + will contain whatever the necessary state information is to allow + the stream to continue to encrypt or decrypt data. + + MAC secret + The MAC secret for this connection as generated above. + + sequence number + Each connection state contains a sequence number, which is + maintained separately for read and write states. The sequence + number must be set to zero whenever a connection state is made + the active state. Sequence numbers are of type uint64 and may not + exceed 2^64-1. A sequence number is incremented after each + record: specifically, the first record which is transmitted under + a particular connection state should use sequence number 0. + +6.2. Record layer + + The TLS Record Layer receives uninterpreted data from higher layers + in non-empty blocks of arbitrary size. + +6.2.1. Fragmentation + + The record layer fragments information blocks into TLSPlaintext + records carrying data in chunks of 2^14 bytes or less. Client message + boundaries are not preserved in the record layer (i.e., multiple + client messages of the same ContentType may be coalesced into a + single TLSPlaintext record, or a single message may be fragmented + across several records). + + struct { + uint8 major, minor; + } ProtocolVersion; + + + +Dierks & Allen Standards Track [Page 16] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + enum { + change_cipher_spec(20), alert(21), handshake(22), + application_data(23), (255) + } ContentType; + + struct { + ContentType type; + ProtocolVersion version; + uint16 length; + opaque fragment[TLSPlaintext.length]; + } TLSPlaintext; + + type + The higher level protocol used to process the enclosed fragment. + + version + The version of the protocol being employed. This document + describes TLS Version 1.0, which uses the version { 3, 1 }. The + version value 3.1 is historical: TLS version 1.0 is a minor + modification to the SSL 3.0 protocol, which bears the version + value 3.0. (See Appendix A.1). + + length + The length (in bytes) of the following TLSPlaintext.fragment. + The length should not exceed 2^14. + + fragment + The application data. This data is transparent and treated as an + independent block to be dealt with by the higher level protocol + specified by the type field. + + Note: Data of different TLS Record layer content types may be + interleaved. Application data is generally of lower precedence + for transmission than other content types. + +6.2.2. Record compression and decompression + + All records are compressed using the compression algorithm defined in + the current session state. There is always an active compression + algorithm; however, initially it is defined as + CompressionMethod.null. The compression algorithm translates a + TLSPlaintext structure into a TLSCompressed structure. Compression + functions are initialized with default state information whenever a + connection state is made active. + + + + + + + +Dierks & Allen Standards Track [Page 17] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Compression must be lossless and may not increase the content length + by more than 1024 bytes. If the decompression function encounters a + TLSCompressed.fragment that would decompress to a length in excess of + 2^14 bytes, it should report a fatal decompression failure error. + + struct { + ContentType type; /* same as TLSPlaintext.type */ + ProtocolVersion version;/* same as TLSPlaintext.version */ + uint16 length; + opaque fragment[TLSCompressed.length]; + } TLSCompressed; + + length + The length (in bytes) of the following TLSCompressed.fragment. + The length should not exceed 2^14 + 1024. + + fragment + The compressed form of TLSPlaintext.fragment. + + Note: A CompressionMethod.null operation is an identity operation; no + fields are altered. + + Implementation note: + Decompression functions are responsible for ensuring that + messages cannot cause internal buffer overflows. + +6.2.3. Record payload protection + + The encryption and MAC functions translate a TLSCompressed structure + into a TLSCiphertext. The decryption functions reverse the process. + The MAC of the record also includes a sequence number so that + missing, extra or repeated messages are detectable. + + struct { + ContentType type; + ProtocolVersion version; + uint16 length; + select (CipherSpec.cipher_type) { + case stream: GenericStreamCipher; + case block: GenericBlockCipher; + } fragment; + } TLSCiphertext; + + type + The type field is identical to TLSCompressed.type. + + version + The version field is identical to TLSCompressed.version. + + + +Dierks & Allen Standards Track [Page 18] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + length + The length (in bytes) of the following TLSCiphertext.fragment. + The length may not exceed 2^14 + 2048. + + fragment + The encrypted form of TLSCompressed.fragment, with the MAC. + +6.2.3.1. Null or standard stream cipher + + Stream ciphers (including BulkCipherAlgorithm.null - see Appendix + A.6) convert TLSCompressed.fragment structures to and from stream + TLSCiphertext.fragment structures. + + stream-ciphered struct { + opaque content[TLSCompressed.length]; + opaque MAC[CipherSpec.hash_size]; + } GenericStreamCipher; + + The MAC is generated as: + + HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type + + TLSCompressed.version + TLSCompressed.length + + TLSCompressed.fragment)); + + where "+" denotes concatenation. + + seq_num + The sequence number for this record. + + hash + The hashing algorithm specified by + SecurityParameters.mac_algorithm. + + Note that the MAC is computed before encryption. The stream cipher + encrypts the entire block, including the MAC. For stream ciphers that + do not use a synchronization vector (such as RC4), the stream cipher + state from the end of one record is simply used on the subsequent + packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL, encryption + consists of the identity operation (i.e., the data is not encrypted + and the MAC size is zero implying that no MAC is used). + TLSCiphertext.length is TLSCompressed.length plus + CipherSpec.hash_size. + +6.2.3.2. CBC block cipher + + For block ciphers (such as RC2 or DES), the encryption and MAC + functions convert TLSCompressed.fragment structures to and from block + TLSCiphertext.fragment structures. + + + +Dierks & Allen Standards Track [Page 19] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + block-ciphered struct { + opaque content[TLSCompressed.length]; + opaque MAC[CipherSpec.hash_size]; + uint8 padding[GenericBlockCipher.padding_length]; + uint8 padding_length; + } GenericBlockCipher; + + The MAC is generated as described in Section 6.2.3.1. + + padding + Padding that is added to force the length of the plaintext to be + an integral multiple of the block cipher's block length. The + padding may be any length up to 255 bytes long, as long as it + results in the TLSCiphertext.length being an integral multiple of + the block length. Lengths longer than necessary might be + desirable to frustrate attacks on a protocol based on analysis of + the lengths of exchanged messages. Each uint8 in the padding data + vector must be filled with the padding length value. + + padding_length + The padding length should be such that the total size of the + GenericBlockCipher structure is a multiple of the cipher's block + length. Legal values range from zero to 255, inclusive. This + length specifies the length of the padding field exclusive of the + padding_length field itself. + + The encrypted data length (TLSCiphertext.length) is one more than the + sum of TLSCompressed.length, CipherSpec.hash_size, and + padding_length. + + Example: If the block length is 8 bytes, the content length + (TLSCompressed.length) is 61 bytes, and the MAC length is 20 + bytes, the length before padding is 82 bytes. Thus, the + padding length modulo 8 must be equal to 6 in order to make + the total length an even multiple of 8 bytes (the block + length). The padding length can be 6, 14, 22, and so on, + through 254. If the padding length were the minimum necessary, + 6, the padding would be 6 bytes, each containing the value 6. + Thus, the last 8 octets of the GenericBlockCipher before block + encryption would be xx 06 06 06 06 06 06 06, where xx is the + last octet of the MAC. + + Note: With block ciphers in CBC mode (Cipher Block Chaining) the + initialization vector (IV) for the first record is generated with + the other keys and secrets when the security parameters are set. + The IV for subsequent records is the last ciphertext block from + the previous record. + + + + +Dierks & Allen Standards Track [Page 20] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +6.3. Key calculation + + The Record Protocol requires an algorithm to generate keys, IVs, and + MAC secrets from the security parameters provided by the handshake + protocol. + + The master secret is hashed into a sequence of secure bytes, which + are assigned to the MAC secrets, keys, and non-export IVs required by + the current connection state (see Appendix A.6). CipherSpecs require + a client write MAC secret, a server write MAC secret, a client write + key, a server write key, a client write IV, and a server write IV, + which are generated from the master secret in that order. Unused + values are empty. + + When generating keys and MAC secrets, the master secret is used as an + entropy source, and the random values provide unencrypted salt + material and IVs for exportable ciphers. + + To generate the key material, compute + + key_block = PRF(SecurityParameters.master_secret, + "key expansion", + SecurityParameters.server_random + + SecurityParameters.client_random); + + until enough output has been generated. Then the key_block is + partitioned as follows: + + client_write_MAC_secret[SecurityParameters.hash_size] + server_write_MAC_secret[SecurityParameters.hash_size] + client_write_key[SecurityParameters.key_material_length] + server_write_key[SecurityParameters.key_material_length] + client_write_IV[SecurityParameters.IV_size] + server_write_IV[SecurityParameters.IV_size] + + The client_write_IV and server_write_IV are only generated for non- + export block ciphers. For exportable block ciphers, the + initialization vectors are generated later, as described below. Any + extra key_block material is discarded. + + Implementation note: + The cipher spec which is defined in this document which requires + the most material is 3DES_EDE_CBC_SHA: it requires 2 x 24 byte + keys, 2 x 20 byte MAC secrets, and 2 x 8 byte IVs, for a total of + 104 bytes of key material. + + + + + + +Dierks & Allen Standards Track [Page 21] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Exportable encryption algorithms (for which CipherSpec.is_exportable + is true) require additional processing as follows to derive their + final write keys: + + final_client_write_key = + PRF(SecurityParameters.client_write_key, + "client write key", + SecurityParameters.client_random + + SecurityParameters.server_random); + final_server_write_key = + PRF(SecurityParameters.server_write_key, + "server write key", + SecurityParameters.client_random + + SecurityParameters.server_random); + + Exportable encryption algorithms derive their IVs solely from the + random values from the hello messages: + + iv_block = PRF("", "IV block", SecurityParameters.client_random + + SecurityParameters.server_random); + + The iv_block is partitioned into two initialization vectors as the + key_block was above: + + client_write_IV[SecurityParameters.IV_size] + server_write_IV[SecurityParameters.IV_size] + + Note that the PRF is used without a secret in this case: this just + means that the secret has a length of zero bytes and contributes + nothing to the hashing in the PRF. + +6.3.1. Export key generation example + + TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 requires five random bytes for + each of the two encryption keys and 16 bytes for each of the MAC + keys, for a total of 42 bytes of key material. The PRF output is + stored in the key_block. The key_block is partitioned, and the write + keys are salted because this is an exportable encryption algorithm. + + key_block = PRF(master_secret, + "key expansion", + server_random + + client_random)[0..41] + client_write_MAC_secret = key_block[0..15] + server_write_MAC_secret = key_block[16..31] + client_write_key = key_block[32..36] + server_write_key = key_block[37..41] + + + + +Dierks & Allen Standards Track [Page 22] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + final_client_write_key = PRF(client_write_key, + "client write key", + client_random + + server_random)[0..15] + final_server_write_key = PRF(server_write_key, + "server write key", + client_random + + server_random)[0..15] + + iv_block = PRF("", "IV block", client_random + + server_random)[0..15] + client_write_IV = iv_block[0..7] + server_write_IV = iv_block[8..15] + +7. The TLS Handshake Protocol + + The TLS Handshake Protocol consists of a suite of three sub-protocols + which are used to allow peers to agree upon security parameters for + the record layer, authenticate themselves, instantiate negotiated + security parameters, and report error conditions to each other. + + The Handshake Protocol is responsible for negotiating a session, + which consists of the following items: + + session identifier + An arbitrary byte sequence chosen by the server to identify an + active or resumable session state. + + peer certificate + X509v3 [X509] certificate of the peer. This element of the state + may be null. + + compression method + The algorithm used to compress data prior to encryption. + + cipher spec + Specifies the bulk data encryption algorithm (such as null, DES, + etc.) and a MAC algorithm (such as MD5 or SHA). It also defines + cryptographic attributes such as the hash_size. (See Appendix A.6 + for formal definition) + + master secret + 48-byte secret shared between the client and server. + + is resumable + A flag indicating whether the session can be used to initiate new + connections. + + + + +Dierks & Allen Standards Track [Page 23] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + These items are then used to create security parameters for use by + the Record Layer when protecting application data. Many connections + can be instantiated using the same session through the resumption + feature of the TLS Handshake Protocol. + +7.1. Change cipher spec protocol + + The change cipher spec protocol exists to signal transitions in + ciphering strategies. The protocol consists of a single message, + which is encrypted and compressed under the current (not the pending) + connection state. The message consists of a single byte of value 1. + + struct { + enum { change_cipher_spec(1), (255) } type; + } ChangeCipherSpec; + + The change cipher spec message is sent by both the client and server + to notify the receiving party that subsequent records will be + protected under the newly negotiated CipherSpec and keys. Reception + of this message causes the receiver to instruct the Record Layer to + immediately copy the read pending state into the read current state. + Immediately after sending this message, the sender should instruct + the record layer to make the write pending state the write active + state. (See section 6.1.) The change cipher spec message is sent + during the handshake after the security parameters have been agreed + upon, but before the verifying finished message is sent (see section + 7.4.9). + +7.2. Alert protocol + + One of the content types supported by the TLS Record layer is the + alert type. Alert messages convey the severity of the message and a + description of the alert. Alert messages with a level of fatal result + in the immediate termination of the connection. In this case, other + connections corresponding to the session may continue, but the + session identifier must be invalidated, preventing the failed session + from being used to establish new connections. Like other messages, + alert messages are encrypted and compressed, as specified by the + current connection state. + + enum { warning(1), fatal(2), (255) } AlertLevel; + + enum { + close_notify(0), + unexpected_message(10), + bad_record_mac(20), + decryption_failed(21), + record_overflow(22), + + + +Dierks & Allen Standards Track [Page 24] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + decompression_failure(30), + handshake_failure(40), + bad_certificate(42), + unsupported_certificate(43), + certificate_revoked(44), + certificate_expired(45), + certificate_unknown(46), + illegal_parameter(47), + unknown_ca(48), + access_denied(49), + decode_error(50), + decrypt_error(51), + export_restriction(60), + protocol_version(70), + insufficient_security(71), + internal_error(80), + user_canceled(90), + no_renegotiation(100), + (255) + } AlertDescription; + + struct { + AlertLevel level; + AlertDescription description; + } Alert; + +7.2.1. Closure alerts + + The client and the server must share knowledge that the connection is + ending in order to avoid a truncation attack. Either party may + initiate the exchange of closing messages. + + close_notify + This message notifies the recipient that the sender will not send + any more messages on this connection. The session becomes + unresumable if any connection is terminated without proper + close_notify messages with level equal to warning. + + Either party may initiate a close by sending a close_notify alert. + Any data received after a closure alert is ignored. + + Each party is required to send a close_notify alert before closing + the write side of the connection. It is required that the other party + respond with a close_notify alert of its own and close down the + connection immediately, discarding any pending writes. It is not + required for the initiator of the close to wait for the responding + close_notify alert before closing the read side of the connection. + + + + +Dierks & Allen Standards Track [Page 25] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + If the application protocol using TLS provides that any data may be + carried over the underlying transport after the TLS connection is + closed, the TLS implementation must receive the responding + close_notify alert before indicating to the application layer that + the TLS connection has ended. If the application protocol will not + transfer any additional data, but will only close the underlying + transport connection, then the implementation may choose to close the + transport without waiting for the responding close_notify. No part of + this standard should be taken to dictate the manner in which a usage + profile for TLS manages its data transport, including when + connections are opened or closed. + + NB: It is assumed that closing a connection reliably delivers + pending data before destroying the transport. + +7.2.2. Error alerts + + Error handling in the TLS Handshake protocol is very simple. When an + error is detected, the detecting party sends a message to the other + party. Upon transmission or receipt of an fatal alert message, both + parties immediately close the connection. Servers and clients are + required to forget any session-identifiers, keys, and secrets + associated with a failed connection. The following error alerts are + defined: + + unexpected_message + An inappropriate message was received. This alert is always fatal + and should never be observed in communication between proper + implementations. + + bad_record_mac + This alert is returned if a record is received with an incorrect + MAC. This message is always fatal. + + decryption_failed + A TLSCiphertext decrypted in an invalid way: either it wasn`t an + even multiple of the block length or its padding values, when + checked, weren`t correct. This message is always fatal. + + record_overflow + A TLSCiphertext record was received which had a length more than + 2^14+2048 bytes, or a record decrypted to a TLSCompressed record + with more than 2^14+1024 bytes. This message is always fatal. + + decompression_failure + The decompression function received improper input (e.g. data + that would expand to excessive length). This message is always + fatal. + + + +Dierks & Allen Standards Track [Page 26] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + handshake_failure + Reception of a handshake_failure alert message indicates that the + sender was unable to negotiate an acceptable set of security + parameters given the options available. This is a fatal error. + + bad_certificate + A certificate was corrupt, contained signatures that did not + verify correctly, etc. + + unsupported_certificate + A certificate was of an unsupported type. + + certificate_revoked + A certificate was revoked by its signer. + + certificate_expired + A certificate has expired or is not currently valid. + + certificate_unknown + Some other (unspecified) issue arose in processing the + certificate, rendering it unacceptable. + + illegal_parameter + A field in the handshake was out of range or inconsistent with + other fields. This is always fatal. + + unknown_ca + A valid certificate chain or partial chain was received, but the + certificate was not accepted because the CA certificate could not + be located or couldn`t be matched with a known, trusted CA. This + message is always fatal. + + access_denied + A valid certificate was received, but when access control was + applied, the sender decided not to proceed with negotiation. + This message is always fatal. + + decode_error + A message could not be decoded because some field was out of the + specified range or the length of the message was incorrect. This + message is always fatal. + + decrypt_error + A handshake cryptographic operation failed, including being + unable to correctly verify a signature, decrypt a key exchange, + or validate a finished message. + + + + + +Dierks & Allen Standards Track [Page 27] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + export_restriction + A negotiation not in compliance with export restrictions was + detected; for example, attempting to transfer a 1024 bit + ephemeral RSA key for the RSA_EXPORT handshake method. This + message is always fatal. + + protocol_version + The protocol version the client has attempted to negotiate is + recognized, but not supported. (For example, old protocol + versions might be avoided for security reasons). This message is + always fatal. + + insufficient_security + Returned instead of handshake_failure when a negotiation has + failed specifically because the server requires ciphers more + secure than those supported by the client. This message is always + fatal. + + internal_error + An internal error unrelated to the peer or the correctness of the + protocol makes it impossible to continue (such as a memory + allocation failure). This message is always fatal. + + user_canceled + This handshake is being canceled for some reason unrelated to a + protocol failure. If the user cancels an operation after the + handshake is complete, just closing the connection by sending a + close_notify is more appropriate. This alert should be followed + by a close_notify. This message is generally a warning. + + no_renegotiation + Sent by the client in response to a hello request or by the + server in response to a client hello after initial handshaking. + Either of these would normally lead to renegotiation; when that + is not appropriate, the recipient should respond with this alert; + at that point, the original requester can decide whether to + proceed with the connection. One case where this would be + appropriate would be where a server has spawned a process to + satisfy a request; the process might receive security parameters + (key length, authentication, etc.) at startup and it might be + difficult to communicate changes to these parameters after that + point. This message is always a warning. + + For all errors where an alert level is not explicitly specified, the + sending party may determine at its discretion whether this is a fatal + error or not; if an alert with a level of warning is received, the + + + + + +Dierks & Allen Standards Track [Page 28] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + receiving party may decide at its discretion whether to treat this as + a fatal error or not. However, all messages which are transmitted + with a level of fatal must be treated as fatal messages. + +7.3. Handshake Protocol overview + + The cryptographic parameters of the session state are produced by the + TLS Handshake Protocol, which operates on top of the TLS Record + Layer. When a TLS client and server first start communicating, they + agree on a protocol version, select cryptographic algorithms, + optionally authenticate each other, and use public-key encryption + techniques to generate shared secrets. + + The TLS Handshake Protocol involves the following steps: + + - Exchange hello messages to agree on algorithms, exchange random + values, and check for session resumption. + + - Exchange the necessary cryptographic parameters to allow the + client and server to agree on a premaster secret. + + - Exchange certificates and cryptographic information to allow the + client and server to authenticate themselves. + + - Generate a master secret from the premaster secret and exchanged + random values. + + - Provide security parameters to the record layer. + + - Allow the client and server to verify that their peer has + calculated the same security parameters and that the handshake + occurred without tampering by an attacker. + + Note that higher layers should not be overly reliant on TLS always + negotiating the strongest possible connection between two peers: + there are a number of ways a man in the middle attacker can attempt + to make two entities drop down to the least secure method they + support. The protocol has been designed to minimize this risk, but + there are still attacks available: for example, an attacker could + block access to the port a secure service runs on, or attempt to get + the peers to negotiate an unauthenticated connection. The fundamental + rule is that higher levels must be cognizant of what their security + requirements are and never transmit information over a channel less + secure than what they require. The TLS protocol is secure, in that + any cipher suite offers its promised level of security: if you + negotiate 3DES with a 1024 bit RSA key exchange with a host whose + certificate you have verified, you can expect to be that secure. + + + + +Dierks & Allen Standards Track [Page 29] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + However, you should never send data over a link encrypted with 40 bit + security unless you feel that data is worth no more than the effort + required to break that encryption. + + These goals are achieved by the handshake protocol, which can be + summarized as follows: The client sends a client hello message to + which the server must respond with a server hello message, or else a + fatal error will occur and the connection will fail. The client hello + and server hello are used to establish security enhancement + capabilities between client and server. The client hello and server + hello establish the following attributes: Protocol Version, Session + ID, Cipher Suite, and Compression Method. Additionally, two random + values are generated and exchanged: ClientHello.random and + ServerHello.random. + + The actual key exchange uses up to four messages: the server + certificate, the server key exchange, the client certificate, and the + client key exchange. New key exchange methods can be created by + specifying a format for these messages and defining the use of the + messages to allow the client and server to agree upon a shared + secret. This secret should be quite long; currently defined key + exchange methods exchange secrets which range from 48 to 128 bytes in + length. + + Following the hello messages, the server will send its certificate, + if it is to be authenticated. Additionally, a server key exchange + message may be sent, if it is required (e.g. if their server has no + certificate, or if its certificate is for signing only). If the + server is authenticated, it may request a certificate from the + client, if that is appropriate to the cipher suite selected. Now the + server will send the server hello done message, indicating that the + hello-message phase of the handshake is complete. The server will + then wait for a client response. If the server has sent a certificate + request message, the client must send the certificate message. The + client key exchange message is now sent, and the content of that + message will depend on the public key algorithm selected between the + client hello and the server hello. If the client has sent a + certificate with signing ability, a digitally-signed certificate + verify message is sent to explicitly verify the certificate. + + At this point, a change cipher spec message is sent by the client, + and the client copies the pending Cipher Spec into the current Cipher + Spec. The client then immediately sends the finished message under + the new algorithms, keys, and secrets. In response, the server will + send its own change cipher spec message, transfer the pending to the + current Cipher Spec, and send its finished message under the new + + + + + +Dierks & Allen Standards Track [Page 30] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Cipher