RFC 1751
A Convention for Human-Readable 128-bit Keys
RFC 1751: A Convention for Human-Readable 128-bit Keys 🎀
Okay bestie, this one's from December 1994 and it's by D. McDonald (Daniel L. McDonald) at the NRL 💅. It's Informational and it's from the Network Working Group. The header doesn't say it obsoletes or updates anything, so it's a standalone little gem ✨.
Status of this Memo 🌸
This memo gives information to the Internet community. It does not specify an Internet standard of any kind, and distribution of the memo is unlimited 💜.
Introduction 🦋
So the Internet community has finally started taking security seriously, and honestly, it's about time 🙌. Newer standards, like version 2 of SNMP [GM93], have explicit requirements for an authentication mechanism. Those need a keyed message-digest algorithm, MD5 [Riv92], with a key size of 128-bits. A 128-bit key is strong enough, but it's brutal for most people to read, remember, and type 😭. This memo proposes a convention for Internet applications & protocols that use 128-bit cryptographic keys, so we can all be less miserable about it 🫶.
A Solution Already Exists ✨
Okay, plot twist: someone already solved part of this. The S/Key(tm) one-time password system [Hal94] uses MD4 (and now MD5, as well) to compute one-time passwords 🔐. It takes the 128-bit MD4 result and squishes it down to a 64-bit result. Even at that size, 64-bit one-time passwords are still a lot for ordinary people to remember and enter 💀. So the S/Key authors came up with a way to make the 64-bit one-time password easy to enter 🧚.
Their genius idea was to turn the password into a string of small English words 👑. English words are way easier for people to remember and type, so it's giving main character energy 💅. The S/Key authors started with a dictionary of 2048 English words, ranging in length from one to four characters. The space covered by a 64-bit key (2^64) could be covered by six words from this dictionary (2^66), with room left over for parity 🍓. For example, an S/Key one-time password with the hex value:
EB33 F77E E73D 4053would become these six English words:
TIDE ITCH SLOW REIN RULE MOTAlso, it's undesirable to have different dictionaries for different languages, because interoperability is everything 🌈. The current dictionary only uses characters from the invariant portion of ISO-646. And finally, there's already an installed base of users and applications using this dictionary, so changing it is a no-go 🙈.
The Proposal 💖
The code (see Appendix A) that S/Key uses to convert 64-bit numbers into six English words has two primitives that convert in either direction 🔥. The primitive btoe(char *engout,char *c) takes a 64-bit quantity referenced by c and places English words in the string referenced by engout. The primitive etob(char *out,char *e) does the opposite, taking an input string of English words referenced by e and placing the 64-bit result into the buffer referenced by out ✨.
Both of those primitives can be applied to both halves of a 128-bit key, or both halves of a string of twelve English words, which is so clean 😭. Two new primitives (see Appendix B), key2eng(char *engout,char *key) and eng2key(char *keyout,char *eng), act as wrappers. They call the S/Key primitives twice, once for each half of the 128-bit key or string of twelve words 🎀.
For example, the 128-bit key:
CCAC 2AED 5910 56BE 4F90 FD44 1C53 4766would become:
RASH BUSH MILK LOOK BAD BRIM AVID GAFF BAIT ROT POD LOVELikewise, a user should be able to type in:
TROD MUTE TAIL WARM CHAR KONG HAAG CITY BORE O TEAL AWLas a key, and the machine should translate it to:
EFF8 1F9B FBC6 5350 920C DD74 16DE 8009Okay, this part is critical 🚨. If this proposal is going to work, the dictionary of English words cannot change between implementations. A freely redistributable reference implementation is given in Appendices A and B 🫶.
Security Considerations 💀
This document recommends a method of representing 128-bit keys using strings of English words. Since those strings are easy to remember, people might accidentally build easy-to-guess strings of English words 🙈. And easy-to-guess strings bring the risk of a sentential equivalent of a dictionary attack 😱. To maximize the strength of any authentication mechanism that uses 128-bit keys, the keys must be sufficiently obscure. In particular, people should avoid the temptation to devise sentences 🚫.
Acknowledgements 🌸
S/Key is a registered trademark of Bell Communications Research 💅.
Thanks to Randall Atkinson for the bulk of the security considerations section, and for general advice 🙌. Thanks also to Phil Karn and Neil Haller for producing the S/Key one-time password system, which inspired this whole document 🥹.
References 📚
[GM93] Galvin, J. and K. McCloghrie, "Security Protocols for version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1446, Trusted Information Systems, Hughes LAN Systems, April 1993.
[Hal94] Haller, N., "The S/Key(tm) One-Time Password System", Proceedings of the Symposium on Network & Distributed Systems Security, Internet Society, San Diego, February 1994.
[Riv92] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, MIT Laboratory for Computer Science and RSA Data Security, Inc., April 1992.
