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+Network Working Group N. Haller
+Request for Comments: 1760 Bellcore
+Category: Informational February 1995
+
+
+ The S/KEY One-Time Password System
+
+Status of this Memo
+
+ This memo provides information for the Internet community. This memo
+ does not specify an Internet standard of any kind. Distribution of
+ this memo is unlimited.
+
+Abstract
+
+ This document describes the S/KEY* One-Time Password system as
+ released for public use by Bellcore and as described in reference
+ [3]. A reference implementation and documentation are available by
+ anonymous ftp from ftp.bellcore.com in the directories pub/nmh/...
+
+Overview
+
+ One form of attack on computing system connected to the Internet is
+ eavesdropping on network connections to obtain login id's and
+ passwords of legitimate users. The captured login id and password
+ are, at a later time, used gain access to the system. The S/KEY
+ One-Time Password system is designed to counter this type of attack,
+ called a replay attack.
+
+ With the S/KEY system, only a single use password ever crosses the
+ network. The user's secret pass-phrase never crosses the network at
+ any time, including during login or when executing other commands
+ requiring authentication such as the UNIX commands passwd or su.
+ Thus, it is not vulnerable to eavesdropping/replay attacks. Added
+ security is provided by the property that no secret information need
+ be stored on any system, including the host being protected.
+
+ The S/KEY system protects against external passive attacks against
+ the authentication subsystem. It does not prevent a network
+ eavesdropper from gaining access to private information, and does not
+ provide protection against "inside jobs" or against active attacks
+ where the potential intruder as able to intercept and modify the
+ packet stream.
+
+
+
+
+
+
+
+
+Haller [Page 1]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+Introduction
+
+ There are two sides to the operation of the S/KEY one-time password
+ system. On the client side, the appropriate one-time password must
+ be generated. On the host side, the server must verify the one-time
+ password and permit the secure changing of the user's secret pass-
+ phrase.
+
+ An S/KEY system client passes the user's secret pass-phrase through
+ multiple applications of a secure hash function to produce a one-time
+ password. On each use, the number of applications is reduced by one.
+ Thus a unique sequence of passwords is generated. The S/KEY system
+ host verifies the one-time password by making one pass though the
+ secure hash function and comparing the result with the previous one-
+ time password. This technique was first suggested by Leslie Lamport
+ [1].
+
+Secure Hash Function
+
+ A secure hash function is a function that is easy to compute in the
+ forward direction, but computationally infeasible to invert. The
+ S/KEY system is based on the MD4 Message Digest algorithm designed by
+ Ronald Rivest [2]. Since the S/KEY authentication system went into
+ use, the MD5 Message Digest was released. We have chosen to continue
+ to use MD4 due the large number of client programs that have been
+ distributed. Some sites have generated functionally similar systems
+ based on MD5. Clearly clients and hosts must use the same secure
+ hash function to interoperate.
+
+ The S/KEY system one-time passwords are 64 bits in length. This is
+ believed to be long enough to be secure and short enough to be
+ manually entered (see below, Form of Passwords) when necessary.
+
+ The S/KEY system applies the secure hash function multiple times,
+ producing a 64 bit final output. MD4 accepts an arbitrary number of
+ bits as input and produces a 128 bit output. The S/KEY secure hash
+ function consists of applying MD4 to a 64 bit input and folding the
+ output of MD4 with exclusive or to produce a 64 bit output.
+
+Generation of One-Time Passwords
+
+ This section describes the computation of the S/KEY one-time
+ passwords. It consists of a preparatory step in which all inputs are
+ combined, a generation step where the secure hash function is applied
+ multiple times, and an output function where the 64 bit one-time
+
+
+
+
+
+
+Haller [Page 2]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+ password is displayed in readable form.
+
+ The client's secret pass phrase may be of any length and should be
+ more than eight characters. As the S/KEY secure hash function
+ described above accepts a 64 bit input, a preparatory step is needed.
+ In this step, the pass phrase is concatenated with a seed that is
+ transmitted from the server in clear text. This non-secret seed
+ allows a client to use the same secret pass phrase on multiple
+ machines (using different seeds) and to safely recycle secret
+ passwords by changing the seed. (For ease in parsing, the seed may
+ not contain any blanks, and should consist of strictly alphanumeric
+ characters.) The result of the concatenation is passed through MD4,
+ and then reduced to 64 bits by exclusive-OR of the two 8-byte halves.
+
+ The following code fragment uses the MD4 implementation defined in
+ RFC 1320 [2] and defines the preparatory step:
+
+ strcpy(buf,seed);
+ strcat(buf,passwd);
+ MDbegin(&md)
+ MDupdate(&md,(unsigned char *)buf,8*buflen);
+
+ /* Fold result to 64 bits */
+ md.buffer[0] ^= md.buffer[2];
+ md.buffer[1] ^= md.buffer[3];
+
+ A sequence of one-time passwords is produced by applying the secure
+ hash function multiple times to the output of the preparatory step
+ (called S). That is, the first one-time password is produced by
+ passing S through the secure hash function a number of times (N)
+ specified by the user. The next one-time password is generated by
+ passing S though the secure hash function N-1 times. An eavesdropper
+ who has monitored the transmission of a one-time password would not
+ be able to generate any succeeding password because doing so would
+ require inverting the hash function.