Spec. At this point, the handshake is complete and the client + and server may begin to exchange application layer data. (See flow + chart below.) + + Client Server + + ClientHello --------> + ServerHello + Certificate* + ServerKeyExchange* + CertificateRequest* + <-------- ServerHelloDone + Certificate* + ClientKeyExchange + CertificateVerify* + [ChangeCipherSpec] + Finished --------> + [ChangeCipherSpec] + <-------- Finished + Application Data <-------> Application Data + + Fig. 1 - Message flow for a full handshake + + * Indicates optional or situation-dependent messages that are not + always sent. + + Note: To help avoid pipeline stalls, ChangeCipherSpec is an + independent TLS Protocol content type, and is not actually a TLS + handshake message. + + When the client and server decide to resume a previous session or + duplicate an existing session (instead of negotiating new security + parameters) the message flow is as follows: + + The client sends a ClientHello using the Session ID of the session to + be resumed. The server then checks its session cache for a match. If + a match is found, and the server is willing to re-establish the + connection under the specified session state, it will send a + ServerHello with the same Session ID value. At this point, both + client and server must send change cipher spec messages and proceed + directly to finished messages. Once the re-establishment is complete, + the client and server may begin to exchange application layer data. + (See flow chart below.) If a Session ID match is not found, the + server generates a new session ID and the TLS client and server + perform a full handshake. + + + + + + +Dierks & Allen Standards Track [Page 31] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Client Server + + ClientHello --------> + ServerHello + [ChangeCipherSpec] + <-------- Finished + [ChangeCipherSpec] + Finished --------> + Application Data <-------> Application Data + + Fig. 2 - Message flow for an abbreviated handshake + + The contents and significance of each message will be presented in + detail in the following sections. + +7.4. Handshake protocol + + The TLS Handshake Protocol is one of the defined higher level clients + of the TLS Record Protocol. This protocol is used to negotiate the + secure attributes of a session. Handshake messages are supplied to + the TLS Record Layer, where they are encapsulated within one or more + TLSPlaintext structures, which are processed and transmitted as + specified by the current active session state. + + enum { + hello_request(0), client_hello(1), server_hello(2), + certificate(11), server_key_exchange (12), + certificate_request(13), server_hello_done(14), + certificate_verify(15), client_key_exchange(16), + finished(20), (255) + } HandshakeType; + + struct { + HandshakeType msg_type; /* handshake type */ + uint24 length; /* bytes in message */ + select (HandshakeType) { + case hello_request: HelloRequest; + case client_hello: ClientHello; + case server_hello: ServerHello; + case certificate: Certificate; + case server_key_exchange: ServerKeyExchange; + case certificate_request: CertificateRequest; + case server_hello_done: ServerHelloDone; + case certificate_verify: CertificateVerify; + case client_key_exchange: ClientKeyExchange; + case finished: Finished; + } body; + } Handshake; + + + +Dierks & Allen Standards Track [Page 32] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + The handshake protocol messages are presented below in the order they + must be sent; sending handshake messages in an unexpected order + results in a fatal error. Unneeded handshake messages can be omitted, + however. Note one exception to the ordering: the Certificate message + is used twice in the handshake (from server to client, then from + client to server), but described only in its first position. The one + message which is not bound by these ordering rules in the Hello + Request message, which can be sent at any time, but which should be + ignored by the client if it arrives in the middle of a handshake. + +7.4.1. Hello messages + + The hello phase messages are used to exchange security enhancement + capabilities between the client and server. When a new session + begins, the Record Layer's connection state encryption, hash, and + compression algorithms are initialized to null. The current + connection state is used for renegotiation messages. + +7.4.1.1. Hello request + + When this message will be sent: + The hello request message may be sent by the server at any time. + + Meaning of this message: + Hello request is a simple notification that the client should + begin the negotiation process anew by sending a client hello + message when convenient. This message will be ignored by the + client if the client is currently negotiating a session. This + message may be ignored by the client if it does not wish to + renegotiate a session, or the client may, if it wishes, respond + with a no_renegotiation alert. Since handshake messages are + intended to have transmission precedence over application data, + it is expected that the negotiation will begin before no more + than a few records are received from the client. If the server + sends a hello request but does not receive a client hello in + response, it may close the connection with a fatal alert. + + After sending a hello request, servers should not repeat the request + until the subsequent handshake negotiation is complete. + + Structure of this message: + struct { } HelloRequest; + + Note: This message should never be included in the message hashes which + are maintained throughout the handshake and used in the finished + messages and the certificate verify message. + + + + + +Dierks & Allen Standards Track [Page 33] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +7.4.1.2. Client hello + + When this message will be sent: + When a client first connects to a server it is required to send + the client hello as its first message. The client can also send a + client hello in response to a hello request or on its own + initiative in order to renegotiate the security parameters in an + existing connection. + + Structure of this message: + The client hello message includes a random structure, which is + used later in the protocol. + + struct { + uint32 gmt_unix_time; + opaque random_bytes[28]; + } Random; + + gmt_unix_time + The current time and date in standard UNIX 32-bit format (seconds + since the midnight starting Jan 1, 1970, GMT) according to the + sender's internal clock. Clocks are not required to be set + correctly by the basic TLS Protocol; higher level or application + protocols may define additional requirements. + + random_bytes + 28 bytes generated by a secure random number generator. + + The client hello message includes a variable length session + identifier. If not empty, the value identifies a session between the + same client and server whose security parameters the client wishes to + reuse. The session identifier may be from an earlier connection, this + connection, or another currently active connection. The second option + is useful if the client only wishes to update the random structures + and derived values of a connection, while the third option makes it + possible to establish several independent secure connections without + repeating the full handshake protocol. These independent connections + may occur sequentially or simultaneously; a SessionID becomes valid + when the handshake negotiating it completes with the exchange of + Finished messages and persists until removed due to aging or because + a fatal error was encountered on a connection associated with the + session. The actual contents of the SessionID are defined by the + server. + + opaque SessionID<0..32>; + + + + + + +Dierks & Allen Standards Track [Page 34] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Warning: + Because the SessionID is transmitted without encryption or + immediate MAC protection, servers must not place confidential + information in session identifiers or let the contents of fake + session identifiers cause any breach of security. (Note that the + content of the handshake as a whole, including the SessionID, is + protected by the Finished messages exchanged at the end of the + handshake.) + + The CipherSuite list, passed from the client to the server in the + client hello message, contains the combinations of cryptographic + algorithms supported by the client in order of the client's + preference (favorite choice first). Each CipherSuite defines a key + exchange algorithm, a bulk encryption algorithm (including secret key + length) and a MAC algorithm. The server will select a cipher suite + or, if no acceptable choices are presented, return a handshake + failure alert and close the connection. + + uint8 CipherSuite[2]; /* Cryptographic suite selector */ + + The client hello includes a list of compression algorithms supported + by the client, ordered according to the client's preference. + + enum { null(0), (255) } CompressionMethod; + + struct { + ProtocolVersion client_version; + Random random; + SessionID session_id; + CipherSuite cipher_suites<2..2^16-1>; + CompressionMethod compression_methods<1..2^8-1>; + } ClientHello; + + client_version + The version of the TLS protocol by which the client wishes to + communicate during this session. This should be the latest + (highest valued) version supported by the client. For this + version of the specification, the version will be 3.1 (See + Appendix E for details about backward compatibility). + + random + A client-generated random structure. + + session_id + The ID of a session the client wishes to use for this connection. + This field should be empty if no session_id is available or the + client wishes to generate new security parameters. + + + + +Dierks & Allen Standards Track [Page 35] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + cipher_suites + This is a list of the cryptographic options supported by the + client, with the client's first preference first. If the + session_id field is not empty (implying a session resumption + request) this vector must include at least the cipher_suite from + that session. Values are defined in Appendix A.5. + + compression_methods + This is a list of the compression methods supported by the + client, sorted by client preference. If the session_id field is + not empty (implying a session resumption request) it must include + the compression_method from that session. This vector must + contain, and all implementations must support, + CompressionMethod.null. Thus, a client and server will always be + able to agree on a compression method. + + After sending the client hello message, the client waits for a server + hello message. Any other handshake message returned by the server + except for a hello request is treated as a fatal error. + + Forward compatibility note: + In the interests of forward compatibility, it is permitted for a + client hello message to include extra data after the compression + methods. This data must be included in the handshake hashes, but + must otherwise be ignored. This is the only handshake message for + which this is legal; for all other messages, the amount of data + in the message must match the description of the message + precisely. + +7.4.1.3. Server hello + + When this message will be sent: + The server will send this message in response to a client hello + message when it was able to find an acceptable set of algorithms. + If it cannot find such a match, it will respond with a handshake + failure alert. + + Structure of this message: + struct { + ProtocolVersion server_version; + Random random; + SessionID session_id; + CipherSuite cipher_suite; + CompressionMethod compression_method; + } ServerHello; + + + + + + +Dierks & Allen Standards Track [Page 36] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + server_version + This field will contain the lower of that suggested by the client + in the client hello and the highest supported by the server. For + this version of the specification, the version is 3.1 (See + Appendix E for details about backward compatibility). + + random + This structure is generated by the server and must be different + from (and independent of) ClientHello.random. + + session_id + This is the identity of the session corresponding to this + connection. If the ClientHello.session_id was non-empty, the + server will look in its session cache for a match. If a match is + found and the server is willing to establish the new connection + using the specified session state, the server will respond with + the same value as was supplied by the client. This indicates a + resumed session and dictates that the parties must proceed + directly to the finished messages. Otherwise this field will + contain a different value identifying the new session. The server + may return an empty session_id to indicate that the session will + not be cached and therefore cannot be resumed. If a session is + resumed, it must be resumed using the same cipher suite it was + originally negotiated with. + + cipher_suite + The single cipher suite selected by the server from the list in + ClientHello.cipher_suites. For resumed sessions this field is the + value from the state of the session being resumed. + + compression_method + The single compression algorithm selected by the server from the + list in ClientHello.compression_methods. For resumed sessions + this field is the value from the resumed session state. + +7.4.2. Server certificate + + When this message will be sent: + The server must send a certificate whenever the agreed-upon key + exchange method is not an anonymous one. This message will always + immediately follow the server hello message. + + Meaning of this message: + The certificate type must be appropriate for the selected cipher + suite's key exchange algorithm, and is generally an X.509v3 + certificate. It must contain a key which matches the key exchange + method, as follows. Unless otherwise specified, the signing + + + + +Dierks & Allen Standards Track [Page 37] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + algorithm for the certificate must be the same as the algorithm + for the certificate key. Unless otherwise specified, the public + key may be of any length. + + Key Exchange Algorithm Certificate Key Type + + RSA RSA public key; the certificate must + allow the key to be used for encryption. + + RSA_EXPORT RSA public key of length greater than + 512 bits which can be used for signing, + or a key of 512 bits or shorter which + can be used for either encryption or + signing. + + DHE_DSS DSS public key. + + DHE_DSS_EXPORT DSS public