Author's Address 📮
Daniel L. McDonald United States Naval Research Laboratory Code 5544 4555 Overlook Ave. SW Washington, DC 20375
Phone: (202) 404-7122 EMail: danmcd@itd.nrl.navy.mil
Appendix A - Source for S/Key 8-bytes to/from Words Routines (put.c) 👩💻
This code originally came from the source for S/Key(TM), which is available in the directory ftp://thumper.bellcore.com/pub/nmh. It has been modified only to remove explicit S/Key(TM) references 🧚.
/* This code originally appeared in the source for S/Key(TM),
* available in the directory
* ftp://thumper.bellcore.com/pub/nmh
*
* It has been modified only to remove explicit S/Key(TM) references.
*/
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>
#ifdef __STDC__
#define __ARGS(x) x
#else
#define __ARGS(x) ()
#endif
static unsigned long extract __ARGS((char *s,int start,int length));
static void standard __ARGS((char *word));
static void insert __ARGS((char *s, int x, int start, int length));
static int wsrch __ARGS((char *w,int low,int high));
/* Dictionary for integer-word translations */
char Wp[2048][4] = { "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", "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",
"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",Part 1 ends right there at the dictionary, so the word list and the rest of the appendix are coming in part 2 🧚💜
okay bestie, the word list keeps going 📚✨ here's the next chunk, plus the encoder and decoder code 💅
"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", "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", "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",
"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"
};
/* Encode 8 bytes in 'c' as a string of English words.
* Returns a pointer to a static buffer
*/
char *
btoe(engout,c)
char *c, *engout;
{
char cp[9]; /* add in room for the parity 2 bits*/
int p,i ;
engout[0] = '\0';
memcpy(cp, c,8);
/* compute parity */
for(p = 0,i = 0; i < 64;i += 2)
p += extract(cp,i,2);
cp[8] = (char)p << 6;
strncat(engout,&Wp[extract(cp, 0,11)][0],4);
strcat(engout," ");
strncat(engout,&Wp[extract(cp,11,11)][0],4);
strcat(engout," ");
strncat(engout,&Wp[extract(cp,22,11)][0],4);
strcat(engout," ");
strncat(engout,&Wp[extract(cp,33,11)][0],4);
strcat(engout," ");
strncat(engout,&Wp[extract(cp,44,11)][0],4);
strcat(engout," ");
strncat(engout,&Wp[extract(cp,55,11)][0],4);
#ifdef notdef
printf("engout is %s\n\r",engout);
#endif
return(engout);
}
/* convert English to binary
* returns 1 OK - all good words and parity is OK
* 0 word not in data base
* -1 badly formed in put ie > 4 char word
* -2 words OK but parity is wrong
*/
int
etob(out, e)
char *out;
char *e;{
char *word;
int i, p, v,l, low,high;
char b[9];
char input[36];
if(e == NULL)
return -1;
strncpy(input,e,sizeof(input));
memset(b, 0, sizeof(b));
memset(out, 0, 8);
for(i=0,p=0;i<6;i++,p+=11){
if((word = strtok(i == 0 ? input : NULL," ")) == NULL)
return -1;
l = strlen(word);
if(l > 4 || l < 1){
return -1;
} else if(l < 4){
low = 0;
high = 570;
} else {
low = 571;
high = 2047;
}
standard(word);
if( (v = wsrch(word,low,high)) < 0 )
return 0;
insert(b,v,p,11);
}
/* now check the parity of what we got */
for(p = 0, i = 0; i < 64; i +=2)
p += extract(b, i, 2);
if( (p & 3) != extract(b, 64,2) )
return -2;
memcpy(out,b,8);
return 1;
}okay so etob is where the magic happens 🫶 it chops your English string into six words with strtok, then looks each word up in the dictionary and packs each index into 11 bits. 💅 Words of 1 to 3 letters search the 0 to 570 range, and 4-letter words search 571 to 2047. Anything else is a no-go 🙈
And then there's the parity check, which is giving "double-check the homework" energy 📚 It adds up the 2-bit chunks, masks them, and compares the result against the last 2 bits. If they don't match, you get -2. Periodt 🎀
The return values are a whole mood: -1 for a badly formed string, 0 if a word isn't in the dictionary, -2 if the words are fine but the parity is off, and 1 if everything slays ✨
/* Display 8 bytes as a series of 16-bit hex digits */
char *
put8(out,s)
char *out;
char *s;
{
sprintf(out,"%02X%02X %02X%02X %02X%02X %02X%02X",
s[0] & 0xff,s[1] & 0xff,s[2] & 0xff,
s[3] & 0xff,s[4] & 0xff,s[5] & 0xff,
s[6] & 0xff,s[7] & 0xff);
return out;
}
#ifdef notdef
/* Encode 8 bytes in 'cp' as stream of ascii letters.