+
+Form of Passwords
+
+ The one-time password generated by the above procedure is 64 bits in
+ length. Entering a 64 bit number is a difficult and error prone
+ process. Some S/KEY system one-time password calculator programs
+ insert this password into the input stream, others make it available
+ for system cut and paste. Some arrangements require the one-time
+ password to be entered manually. The S/KEY system is designed to
+ facilitate this manual entry without impeding automatic methods. The
+ one-time password is therefore converted to, and accepted as, a
+ sequence of six short (1 to 4 letter) English words. Each word is
+ chosen from a dictionary of 2048 words; at 11 bits per word, all
+
+
+
+Haller [Page 3]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+ one-time passwords may be encoded. Interoperability requires at all
+ S/KEY system hosts and calculators use the same dictionary. The
+ standard dictionary is attached to this RFC.
+
+Verification of One-Time Passwords
+
+ A function on the host system that requires S/KEY authentication is
+ expected to issue an S/KEY challenge. This challenge give the client
+ the current S/KEY parameters - the sequence number and seed. It is
+ important that the S/KEY challenge be in a standard format so that
+ automated clients (see below) can recognize the challenge and extract
+ the parameters. The format of the challenge is:
+
+ s/key sequence_integer seed
+
+ The three tokens are separated by single space characters. The
+ challenge is terminated by a blank or a newline.
+
+ Given the parameters and the secret pass phrase, the client can
+ compute (or lookup) the one time password. It then passes it to the
+ host system where it can be verified.
+
+ The host system has a file (on the UNIX reference implementation it
+ is /etc/skeykeys) containing, for each user, the one-time password
+ from the last successful login, or it may be initialized with the
+ first one-time password of the sequence using the keyinit command
+ (this command name may be implementation dependent). To verify an
+ authentication attempt, it passes the transmitted one-time password
+ through the secure hash function one time. If the result of this
+ operation matches the stored previous one-time password, the
+ authentication is successful and the accepted one-time password is
+ stored for future use.
+
+ Because the number of hash function applications executed by the
+ client decreases by one each time, at some point the user must
+ reinitialize the system of be unable to login again. This is done by
+ using the keyinit command which allows the changing of the secret
+ pass phrase, the iteration count, and the seed. A frequent technique
+ is to increment a trailing digit(s) of the seed and to reset the
+ iteration count (to something in range of 500-1000).
+
+Clients
+
+ Several programs are available to calculate S/KEY one time passwords.
+ Included in the reference implementation are command line interfaces
+ for UNIX and PC systems (key), TSR interfaces for PCs (ctkey,
+ termkey, and popkey), and GUI interfaces for Macintosh and Windows
+ (keyapp and un-named Macintosh interface).
+
+
+
+Haller [Page 4]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+ The most basic calculator is the key command whose format is:
+
+ key [-n count] sequence seed
+
+ The optional count is used to display more than a single one time
+ password. This is useful to create a paper list of one time
+ passwords.
+
+ The most automated calculator is the termkey program that runs as a
+ Terminate and Stay Resident (TSR) program on a PC. It scans the
+ screen to find the S/KEY parameters, prompts for the secret pass
+ phrase, and stuffs the one time password into the keyboard buffer.
+
+Acknowledgements
+
+ The idea behind S/KEY authentication was first proposed by Leslie
+ Lamport [1]. The specific system described was proposed by Phil
+ Karn, who also wrote most of the reference implementation.
+
+References
+
+ [1] Lamport, L., "Password Authentication with Insecure
+ Communication", Communications of the ACM 24.11, November 1981,
+ 770-772.
+
+ [2] Rivest, R., "The MD4 Message-Digest Algorithm", RFC 1320, MIT and
+ RSA Data Security, Inc., April 1992
+
+ [3] Haller, N., "The S/KEY One-Time Password System", Proceedings of
+ the ISOC Symposium on Network and Distributed System Security,
+ February 1994, San Diego, CA
+
+ [4] Haller, N., and R. Atkinson, "On Internet Authentication", RFC
+ 1704, Bell Communications Research and Naval Research Laboratory,
+ October 1994
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Haller [Page 5]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+Security Considerations
+
+ This entire document is about Security Considerations.