key. + + DHE_RSA RSA public key which can be used for + signing. + + DHE_RSA_EXPORT RSA public key which can be used for + signing. + + DH_DSS Diffie-Hellman key. The algorithm used + to sign the certificate should be DSS. + + DH_RSA Diffie-Hellman key. The algorithm used + to sign the certificate should be RSA. + + All certificate profiles, key and cryptographic formats are defined + by the IETF PKIX working group [PKIX]. When a key usage extension is + present, the digitalSignature bit must be set for the key to be + eligible for signing, as described above, and the keyEncipherment bit + must be present to allow encryption, as described above. The + keyAgreement bit must be set on Diffie-Hellman certificates. + + As CipherSuites which specify new key exchange methods are specified + for the TLS Protocol, they will imply certificate format and the + required encoded keying information. + + Structure of this message: + opaque ASN.1Cert<1..2^24-1>; + + struct { + ASN.1Cert certificate_list<0..2^24-1>; + } Certificate; + + + +Dierks & Allen Standards Track [Page 38] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + certificate_list + This is a sequence (chain) of X.509v3 certificates. The sender's + certificate must come first in the list. Each following + certificate must directly certify the one preceding it. Because + certificate validation requires that root keys be distributed + independently, the self-signed certificate which specifies the + root certificate authority may optionally be omitted from the + chain, under the assumption that the remote end must already + possess it in order to validate it in any case. + + The same message type and structure will be used for the client's + response to a certificate request message. Note that a client may + send no certificates if it does not have an appropriate certificate + to send in response to the server's authentication request. + + Note: PKCS #7 [PKCS7] is not used as the format for the certificate + vector because PKCS #6 [PKCS6] extended certificates are not + used. Also PKCS #7 defines a SET rather than a SEQUENCE, making + the task of parsing the list more difficult. + +7.4.3. Server key exchange message + + When this message will be sent: + This message will be sent immediately after the server + certificate message (or the server hello message, if this is an + anonymous negotiation). + + The server key exchange message is sent by the server only when + the server certificate message (if sent) does not contain enough + data to allow the client to exchange a premaster secret. This is + true for the following key exchange methods: + + RSA_EXPORT (if the public key in the server certificate is + longer than 512 bits) + DHE_DSS + DHE_DSS_EXPORT + DHE_RSA + DHE_RSA_EXPORT + DH_anon + + It is not legal to send the server key exchange message for the + following key exchange methods: + + RSA + RSA_EXPORT (when the public key in the server certificate is + less than or equal to 512 bits in length) + DH_DSS + DH_RSA + + + +Dierks & Allen Standards Track [Page 39] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Meaning of this message: + This message conveys cryptographic information to allow the + client to communicate the premaster secret: either an RSA public + key to encrypt the premaster secret with, or a Diffie-Hellman + public key with which the client can complete a key exchange + (with the result being the premaster secret.) + + As additional CipherSuites are defined for TLS which include new key + exchange algorithms, the server key exchange message will be sent if + and only if the certificate type associated with the key exchange + algorithm does not provide enough information for the client to + exchange a premaster secret. + + Note: According to current US export law, RSA moduli larger than 512 + bits may not be used for key exchange in software exported from + the US. With this message, the larger RSA keys encoded in + certificates may be used to sign temporary shorter RSA keys for + the RSA_EXPORT key exchange method. + + Structure of this message: + enum { rsa, diffie_hellman } KeyExchangeAlgorithm; + + struct { + opaque rsa_modulus<1..2^16-1>; + opaque rsa_exponent<1..2^16-1>; + } ServerRSAParams; + + rsa_modulus + The modulus of the server's temporary RSA key. + + rsa_exponent + The public exponent of the server's temporary RSA key. + + struct { + opaque dh_p<1..2^16-1>; + opaque dh_g<1..2^16-1>; + opaque dh_Ys<1..2^16-1>; + } ServerDHParams; /* Ephemeral DH parameters */ + + dh_p + The prime modulus used for the Diffie-Hellman operation. + + dh_g + The generator used for the Diffie-Hellman operation. + + dh_Ys + The server's Diffie-Hellman public value (g^X mod p). + + + + +Dierks & Allen Standards Track [Page 40] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + struct { + select (KeyExchangeAlgorithm) { + case diffie_hellman: + ServerDHParams params; + Signature signed_params; + case rsa: + ServerRSAParams params; + Signature signed_params; + }; + } ServerKeyExchange; + + params + The server's key exchange parameters. + + signed_params + For non-anonymous key exchanges, a hash of the corresponding + params value, with the signature appropriate to that hash + applied. + + md5_hash + MD5(ClientHello.random + ServerHello.random + ServerParams); + + sha_hash + SHA(ClientHello.random + ServerHello.random + ServerParams); + + enum { anonymous, rsa, dsa } SignatureAlgorithm; + + select (SignatureAlgorithm) + { case anonymous: struct { }; + case rsa: + digitally-signed struct { + opaque md5_hash[16]; + opaque sha_hash[20]; + }; + case dsa: + digitally-signed struct { + opaque sha_hash[20]; + }; + } Signature; + +7.4.4. Certificate request + + When this message will be sent: + A non-anonymous server can optionally request a certificate from + the client, if appropriate for the selected cipher suite. This + message, if sent, will immediately follow the Server Key Exchange + message (if it is sent; otherwise, the Server Certificate + message). + + + +Dierks & Allen Standards Track [Page 41] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Structure of this message: + enum { + rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), + (255) + } ClientCertificateType; + + opaque DistinguishedName<1..2^16-1>; + + struct { + ClientCertificateType certificate_types<1..2^8-1>; + DistinguishedName certificate_authorities<3..2^16-1>; + } CertificateRequest; + + certificate_types + This field is a list of the types of certificates requested, + sorted in order of the server's preference. + + certificate_authorities + A list of the distinguished names of acceptable certificate + authorities. These distinguished names may specify a desired + distinguished name for a root CA or for a subordinate CA; + thus, this message can be used both to describe known roots + and a desired authorization space. + + Note: DistinguishedName is derived from [X509]. + + Note: It is a fatal handshake_failure alert for an anonymous server to + request client identification. + +7.4.5. Server hello done + + When this message will be sent: + The server hello done message is sent by the server to indicate + the end of the server hello and associated messages. After + sending this message the server will wait for a client response. + + Meaning of this message: + This message means that the server is done sending messages to + support the key exchange, and the client can proceed with its + phase of the key exchange. + + Upon receipt of the server hello done message the client should + verify that the server provided a valid certificate if required + and check that the server hello parameters are acceptable. + + Structure of this message: + struct { } ServerHelloDone; + + + + +Dierks & Allen Standards Track [Page 42] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +7.4.6. Client certificate + + When this message will be sent: + This is the first message the client can send after receiving a + server hello done message. This message is only sent if the + server requests a certificate. If no suitable certificate is + available, the client should send a certificate message + containing no certificates. If client authentication is required + by the server for the handshake to continue, it may respond with + a fatal handshake failure alert. Client certificates are sent + using the Certificate structure defined in Section 7.4.2. + + Note: When using a static Diffie-Hellman based key exchange method + (DH_DSS or DH_RSA), if client authentication is requested, the + Diffie-Hellman group and generator encoded in the client's + certificate must match the server specified Diffie-Hellman + parameters if the client's parameters are to be used for the key + exchange. + +7.4.7. Client key exchange message + + When this message will be sent: + This message is always sent by the client. It will immediately + follow the client certificate message, if it is sent. Otherwise + it will be the first message sent by the client after it receives + the server hello done message. + + Meaning of this message: + With this message, the premaster secret is set, either though + direct transmission of the RSA-encrypted secret, or by the + transmission of Diffie-Hellman parameters which will allow each + side to agree upon the same premaster secret. When the key + exchange method is DH_RSA or DH_DSS, client certification has + been requested, and the client was able to respond with a + certificate which contained a Diffie-Hellman public key whose + parameters (group and generator) matched those specified by the + server in its certificate, this message will not contain any + data. + + Structure of this message: + The choice of messages depends on which key exchange method has + been selected. See Section 7.4.3 for the KeyExchangeAlgorithm + definition. + + struct { + select (KeyExchangeAlgorithm) { + case rsa: EncryptedPreMasterSecret; + case diffie_hellman: ClientDiffieHellmanPublic; + + + +Dierks & Allen Standards Track [Page 43] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + } exchange_keys; + } ClientKeyExchange; + +7.4.7.1. RSA encrypted premaster secret message + + Meaning of this message: + If RSA is being used for key agreement and authentication, the + client generates a 48-byte premaster secret, encrypts it using + the public key from the server's certificate or the temporary RSA + key provided in a server key exchange message, and sends the + result in an encrypted premaster secret message. This structure + is a variant of the client key exchange message, not a message in + itself. + + Structure of this message: + struct { + ProtocolVersion client_version; + opaque random[46]; + } PreMasterSecret; + + client_version + The latest (newest) version supported by the client. This is + used to detect version roll-back attacks. Upon receiving the + premaster secret, the server should check that this value + matches the value transmitted by the client in the client + hello message. + + random + 46 securely-generated random bytes. + + struct { + public-key-encrypted PreMasterSecret pre_master_secret; + } EncryptedPreMasterSecret; + + Note: An attack discovered by Daniel Bleichenbacher [BLEI] can be used + to attack a TLS server which is using PKCS#1 encoded RSA. The + attack takes advantage of the fact that by failing in different + ways, a TLS server can be coerced into revealing whether a + particular message, when decrypted, is properly PKCS#1 formatted + or not. + + The best way to avoid vulnerability to this attack is to treat + incorrectly formatted messages in a manner indistinguishable from + correctly formatted RSA blocks. Thus, when it receives an + incorrectly formatted RSA block, a server should generate a + random 48-byte value and proceed using it as the premaster + secret. Thus, the server will act identically whether the + received RSA block is correctly encoded or not. + + + +Dierks & Allen Standards Track [Page 44] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + pre_master_secret + This random value is generated by the client and is used to + generate the master secret, as specified in Section 8.1. + +7.4.7.2. Client Diffie-Hellman public value + + Meaning of this message: + This structure conveys the client's Diffie-Hellman public value + (Yc) if it was not already included in the client's certificate. + The encoding used for Yc is determined by the enumerated + PublicValueEncoding. This structure is a variant of the client + key exchange message, not a message in itself. + + Structure of this message: + enum { implicit, explicit } PublicValueEncoding; + + implicit + If the client certificate already contains a suitable + Diffie-Hellman key, then Yc is implicit and does not need to + be sent again. In this case, the Client Key Exchange message + will be sent, but will be empty. + + explicit + Yc needs to be sent. + + struct { + select (PublicValueEncoding) { + case implicit: struct { }; + case explicit: opaque dh_Yc<1..2^16-1>; + } dh_public; + } ClientDiffieHellmanPublic; + + dh_Yc + The client's Diffie-Hellman public value (Yc). + +7.4.8. Certificate verify + + When this message will be sent: + This message is used to provide explicit verification of a client + certificate. This message is only sent following a client + certificate that has signing capability (i.e. all certificates + except those containing fixed Diffie-Hellman parameters). When + sent, it will immediately follow the client key exchange message. + + Structure of this message: + struct { + Signature signature; + } CertificateVerify; + + + +Dierks & Allen Standards Track [Page 45] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + The Signature type is defined in 7.4.3. + + CertificateVerify.signature.md5_hash + MD5(handshake_messages); + + Certificate.signature.sha_hash + SHA(handshake_messages); + + Here handshake_messages refers to all handshake messages sent or + received starting at client hello up to but not including this + message, including the type and length fields of the handshake + messages. This is the concatenation of all the Handshake structures + as defined in 7.4 exchanged thus far. + +7.4.9. Finished + + When this message will be sent: + A finished message is always sent immediately after a change + cipher spec message to verify that the key exchange and + authentication processes were successful. It is essential that a + change cipher spec message be received between the other + handshake messages and the Finished message. + + Meaning of this message: + The finished message is the first protected with the just- + negotiated algorithms, keys, and secrets. Recipients of finished + messages must verify that the contents are correct. Once a side + has sent its Finished message and received and validated the + Finished message from its peer, it may begin to send and receive + application data over the connection. + + struct { + opaque verify_data[12]; + } Finished; + + verify_data + PRF(master_secret, finished_label, MD5(handshake_messages) + + SHA-1(handshake_messages)) [0..11]; + + finished_label + For Finished messages sent by the client, the string "client + finished". For Finished messages sent by the server, the + string "server finished". + + handshake_messages + All of the data from all handshake messages up to but not + including this message. This is only data visible at the + handshake layer and does not include record layer headers. + + + +Dierks & Allen Standards Track [Page 46] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + This is the concatenation of all the Handshake structures as + defined in 7.4 exchanged thus far. + + It is a fatal error if a finished message is not preceded by a change + cipher spec message at the appropriate point in the handshake. + + The hash contained in finished messages sent by the server + incorporate Sender.server; those sent by the client incorporate + Sender.client. The value handshake_messages includes all handshake + messages starting at client hello up to, but not including, this + finished message. This may be different from handshake_messages in + Section 7.4.8 because it would include the certificate verify message + (if sent). Also, the handshake_messages for the finished message sent + by the client will be different from that for the finished message + sent by the server, because the one which is sent second will include + the prior one. + + Note: Change cipher spec messages, alerts and any other record types + are not handshake messages and are not included in the hash + computations. Also, Hello Request messages are omitted from + handshake hashes. + +8. Cryptographic computations + + In order to begin connection protection, the TLS Record Protocol + requires specification of a suite of algorithms, a master secret, and + the client and server random values. The authentication, encryption, + and MAC algorithms are determined by the cipher_suite selected by the + server and revealed in the server hello message. The compression + algorithm is negotiated in the hello messages, and the random values + are exchanged in the hello messages. All that remains is to calculate + the master secret. + +8.1. Computing the master secret + + For all key exchange methods, the same algorithm is used to convert + the pre_master_secret into the master_secret. The pre_master_secret + should be deleted from memory once the master_secret has been + computed. + + master_secret = PRF(pre_master_secret, "master secret", + ClientHello.random + ServerHello.random) + [0..47]; + + The master secret is always exactly 48 bytes in length. The length of + the premaster secret will vary depending on key exchange method. + + + + + +Dierks & Allen Standards Track [Page 47] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +8.1.1. RSA + + When RSA is used for server authentication and key exchange, a 48- + byte pre_master_secret is generated by the client, encrypted under + the server's public key, and sent to the server. The server uses its + private key to decrypt the pre_master_secret. Both parties then + convert the pre_master_secret into the master_secret, as specified + above. + + RSA digital signatures are performed using PKCS #1 [PKCS1] block type + 1. RSA public key encryption is performed using PKCS #1 block type 2. + +8.1.2. Diffie-Hellman + + A conventional Diffie-Hellman computation is performed. The + negotiated key (Z) is used as the pre_master_secret, and is converted + into the master_secret, as specified above. + + Note: Diffie-Hellman parameters are specified by the server, and may + be either ephemeral or contained within the server's certificate. + +9. Mandatory Cipher Suites + + In the absence of an application profile standard specifying + otherwise, a TLS compliant application MUST implement the cipher + suite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA. + +10. Application data protocol + + Application data messages are carried by the Record Layer and are + fragmented, compressed and encrypted based on the current connection + state. The messages are treated as transparent data to the record + layer. + + + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 48] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +A. Protocol constant values + + This section describes protocol types and constants. + +A.1. Record layer + + struct { + uint8 major, minor; + } ProtocolVersion; + + ProtocolVersion version = { 3, 1 }; /* TLS v1.0 */ + + enum { + change_cipher_spec(20), alert(21), handshake(22), + application_data(23), (255) + } ContentType; + + struct { + ContentType type; + ProtocolVersion version; + uint16 length; + opaque fragment[TLSPlaintext.length]; + } TLSPlaintext; + + struct { + ContentType type; + ProtocolVersion version; + uint16 length; + opaque fragment[TLSCompressed.length]; + } TLSCompressed; + + struct { + ContentType type; + ProtocolVersion version; + uint16 length; + select (CipherSpec.cipher_type) { + case stream: GenericStreamCipher; + case block: GenericBlockCipher; + } fragment; + } TLSCiphertext; + + stream-ciphered struct { + opaque content[TLSCompressed.length]; + opaque MAC[CipherSpec.hash_size]; + } GenericStreamCipher; + + block-ciphered struct { + opaque content[TLSCompressed.length]; + + + +Dierks & Allen Standards Track [Page 49] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + opaque MAC[CipherSpec.hash_size]; + uint8 padding[GenericBlockCipher.padding_length]; + uint8 padding_length; + } GenericBlockCipher; + +A.2. Change cipher specs message + + struct { + enum { change_cipher_spec(1), (255) } type; + } ChangeCipherSpec; + +A.3. Alert messages + + enum { warning(1), fatal(2), (255) } AlertLevel; + + enum { + close_notify(0), + unexpected_message(10), + bad_record_mac(20), + decryption_failed(21), + record_overflow(22), + decompression_failure(30), + handshake_failure(40), + bad_certificate(42), + unsupported_certificate(43), + certificate_revoked(44), + certificate_expired(45), + certificate_unknown(46), + illegal_parameter(47), + unknown_ca(48), + access_denied(49), + decode_error(50), + decrypt_error(51), + export_restriction(60), + protocol_version(70), + insufficient_security(71), + internal_error(80), + user_canceled(90), + no_renegotiation(100), + (255) + } AlertDescription; + + struct { + AlertLevel level; + AlertDescription description; + } Alert; + + + + + +Dierks & Allen Standards Track [Page 50] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +A.4. Handshake protocol + + enum { + hello_request(0), client_hello(1), server_hello(2), + certificate(11), server_key_exchange (12), + certificate_request(13), server_hello_done(14), + certificate_verify(15), client_key_exchange(16), + finished(20), (255) + } HandshakeType; + + struct { + HandshakeType msg_type; + uint24 length; + select (HandshakeType) { + case hello_request: HelloRequest; + case client_hello: ClientHello; + case server_hello: ServerHello; + case certificate: Certificate; + case server_key_exchange: ServerKeyExchange; + case certificate_request: CertificateRequest; + case server_hello_done: ServerHelloDone; + case certificate_verify: CertificateVerify; + case client_key_exchange: ClientKeyExchange; + case finished: Finished; + } body; + } Handshake; + +A.4.1. Hello messages + + struct { } HelloRequest; + + struct { + uint32 gmt_unix_time; + opaque random_bytes[28]; + } Random; + + opaque SessionID<0..32>; + + uint8 CipherSuite[2]; + + enum { null(0), (255) } CompressionMethod; + + struct { + ProtocolVersion client_version; + Random random; + SessionID session_id; + CipherSuite cipher_suites<2..2^16-1>; + CompressionMethod compression_methods<1..2^8-1>; + + + +Dierks & Allen Standards Track [Page 51] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + } ClientHello; + + struct { + ProtocolVersion server_version; + Random random; + SessionID session_id; + CipherSuite cipher_suite; + CompressionMethod compression_method; + } ServerHello; + +A.4.2. Server authentication and key exchange messages + + opaque ASN.1Cert<2^24-1>; + + struct { + ASN.1Cert certificate_list<1..2^24-1>; + } Certificate; + + enum { rsa, diffie_hellman } KeyExchangeAlgorithm; + + struct { + opaque RSA_modulus<1..2^16-1>; + opaque RSA_exponent<1..2^16-1>; + } ServerRSAParams; + + struct { + opaque DH_p<1..2^16-1>; + opaque DH_g<1..2^16-1>; + opaque DH_Ys<1..2^16-1>; + } ServerDHParams; + + struct { + select (KeyExchangeAlgorithm) { + case diffie_hellman: + ServerDHParams params; + Signature signed_params; + case rsa: + ServerRSAParams params; + Signature signed_params; + }; + } ServerKeyExchange; + + enum { anonymous, rsa, dsa } SignatureAlgorithm; + + select (SignatureAlgorithm) + { case anonymous: struct { }; + case rsa: + digitally-signed struct { + + + +Dierks & Allen Standards Track [Page 52] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + opaque md5_hash[16]; + opaque sha_hash[20]; + }; + case dsa: + digitally-signed struct { + opaque sha_hash[20]; + }; + } Signature; + + enum { + rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), + (255) + } ClientCertificateType; + + opaque DistinguishedName<1..2^16-1>; + + struct { + ClientCertificateType certificate_types<1..2^8-1>; + DistinguishedName certificate_authorities<3..2^16-1>; + } CertificateRequest; + + struct { } ServerHelloDone; + +A.4.3. Client authentication and key exchange messages + + struct { + select (KeyExchangeAlgorithm) { + case rsa: EncryptedPreMasterSecret; + case diffie_hellman: DiffieHellmanClientPublicValue; + } exchange_keys; + } ClientKeyExchange; + + struct { + ProtocolVersion client_version; + opaque random[46]; + + } PreMasterSecret; + + struct { + public-key-encrypted PreMasterSecret pre_master_secret; + } EncryptedPreMasterSecret; + + enum { implicit, explicit } PublicValueEncoding; + + struct { + select (PublicValueEncoding) { + case implicit: struct {}; + case explicit: opaque DH_Yc<1..2^16-1>; + + + +Dierks & Allen Standards Track [Page 53] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + } dh_public; + } ClientDiffieHellmanPublic; + + struct { + Signature signature; + } CertificateVerify; + +A.4.4. Handshake finalization message + + struct { + opaque verify_data[12]; + } Finished; + +A.5. The CipherSuite + + The following values define the CipherSuite codes used in the client + hello and server hello messages. + + A CipherSuite defines a cipher specification supported in TLS Version + 1.0. + + TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a + TLS connection during the first handshake on that channel, but must + not be negotiated, as it provides no more protection than an + unsecured connection. + + CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 }; + + The following CipherSuite definitions require that the server provide + an RSA certificate that can be used for key exchange. The server may + request either an RSA or a DSS signature-capable certificate in the + certificate request message. + + CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 }; + CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 }; + CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 }; + CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 }; + CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 }; + CipherSuite TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x06 }; + CipherSuite TLS_RSA_WITH_IDEA_CBC_SHA = { 0x00,0x07 }; + CipherSuite TLS_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x08 }; + CipherSuite TLS_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 }; + CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A }; + + The following CipherSuite definitions are used for server- + authenticated (and optionally client-authenticated) Diffie-Hellman. + DH denotes cipher suites in which the server's certificate contains + the Diffie-Hellman parameters signed by the certificate authority + + + +Dierks & Allen Standards Track [Page 54] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + (CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman + parameters are signed by a DSS or RSA certificate, which has been + signed by the CA. The signing algorithm used is specified after the + DH or DHE parameter. The server can request an RSA or DSS signature- + capable certificate from the client for client authentication or it + may request a Diffie-Hellman certificate. Any Diffie-Hellman + certificate provided by the client must use the parameters (group and + generator) described by the server. + + CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B }; + CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C }; + CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; + CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E }; + CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F }; + CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; + CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 }; + CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 }; + CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; + CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 }; + CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 }; + CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 }; + + The following cipher suites are used for completely anonymous + Diffie-Hellman communications in which neither party is + authenticated. Note that this mode is vulnerable to man-in-the-middle + attacks and is therefore deprecated. + + CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 }; + CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 }; + CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 }; + CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA = { 0x00,0x1A }; + CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B }; + + Note: All cipher suites whose first byte is 0xFF are considered + private and can be used for defining local/experimental + algorithms. Interoperability of such types is a local matter. + + Note: Additional cipher suites can be registered by publishing an RFC + which specifies the cipher suites, including the necessary TLS + protocol information, including message encoding, premaster + secret derivation, symmetric encryption and MAC calculation and + appropriate reference information for the algorithms involved. + The RFC editor's office may, at its discretion, choose to publish + specifications for cipher suites which are not completely + described (e.g., for classified algorithms) if it finds the + specification to be of technical interest and completely + specified. + + + + +Dierks & Allen Standards Track [Page 55] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are + reserved to avoid collision with Fortezza-based cipher suites in + SSL 3. + +A.6. The Security Parameters + + These security parameters are determined by the TLS Handshake + Protocol and provided as parameters to the TLS Record Layer in order + to initialize a connection state. SecurityParameters includes: + + enum { null(0), (255) } CompressionMethod; + + enum { server, client } ConnectionEnd; + + enum { null, rc4, rc2, des, 3des, des40, idea } + BulkCipherAlgorithm; + + enum { stream, block } CipherType; + + enum { true, false } IsExportable; + + enum { null, md5, sha } MACAlgorithm; + + /* The algorithms specified in CompressionMethod, + BulkCipherAlgorithm, and MACAlgorithm may be added to. */ + + struct { + ConnectionEnd entity; + BulkCipherAlgorithm bulk_cipher_algorithm; + CipherType cipher_type; + uint8 key_size; + uint8 key_material_length; + IsExportable is_exportable; + MACAlgorithm mac_algorithm; + uint8 hash_size; + CompressionMethod compression_algorithm; + opaque master_secret[48]; + opaque client_random[32]; + opaque server_random[32]; + } SecurityParameters; + + + + + + + + + + + +Dierks & Allen Standards Track [Page 56] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +B. Glossary + + application protocol + An application protocol is a protocol that normally layers + directly on top of the transport layer (e.g., TCP/IP). Examples + include HTTP, TELNET, FTP, and SMTP. + + asymmetric cipher + See public key cryptography. + + authentication + Authentication is the ability of one entity to determine the + identity of another entity. + + block cipher + A block cipher is an algorithm that operates on plaintext in + groups of bits, called blocks. 64 bits is a common block size. + + bulk cipher + A symmetric encryption algorithm used to encrypt large quantities + of data. + + cipher block chaining (CBC) + CBC is a mode in which every plaintext block encrypted with a + block cipher is first exclusive-ORed with the previous ciphertext + block (or, in the case of the first block, with the + initialization vector). For decryption, every block is first + decrypted, then exclusive-ORed with the previous ciphertext block + (or IV). + + certificate + As part of the X.509 protocol (a.k.a. ISO Authentication + framework), certificates are assigned by a trusted Certificate + Authority and provide a strong binding between a party's identity + or some other attributes and its public key. + + client + The application entity that initiates a TLS connection to a + server. This may or may not imply that the client initiated the + underlying transport connection. The primary operational + difference between the server and client is that the server is + generally authenticated, while the client is only optionally + authenticated. + + client write key + The key used to encrypt data written by the client. + + + + + +Dierks & Allen Standards Track [Page 57] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + client write MAC secret + The secret data used to authenticate data written by the client. + + connection + A connection is a transport (in the OSI layering model + definition) that provides a suitable type of service. For TLS, + such connections are peer to peer relationships. The connections + are transient. Every connection is associated with one session. + + Data Encryption Standard + DES is a very widely used symmetric encryption algorithm. DES is + a block cipher with a 56 bit key and an 8 byte block size. Note + that in TLS, for key generation purposes, DES is treated as + having an 8 byte key length (64 bits), but it still only provides + 56 bits of protection. (The low bit of each key byte is presumed + to be set to produce odd parity in that key byte.) DES can also + be operated in a mode where three independent keys and three + encryptions are used for each block of data; this uses 168 bits + of key (24 bytes in the TLS key generation method) and provides + the equivalent of 112 bits of security. [DES], [3DES] + + Digital Signature Standard (DSS) + A standard for digital signing, including the Digital Signing + Algorithm, approved by the National Institute of Standards and + Technology, defined in NIST FIPS PUB 186, "Digital Signature + Standard," published May, 1994 by the U.S. Dept. of Commerce. + [DSS] + + digital signatures + Digital signatures utilize public key cryptography and one-way + hash functions to produce a signature of the data that can be + authenticated, and is difficult to forge or repudiate. + + handshake + An initial negotiation between client and server that establishes + the parameters of their transactions. + + Initialization Vector (IV) + When a block cipher is used in CBC mode, the initialization + vector is exclusive-ORed with the first plaintext block prior to + encryption. + + IDEA + A 64-bit block cipher designed by Xuejia Lai and James Massey. + [IDEA] + + + + + + +Dierks & Allen Standards Track [Page 58] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Message Authentication Code (MAC) + A Message Authentication Code is a one-way hash computed from a + message and some secret data. It is difficult to forge without + knowing the secret data. Its purpose is to detect if the message + has been altered. + + master secret + Secure secret data used for generating encryption keys, MAC + secrets, and IVs. + + MD5 + MD5 is a secure hashing function that converts an arbitrarily + long data stream into a digest of fixed size (16 bytes). [MD5] + + public key cryptography + A class of cryptographic techniques employing two-key ciphers. + Messages encrypted with the public key can only be decrypted with + the associated private key. Conversely, messages signed with the + private key can be verified with the public key. + + one-way hash function + A one-way transformation that converts an arbitrary amount of + data into a fixed-length hash. It is computationally hard to + reverse the transformation or to find collisions. MD5 and SHA are + examples of one-way hash functions. + + RC2 + A block cipher developed by Ron Rivest at RSA Data Security, Inc. + [RSADSI] described in [RC2]. + + RC4 + A stream cipher licensed by RSA Data Security [RSADSI]. A + compatible cipher is described in [RC4]. + + RSA + A very widely used public-key algorithm that can be used for + either encryption or digital signing. [RSA] + + salt + Non-secret random data used to make export encryption keys resist + precomputation attacks. + + server + The server is the application entity that responds to requests + for connections from clients. See also under client. + + + + + + +Dierks & Allen Standards Track [Page 59] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + session + A TLS session is an association between a client and a server. + Sessions are created by the handshake protocol. Sessions define a + set of cryptographic security parameters, which can be shared + among multiple connections. Sessions are used to avoid the + expensive negotiation of new security parameters for each + connection. + + session identifier + A session identifier is a value generated by a server that + identifies a particular session. + + server write key + The key used to encrypt data written by the server. + + server write MAC secret + The secret data used to authenticate data written by the server. + + SHA + The Secure Hash Algorithm is defined in FIPS PUB 180-1. It + produces a 20-byte output. Note that all references to SHA + actually use the modified SHA-1 algorithm. [SHA] + + SSL + Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on + SSL Version 3.0 + + stream cipher + An encryption algorithm that converts a key into a + cryptographically-strong keystream, which is then exclusive-ORed + with the plaintext. + + symmetric cipher + See bulk cipher. + + Transport Layer Security (TLS) + This protocol; also, the Transport Layer Security working group + of the Internet Engineering Task Force (IETF). See "Comments" at + the end of this document. + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 60] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +C. CipherSuite definitions + +CipherSuite Is Key Cipher Hash + Exportable Exchange + +TLS_NULL_WITH_NULL_NULL * NULL NULL NULL +TLS_RSA_WITH_NULL_MD5 * RSA NULL MD5 +TLS_RSA_WITH_NULL_SHA * RSA NULL SHA +TLS_RSA_EXPORT_WITH_RC4_40_MD5 * RSA_EXPORT RC4_40 MD5 +TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5 +TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA +TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 * RSA_EXPORT RC2_CBC_40 MD5 +TLS_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA +TLS_RSA_EXPORT_WITH_DES40_CBC_SHA * RSA_EXPORT DES40_CBC SHA +TLS_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA +TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA +TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA * DH_DSS_EXPORT DES40_CBC SHA +TLS_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA +TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA +TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA * DH_RSA_EXPORT DES40_CBC SHA +TLS_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA +TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA +TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA * DHE_DSS_EXPORT DES40_CBC SHA +TLS_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA +TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA +TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA * DHE_RSA_EXPORT DES40_CBC SHA +TLS_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA +TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA +TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 * DH_anon_EXPORT RC4_40 MD5 +TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5 +TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA DH_anon DES40_CBC SHA +TLS_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA +TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA + + + * Indicates IsExportable is True + + Key + Exchange + Algorithm Description Key size limit + + DHE_DSS Ephemeral DH with DSS signatures None + DHE_DSS_EXPORT Ephemeral DH with DSS signatures DH = 512 bits + DHE_RSA Ephemeral DH with RSA signatures None + DHE_RSA_EXPORT Ephemeral DH with RSA signatures DH = 512 bits, + RSA = none + DH_anon Anonymous DH, no signatures None + DH_anon_EXPORT Anonymous DH, no signatures DH = 512 bits + + + +Dierks & Allen Standards Track [Page 61] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + DH_DSS DH with DSS-based certificates None + DH_DSS_EXPORT DH with DSS-based certificates DH = 512 bits + DH_RSA DH with RSA-based certificates None + DH_RSA_EXPORT DH with RSA-based certificates DH = 512 bits, + RSA = none + NULL No key exchange N/A + RSA RSA key exchange None + RSA_EXPORT RSA key exchange RSA = 512 bits + + Key size limit + The key size limit gives the size of the largest public key that + can be legally used for encryption in cipher suites that are + exportable. + + Key Expanded Effective IV Block + Cipher Type Material Key Material Key Bits Size Size + + NULL * Stream 0 0 0 0 N/A + IDEA_CBC Block 16 16 128 8 8 + RC2_CBC_40 * Block 5 16 40 8 8 + RC4_40 * Stream 5 16 40 0 N/A + RC4_128 Stream 16 16 128 0 N/A + DES40_CBC * Block 5 8 40 8 8 + DES_CBC Block 8 8 56 8 8 + 3DES_EDE_CBC Block 24 24 168 8 8 + + * Indicates IsExportable is true. + + Type + Indicates whether this is a stream cipher or a block cipher + running in CBC mode. + + Key Material + The number of bytes from the key_block that are used for + generating the write keys. + + Expanded Key Material + The number of bytes actually fed into the encryption algorithm + + Effective Key Bits + How much entropy material is in the key material being fed into + the encryption routines. + + IV Size + How much data needs to be generated for the initialization + vector. Zero for stream ciphers; equal to the block size for + block ciphers. + + + + +Dierks & Allen Standards Track [Page 62] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Block Size + The amount of data a block cipher enciphers in one chunk; a + block cipher running in CBC mode can only encrypt an even + multiple of its block size. + + Hash Hash Padding + function Size Size + NULL 0 0 + MD5 16 48 + SHA 20 40 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 63] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +D. Implementation Notes + + The TLS protocol cannot prevent many common security mistakes. This + section provides several recommendations to assist implementors. + +D.1. Temporary RSA keys + + US Export restrictions limit RSA keys used for encryption to 512 + bits, but do not place any limit on lengths of RSA keys used for + signing operations. Certificates often need to be larger than 512 + bits, since 512-bit RSA keys are not secure enough for high-value + transactions or for applications requiring long-term security. Some + certificates are also designated signing-only, in which case they + cannot be used for key exchange. + + When the public key in the certificate cannot be used for encryption, + the server signs a temporary RSA key, which is then exchanged. In + exportable applications, the temporary RSA key should be the maximum + allowable length (i.e., 512 bits). Because 512-bit RSA keys are + relatively insecure, they should be changed often. For typical + electronic commerce applications, it is suggested that keys be + changed daily or every 500 transactions, and more often if possible. + Note that while it is acceptable to use the same temporary key for + multiple transactions, it must be signed each time it is used. + + RSA key generation is a time-consuming process. In many cases, a + low-priority process can be assigned the task of key generation. + + Whenever a new key is completed, the existing temporary key can be + replaced with the new one. + +D.2. Random Number Generation and Seeding + + TLS requires a cryptographically-secure pseudorandom number generator + (PRNG). Care must be taken in designing and seeding PRNGs. PRNGs + based on secure hash operations, most notably MD5 and/or SHA, are + acceptable, but cannot provide more security than the size of the + random number generator state. (For example, MD5-based PRNGs usually + provide 128 bits of state.) + + To estimate the amount of seed material being produced, add the + number of bits of unpredictable information in each seed byte. For + example, keystroke timing values taken from a PC compatible's 18.2 Hz + timer provide 1 or 2 secure bits each, even though the total size of + the counter value is 16 bits or more. To seed a 128-bit PRNG, one + would thus require approximately 100 such timer values. + + + + + +Dierks & Allen Standards Track [Page 64] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Warning: The seeding functions in RSAREF and versions of BSAFE prior to + 3.0 are order-independent. For example, if 1000 seed bits are + supplied, one at a time, in 1000 separate calls to the seed + function, the PRNG will end up in a state which depends only + on the number of 0 or 1 seed bits in the seed data (i.e., + there are 1001 possible final states). Applications using + BSAFE or RSAREF must take extra care to ensure proper seeding. + This may be accomplished by accumulating seed bits into a + buffer and processing them all at once or by processing an + incrementing counter with every seed bit; either method will + reintroduce order dependence into the seeding process. + +D.3. Certificates and authentication + + Implementations are responsible for verifying the integrity of + certificates and should generally support certificate revocation + messages. Certificates should always be verified to ensure proper + signing by a trusted Certificate Authority (CA). The selection and + addition of trusted CAs should be done very carefully. Users should + be able to view information about the certificate and root CA. + +D.4. CipherSuites + + TLS supports a range of key sizes and security levels, including some + which provide no or minimal security. A proper implementation will + probably not support many cipher suites. For example, 40-bit + encryption is easily broken, so implementations requiring strong + security should not allow 40-bit keys. Similarly, anonymous Diffie- + Hellman is strongly discouraged because it cannot prevent man-in- + the-middle attacks. Applications should also enforce minimum and + maximum key sizes. For example, certificate chains containing 512-bit + RSA keys or signatures are not appropriate for high-security + applications. + + + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 65] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +E. Backward Compatibility With SSL + + For historical reasons and in order to avoid a profligate consumption + of reserved port numbers, application protocols which are secured by + TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share the same + connection port: for example, the https protocol (HTTP secured by SSL + or TLS) uses port 443 regardless of which security protocol it is + using. Thus, some mechanism must be determined to distinguish and + negotiate among the various protocols. + + TLS version 1.0 and SSL 3.0 are very similar; thus, supporting both + is easy. TLS clients who wish to negotiate with SSL 3.0 servers + should send client hello messages using the SSL 3.0 record format and + client hello structure, sending {3, 1} for the version field to note + that they support TLS 1.0. If the server supports only SSL 3.0, it + will respond with an SSL 3.0 server hello; if it supports TLS, with a + TLS server hello. The negotiation then proceeds as appropriate for + the negotiated protocol. + + Similarly, a TLS server which wishes to interoperate with SSL 3.0 + clients should accept SSL 3.0 client hello messages and respond with + an SSL 3.0 server hello if an SSL 3.0 client hello is received which + has a version field of {3, 0}, denoting that this client does not + support TLS. + + Whenever a client already knows the highest protocol known to a + server (for example, when resuming a session), it should initiate the + connection in that native protocol. + + TLS 1.0 clients that support SSL Version 2.0 servers must send SSL + Version 2.0 client hello messages [SSL2]. TLS servers should accept + either client hello format if they wish to support SSL 2.0 clients on + the same connection port. The only deviations from the Version 2.0 + specification are the ability to specify a version with a value of + three and the support for more ciphering types in the CipherSpec. + + Warning: The ability to send Version 2.0 client hello messages will be + phased out with all due haste. Implementors should make every + effort to move forward as quickly as possible. Version 3.0 + provides better mechanisms for moving to newer versions. + + The following cipher specifications are carryovers from SSL Version + 2.0. These are assumed to use RSA for key exchange and + authentication. + + V2CipherSpec TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 }; + V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 }; + V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 }; + + + +Dierks & Allen Standards Track [Page 66] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5 + = { 0x04,0x00,0x80 }; + V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 }; + V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 }; + V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 }; + + Cipher specifications native to TLS can be included in Version 2.0 + client hello messages using the syntax below. Any V2CipherSpec + element with its first byte equal to zero will be ignored by Version + 2.0 servers. Clients sending any of the above V2CipherSpecs should + also include the TLS equivalent (see Appendix A.5): + + V2CipherSpec (see TLS name) = { 0x00, CipherSuite }; + +E.1. Version 2 client hello + + The Version 2.0 client hello message is presented below using this + document's presentation model. The true definition is still assumed + to be the SSL Version 2.0 specification. + + uint8 V2CipherSpec[3]; + + struct { + uint8 msg_type; + Version version; + uint16 cipher_spec_length; + uint16 session_id_length; + uint16 challenge_length; + V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length]; + opaque session_id[V2ClientHello.session_id_length]; + Random challenge; + } V2ClientHello; + + msg_type + This field, in conjunction with the version field, identifies a + version 2 client hello message. The value should be one (1). + + version + The highest version of the protocol supported by the client + (equals ProtocolVersion.version, see Appendix A.1). + + cipher_spec_length + This field is the total length of the field cipher_specs. It + cannot be zero and must be a multiple of the V2CipherSpec length + (3). + + + + + + +Dierks & Allen Standards Track [Page 67] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + session_id_length + This field must have a value of either zero or 16. If zero, the + client is creating a new session. If 16, the session_id field + will contain the 16 bytes of session identification. + + challenge_length + The length in bytes of the client's challenge to the server to + authenticate itself. This value must be 32. + + cipher_specs + This is a list of all CipherSpecs the client is willing and able + to use. There must be at least one CipherSpec acceptable to the + server. + + session_id + If this field's length is not zero, it will contain the + identification for a session that the client wishes to resume. + + challenge + The client challenge to the server for the server to identify + itself is a (nearly) arbitrary length random. The TLS server will + right justify the challenge data to become the ClientHello.random + data (padded with leading zeroes, if necessary), as specified in + this protocol specification. If the length of the challenge is + greater than 32 bytes, only the last 32 bytes are used. It is + legitimate (but not necessary) for a V3 server to reject a V2 + ClientHello that has fewer than 16 bytes of challenge data. + + Note: Requests to resume a TLS session should use a TLS client hello. + +E.2. Avoiding man-in-the-middle version rollback + + When TLS clients fall back to Version 2.0 compatibility mode, they + should use special PKCS #1 block formatting. This is done so that TLS + servers will reject Version 2.0 sessions with TLS-capable clients. + + When TLS clients are in Version 2.0 compatibility mode, they set the + right-hand (least-significant) 8 random bytes of the PKCS padding + (not including the terminal null of the padding) for the RSA + encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY + to 0x03 (the other padding bytes are random). After decrypting the + ENCRYPTED-KEY-DATA field, servers that support TLS should issue an + error if these eight padding bytes are 0x03. Version 2.0 servers + receiving blocks padded in this manner will proceed normally. + + + + + + + +Dierks & Allen Standards Track [Page 68] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +F. Security analysis + + The TLS protocol is designed to establish a secure connection between + a client and a server communicating over an insecure channel. This + document makes several traditional assumptions, including that + attackers have substantial computational resources and cannot obtain + secret information from sources outside the protocol. Attackers are + assumed to have the ability to capture, modify, delete, replay, and + otherwise tamper with messages sent over the communication channel. + This appendix outlines how TLS has been designed to resist a variety + of attacks. + +F.1. Handshake protocol + + The handshake protocol is responsible for selecting a CipherSpec and + generating a Master Secret, which together comprise the primary + cryptographic parameters associated with a secure session. The + handshake protocol can also optionally authenticate parties who have + certificates signed by a trusted certificate authority. + +F.1.1. Authentication and key exchange + + TLS supports three authentication modes: authentication of both + parties, server authentication with an unauthenticated client, and + total anonymity. Whenever the server is authenticated, the channel is + secure against man-in-the-middle attacks, but completely anonymous + sessions are inherently vulnerable to such attacks. Anonymous + servers cannot authenticate clients. If the server is authenticated, + its certificate message must provide a valid certificate chain + leading to an acceptable certificate authority. Similarly, + authenticated clients must supply an acceptable certificate to the + server. Each party is responsible for verifying that the other's + certificate is valid and has not expired or been revoked. + + The general goal of the key exchange process is to create a + pre_master_secret known to the communicating parties and not to + attackers. The pre_master_secret will be used to generate the + master_secret (see Section 8.1). The master_secret is required to + generate the certificate verify and finished messages, encryption + keys, and MAC secrets (see Sections 7.4.8, 7.4.9 and 6.3). By sending + a correct finished message, parties thus prove that they know the + correct pre_master_secret. + +F.1.1.1. Anonymous key exchange + + Completely anonymous sessions can be established using RSA or + Diffie-Hellman for key exchange. With anonymous RSA, the client + encrypts a pre_master_secret with the server's uncertified public key + + + +Dierks & Allen Standards Track [Page 69] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + extracted from the server key exchange message. The result is sent in + a client key exchange message. Since eavesdroppers do not know the + server's private key, it will be infeasible for them to decode the + pre_master_secret. (Note that no anonymous RSA Cipher Suites are + defined in this document). + + With Diffie-Hellman, the server's public parameters are contained in + the server key exchange message and the client's are sent in the + client key exchange message. Eavesdroppers who do not know the + private values should not be able to find the Diffie-Hellman result + (i.e. the pre_master_secret). + + Warning: Completely anonymous connections only provide protection + against passive eavesdropping. Unless an independent tamper- + proof channel is used to verify that the finished messages + were not replaced by an attacker, server authentication is + required in environments where active man-in-the-middle + attacks are a concern. + +F.1.1.2. RSA key exchange and authentication + + With RSA, key exchange and server authentication are combined. The + public key may be either contained in the server's certificate or may + be a temporary RSA key sent in a server key exchange message. When + temporary RSA keys are used, they are signed by the server's RSA or + DSS certificate. The signature includes the current + ClientHello.random, so old signatures and temporary keys cannot be + replayed. Servers may use a single temporary RSA key for multiple + negotiation sessions. + + Note: The temporary RSA key option is useful if servers need large + certificates but must comply with government-imposed size limits + on keys used for key exchange. + + After verifying the server's certificate, the client encrypts a + pre_master_secret with the server's public key. By successfully + decoding the pre_master_secret and producing a correct finished + message, the server demonstrates that it knows the private key + corresponding to the server certificate. + + When RSA is used for key exchange, clients are authenticated using + the certificate verify message (see Section 7.4.8). The client signs + a value derived from the master_secret and all preceding handshake + messages. These handshake messages include the server certificate, + which binds the signature to the server, and ServerHello.random, + which binds the signature to the current handshake process. + + + + + +Dierks & Allen Standards Track [Page 70] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +F.1.1.3. Diffie-Hellman key exchange with authentication + + When Diffie-Hellman key exchange is used, the server can either + supply a certificate containing fixed Diffie-Hellman parameters or + can use the server key exchange message to send a set of temporary + Diffie-Hellman parameters signed with a DSS or RSA certificate. + Temporary parameters are hashed with the hello.random values before + signing to ensure that attackers do not replay old parameters. In + either case, the client can verify the certificate or signature to + ensure that the parameters belong to the server. + + If the client has a certificate containing fixed Diffie-Hellman + parameters, its certificate contains the information required to + complete the key exchange. Note that in this case the client and + server will generate the same Diffie-Hellman result (i.e., + pre_master_secret) every time they communicate. To prevent the + pre_master_secret from staying in memory any longer than necessary, + it should be converted into the master_secret as soon as possible. + Client Diffie-Hellman parameters must be compatible with those + supplied by the server for the key exchange to work. + + If the client has a standard DSS or RSA certificate or is + unauthenticated, it sends a set of temporary parameters to the server + in the client key exchange message, then optionally uses a + certificate verify message to authenticate itself. + +F.1.2. Version rollback attacks + + Because TLS includes substantial improvements over SSL Version 2.0, + attackers may try to make TLS-capable clients and servers fall back + to Version 2.0. This attack can occur if (and only if) two TLS- + capable parties use an SSL 2.0 handshake. + + Although the solution using non-random PKCS #1 block type 2 message + padding is inelegant, it provides a reasonably secure way for Version + 3.0 servers to detect the attack. This solution is not secure against + attackers who can brute force the key and substitute a new + ENCRYPTED-KEY-DATA message containing the same key (but with normal + padding) before the application specified wait threshold has expired. + Parties concerned about attacks of this scale should not be using + 40-bit encryption keys anyway. Altering the padding of the least- + significant 8 bytes of the PKCS padding does not impact security for + the size of the signed hashes and RSA key lengths used in the + protocol, since this is essentially equivalent to increasing the + input block size by 8 bytes. + + + + + + +Dierks & Allen Standards Track [Page 71] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +F.1.3. Detecting attacks against the handshake protocol + + An attacker might try to influence the handshake exchange to make the + parties select different encryption algorithms than they would + normally choose. Because many implementations will support 40-bit + exportable encryption and some may even support null encryption or + MAC algorithms, this attack is of particular concern. + + For this attack, an attacker must actively change one or more + handshake messages. If this occurs, the client and server will + compute different values for the handshake message hashes. As a + result, the parties will not accept each others' finished messages. + Without the master_secret, the attacker cannot repair the finished + messages, so the attack will be discovered. + +F.1.4. Resuming sessions + + When a connection is established by resuming a session, new + ClientHello.random and ServerHello.random values are hashed with the + session's master_secret. Provided that the master_secret has not been + compromised and that the secure hash operations used to produce the + encryption keys and MAC secrets are secure, the connection should be + secure and effectively independent from previous connections. + Attackers cannot use known encryption keys or MAC secrets to + compromise the master_secret without breaking the secure hash + operations (which use both SHA and MD5). + + Sessions cannot be resumed unless both the client and server agree. + If either party suspects that the session may have been compromised, + or that certificates may have expired or been revoked, it should + force a full handshake. An upper limit of 24 hours is suggested for + session ID lifetimes, since an attacker who obtains a master_secret + may be able to impersonate the compromised party until the + corresponding session ID is retired. Applications that may be run in + relatively insecure environments should not write session IDs to + stable storage. + +F.1.5. MD5 and SHA + + TLS uses hash functions very conservatively. Where possible, both MD5 + and SHA are used in tandem to ensure that non-catastrophic flaws in + one algorithm will not break the overall protocol. + +F.2. Protecting application data + + The master_secret is hashed with the ClientHello.random and + ServerHello.random to produce unique data encryption keys and MAC + secrets for each connection. + + + +Dierks & Allen Standards Track [Page 72] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Outgoing data is protected with a MAC before transmission. To prevent + message replay or modification attacks, the MAC is computed from the + MAC secret, the sequence number, the message length, the message + contents, and two fixed character strings. The message type field is + necessary to ensure that messages intended for one TLS Record Layer + client are not redirected to another. The sequence number ensures + that attempts to delete or reorder messages will be detected. Since + sequence numbers are 64-bits long, they should never overflow. + Messages from one party cannot be inserted into the other's output, + since they use independent MAC secrets. Similarly, the server-write + and client-write keys are independent so stream cipher keys are used + only once. + + If an attacker does break an encryption key, all messages encrypted + with it can be read. Similarly, compromise of a MAC key can make + message modification attacks possible. Because MACs are also + encrypted, message-alteration attacks generally require breaking the + encryption algorithm as well as the MAC. + + Note: MAC secrets may be larger than encryption keys, so messages can + remain tamper resistant even if encryption keys are broken. + +F.3. Final notes + + For TLS to be able to provide a secure connection, both the client + and server systems, keys, and applications must be secure. In + addition, the implementation must be free of security errors. + + The system is only as strong as the weakest key exchange and + authentication algorithm supported, and only trustworthy + cryptographic functions should be used. Short public keys, 40-bit + bulk encryption keys, and anonymous servers should be used with great + caution. Implementations and users must be careful when deciding + which certificates and certificate authorities are acceptable; a + dishonest certificate authority can do tremendous damage. + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 73] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +G. Patent Statement + + Some of the cryptographic algorithms proposed for use in this + protocol have patent claims on them. In addition Netscape + Communications Corporation has a patent claim on the Secure Sockets + Layer (SSL) work that this standard is based on. The Internet + Standards Process as defined in RFC 2026 requests that a statement be + obtained from a Patent holder indicating that a license will be made + available to applicants under reasonable terms and conditions. + + The Massachusetts Institute of Technology has granted RSA Data + Security, Inc., exclusive sub-licensing rights to the following + patent issued in the United States: + + Cryptographic Communications System and Method ("RSA"), No. + 4,405,829 + + Netscape Communications Corporation has been issued the following + patent in the United States: + + Secure Socket Layer Application Program Apparatus And Method + ("SSL"), No. 5,657,390 + + Netscape Communications has issued the following statement: + + Intellectual Property Rights + + Secure Sockets Layer + + The United States Patent and Trademark Office ("the PTO") + recently issued U.S. Patent No. 5,657,390 ("the SSL Patent") to + Netscape for inventions described as Secure Sockets Layers + ("SSL"). The IETF is currently considering adopting SSL as a + transport protocol with security features. Netscape encourages + the royalty-free adoption and use of the SSL protocol upon the + following terms and conditions: + + * If you already have a valid SSL Ref license today which + includes source code from Netscape, an additional patent + license under the SSL patent is not required. + + * If you don't have an SSL Ref license, you may have a royalty + free license to build implementations covered by the SSL + Patent Claims or the IETF TLS specification provided that you + do not to assert any patent rights against Netscape or other + companies for the implementation of SSL or the IETF TLS + recommendation. + + + + +Dierks & Allen Standards Track [Page 74] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + What are "Patent Claims": + + Patent claims are claims in an issued foreign or domestic patent + that: + + 1) must be infringed in order to implement methods or build + products according to the IETF TLS specification; or + + 2) patent claims which require the elements of the SSL patent + claims and/or their equivalents to be infringed. + + The Internet Society, Internet Architecture Board, Internet + Engineering Steering Group and the Corporation for National Research + Initiatives take no position on the validity or scope of the patents + and patent applications, nor on the appropriateness of the terms of + the assurance. The Internet Society and other groups mentioned above + have not made any determination as to any other intellectual property + rights which may apply to the practice of this standard. Any further + consideration of these matters is the user's own responsibility. + +Security Considerations + + Security issues are discussed throughout this memo. + +References + + [3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To DES," + IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41. + + [BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against + Protocols Based on RSA Encryption Standard PKCS #1" in + Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, pages: + 1--12, 1998. + + [DES] ANSI X3.106, "American National Standard for Information + Systems-Data Link Encryption," American National Standards + Institute, 1983. + + [DH1] W. Diffie and M. E. Hellman, "New Directions in + Cryptography," IEEE Transactions on Information Theory, V. + IT-22, n. 6, Jun 1977, pp. 74-84. + + [DSS] NIST FIPS PUB 186, "Digital Signature Standard," National + Institute of Standards and Technology, U.S. Department of + Commerce, May 18, 1994. + + [FTP] Postel J., and J. Reynolds, "File Transfer Protocol", STD 9, + RFC 959, October 1985. + + + +Dierks & Allen Standards Track [Page 75] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + [HTTP] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext + Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. + + [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- + Hashing for Message Authentication," RFC 2104, February + 1997. + + [IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH + Series in Information Processing, v. 1, Konstanz: Hartung- + Gorre Verlag, 1992. + + [MD2] Kaliski, B., "The MD2 Message Digest Algorithm", RFC 1319, + April 1992. + + [MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, + April 1992. + + [PKCS1] RSA Laboratories, "PKCS #1: RSA Encryption Standard," + version 1.5, November 1993. + + [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax + Standard," version 1.5, November 1993. + + [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax + Standard," version 1.5, November 1993. + + [PKIX] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet + Public Key Infrastructure: Part I: X.509 Certificate and CRL + Profile", RFC 2459, January 1999. + + [RC2] Rivest, R., "A Description of the RC2(r) Encryption + Algorithm", RFC 2268, January 1998. + + [RC4] Thayer, R. and K. Kaukonen, A Stream Cipher Encryption + Algorithm, Work in Progress. + + [RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for + Obtaining Digital Signatures and Public-Key Cryptosystems," + Communications of the ACM, v. 21, n. 2, Feb 1978, pp. 120- + 126. + + [RSADSI] Contact RSA Data Security, Inc., Tel: 415-595-8782 + + [SCH] B. Schneier. Applied Cryptography: Protocols, Algorithms, + and Source Code in C, Published by John Wiley & Sons, Inc. + 1994. + + + + + +Dierks & Allen Standards Track [Page 76] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + [SHA] NIST FIPS PUB 180-1, "Secure Hash Standard," National + Institute of Standards and Technology, U.S. Department of + Commerce, Work in Progress, May 31, 1994. + + [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications + Corp., Feb 9, 1995. + + [SSL3] A. Frier, P. Karlton, and P. Kocher, "The SSL 3.0 Protocol", + Netscape Communications Corp., Nov 18, 1996. + + [TCP] Postel, J., "Transmission Control Protocol," STD 7, RFC 793, + September 1981. + + [TEL] Postel J., and J. Reynolds, "Telnet Protocol + Specifications", STD 8, RFC 854, May 1993. + + [TEL] Postel J., and J. Reynolds, "Telnet Option Specifications", + STD 8, RFC 855, May 1993. + + [X509] CCITT. Recommendation X.509: "The Directory - Authentication + Framework". 1988. + + [XDR] R. Srinivansan, Sun Microsystems, RFC-1832: XDR: External + Data Representation Standard, August 1995. + +Credits + + Win Treese + Open Market + + EMail: treese@openmarket.com + + + Editors + + Christopher Allen Tim Dierks + Certicom Certicom + + EMail: callen@certicom.com EMail: tdierks@certicom.com + + + Authors' Addresses + + Tim Dierks Philip L. Karlton + Certicom Netscape Communications + + EMail: tdierks@certicom.com + + + + +Dierks & Allen Standards Track [Page 77] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Alan O. Freier Paul C. Kocher + Netscape Communications Independent Consultant + + EMail: freier@netscape.com EMail: pck@netcom.com + + + Other contributors + + Martin Abadi Robert Relyea + Digital Equipment Corporation Netscape Communications + + EMail: ma@pa.dec.com EMail: relyea@netscape.com + + Ran Canetti Jim Roskind + IBM Watson Research Center Netscape Communications + + EMail: canetti@watson.ibm.com EMail: jar@netscape.com + + + Taher Elgamal Micheal J. Sabin, Ph. D. + Securify Consulting Engineer + + EMail: elgamal@securify.com EMail: msabin@netcom.com + + + Anil R. Gangolli Dan Simon + Structured Arts Computing Corp. Microsoft + + EMail: gangolli@structuredarts.com EMail: dansimon@microsoft.com + + + Kipp E.B. Hickman Tom Weinstein + Netscape Communications Netscape Communications + + EMail: kipp@netscape.com EMail: tomw@netscape.com + + + Hugo Krawczyk + IBM Watson Research Center + + EMail: hugo@watson.ibm.com + +Comments + + The discussion list for the IETF TLS working group is located at the + e-mail address <ietf-tls@lists.consensus.com>. Information on the + group and information on how to subscribe to the list is at + <http://lists.consensus.com/>. + + + +Dierks & Allen Standards Track [Page 78] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + + Archives of the list can be found at: + <http://www.imc.org/ietf-tls/mail-archive/> + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 79] + +RFC 2246 The TLS Protocol Version 1.0 January 1999 + + +Full Copyright Statement + + Copyright (C) The Internet Society (1999). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + + + + + + + + + + + + + + + + + + + + + + + +Dierks & Allen Standards Track [Page 80] + |