* Provided as a possible alternative to btoe()
*/
char *
btoc(cp)
char *cp;
{
int i;
static char out[31];
/* code out put by characters 6 bits each added to 0x21 (!)*/
for(i=0;i <= 10;i++){
/* last one is only 4 bits not 6*/
out[i] = '!'+ extract(cp,6*i,i >= 10 ? 4:6);
}
out[i] = '\0';
return(out);
}
#endifput8 is the glow-up 🦋 it turns the 8 bytes into 4 groups of 16-bit hex digits, so they're easy to read. Then there's the #ifdef notdef block with btoc, which is a possible alternative to btoe, not the main event 🌸 It's wrapped in #ifdef notdef, so it's tucked away and not part of the main build 💜
Internal subroutines for word encoding/decoding
Okay now the behind-the-scenes crew 🧚 These are static, which means they're internal helpers, not the main stars ✨
Dictionary binary search
/* Dictionary binary search */
static int
wsrch(w,low,high)
char *w;
int low, high;
{
int i,j;
for(;;){
i = (low + high)/2;
if((j = strncmp(w,Wp[i],4)) == 0)
return i; /* Found it */
if(high == low+1){
/* Avoid effects of integer truncation in /2 */
if(strncmp(w,Wp[high],4) == 0)
return high;
else
return -1;
}
if(low >= high)
return -1;
/* I don't *think* this can happen...*/
if(j < 0)
high = i; /* Search lower half */
else
low = i; /* Search upper half */
}
}wsrch is a binary search 🔍 It keeps halving the range and comparing the first 4 characters of the word against Wp[i] until it finds a match, or gives up and returns -1 🙃 It's giving "guess the number" but make it iconic 👑
static void
insert(s, x, start, length)
char *s;
int x;
int start, length;
{
unsigned char cl;
unsigned char cc;
unsigned char cr;
unsigned long y;
int shift;
assert(length <= 11);
assert(start >= 0);
assert(length >= 0);
assert(start +length <= 66);
shift = ((8 -(( start + length) % 8))%8);
y = (long) x << shift;
cl = (y >> 16) & 0xff;
cc = (y >> 8) & 0xff;
cr = y & 0xff;
if(shift + length > 16){
s[start /8] |= cl;
s[start/8 +1] |= cc;
s[start/8 +2] |= cr;
} else if(shift +length > 8){
s[start/8] |= cc;
s[start/8 + 1] |= cr;
} else {
s[start/8] |= cr;
}
}insert is the packing queen 👑 It shifts the 11-bit index into place and ORs it into the byte array, and it asserts its inputs first, just to be safe 🫶
static void
standard(word)
register char *word;
{
while(*word){
if(!isascii(*word))
break;
if(islower(*word))
*word = toupper(*word);
if(*word == '1')
*word = 'L';
if(*word == '0')
*word = 'O';
if(*word == '5')
*word = 'S';
word++;
}
}standard is the tidy-up step 🧹 It uppercases the letters and swaps the lookalike digits: 1 becomes L, 0 becomes O, and 5 becomes S. Iconic lookalike energy 🙈
/* Extract 'length' bits from the char array 's'
starting with bit 'start' */
static unsigned long
extract(s, start, length)
char *s;
int start, length;
{
unsigned char cl;
unsigned char cc;
unsigned char cr;
unsigned long x;
assert(length <= 11);
assert(start >= 0);
assert(length >= 0);
assert(start +length <= 66);
cl = s[start/8];
cc = s[start/8 +1];
cr = s[start/8 +2];
x = ((long)(cl<<8 | cc) <<8 | cr) ;
x = x >> (24 - (length + (start %8)));
x =( x & (0xffff >> (16-length) ) );
return(x);
}extract is insert's mirror image 🪞 It pulls length bits back out, starting from start, which is exactly what the parity check above depends on 💖
Appendix B - Source for 128-bit key to/from English words (convert.c) 🎀
/* convert.c -- Wrapper to S/Key binary-to-English routines.
Daniel L. McDonald -- U. S. Naval Research Laboratory. */
#include <string.h>
/* eng2key() assumes words must be separated by spaces only.
eng2key() returns
1 if succeeded
0 if word not in dictionary
-1 if badly formed string
-2 if words are okay but parity is wrong.
(see etob() in S/Key)
*/
int eng2key(keyout,eng)
char *keyout,*eng;
{
int rc=0,state=1;
char *eng2;
/* Find pointer to word 7. */
for (eng2 = eng; rc<7 && (*(++eng2) != '\0'); )
if (*eng2 != ' ')
{
rc += state;
state = 0;
}
else state=1;
if ( (rc = etob(keyout,eng)) != 1)
return rc;
rc = etob(keyout+8,eng2);
return rc;
}
/* key2eng() assumes string referenced by
engout has at least 60 characters
(4*12 + 11 spaces + '\0') of space.
key2eng() returns pointer to engout.
*/
char *key2eng(engout,key)
char *engout,*key;
{
btoe(engout,key);
strcat(engout," ");
btoe(engout+strlen(engout),key+8);
return engout;
}And that's the wrapper 🌈 convert.c is the bestie that ties it all together. eng2key takes the English words and hands them to etob in two chunks, with word 7 as the split point, and key2eng goes the other way with two btoe calls and a space in between 💜 Honestly obsessed 😭
📦 where this page comes from
- ietf: rfc1751 1994-12
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms