PGP word list

The PGP Word List ("Pretty Good Privacy word list", also called a biometric word list for reasons explained below) is a list of words for conveying data bytes in a clear unambiguous way via a voice channel. They are analogous in purpose to the NATO phonetic alphabet used by pilots, except a longer list of words is used, each word corresponding to one of the 256 distinct numeric byte values.

## Contents

* 1 History and structure
* 2 Word lists
* 3 Examples
* 4 Other word lists for data
* 5 References

## History and structure

The PGP Word List was designed in 1995 by Patrick Juola, a computational linguist, and Philip Zimmermann, creator of PGP.[1][2] The words were carefully chosen for their phonetic distinctiveness, using genetic algorithms to select lists of words that had optimum separations in phoneme space. The candidate word lists were randomly drawn from Grady Ward's Moby Pronunciator list as raw material for the search, successively refined by the genetic algorithms. The automated search converged to an optimized solution in about 40 hours on a DEC Alpha, a particularly fast machine in that era.

The Zimmermann–Juola list was originally designed to be used in PGPfone, a secure VoIP application, to allow the two parties to verbally compare a short authentication string to detect a man-in-the-middle attack (MiTM). It was called a biometric word list because the authentication depended on the two human users recognizing each other's distinct voices as they read and compared the words over the voice channel, binding the identity of the speaker with the words, which helped protect against the MiTM attack. The list can be used in many other situations where a biometric binding of identity is not needed, so calling it a biometric word list may be imprecise. Later, it was used in PGP to compare and verify PGP public key fingerprints over a voice channel. This is known in PGP applications as the "biometric" representation. When it was applied to PGP, the list of words was further refined, with contributions by Jon Callas. More recently, it has been used in Zfone and the ZRTP protocol, the successor to PGPfone.

The list is actually composed of two lists, each containing 256 phonetically distinct words, in which each word represents a different byte value between 0 and 255. Two lists are used because reading aloud long random sequences of human words usually risks three kinds of errors: 1) transposition of two consecutive words, 2) duplicate words, or 3) omitted words. To detect all three kinds of errors, the two lists are used alternately for the even-offset bytes and the odd-offset bytes in the byte sequence. Each byte value is actually represented by two different words, depending on whether that byte appears at an even or an odd offset from the beginning of the byte sequence. The two lists are readily distinguished by the number of syllables; the even list has words of two syllables, the odd list has three. The two lists have a maximum word length of 9 and 11 letters, respectively. Using a two-list scheme was suggested by Zhahai Stewart.

## Word lists

Here are the two lists of words as presented in the PGPfone Owner's Manual.[3]

Hex | Even Word | Odd Word

|
|

00 | aardvark | adroitness
01 | absurd | adviser
02 | accrue | aftermath
03 | acme | aggregate
04 | adrift | alkali
05 | adult | almighty
06 | afflict | amulet
07 | ahead | amusement
08 | aimless | antenna
09 | Algol | applicant
0A | allow | Apollo
0B | alone | armistice
0C | ammo | article
0D | ancient | asteroid
0E | apple | Atlantic
0F | artist | atmosphere
10 | assume | autopsy
11 | Athens | Babylon
12 | atlas | backwater
13 | Aztec | barbecue
14 | baboon | belowground
15 | backfield | bifocals
16 | backward | bodyguard
17 | banjo | bookseller
18 | beaming | borderline
19 | bedlamp | bottomless
1A | beehive | Bradbury
1B | beeswax | bravado
1C | befriend | Brazilian
1D | Belfast | breakaway
1E | berserk | Burlington
1F | billiard | businessman
20 | bison | butterfat
21 | blackjack | Camelot
22 | blockade | candidate
23 | blowtorch | cannonball
24 | bluebird | Capricorn
25 | bombast | caravan
26 | bookshelf | caretaker
27 | brackish | celebrate
28 | breadline | cellulose
29 | breakup | certify
2A | brickyard | chambermaid
2B | briefcase | Cherokee
2C | Burbank | Chicago
2D | button | clergyman
2E | buzzard | coherence
2F | cement | combustion
30 | chairlift | commando
31 | chatter | company
32 | checkup | component
33 | chisel | concurrent
34 | choking | confidence
35 | chopper | conformist
36 | Christmas | congregate
37 | clamshell | consensus
38 | classic | consulting
39 | classroom | corporate
3A | cleanup | corrosion
3B | clockwork | councilman
3C | cobra | crossover
3D | commence | crucifix
3E | concert | cumbersome
3F | cowbell | customer
Hex | Even Word | Odd Word

