summaryrefslogtreecommitdiff
path: root/doc/rfc/rfc4868.txt
diff options
context:
space:
mode:
Diffstat (limited to 'doc/rfc/rfc4868.txt')
-rw-r--r--doc/rfc/rfc4868.txt1179
1 files changed, 1179 insertions, 0 deletions
diff --git a/doc/rfc/rfc4868.txt b/doc/rfc/rfc4868.txt
new file mode 100644
index 0000000..c077acd
--- /dev/null
+++ b/doc/rfc/rfc4868.txt
@@ -0,0 +1,1179 @@
+
+
+
+
+
+
+Network Working Group S. Kelly
+Request for Comments: 4868 Aruba Networks
+Category: Standards Track S. Frankel
+ NIST
+ May 2007
+
+
+ Using HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512 with IPsec
+
+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 IETF Trust (2007).
+
+Abstract
+
+ This specification describes the use of Hashed Message Authentication
+ Mode (HMAC) in conjunction with the SHA-256, SHA-384, and SHA-512
+ algorithms in IPsec. These algorithms may be used as the basis for
+ data origin authentication and integrity verification mechanisms for
+ the Authentication Header (AH), Encapsulating Security Payload (ESP),
+ Internet Key Exchange Protocol (IKE), and IKEv2 protocols, and also
+ as Pseudo-Random Functions (PRFs) for IKE and IKEv2. Truncated
+ output lengths are specified for the authentication-related variants,
+ with the corresponding algorithms designated as HMAC-SHA-256-128,
+ HMAC-SHA-384-192, and HMAC-SHA-512-256. The PRF variants are not
+ truncated, and are called PRF-HMAC-SHA-256, PRF-HMAC-SHA-384, and
+ PRF-HMAC-SHA-512.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 1]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+Table of Contents
+
+ 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 2. The HMAC-SHA-256+ Algorithms . . . . . . . . . . . . . . . . . 3
+ 2.1. Keying Material . . . . . . . . . . . . . . . . . . . . . 3
+ 2.1.1. Data Origin Authentication and Integrity
+ Verification Usage . . . . . . . . . . . . . . . . . . 4
+ 2.1.2. Pseudo-Random Function (PRF) Usage . . . . . . . . . . 4
+ 2.1.3. Randomness and Key Strength . . . . . . . . . . . . . 5
+ 2.1.4. Key Distribution . . . . . . . . . . . . . . . . . . . 5
+ 2.1.5. Refreshing Keys . . . . . . . . . . . . . . . . . . . 5
+ 2.2. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 6
+ 2.3. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 6
+ 2.4. Using HMAC-SHA-256+ as PRFs in IKE and IKEv2 . . . . . . . 7
+ 2.5. Interactions with the ESP, IKE, or IKEv2 Cipher
+ Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 7
+ 2.6. HMAC-SHA-256+ Parameter Summary . . . . . . . . . . . . . 7
+ 2.7. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . 7
+ 2.7.1. PRF Test Vectors . . . . . . . . . . . . . . . . . . . 8
+ 2.7.2. Authenticator Test Vectors . . . . . . . . . . . . . . 11
+ 3. Security Considerations . . . . . . . . . . . . . . . . . . . 17
+ 3.1. HMAC Key Length vs Truncation Length . . . . . . . . . . . 17
+ 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
+ 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
+ 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
+ 6.1. Normative References . . . . . . . . . . . . . . . . . . . 19
+ 6.2. Informative References . . . . . . . . . . . . . . . . . . 20
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 2]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+1. Introduction
+
+ This document specifies the use of SHA-256, SHA-384, and SHA-512
+ [SHA2-1] combined with HMAC [HMAC] as data origin authentication and
+ integrity verification mechanisms for the IPsec AH [AH], ESP [ESP],
+ IKE [IKE], and IKEv2 [IKEv2] protocol. Output truncation is
+ specified for these variants, with the corresponding algorithms
+ designated as HMAC-SHA-256-128, HMAC-SHA-384-192, and HMAC-SHA-512-
+ 256. These truncation lengths are chosen in accordance with the
+ birthday bound for each algorithm.
+
+ This specification also describes untruncated variants of these
+ algorithms as Pseudo-Random Functions (PRFs) for use with IKE and
+ IKEv2, and those algorithms are called PRF-HMAC-SHA-256, PRF-HMAC-
+ SHA-384, and PRF-HMAC-SHA-512. For ease of reference, these PRF
+ algorithms and the authentication variants described above are
+ collectively referred to below as "the HMAC-SHA-256+ algorithms".