+
+Author's Address
+
+ Neil Haller
+ Bellcore
+ MRE 2Q-280
+ 445 South Street
+ Morristown, NJ, 07960-6438, USA
+
+ Phone: +1 201 829-4478
+ Fax: +1 201 829-2504
+ EMail: nmh@bellcore.com
+
+
+
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+
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+
+
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+
+
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+
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+
+
+
+Haller [Page 6]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+Dictionary for Converting Between S/KEY 6-Word and Binary Formats
+
+ This dictionary is from the module put.c. The code for this module,
+ and an implementation of the entire S/KEY One Time Password System is
+ available by anonymous ftp from ftp.bellcore.com in the directory
+ pub/nmh/skey.
+
+
+{ "A", "ABE", "ACE", "ACT", "AD", "ADA", "ADD",
+"AGO", "AID", "AIM", "AIR", "ALL", "ALP", "AM", "AMY",
+"AN", "ANA", "AND", "ANN", "ANT", "ANY", "APE", "APS",
+"APT", "ARC", "ARE", "ARK", "ARM", "ART", "AS", "ASH",
+"ASK", "AT", "ATE", "AUG", "AUK", "AVE", "AWE", "AWK",
+"AWL", "AWN", "AX", "AYE", "BAD", "BAG", "BAH", "BAM",
+"BAN", "BAR", "BAT", "BAY", "BE", "BED", "BEE", "BEG",
+"BEN", "BET", "BEY", "BIB", "BID", "BIG", "BIN", "BIT",
+"BOB", "BOG", "BON", "BOO", "BOP", "BOW", "BOY", "BUB",
+"BUD", "BUG", "BUM", "BUN", "BUS", "BUT", "BUY", "BY",
+"BYE", "CAB", "CAL", "CAM", "CAN", "CAP", "CAR", "CAT",
+"CAW", "COD", "COG", "COL", "CON", "COO", "COP", "COT",
+"COW", "COY", "CRY", "CUB", "CUE", "CUP", "CUR", "CUT",
+"DAB", "DAD", "DAM", "DAN", "DAR", "DAY", "DEE", "DEL",
+"DEN", "DES", "DEW", "DID", "DIE", "DIG", "DIN", "DIP",
+"DO", "DOE", "DOG", "DON", "DOT", "DOW", "DRY", "DUB",
+"DUD", "DUE", "DUG", "DUN", "EAR", "EAT", "ED", "EEL",
+"EGG", "EGO", "ELI", "ELK", "ELM", "ELY", "EM", "END",
+"EST", "ETC", "EVA", "EVE", "EWE", "EYE", "FAD", "FAN",
+"FAR", "FAT", "FAY", "FED", "FEE", "FEW", "FIB", "FIG",
+"FIN", "FIR", "FIT", "FLO", "FLY", "FOE", "FOG", "FOR",
+"FRY", "FUM", "FUN", "FUR", "GAB", "GAD", "GAG", "GAL",
+"GAM", "GAP", "GAS", "GAY", "GEE", "GEL", "GEM", "GET",
+"GIG", "GIL", "GIN", "GO", "GOT", "GUM", "GUN", "GUS",
+"GUT", "GUY", "GYM", "GYP", "HA", "HAD", "HAL", "HAM",
+"HAN", "HAP", "HAS", "HAT", "HAW", "HAY", "HE", "HEM",
+"HEN", "HER", "HEW", "HEY", "HI", "HID", "HIM", "HIP",
+"HIS", "HIT", "HO", "HOB", "HOC", "HOE", "HOG", "HOP",
+"HOT", "HOW", "HUB", "HUE", "HUG", "HUH", "HUM", "HUT",
+"I", "ICY", "IDA", "IF", "IKE", "ILL", "INK", "INN",
+"IO", "ION", "IQ", "IRA", "IRE", "IRK", "IS", "IT",
+"ITS", "IVY", "JAB", "JAG", "JAM", "JAN", "JAR", "JAW",
+"JAY", "JET", "JIG", "JIM", "JO", "JOB", "JOE", "JOG",
+"JOT", "JOY", "JUG", "JUT", "KAY", "KEG", "KEN", "KEY",
+"KID", "KIM", "KIN", "KIT", "LA", "LAB", "LAC", "LAD",
+"LAG", "LAM", "LAP", "LAW", "LAY", "LEA", "LED", "LEE",