|
|

40 | crackdown | Dakota
41 | cranky | decadence
42 | crowfoot | December
43 | crucial | decimal
44 | crumpled | designing
45 | crusade | detector
46 | cubic | detergent
47 | dashboard | determine
48 | deadbolt | dictator
49 | deckhand | dinosaur
4A | dogsled | direction
4B | dragnet | disable
4C | drainage | disbelief
4D | dreadful | disruptive
4E | drifter | distortion
4F | dropper | document
50 | drumbeat | embezzle
51 | drunken | enchanting
52 | Dupont | enrollment
53 | dwelling | enterprise
54 | eating | equation
55 | edict | equipment
56 | egghead | escapade
57 | eightball | Eskimo
58 | endorse | everyday
59 | endow | examine
5A | enlist | existence
5B | erase | exodus
5C | escape | fascinate
5D | exceed | filament
5E | eyeglass | finicky
5F | eyetooth | forever
60 | facial | fortitude
61 | fallout | frequency
62 | flagpole | gadgetry
63 | flatfoot | Galveston
64 | flytrap | getaway
65 | fracture | glossary
66 | framework | gossamer
67 | freedom | graduate
68 | frighten | gravity
69 | gazelle | guitarist
6A | Geiger | hamburger
6B | glitter | Hamilton
6C | glucose | handiwork
6D | goggles | hazardous
6E | goldfish | headwaters
6F | gremlin | hemisphere
70 | guidance | hesitate
71 | hamlet | hideaway
72 | highchair | holiness
73 | hockey | hurricane
74 | indoors | hydraulic
75 | indulge | impartial
76 | inverse | impetus
77 | involve | inception
78 | island | indigo
79 | jawbone | inertia
7A | keyboard | infancy
7B | kickoff | inferno
7C | kiwi | informant
7D | klaxon | insincere
7E | locale | insurgent
7F | lockup | integrate
Hex | Even Word | Odd Word

|
|

80 | merit | intention
81 | minnow | inventive
82 | miser | Istanbul
83 | Mohawk | Jamaica
84 | mural | Jupiter
85 | music | leprosy
86 | necklace | letterhead
87 | Neptune | liberty
88 | newborn | maritime
89 | nightbird | matchmaker
8A | Oakland | maverick
8B | obtuse | Medusa
8C | offload | megaton
8D | optic | microscope
8E | orca | microwave
8F | payday | midsummer
90 | peachy | millionaire
91 | pheasant | miracle
92 | physique | misnomer
93 | playhouse | molasses
94 | Pluto | molecule
95 | preclude | Montana
96 | prefer | monument
97 | preshrunk | mosquito
98 | printer | narrative
99 | prowler | nebula
9A | pupil | newsletter
9B | puppy | Norwegian
9C | python | October
9D | quadrant | Ohio
9E | quiver | onlooker
9F | quota | opulent
A0 | ragtime | Orlando
A1 | ratchet | outfielder
A2 | rebirth | Pacific
A3 | reform | pandemic
A4 | regain | Pandora
A5 | reindeer | paperweight
A6 | rematch | paragon
A7 | repay | paragraph
A8 | retouch | paramount
A9 | revenge | passenger
AA | reward | pedigree
AB | rhythm | Pegasus
AC | ribcage | penetrate
AD | ringbolt | perceptive
AE | robust | performance
AF | rocker | pharmacy
B0 | ruffled | phonetic
B1 | sailboat | photograph
B2 | sawdust | pioneer
B3 | scallion | pocketful
B4 | scenic | politeness
B5 | scorecard | positive
B6 | Scotland | potato
B7 | seabird | processor
B8 | select | provincial
B9 | sentence | proximate
BA | shadow | puberty
BB | shamrock | publisher
BC | showgirl | pyramid
BD | skullcap | quantity
BE | skydive | racketeer
BF | slingshot | rebellion
Hex | Even Word | Odd Word