+
+ The goal of the PRF variants are to provide secure pseudo-random
+ functions suitable for generation of keying material and other
+ protocol-specific numeric quantities, while the goal of the
+ authentication variants is to ensure that packets are authentic and
+ cannot be modified in transit. The relative security of HMAC-SHA-
+ 256+ when used in either case is dependent on the distribution scope
+ and unpredictability of the associated secret key. If the key is
+ unpredictable and known only by the sender and recipient, these
+ algorithms ensure that only parties holding an identical key can
+ derive the associated values.
+
+2. The HMAC-SHA-256+ Algorithms
+
+ [SHA2-1] and [SHA2-2] describe the underlying SHA-256, SHA-384, and
+ SHA-512 algorithms, while [HMAC] describes the HMAC algorithm. The
+ HMAC algorithm provides a framework for inserting various hashing
+ algorithms such as SHA-256, and [SHA256+] describes combined usage of
+ these algorithms. The following sections describe the various
+ characteristics and requirements of the HMAC-SHA-256+ algorithms when
+ used with IPsec.
+
+2.1. Keying Material
+
+ Requirements for keying material vary depending on whether the
+ algorithm is functioning as a PRF or as an authentication/integrity
+ mechanism. In the case of authentication/integrity, key lengths are
+ fixed according to the output length of the algorithm in use. In the
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 3]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ case of PRFs, key lengths are variable, but guidance is given to
+ ensure interoperability. These distinctions are described further
+ below.
+
+ Before describing key requirements for each usage, it is important to
+ clarify some terms we use below:
+
+ Block size: the size of the data block the underlying hash algorithm
+ operates upon. For SHA-256, this is 512 bits, for SHA-384 and
+ SHA-512, this is 1024 bits.
+
+ Output length: the size of the hash value produced by the underlying
+ hash algorithm. For SHA-256, this is 256 bits, for SHA-384 this
+ is 384 bits, and for SHA-512, this is 512 bits.
+
+ Authenticator length: the size of the "authenticator" in bits. This
+ only applies to authentication/integrity related algorithms, and
+ refers to the bit length remaining after truncation. In this
+ specification, this is always half the output length of the
+ underlying hash algorithm.
+
+2.1.1. Data Origin Authentication and Integrity Verification Usage
+
+ HMAC-SHA-256+ are secret key algorithms. While no fixed key length
+ is specified in [HMAC], this specification requires that when used as
+ an integrity/authentication algorithm, a fixed key length equal to
+ the output length of the hash functions MUST be supported, and key
+ lengths other than the output length of the associated hash function
+ MUST NOT be supported.
+
+ These key length restrictions are based in part on the
+ recommendations in [HMAC] (key lengths less than the output length
+ decrease security strength, and keys longer than the output length do
+ not significantly increase security strength), and in part because
+ allowing variable length keys for IPsec authenticator functions would
+ create interoperability issues.
+
+2.1.2. Pseudo-Random Function (PRF) Usage
+
+ IKE and IKEv2 use PRFs for generating keying material and for
+ authentication of the IKE Security Association. The IKEv2
+ specification differentiates between PRFs with fixed key sizes and
+ those with variable key sizes, and so we give some special guidance
+ for this below.
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 4]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ When a PRF described in this document is used with IKE or IKEv2, it
+ is considered to have a variable key length, and keys are derived in
+ the following ways (note that we simply reiterate that which is
+ specified in [HMAC]):
+
+ o If the length of the key is exactly the algorithm block size, use
+ it as-is.
+
+ o If the key is shorter than the block size, lengthen it to exactly
+ the block size by padding it on the right with zero bits.
+ However, note that [HMAC] strongly discourages a key length less
+ than the output length. Nonetheless, we describe handling of
+ shorter lengths here in recognition of shorter lengths typically
+ chosen for IKE or IKEv2 pre-shared keys.
+
+ o If the key is longer than the block size, shorten it by computing
+ the corresponding hash algorithm output over the entire key value,
+ and treat the resulting output value as your HMAC key. Note that
+ this will always result in a key that is less than the block size
+ in length, and this key value will therefore require zero-padding
+ (as described above) prior to use.
+
+2.1.3. Randomness and Key Strength
+
+ [HMAC] discusses requirements for key material, including a
+ requirement for strong randomness. Therefore, a strong pseudo-random
+ function MUST be used to generate the required key for use with HMAC-
+ SHA-256+. At the time of this writing there are no published weak
+ keys for use with any HMAC-SHA-256+ algorithms.
+
+2.1.4. Key Distribution
+
+ [ARCH] describes the general mechanism for obtaining keying material
+ when multiple keys are required for a single SA (e.g., when an ESP SA
+ requires a key for confidentiality and a key for authentication). In
+ order to provide data origin authentication and integrity
+ verification, the key distribution mechanism must ensure that unique
+ keys are allocated and that they are distributed only to the parties
+ participating in the communication.