+"LEG", "LEN", "LEO", "LET", "LEW", "LID", "LIE", "LIN",
+"LIP", "LIT", "LO", "LOB", "LOG", "LOP", "LOS", "LOT",
+"LOU", "LOW", "LOY", "LUG", "LYE", "MA", "MAC", "MAD",
+"MAE", "MAN", "MAO", "MAP", "MAT", "MAW", "MAY", "ME",
+
+
+
+Haller [Page 7]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+"MEG", "MEL", "MEN", "MET", "MEW", "MID", "MIN", "MIT",
+"MOB", "MOD", "MOE", "MOO", "MOP", "MOS", "MOT", "MOW",
+"MUD", "MUG", "MUM", "MY", "NAB", "NAG", "NAN", "NAP",
+"NAT", "NAY", "NE", "NED", "NEE", "NET", "NEW", "NIB",
+"NIL", "NIP", "NIT", "NO", "NOB", "NOD", "NON", "NOR",
+"NOT", "NOV", "NOW", "NU", "NUN", "NUT", "O", "OAF",
+"OAK", "OAR", "OAT", "ODD", "ODE", "OF", "OFF", "OFT",
+"OH", "OIL", "OK", "OLD", "ON", "ONE", "OR", "ORB",
+"ORE", "ORR", "OS", "OTT", "OUR", "OUT", "OVA", "OW",
+"OWE", "OWL", "OWN", "OX", "PA", "PAD", "PAL", "PAM",
+"PAN", "PAP", "PAR", "PAT", "PAW", "PAY", "PEA", "PEG",
+"PEN", "PEP", "PER", "PET", "PEW", "PHI", "PI", "PIE",
+"PIN", "PIT", "PLY", "PO", "POD", "POE", "POP", "POT",
+"POW", "PRO", "PRY", "PUB", "PUG", "PUN", "PUP", "PUT",
+"QUO", "RAG", "RAM", "RAN", "RAP", "RAT", "RAW", "RAY",
+"REB", "RED", "REP", "RET", "RIB", "RID", "RIG", "RIM",
+"RIO", "RIP", "ROB", "ROD", "ROE", "RON", "ROT", "ROW",
+"ROY", "RUB", "RUE", "RUG", "RUM", "RUN", "RYE", "SAC",
+"SAD", "SAG", "SAL", "SAM", "SAN", "SAP", "SAT", "SAW",
+"SAY", "SEA", "SEC", "SEE", "SEN", "SET", "SEW", "SHE",
+"SHY", "SIN", "SIP", "SIR", "SIS", "SIT", "SKI", "SKY",
+"SLY", "SO", "SOB", "SOD", "SON", "SOP", "SOW", "SOY",
+"SPA", "SPY", "SUB", "SUD", "SUE", "SUM", "SUN", "SUP",
+"TAB", "TAD", "TAG", "TAN", "TAP", "TAR", "TEA", "TED",
+"TEE", "TEN", "THE", "THY", "TIC", "TIE", "TIM", "TIN",
+"TIP", "TO", "TOE", "TOG", "TOM", "TON", "TOO", "TOP",
+"TOW", "TOY", "TRY", "TUB", "TUG", "TUM", "TUN", "TWO",
+"UN", "UP", "US", "USE", "VAN", "VAT", "VET", "VIE",
+"WAD", "WAG", "WAR", "WAS", "WAY", "WE", "WEB", "WED",
+"WEE", "WET", "WHO", "WHY", "WIN", "WIT", "WOK", "WON",
+"WOO", "WOW", "WRY", "WU", "YAM", "YAP", "YAW", "YE",
+"YEA", "YES", "YET", "YOU", "ABED", "ABEL", "ABET", "ABLE",
+"ABUT", "ACHE", "ACID", "ACME", "ACRE", "ACTA", "ACTS", "ADAM",
+"ADDS", "ADEN", "AFAR", "AFRO", "AGEE", "AHEM", "AHOY", "AIDA",
+"AIDE", "AIDS", "AIRY", "AJAR", "AKIN", "ALAN", "ALEC", "ALGA",
+"ALIA", "ALLY", "ALMA", "ALOE", "ALSO", "ALTO", "ALUM", "ALVA",
+"AMEN", "AMES", "AMID", "AMMO", "AMOK", "AMOS", "AMRA", "ANDY",
+"ANEW", "ANNA", "ANNE", "ANTE", "ANTI", "AQUA", "ARAB", "ARCH",
+"AREA", "ARGO", "ARID", "ARMY", "ARTS", "ARTY", "ASIA", "ASKS",
+"ATOM", "AUNT", "AURA", "AUTO", "AVER", "AVID", "AVIS", "AVON",
+"AVOW", "AWAY", "AWRY", "BABE", "BABY", "BACH", "BACK", "BADE",
+"BAIL", "BAIT", "BAKE", "BALD", "BALE", "BALI", "BALK", "BALL",
+"BALM", "BAND", "BANE", "BANG", "BANK", "BARB", "BARD", "BARE",
+"BARK", "BARN", "BARR", "BASE", "BASH", "BASK", "BASS", "BATE",
+"BATH", "BAWD", "BAWL", "BEAD", "BEAK", "BEAM", "BEAN", "BEAR",
+"BEAT", "BEAU", "BECK", "BEEF", "BEEN", "BEER", "BEET", "BELA",
+"BELL", "BELT", "BEND", "BENT", "BERG", "BERN", "BERT", "BESS",
+"BEST", "BETA", "BETH", "BHOY", "BIAS", "BIDE", "BIEN", "BILE",
+
+
+
+Haller [Page 8]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+"BILK", "BILL", "BIND", "BING", "BIRD", "BITE", "BITS", "BLAB",
+"BLAT", "BLED", "BLEW", "BLOB", "BLOC", "BLOT", "BLOW", "BLUE",
+"BLUM", "BLUR", "BOAR", "BOAT", "BOCA", "BOCK", "BODE", "BODY",
+"BOGY", "BOHR", "BOIL", "BOLD", "BOLO", "BOLT", "BOMB", "BONA",
+"BOND", "BONE", "BONG", "BONN", "BONY", "BOOK", "BOOM", "BOON",
+"BOOT", "BORE", "BORG", "BORN", "BOSE", "BOSS", "BOTH", "BOUT",
+"BOWL", "BOYD", "BRAD", "BRAE", "BRAG", "BRAN", "BRAY", "BRED",
+"BREW", "BRIG", "BRIM", "BROW", "BUCK", "BUDD", "BUFF", "BULB",
+"BULK", "BULL", "BUNK", "BUNT", "BUOY", "BURG", "BURL", "BURN",
+"BURR", "BURT", "BURY", "BUSH", "BUSS", "BUST", "BUSY", "BYTE",
+"CADY", "CAFE", "CAGE", "CAIN", "CAKE", "CALF", "CALL", "CALM",
+"CAME", "CANE", "CANT", "CARD", "CARE", "CARL", "CARR", "CART",
+"CASE", "CASH", "CASK", "CAST", "CAVE", "CEIL", "CELL", "CENT",
+"CERN", "CHAD", "CHAR", "CHAT", "CHAW", "CHEF", "CHEN", "CHEW",
+"CHIC", "CHIN", "CHOU", "CHOW", "CHUB", "CHUG", "CHUM", "CITE",
+"CITY", "CLAD", "CLAM", "CLAN", "CLAW", "CLAY", "CLOD", "CLOG",
+"CLOT", "CLUB", "CLUE", "COAL", "COAT", "COCA", "COCK", "COCO",
+"CODA", "CODE", "CODY", "COED", "COIL", "COIN", "COKE", "COLA",
+"COLD", "COLT", "COMA", "COMB", "COME", "COOK", "COOL", "COON",
+"COOT", "CORD", "CORE", "CORK", "CORN", "COST", "COVE", "COWL",
+"CRAB", "CRAG", "CRAM", "CRAY", "CREW", "CRIB", "CROW", "CRUD",
+"CUBA", "CUBE", "CUFF", "CULL", "CULT", "CUNY", "CURB", "CURD",
+"CURE", "CURL", "CURT", "CUTS", "DADE", "DALE", "DAME", "DANA",
+"DANE", "DANG", "DANK", "DARE", "DARK", "DARN", "DART", "DASH",
+"DATA", "DATE", "DAVE", "DAVY", "DAWN", "DAYS", "DEAD", "DEAF",
+"DEAL", "DEAN", "DEAR", "DEBT", "DECK", "DEED", "DEEM", "DEER",
+"DEFT", "DEFY", "DELL", "DENT", "DENY", "DESK", "DIAL", "DICE",
+"DIED", "DIET", "DIME", "DINE", "DING", "DINT", "DIRE", "DIRT",
+"DISC", "DISH", "DISK", "DIVE", "DOCK", "DOES", "DOLE", "DOLL",
+"DOLT", "DOME", "DONE", "DOOM", "DOOR", "DORA", "DOSE", "DOTE",
+"DOUG", "DOUR", "DOVE", "DOWN", "DRAB", "DRAG", "DRAM", "DRAW",
+"DREW", "DRUB", "DRUG", "DRUM", "DUAL", "DUCK", "DUCT", "DUEL",
+"DUET", "DUKE", "DULL", "DUMB", "DUNE", "DUNK", "DUSK", "DUST",
+"DUTY", "EACH", "EARL", "EARN", "EASE", "EAST", "EASY", "EBEN",
+"ECHO", "EDDY", "EDEN", "EDGE", "EDGY", "EDIT", "EDNA", "EGAN",
+"ELAN", "ELBA", "ELLA", "ELSE", "EMIL", "EMIT", "EMMA", "ENDS",
+"ERIC", "EROS", "EVEN", "EVER", "EVIL", "EYED", "FACE", "FACT",
+"FADE", "FAIL", "FAIN", "FAIR", "FAKE", "FALL", "FAME", "FANG",
+"FARM", "FAST", "FATE", "FAWN", "FEAR", "FEAT", "FEED", "FEEL",
+"FEET", "FELL", "FELT", "FEND", "FERN", "FEST", "FEUD", "FIEF",
+"FIGS", "FILE", "FILL", "FILM", "FIND", "FINE", "FINK", "FIRE",
+"FIRM", "FISH", "FISK", "FIST", "FITS", "FIVE", "FLAG", "FLAK",
+"FLAM", "FLAT", "FLAW", "FLEA", "FLED", "FLEW", "FLIT", "FLOC",
+"FLOG", "FLOW", "FLUB", "FLUE", "FOAL", "FOAM", "FOGY", "FOIL",
+"FOLD", "FOLK", "FOND", "FONT", "FOOD", "FOOL", "FOOT", "FORD",
+"FORE", "FORK", "FORM", "FORT", "FOSS", "FOUL", "FOUR", "FOWL",
+"FRAU", "FRAY", "FRED", "FREE", "FRET", "FREY", "FROG", "FROM",
+"FUEL", "FULL", "FUME", "FUND", "FUNK", "FURY", "FUSE", "FUSS",
+
+
+
+Haller [Page 9]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+"GAFF", "GAGE", "GAIL", "GAIN", "GAIT", "GALA", "GALE", "GALL",
+"GALT", "GAME", "GANG", "GARB", "GARY", "GASH", "GATE", "GAUL",
+"GAUR", "GAVE", "GAWK", "GEAR", "GELD", "GENE", "GENT", "GERM",
+"GETS", "GIBE", "GIFT", "GILD", "GILL", "GILT", "GINA", "GIRD",
+"GIRL", "GIST", "GIVE", "GLAD", "GLEE", "GLEN", "GLIB", "GLOB",
+"GLOM", "GLOW", "GLUE", "GLUM", "GLUT", "GOAD", "GOAL", "GOAT",
+"GOER", "GOES", "GOLD", "GOLF", "GONE", "GONG", "GOOD", "GOOF",
+"GORE", "GORY", "GOSH", "GOUT", "GOWN", "GRAB", "GRAD", "GRAY",
+"GREG", "GREW", "GREY", "GRID", "GRIM", "GRIN", "GRIT", "GROW",
+"GRUB", "GULF", "GULL", "GUNK", "GURU", "GUSH", "GUST", "GWEN",
+"GWYN", "HAAG", "HAAS", "HACK", "HAIL", "HAIR", "HALE", "HALF",
+"HALL", "HALO", "HALT", "HAND", "HANG", "HANK", "HANS", "HARD",
+"HARK", "HARM", "HART", "HASH", "HAST", "HATE", "HATH", "HAUL",
+"HAVE", "HAWK", "HAYS", "HEAD", "HEAL", "HEAR", "HEAT", "HEBE",
+"HECK", "HEED", "HEEL", "HEFT", "HELD", "HELL", "HELM", "HERB",
+"HERD", "HERE", "HERO", "HERS", "HESS", "HEWN", "HICK", "HIDE",
+"HIGH", "HIKE", "HILL", "HILT", "HIND", "HINT", "HIRE", "HISS",
+"HIVE", "HOBO", "HOCK", "HOFF", "HOLD", "HOLE", "HOLM", "HOLT",
+"HOME", "HONE", "HONK", "HOOD", "HOOF", "HOOK", "HOOT", "HORN",
+"HOSE", "HOST", "HOUR", "HOVE", "HOWE", "HOWL", "HOYT", "HUCK",
+"HUED", "HUFF", "HUGE", "HUGH", "HUGO", "HULK", "HULL", "HUNK",
+"HUNT", "HURD", "HURL", "HURT", "HUSH", "HYDE", "HYMN", "IBIS",
+"ICON", "IDEA", "IDLE", "IFFY", "INCA", "INCH", "INTO", "IONS",
+"IOTA", "IOWA", "IRIS", "IRMA", "IRON", "ISLE", "ITCH", "ITEM",
+"IVAN", "JACK", "JADE", "JAIL", "JAKE", "JANE", "JAVA", "JEAN",
+"JEFF", "JERK", "JESS", "JEST", "JIBE", "JILL", "JILT", "JIVE",
+"JOAN", "JOBS", "JOCK", "JOEL", "JOEY", "JOHN", "JOIN", "JOKE",
+"JOLT", "JOVE", "JUDD", "JUDE", "JUDO", "JUDY", "JUJU", "JUKE",
+"JULY", "JUNE", "JUNK", "JUNO", "JURY", "JUST", "JUTE", "KAHN",
+"KALE", "KANE", "KANT", "KARL", "KATE", "KEEL", "KEEN", "KENO",
+"KENT", "KERN", "KERR", "KEYS", "KICK", "KILL", "KIND", "KING",
+"KIRK", "KISS", "KITE", "KLAN", "KNEE", "KNEW", "KNIT", "KNOB",
+"KNOT", "KNOW", "KOCH", "KONG", "KUDO", "KURD", "KURT", "KYLE",
+"LACE", "LACK", "LACY", "LADY", "LAID", "LAIN", "LAIR", "LAKE",
+"LAMB", "LAME", "LAND", "LANE", "LANG", "LARD", "LARK", "LASS",
+"LAST", "LATE", "LAUD", "LAVA", "LAWN", "LAWS", "LAYS", "LEAD",
+"LEAF", "LEAK", "LEAN", "LEAR", "LEEK", "LEER", "LEFT", "LEND",
+"LENS", "LENT", "LEON", "LESK", "LESS", "LEST", "LETS", "LIAR",
+"LICE", "LICK", "LIED", "LIEN", "LIES", "LIEU", "LIFE", "LIFT",
+"LIKE", "LILA", "LILT", "LILY", "LIMA", "LIMB", "LIME", "LIND",
+"LINE", "LINK", "LINT", "LION", "LISA", "LIST", "LIVE", "LOAD",
+"LOAF", "LOAM", "LOAN", "LOCK", "LOFT", "LOGE", "LOIS", "LOLA",
+"LONE", "LONG", "LOOK", "LOON", "LOOT", "LORD", "LORE", "LOSE",
+"LOSS", "LOST", "LOUD", "LOVE", "LOWE", "LUCK", "LUCY", "LUGE",
+"LUKE", "LULU", "LUND", "LUNG", "LURA", "LURE", "LURK", "LUSH",
+"LUST", "LYLE", "LYNN", "LYON", "LYRA", "MACE", "MADE", "MAGI",
+"MAID", "MAIL", "MAIN", "MAKE", "MALE", "MALI", "MALL", "MALT",
+"MANA", "MANN", "MANY", "MARC", "MARE", "MARK", "MARS", "MART",
+
+
+
+Haller [Page 10]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+"MARY", "MASH", "MASK", "MASS", "MAST", "MATE", "MATH", "MAUL",
+"MAYO", "MEAD", "MEAL", "MEAN", "MEAT", "MEEK", "MEET", "MELD",
+"MELT", "MEMO", "MEND", "MENU", "MERT", "MESH", "MESS", "MICE",
+"MIKE", "MILD", "MILE", "MILK", "MILL", "MILT", "MIMI", "MIND",
+"MINE", "MINI", "MINK", "MINT", "MIRE", "MISS", "MIST", "MITE",
+"MITT", "MOAN", "MOAT", "MOCK", "MODE", "MOLD", "MOLE", "MOLL",
+"MOLT", "MONA", "MONK", "MONT", "MOOD", "MOON", "MOOR", "MOOT",
+"MORE", "MORN", "MORT", "MOSS", "MOST", "MOTH", "MOVE", "MUCH",
+"MUCK", "MUDD", "MUFF", "MULE", "MULL", "MURK", "MUSH", "MUST",
+"MUTE", "MUTT", "MYRA", "MYTH", "NAGY", "NAIL", "NAIR", "NAME",
+"NARY", "NASH", "NAVE", "NAVY", "NEAL", "NEAR", "NEAT", "NECK",
+"NEED", "NEIL", "NELL", "NEON", "NERO", "NESS", "NEST", "NEWS",
+"NEWT", "NIBS", "NICE", "NICK", "NILE", "NINA", "NINE", "NOAH",
+"NODE", "NOEL", "NOLL", "NONE", "NOOK", "NOON", "NORM", "NOSE",
+"NOTE", "NOUN", "NOVA", "NUDE", "NULL", "NUMB", "OATH", "OBEY",
+"OBOE", "ODIN", "OHIO", "OILY", "OINT", "OKAY", "OLAF", "OLDY",
+"OLGA", "OLIN", "OMAN", "OMEN", "OMIT", "ONCE", "ONES", "ONLY",
+"ONTO", "ONUS", "ORAL", "ORGY", "OSLO", "OTIS", "OTTO", "OUCH",
+"OUST", "OUTS", "OVAL", "OVEN", "OVER", "OWLY", "OWNS", "QUAD",
+"QUIT", "QUOD", "RACE", "RACK", "RACY", "RAFT", "RAGE", "RAID",
+"RAIL", "RAIN", "RAKE", "RANK", "RANT", "RARE", "RASH", "RATE",
+"RAVE", "RAYS", "READ", "REAL", "REAM", "REAR", "RECK", "REED",
+"REEF", "REEK", "REEL", "REID", "REIN", "RENA", "REND", "RENT",
+"REST", "RICE", "RICH", "RICK", "RIDE", "RIFT", "RILL", "RIME",
+"RING", "RINK", "RISE", "RISK", "RITE", "ROAD", "ROAM", "ROAR",
+"ROBE", "ROCK", "RODE", "ROIL", "ROLL", "ROME", "ROOD", "ROOF",
+"ROOK", "ROOM", "ROOT", "ROSA", "ROSE", "ROSS", "ROSY", "ROTH",
+"ROUT", "ROVE", "ROWE", "ROWS", "RUBE", "RUBY", "RUDE", "RUDY",
+"RUIN", "RULE", "RUNG", "RUNS", "RUNT", "RUSE", "RUSH", "RUSK",
+"RUSS", "RUST", "RUTH", "SACK", "SAFE", "SAGE", "SAID", "SAIL",
+"SALE", "SALK", "SALT", "SAME", "SAND", "SANE", "SANG", "SANK",
+"SARA", "SAUL", "SAVE", "SAYS", "SCAN", "SCAR", "SCAT", "SCOT",
+"SEAL", "SEAM", "SEAR", "SEAT", "SEED", "SEEK", "SEEM", "SEEN",
+"SEES", "SELF", "SELL", "SEND", "SENT", "SETS", "SEWN", "SHAG",
+"SHAM", "SHAW", "SHAY", "SHED", "SHIM", "SHIN", "SHOD", "SHOE",
+"SHOT", "SHOW", "SHUN", "SHUT", "SICK", "SIDE", "SIFT", "SIGH",
+"SIGN", "SILK", "SILL", "SILO", "SILT", "SINE", "SING", "SINK",
+"SIRE", "SITE", "SITS", "SITU", "SKAT", "SKEW", "SKID", "SKIM",
+"SKIN", "SKIT", "SLAB", "SLAM", "SLAT", "SLAY", "SLED", "SLEW",
+"SLID", "SLIM", "SLIT", "SLOB", "SLOG", "SLOT", "SLOW", "SLUG",
+"SLUM", "SLUR", "SMOG", "SMUG", "SNAG", "SNOB", "SNOW", "SNUB",
+"SNUG", "SOAK", "SOAR", "SOCK", "SODA", "SOFA", "SOFT", "SOIL",
+"SOLD", "SOME", "SONG", "SOON", "SOOT", "SORE", "SORT", "SOUL",
+"SOUR", "SOWN", "STAB", "STAG", "STAN", "STAR", "STAY", "STEM",
+"STEW", "STIR", "STOW", "STUB", "STUN", "SUCH", "SUDS", "SUIT",
+"SULK", "SUMS", "SUNG", "SUNK", "SURE", "SURF", "SWAB", "SWAG",
+"SWAM", "SWAN", "SWAT", "SWAY", "SWIM", "SWUM", "TACK", "TACT",
+"TAIL", "TAKE", "TALE", "TALK", "TALL", "TANK", "TASK", "TATE",
+
+
+
+Haller [Page 11]
+
+RFC 1760 The S/KEY One-Time Password System February 1995
+
+
+"TAUT", "TEAL", "TEAM", "TEAR", "TECH", "TEEM", "TEEN", "TEET",
+"TELL", "TEND", "TENT", "TERM", "TERN", "TESS", "TEST", "THAN",
+"THAT", "THEE", "THEM", "THEN", "THEY", "THIN", "THIS", "THUD",
+"THUG", "TICK", "TIDE", "TIDY", "TIED", "TIER", "TILE", "TILL",
+"TILT", "TIME", "TINA", "TINE", "TINT", "TINY", "TIRE", "TOAD",
+"TOGO", "TOIL", "TOLD", "TOLL", "TONE", "TONG", "TONY", "TOOK",
+"TOOL", "TOOT", "TORE", "TORN", "TOTE", "TOUR", "TOUT", "TOWN",
+"TRAG", "TRAM", "TRAY", "TREE", "TREK", "TRIG", "TRIM", "TRIO",
+"TROD", "TROT", "TROY", "TRUE", "TUBA", "TUBE", "TUCK", "TUFT",
+"TUNA", "TUNE", "TUNG", "TURF", "TURN", "TUSK", "TWIG", "TWIN",
+"TWIT", "ULAN", "UNIT", "URGE", "USED", "USER", "USES", "UTAH",
+"VAIL", "VAIN", "VALE", "VARY", "VASE", "VAST", "VEAL", "VEDA",
+"VEIL", "VEIN", "VEND", "VENT", "VERB", "VERY", "VETO", "VICE",
+"VIEW", "VINE", "VISE", "VOID", "VOLT", "VOTE", "WACK", "WADE",
+"WAGE", "WAIL", "WAIT", "WAKE", "WALE", "WALK", "WALL", "WALT",
+"WAND", "WANE", "WANG", "WANT", "WARD", "WARM", "WARN", "WART",
+"WASH", "WAST", "WATS", "WATT", "WAVE", "WAVY", "WAYS", "WEAK",
+"WEAL", "WEAN", "WEAR", "WEED", "WEEK", "WEIR", "WELD", "WELL",
+"WELT", "WENT", "WERE", "WERT", "WEST", "WHAM", "WHAT", "WHEE",
+"WHEN", "WHET", "WHOA", "WHOM", "WICK", "WIFE", "WILD", "WILL",
+"WIND", "WINE", "WING", "WINK", "WINO", "WIRE", "WISE", "WISH",
+"WITH", "WOLF", "WONT", "WOOD", "WOOL", "WORD", "WORE", "WORK",
+"WORM", "WORN", "WOVE", "WRIT", "WYNN", "YALE", "YANG", "YANK",
+"YARD", "YARN", "YAWL", "YAWN", "YEAH", "YEAR", "YELL", "YOGA",
+"YOKE" };
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Haller [Page 12]
+