|
|

C0 | slowdown | recipe
C1 | snapline | recover
C2 | snapshot | repellent
C3 | snowcap | replica
C4 | snowslide | reproduce
C5 | solo | resistor
C6 | southward | responsive
C7 | soybean | retraction
C8 | spaniel | retrieval
C9 | spearhead | retrospect
CA | spellbind | revenue
CB | spheroid | revival
CC | spigot | revolver
CD | spindle | sandalwood
CE | spyglass | sardonic
CF | stagehand | Saturday
D0 | stagnate | savagery
D1 | stairway | scavenger
D2 | standard | sensation
D3 | stapler | sociable
D4 | steamship | souvenir
D5 | sterling | specialist
D6 | stockman | speculate
D7 | stopwatch | stethoscope
D8 | stormy | stupendous
D9 | sugar | supportive
DA | surmount | surrender
DB | suspense | suspicious
DC | sweatband | sympathy
DD | swelter | tambourine
DE | tactics | telephone
DF | talon | therapist
E0 | tapeworm | tobacco
E1 | tempest | tolerance
E2 | tiger | tomorrow
E3 | tissue | torpedo
E4 | tonic | tradition
E5 | topmost | travesty
E6 | tracker | trombonist
E7 | transit | truncated
E8 | trauma | typewriter
E9 | treadmill | ultimate
EA | Trojan | undaunted
EB | trouble | underfoot
EC | tumor | unicorn
ED | tunnel | unify
EE | tycoon | universe
EF | uncut | unravel
F0 | unearth | upcoming
F1 | unwind | vacancy
F2 | uproot | vagabond
F3 | upset | vertigo
F4 | upshot | Virginia
F5 | vapor | visitor
F6 | village | vocalist
F7 | virus | voyager
F8 | Vulcan | warranty
F9 | waffle | Waterloo
FA | wallet | whimsical
FB | watchword | Wichita
FC | wayside | Wilmington
FD | willow | Wyoming
FE | woodlark | yesteryear

## Examples

Each byte in a bytestring is encoded as a single word. A sequence of bytes is rendered in network byte order, from left to right. For example, the leftmost (i.e. byte 0) is considered "even" and is encoded using the PGP Even Word table. The next byte to the right (i.e. byte 1) is considered "odd" and is encoded using the PGP Odd Word table. This process repeats until all bytes are encoded. Thus, "E582" produces "topmost Istanbul", whereas "82E5" produces "miser travesty".

A PGP public key fingerprint that displayed in hexadecimal as

`E582` `94F2` `E9A2` `2748` `6E8B`
`061B` `31CC` `528F` `D7FA` `3F19`

would display in PGP Words (the "biometric" fingerprint) as

`topmost Istanbul` `Pluto vagabond` `treadmill Pacific` `brackish dictator` `goldfish Medusa`
`afflict bravado` `chatter revolver` `Dupont midsummer` `stopwatch whimsical` `cowbell bottomless`

The order of bytes in a bytestring depends on endianness.

## Other word lists for data

There are several other word lists for conveying data in a clear unambiguous way via a voice channel:

* the NATO phonetic alphabet maps individual letters and digits to individual words
* the S/KEY system maps 64 bit numbers to 6 short words of 1 to 4 characters each from a publicly accessible 2048-word dictionary. The same dictionary is used in RFC 1760 and RFC 2289.
* the Diceware system maps five base-6 random digits (almost 13 bits of entropy) to a word from a dictionary of 7,776 distinct words.
* the Electronic Frontier Foundation has published a set of improved word lists based on the same concept[4]
* FIPS 181: Automated Password Generator converts random numbers into somewhat pronounceable "words".
* mnemonic encoding converts 32 bits of data into 3 words from a vocabulary of 1626 words.[5]
* what3words encodes geographic coordinates in 3 dictionary words.
* the BIP39 standard permits encoding a cryptographic key of fixed size (128 or 256 bits, usually the unencrypted master key of a Cryptocurrency wallet) into a short sequence of readable words known as the seed phrase, for the purpose of storing the key offline. This is used in cryptocurrencies such as Bitcoin or Monero.
* Like the PGP word list, the Bytewords standard maps each possible byte to a word. There is only one list, rather than two. The words are uniformly four letters long and can be uniquely identified by their first and last letters

## References

This article incorporates material that is copyrighted by PGP Corporation and has been licensed under the GNU Free Documentation License. (per Jon Callas, CTO, CSO PGP Corporation, 4-Jan-2007)

1. ↑ Juola, Patrick; Zimmermann, Philip (1996). "Whole-word phonetic distances and the PGPfone alphabet". Proceeding of Fourth International Conference on Spoken Language Processing. ICSLP '96. 1. pp. 98–101. doi:10.1109/ICSLP.1996.607046. ISBN 0-7803-3555-4. http://www.mathcs.duq.edu/~juola/papers.d/icslp96.pdf.
2. ↑ Juola, Patrick (1996). "Isolated Word Confusion Metrics and the PGPfone Alphabet". Proceedings of New Methods in Language Processing 2 (Ankara, Turkey: Oxford University, Dept. of Experimental Psychology). Bibcode: 1996cmp.lg....8021J. http://www.mathcs.duq.edu/~juola/papers.d/pgpfonenemlap.ps.
3. ↑ "Archived copy". http://web.mit.edu/network/pgpfone/manual/index.html#PGP000062.
4. ↑ "EFF's New Wordlists for Random Passphrases". 19 July 2016. https://www.eff.org/deeplinks/2016/07/new-wordlists-random-passphrases.
5. ↑ mnemonic encoding and updated code

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