+
+2.1.5. Refreshing Keys
+
+ Currently, there are no practical attacks against the algorithms
+ recommended here, and especially against the key sizes recommended
+ here. However, as noted in [HMAC] "...periodic key refreshment is a
+ fundamental security practice that helps against potential weaknesses
+ of the function and keys, and limits the damage of an exposed key".
+
+
+
+
+Kelly & Frankel Standards Track [Page 5]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Putting this into perspective, this specification requires 256, 384,
+ or 512-bit keys produced by a strong PRF for use as a MAC. A brute
+ force attack on such keys would take longer to mount than the
+ universe has been in existence. On the other hand, weak keys (e.g.,
+ dictionary words) would be dramatically less resistant to attack. It
+ is important to take these points, along with the specific threat
+ model for your particular application and the current state of the
+ art with respect to attacks on SHA-256, SHA-384, and SHA-512 into
+ account when determining an appropriate upper bound for HMAC key
+ lifetimes.
+
+2.2. Padding
+
+ The HMAC-SHA-256 algorithms operate on 512-bit blocks of data, while
+ the HMAC-SHA-384 and HMAC-SHA-512 algorithms operate on 1024-bit
+ blocks of data. Padding requirements are specified in [SHA2-1] as
+ part of the underlying SHA-256, SHA-384, and SHA-512 algorithms, so
+ if you implement according to [SHA2-1], you do not need to add any
+ additional padding as far as the HMAC-SHA-256+ algorithms specified
+ here are concerned. With regard to "implicit packet padding" as
+ defined in [AH], no implicit packet padding is required.
+
+2.3. Truncation
+
+ The HMAC-SHA-256+ algorithms each produce an nnn-bit value, where nnn
+ corresponds to the output bit length of the algorithm, e.g., HMAC-
+ SHA-nnn. For use as an authenticator, this nnn-bit value can be
+ truncated as described in [HMAC]. When used as a data origin
+ authentication and integrity verification algorithm in ESP, AH, IKE,
+ or IKEv2, a truncated value using the first nnn/2 bits -- exactly
+ half the algorithm output size -- MUST be supported. No other
+ authenticator value lengths are supported by this specification.
+
+ Upon sending, the truncated value is stored within the authenticator
+ field. Upon receipt, the entire nnn-bit value is computed and the
+ first nnn/2 bits are compared to the value stored in the
+ authenticator field, with the value of 'nnn' depending on the
+ negotiated algorithm.
+
+ [HMAC] discusses potential security benefits resulting from
+ truncation of the output MAC value, and in general, encourages HMAC
+ users to perform MAC truncation. In the context of IPsec, a
+ truncation length of nnn/2 bits is selected because it corresponds to
+ the birthday attack bound for each of the HMAC-SHA-256+ algorithms,
+ and it simultaneously serves to minimize the additional bits on the
+ wire resulting from use of this facility.
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 6]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+2.4. Using HMAC-SHA-256+ as PRFs in IKE and IKEv2
+
+ The PRF-HMAC-SHA-256 algorithm is identical to HMAC-SHA-256-128,
+ except that variable-length keys are permitted, and the truncation
+ step is NOT performed. Likewise, the implementations of PRF-HMAC-
+ SHA-384 and PRF-HMAC-SHA-512 are identical to those of HMAC-SHA-384-
+ 192 and HMAC-SHA-512-256 respectively, except that again, variable-
+ length keys are permitted, and truncation is NOT performed.
+
+2.5. Interactions with the ESP, IKE, or IKEv2 Cipher Mechanisms
+
+ As of this writing, there are no known issues that preclude the use
+ of the HMAC-SHA-256+ algorithms with any specific cipher algorithm.
+
+2.6. HMAC-SHA-256+ Parameter Summary
+
+ The following table serves to summarize the various quantities
+ associated with the HMAC-SHA-256+ algorithms. In this table, "var"
+ stands for "variable".
+
+ +------------------+--------+--------+--------+--------+------------+
+ | Algorithm | Block | Output | Trunc. | Key | Algorithm |
+ | ID | Size | Length | Length | Length | Type |
+ +==================+========+========+========+========+============+
+ | HMAC-SHA-256-128 | 512 | 256 | 128 | 256 | auth/integ |
+ +------------------+--------+--------+--------+--------+------------+
+ | HMAC-SHA-384-192 | 1024 | 384 | 192 | 384 | auth/integ |
+ +------------------+--------+--------+--------+--------+------------+
+ | HMAC-SHA-512-256 | 1024 | 512 | 256 | 512 | auth/integ |
+ +------------------+--------+--------+--------+--------+------------+
+ | PRF-HMAC-SHA-256 | 512 | 256 | (none) | var | PRF |
+ +------------------+--------+--------+--------+--------+------------+
+ | PRF-HMAC-SHA-384 | 1024 | 384 | (none) | var | PRF |
+ +------------------+--------+--------+--------+--------+------------+
+ | PRF-HMAC-SHA-512 | 1024 | 512 | (none) | var | PRF |
+ +------------------+--------+--------+--------+--------+------------+
+
+
+2.7. Test Vectors
+
+ The following test cases include the key, the data, and the resulting
+ authenticator, and/or PRF values for each algorithm. The values of
+ keys and data are either ASCII character strings (surrounded by
+ double quotes) or hexadecimal numbers. If a value is an ASCII
+ character string, then the HMAC computation for the corresponding
+ test case DOES NOT include the trailing null character ('\0') of the
+ string. The computed HMAC values are all hexadecimal numbers.
+
+
+
+
+Kelly & Frankel Standards Track [Page 7]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+2.7.1. PRF Test Vectors
+
+ These test cases were borrowed from RFC 4231 [HMAC-TEST]. For
+ reference implementations of the underlying hash algorithms, see
+ [SHA256+]. Note that for testing purposes, PRF output is considered
+ to be simply the untruncated algorithm output.
+
+ Test Case PRF-1:
+ Key = 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b (20 bytes)
+
+ Data = 4869205468657265 ("Hi There")
+
+ PRF-HMAC-SHA-256 = b0344c61d8db38535ca8afceaf0bf12b
+ 881dc200c9833da726e9376c2e32cff7
+
+ PRF-HMAC-SHA-384 = afd03944d84895626b0825f4ab46907f
+ 15f9dadbe4101ec682aa034c7cebc59c
+ faea9ea9076ede7f4af152e8b2fa9cb6
+
+ PRF-HMAC-SHA-512 = 87aa7cdea5ef619d4ff0b4241a1d6cb0
+ 2379f4e2ce4ec2787ad0b30545e17cde
+ daa833b7d6b8a702038b274eaea3f4e4
+ be9d914eeb61f1702e696c203a126854
+
+
+ Test Case PRF-2:
+ Key = 4a656665 ("Jefe")
+
+ Data = 7768617420646f2079612077616e7420 ("what do ya want ")
+ 666f72206e6f7468696e673f ("for nothing?")
+
+ PRF-HMAC-SHA-256 = 5bdcc146bf60754e6a042426089575c7
+ 5a003f089d2739839dec58b964ec3843
+
+ PRF-HMAC-SHA-384 = af45d2e376484031617f78d2b58a6b1b
+ 9c7ef464f5a01b47e42ec3736322445e
+ 8e2240ca5e69e2c78b3239ecfab21649
+
+ PRF-HMAC-SHA-512 = 164b7a7bfcf819e2e395fbe73b56e0a3
+ 87bd64222e831fd610270cd7ea250554
+ 9758bf75c05a994a6d034f65f8f0e6fd
+ caeab1a34d4a6b4b636e070a38bce737
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 8]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case PRF-3:
+ Key aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaa (20 bytes)
+
+ Data = dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddd (50 bytes)
+
+ PRF-HMAC-SHA-256 = 773ea91e36800e46854db8ebd09181a7
+ 2959098b3ef8c122d9635514ced565fe
+
+ PRF-HMAC-SHA-384 = 88062608d3e6ad8a0aa2ace014c8a86f
+ 0aa635d947ac9febe83ef4e55966144b
+ 2a5ab39dc13814b94e3ab6e101a34f27
+
+ PRF-HMAC-SHA-512 = fa73b0089d56a284efb0f0756c890be9
+ b1b5dbdd8ee81a3655f83e33b2279d39
+ bf3e848279a722c806b485a47e67c807
+ b946a337bee8942674278859e13292fb
+
+
+ Test Case PRF-4:
+ Key = 0102030405060708090a0b0c0d0e0f10
+ 111213141516171819 (25 bytes)
+
+ Data = cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcd (50 bytes)
+
+ PRF-HMAC-SHA-256 = 82558a389a443c0ea4cc819899f2083a
+ 85f0faa3e578f8077a2e3ff46729665b
+
+ PRF-HMAC-SHA-384 = 3e8a69b7783c25851933ab6290af6ca7
+ 7a9981480850009cc5577c6e1f573b4e
+ 6801dd23c4a7d679ccf8a386c674cffb
+
+ PRF-HMAC-SHA-512 = b0ba465637458c6990e5a8c5f61d4af7
+ e576d97ff94b872de76f8050361ee3db
+ a91ca5c11aa25eb4d679275cc5788063
+ a5f19741120c4f2de2adebeb10a298dd
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 9]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case PRF-5:
+ Key = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaa (131 bytes)
+
+ Data = 54657374205573696e67204c61726765 ("Test Using Large")
+ 72205468616e20426c6f636b2d53697a ("r Than Block-Siz")
+ 65204b6579202d2048617368204b6579 ("e Key - Hash Key")
+ 204669727374 (" First")
+
+
+ PRF-HMAC-SHA-256 = 60e431591ee0b67f0d8a26aacbf5b77f
+ 8e0bc6213728c5140546040f0ee37f54
+
+ PRF-HMAC-SHA-384 = 4ece084485813e9088d2c63a041bc5b4
+ 4f9ef1012a2b588f3cd11f05033ac4c6
+ 0c2ef6ab4030fe8296248df163f44952
+
+ PRF-HMAC-SHA-512 = 80b24263c7c1a3ebb71493c1dd7be8b4
+ 9b46d1f41b4aeec1121b013783f8f352
+ 6b56d037e05f2598bd0fd2215d6a1e52
+ 95e64f73f63f0aec8b915a985d786598
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 10]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case PRF-6:
+
+ Key = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaa (131 bytes)
+
+ Data = 54686973206973206120746573742075 ("This is a test u")
+ 73696e672061206c6172676572207468 ("sing a larger th")
+ 616e20626c6f636b2d73697a65206b65 ("an block-size ke")
+ 7920616e642061206c61726765722074 ("y and a larger t")
+ 68616e20626c6f636b2d73697a652064 ("han block-size d")
+ 6174612e20546865206b6579206e6565 ("ata. The key nee")
+ 647320746f2062652068617368656420 ("ds to be hashed ")
+ 6265666f7265206265696e6720757365 ("before being use")
+ 642062792074686520484d414320616c ("d by the HMAC al")
+ 676f726974686d2e ("gorithm.")
+
+ PRF-HMAC-SHA-256 = 9b09ffa71b942fcb27635fbcd5b0e944
+ bfdc63644f0713938a7f51535c3a35e2
+
+ PRF-HMAC-SHA-384 = 6617178e941f020d351e2f254e8fd32c
+ 602420feb0b8fb9adccebb82461e99c5
+ a678cc31e799176d3860e6110c46523e
+
+ PRF-HMAC-SHA-512 = e37b6a775dc87dbaa4dfa9f96e5e3ffd
+ debd71f8867289865df5a32d20cdc944
+ b6022cac3c4982b10d5eeb55c3e4de15
+ 134676fb6de0446065c97440fa8c6a58
+
+
+2.7.2. Authenticator Test Vectors
+
+ The following sections are test cases for HMAC-SHA256-128, HMAC-
+ SHA384-192, and HMAC-SHA512-256. PRF outputs are also included for
+ convenience. These test cases were generated using the SHA256+
+ reference code provided in [SHA256+].
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 11]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+2.7.2.1. SHA256 Authentication Test Vectors
+
+ Test Case AUTH256-1:
+ Key = 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b (32 bytes)
+
+ Data = 4869205468657265 ("Hi There")
+
+ PRF-HMAC-SHA-256 = 198a607eb44bfbc69903a0f1cf2bbdc5
+ ba0aa3f3d9ae3c1c7a3b1696a0b68cf7
+
+ HMAC-SHA-256-128 = 198a607eb44bfbc69903a0f1cf2bbdc5
+
+
+
+ Test Case AUTH256-2:
+ Key = 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+
+ Data = 7768617420646f2079612077616e7420 ("what do ya want ")
+ 666f72206e6f7468696e673f ("for nothing?")
+
+ PRF-HMAC-SHA-256 = 167f928588c5cc2eef8e3093caa0e87c
+ 9ff566a14794aa61648d81621a2a40c6
+
+ HMAC-SHA-256-128 = 167f928588c5cc2eef8e3093caa0e87c
+
+
+
+ Test Case AUTH256-3:
+ Key = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa (32 bytes)
+
+ Data = dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddd (50 bytes)
+
+ PRF-HMAC-SHA-256 = cdcb1220d1ecccea91e53aba3092f962
+ e549fe6ce9ed7fdc43191fbde45c30b0
+
+ HMAC-SHA-256-128 = cdcb1220d1ecccea91e53aba3092f962
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 12]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case AUTH256-4:
+ Key = 0102030405060708090a0b0c0d0e0f10
+ 1112131415161718191a1b1c1d1e1f20 (32 bytes)
+
+ Data = cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcd (50 bytes)
+
+ PRF-HMAC-SHA-256 = 372efcf9b40b35c2115b1346903d2ef4
+ 2fced46f0846e7257bb156d3d7b30d3f
+
+ HMAC-SHA-256-128 = 372efcf9b40b35c2115b1346903d2ef4
+
+
+2.7.2.2. SHA384 Authentication Test Vectors
+
+ Test Case AUTH384-1:
+ Key = 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b (48 bytes)
+
+ Data = 4869205468657265 ("Hi There")
+
+ PRF-HMAC-SHA-384 = b6a8d5636f5c6a7224f9977dcf7ee6c7
+ fb6d0c48cbdee9737a959796489bddbc
+ 4c5df61d5b3297b4fb68dab9f1b582c2
+
+ HMAC-SHA-384-128 = b6a8d5636f5c6a7224f9977dcf7ee6c7
+ fb6d0c48cbdee973
+
+
+ Test Case AUTH384-2:
+ Key = 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+
+ Data = 7768617420646f2079612077616e7420 ("what do ya want ")
+ 666f72206e6f7468696e673f ("for nothing?")
+
+ PRF-HMAC-SHA-384 = 2c7353974f1842fd66d53c452ca42122
+ b28c0b594cfb184da86a368e9b8e16f5
+ 349524ca4e82400cbde0686d403371c9
+
+ HMAC-SHA-384-192 = 2c7353974f1842fd66d53c452ca42122
+ b28c0b594cfb184d
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 13]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case AUTH384-3:
+ Key = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa (48 bytes)
+
+ Data = dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddd (50 bytes)
+
+ PRF-HMAC-SHA-384 = 809f439be00274321d4a538652164b53
+ 554a508184a0c3160353e3428597003d
+ 35914a18770f9443987054944b7c4b4a
+
+ HMAC-SHA-384-192 = 809f439be00274321d4a538652164b53
+ 554a508184a0c316
+
+
+ Test Case AUTH384-4:
+ Key = 0102030405060708090a0b0c0d0e0f10
+ 1112131415161718191a1b1c1d1e1f20
+ 0a0b0c0d0e0f10111213141516171819 (48 bytes)
+
+ Data = cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcd (50 bytes)
+
+ PRF-HMAC-SHA-384 = 5b540085c6e6358096532b2493609ed1
+ cb298f774f87bb5c2ebf182c83cc7428
+ 707fb92eab2536a5812258228bc96687
+
+ HMAC-SHA-384-192 = 5b540085c6e6358096532b2493609ed1
+ cb298f774f87bb5c
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 14]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+2.7.2.3. SHA512 Authentication Test Vectors
+
+ Test Case AUTH512-1:
+ Key = 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
+ 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b (64 bytes)
+
+ Data = 4869205468657265 ("Hi There")
+
+ PRF-HMAC-SHA-512 = 637edc6e01dce7e6742a99451aae82df
+ 23da3e92439e590e43e761b33e910fb8
+ ac2878ebd5803f6f0b61dbce5e251ff8
+ 789a4722c1be65aea45fd464e89f8f5b
+
+ HMAC-SHA-512-256 = 637edc6e01dce7e6742a99451aae82df
+ 23da3e92439e590e43e761b33e910fb8
+
+
+ Test Case AUTH512-2:
+ Key = 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+ 4a6566654a6566654a6566654a656665 ("JefeJefeJefeJefe")
+
+ Data = 7768617420646f2079612077616e7420 ("what do ya want ")
+ 666f72206e6f7468696e673f ("for nothing?")
+
+ PRF-HMAC-SHA-512 = cb370917ae8a7ce28cfd1d8f4705d614
+ 1c173b2a9362c15df235dfb251b15454
+ 6aa334ae9fb9afc2184932d8695e397b
+ fa0ffb93466cfcceaae38c833b7dba38
+
+ HMAC-SHA-512-256 = cb370917ae8a7ce28cfd1d8f4705d614
+ 1c173b2a9362c15df235dfb251b15454
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 15]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ Test Case AUTH512-3:
+ Key = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa (64 bytes)
+
+ Data = dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddddddddddddddddddddddddddddddd
+ dddd (50 bytes)
+
+ PRF-HMAC-SHA-512 = 2ee7acd783624ca9398710f3ee05ae41
+ b9f9b0510c87e49e586cc9bf961733d8
+ 623c7b55cebefccf02d5581acc1c9d5f
+ b1ff68a1de45509fbe4da9a433922655
+
+ HMAC-SHA-512-256 = 2ee7acd783624ca9398710f3ee05ae41
+ b9f9b0510c87e49e586cc9bf961733d8
+
+
+ Test Case AUTH512-4:
+ Key = 0a0b0c0d0e0f10111213141516171819
+ 0102030405060708090a0b0c0d0e0f10
+ 1112131415161718191a1b1c1d1e1f20
+ 2122232425262728292a2b2c2d2e2f30
+ 3132333435363738393a3b3c3d3e3f40 (64 bytes)
+
+ Data = cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd
+ cdcd (50 bytes)
+
+ PRF-HMAC-SHA-512 = 5e6688e5a3daec826ca32eaea224eff5
+ e700628947470e13ad01302561bab108
+ b8c48cbc6b807dcfbd850521a685babc
+ 7eae4a2a2e660dc0e86b931d65503fd2
+
+ HMAC-SHA-512-256 = 5e6688e5a3daec826ca32eaea224eff5
+ e700628947470e13ad01302561bab108
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 16]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+3. Security Considerations
+
+ In a general sense, the security provided by the HMAC-SHA-256+
+ algorithms is based both upon the strength of the underlying hash
+ algorithm, and upon the additional strength derived from the HMAC
+ construct. At the time of this writing, there are no practical
+ cryptographic attacks against SHA-256, SHA-384, SHA-512, or HMAC.
+ However, as with any cryptographic algorithm, an important component
+ of these algorithms' strength lies in the correctness of the
+ algorithm implementation, the security of the key management
+ mechanism, the strength of the associated secret key, and upon the
+ correctness of the implementation in all of the participating
+ systems. This specification contains test vectors to assist in
+ verifying the correctness of the algorithm implementation, but these
+ in no way verify the correctness (or security) of the surrounding
+ security infrastructure.
+
+3.1. HMAC Key Length vs Truncation Length
+
+ There are important differences between the security levels afforded
+ by HMAC-SHA1-96 [HMAC-SHA1] and the HMAC-SHA-256+ algorithms, but
+ there are also considerations that are somewhat counter-intuitive.
+ There are two different axes along which we gauge the security of
+ these algorithms: HMAC output length and HMAC key length. If we
+ assume the HMAC key is a well-guarded secret that can only be
+ determined through offline attacks on observed values, and that its
+ length is less than or equal to the output length of the underlying
+ hash algorithm, then the key's strength is directly proportional to
+ its length. And if we assume an adversary has no knowledge of the
+ HMAC key, then the probability of guessing a correct MAC value for
+ any given packet is directly proportional to the HMAC output length.
+
+ This specification defines truncation to output lengths of either 128
+ 192, or 256 bits. It is important to note that at this time, it is
+ not clear that HMAC-SHA-256 with a truncation length of 128 bits is
+ any more secure than HMAC-SHA1 with the same truncation length,
+ assuming the adversary has no knowledge of the HMAC key. This is
+ because in such cases, the adversary must predict only those bits
+ that remain after truncation. Since in both cases that output length
+ is the same (128 bits), the adversary's odds of correctly guessing
+ the value are also the same in either case: 1 in 2^128. Again, if we
+ assume the HMAC key remains unknown to the attacker, then only a bias
+ in one of the algorithms would distinguish one from the other.
+ Currently, no such bias is known to exist in either HMAC-SHA1 or
+ HMAC-SHA-256+.
+
+ If, on the other hand, the attacker is focused on guessing the HMAC
+ key, and we assume that the hash algorithms are indistinguishable
+
+
+
+Kelly & Frankel Standards Track [Page 17]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+ when viewed as PRF's, then the HMAC key length provides a direct
+ measure of the underlying security: the longer the key, the harder it
+ is to guess. This means that with respect to passive attacks on the
+ HMAC key, size matters - and the HMAC-SHA-256+ algorithms provide
+ more security in this regard than HMAC-SHA1-96.
+
+4. IANA Considerations
+
+ This document does not specify the conventions for using SHA256+ for
+ IKE Phase 1 negotiations, except to note that IANA has made the
+ following IKE hash algorithm attribute assignments:
+
+ SHA2-256: 4
+
+ SHA2-384: 5
+
+ SHA2-512: 6
+
+ For IKE Phase 2 negotiations, IANA has assigned the following
+ authentication algorithm identifiers:
+
+ HMAC-SHA2-256: 5
+
+ HMAC-SHA2-384: 6
+
+ HMAC-SHA2-512: 7
+
+ For use of HMAC-SHA-256+ as a PRF in IKEv2, IANA has assigned the
+ following IKEv2 Pseudo-random function (type 2) transform
+ identifiers:
+
+ PRF_HMAC_SHA2_256 5
+
+ PRF_HMAC_SHA2_384 6
+
+ PRF_HMAC_SHA2_512 7
+
+ For the use of HMAC-SHA-256+ algorithms for data origin
+ authentication and integrity verification in IKEv2, ESP, or AH, IANA
+ has assigned the following IKEv2 integrity (type 3) transform
+ identifiers:
+
+ AUTH_HMAC_SHA2_256_128 12
+
+ AUTH_HMAC_SHA2_384_192 13
+
+ AUTH_HMAC_SHA2_512_256 14
+
+
+
+
+Kelly & Frankel Standards Track [Page 18]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+5. Acknowledgements
+
+ Portions of this text were unabashedly borrowed from [HMAC-SHA1] and
+ [HMAC-TEST]. Thanks to Hugo Krawczyk for comments and
+ recommendations on early revisions of this document, and thanks also
+ to Russ Housley and Steve Bellovin for various security-related
+ comments and recommendations.
+
+6. References
+
+6.1. Normative References
+
+ [AH] Kent, S., "IP Authentication Header", RFC 4302,
+ December 2005.
+
+ [ARCH] Kent, S. and K. Seo, "Security Architecture for the
+ Internet Protocol", RFC 4301, December 2005.
+
+ [ESP] Kent, S., "IP Encapsulating Security Payload (ESP)",
+ RFC 4303, December 2005.
+
+ [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
+ Hashing for Message Authentication", RFC 2104,
+ February 1997.
+
+ [HMAC-SHA1] Madsen, C. and R. Glenn, "The Use of HMAC-SHA-1-96
+ within ESP and AH", RFC 2404, November 1998.
+
+ [HMAC-TEST] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA-
+ 224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512",
+ RFC 4231, December 2005.
+
+ [IKE] Harkins, D. and D. Carrel, "The Internet Key Exchange
+ (IKE)", RFC 2409, November 1998.
+
+ [IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
+ RFC 4306, December 2005.
+
+ [SHA2-1] NIST, "FIPS PUB 180-2 'Specifications for the Secure
+ Hash Standard'", 2004 FEB, <http://csrc.nist.gov/
+ publications/fips/fips180-2/
+ fips180-2withchangenotice.pdf>.
+
+ [SHA256+] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
+ (SHA and HMAC-SHA)", RFC 4634, July 2006.
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 19]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+6.2. Informative References
+
+ [SHA2-2] NIST, "Descriptions of SHA-256, SHA-384, and SHA-512",
+ 2001 MAY,
+ <http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf>.
+
+Authors' Addresses
+
+ Scott G. Kelly
+ Aruba Networks
+ 1322 Crossman Ave
+ Sunnyvale, CA 94089
+ US
+
+ EMail: scott@hyperthought.com
+
+
+ Sheila Frankel
+ NIST
+ Bldg. 222 Room B264
+ Gaithersburg, MD 20899
+ US
+
+ EMail: sheila.frankel@nist.gov
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 20]
+
+RFC 4868 HMAC-SHA256, SHA384, and SHA512 in IPsec May 2007
+
+
+Full Copyright Statement
+
+ Copyright (C) The IETF Trust (2007).
+
+ This document is subject to the rights, licenses and restrictions
+ contained in BCP 78, and except as set forth therein, the authors
+ retain all their rights.
+
+ This document and the information contained herein are provided on an
+ "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+ OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
+ THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
+
+Intellectual Property
+
+ The IETF takes no position regarding the validity or scope of any
+ Intellectual Property Rights or other rights that might be claimed to
+ pertain to the implementation or use of the technology described in
+ this document or the extent to which any license under such rights
+ might or might not be available; nor does it represent that it has
+ made any independent effort to identify any such rights. Information
+ on the procedures with respect to rights in RFC documents can be
+ found in BCP 78 and BCP 79.
+
+ Copies of IPR disclosures made to the IETF Secretariat and any
+ assurances of licenses to be made available, or the result of an
+ attempt made to obtain a general license or permission for the use of
+ such proprietary rights by implementers or users of this
+ specification can be obtained from the IETF on-line IPR repository at
+ http://www.ietf.org/ipr.
+
+ The IETF invites any interested party to bring to its attention any
+ copyrights, patents or patent applications, or other proprietary
+ rights that may cover technology that may be required to implement
+ this standard. Please address the information to the IETF at
+ ietf-ipr@ietf.org.
+
+Acknowledgement
+
+ Funding for the RFC Editor function is currently provided by the
+ Internet Society.
+
+
+
+
+
+
+
+Kelly & Frankel Standards Track [Page 21]
+