Merge pull request 'Add documentation and LC4 implementation for playing-card-based tables' (#3) from tkterris/ls47:solitaire into master
Reviewed-on: https://gitea.blesmrt.net/exa/ls47/pulls/3
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README.md
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README.md
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@ -142,6 +142,8 @@ stays the same.
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Grab a bag full of tiles and randomly draw them one by one. Key is the 49-item permutation of them.
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## Modifications
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### Key expansion from a password
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Remembering 49-position random permutation that includes weird characters is
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@ -196,6 +198,84 @@ This works because the cipher output is message-dependent: Having a wrong bit
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somewhere in the middle causes avalanche effect and erases any meaning from the
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text after several characters.
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### Alternative playing-card-compatible board
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The following board can be used so that characters and offsets can be easily
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mapped to playing cards, similar to the Solitaire cipher [2]. Using playing
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cards could be more innocuous and easily explainable to the secret police than
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a set of peculiar numbered tiles.
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```
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a b c d e f g
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h i j k l m n
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o p q r s t u
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v w x y z _ .
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, - + * / : ?
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! ' ( ) 1 2 3
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4 5 6 7 8 9 0
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```
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**This board uses a 1-based index**, so `a=1`, `b=2`, and so on. With this layout,
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the following mapping to playing cards is used:
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| **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index |
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|-----------|------|-------|-----------|------|-------|-----------|------|-------|-----------|------|--------|
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| a | A♦ | 1 | n | A♣ | 14 | _ | A♥ | 27 | 1 | A♠ | 40 |
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| b | 2♦ | 2 | o | 2♣ | 15 | . | 2♥ | 28 | 2 | 2♠ | 41 |
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| c | 3♦ | 3 | p | 3♣ | 16 | , | 3♥ | 29 | 3 | 3♠ | 42 |
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| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
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| j | 10♦ | 10 | w | 10♣ | 23 | ! | 10♥ | 39 | 7 | 7♠ | 46 |
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| k | J♦ | 11 | x | J♣ | 24 | ' | J♥ | 39 | 8 | 8♠ | 47 |
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| l | Q♦ | 12 | y | Q♣ | 25 | ( | Q♥ | 39 | 9 | 9♠ | 48 |
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| m | K♦ | 13 | z | K♣ | 26 | ) | K♥ | 39 | 0 | 10♠ | 49 (0) |
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The (x, y) offset can be calculated by first determining the index: take the
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number of the suit (0-3), multiply by 13, and add the card number (using 1 for
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the Ace, 11-13 for face cards). Then, determine the offset from the index
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using the usual modular arithmetic: `x = index % 7` and `y = index / 7`.
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Alphanumeric characters can be easily mapped to cards, with letters mapping to
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Diamonds or Clubs and numbers mapping to Spades (note that Spades face cards
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are ommitted). All of the special characters are mapped to the Hearts, though
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coming up with a mnemonic for the mapping of each special character to each
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Heart is left as an exercise for the reader.
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For an example, view [this image](card-tiles.jpg). In this example, the marker
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is on J♣ (at the top left), and we want to encrypt the plaintext character `e`.
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The image includes the character, index, and offsets for the relevant cards.
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1. From the card mapping, `e` maps to 5♦ (letters `a` through `m` map to Diamonds), which is on the second row.
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1. The marker card, J♣, has:
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- an index of 24 (Clubs are suit 1, and the Jack is the 11th card in the suit): `i = 1 * 13 + 11 = 24`
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- an x-offset of 3: `x = i % 7 = 24 % 7 = 3`
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- a y-offset of 3: `y = i / 7 = 24 / 7 = 3`
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1. Using the marker offsets, the ciphertext card is three rows down and three columns to the right of 5♦, which is 6♠.
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1. From the card mapping, 6♠ maps to `6` (Spades map directly to digits), and has:
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- an index of 45 (Spades are suit 3, and 6 is the 6th card in the suit): `i = 3 * 13 + 6 = 45`
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- an x-offset of 3: `x = i % 7 = 45 % 7 = 3`
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- a y-offset of 6: `y = i / 7 = 45 / 7 = 6`
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1. We then complete the cipher as normal:
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- Output `6` as the ciphertext
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- Rotate the row containing the plaintext card, 5♦
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- Rotate the column containing the ciphertext card, 6♠
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- Move the marker according to the offsets of the ciphertext card, to the right 3 and down 6
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For LC4, the following board could be used:
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```
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a b c d e f
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g h i j k l
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m n o p q r
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s t u v w x
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y z _ 2 3 4
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5 6 7 8 9 #
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```
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The "Hearts" suit would be ommitted from the card mapping table, and the index
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of each of the Spades would be decreased by 13 to compensate. `_` and `#`
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would map to A♠ and 10♠, respectively.
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## References
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[1] *Kaminsky, Alan. "ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication." IACR Cryptology ePrint Archive 2017 (2017): 339.*
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[1] *Kaminsky, Alan. "ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication." IACR Cryptology ePrint Archive 2017 (2017): 339.*
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[2] *Schneier, Bruce. ["The Solitaire Encryption Algorithm"](https://www.schneier.com/academic/solitaire/).*
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BIN
card-tiles.jpg
Normal file
BIN
card-tiles.jpg
Normal file
Binary file not shown.
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After Width: | Height: | Size: 168 KiB |
26
lc4.py
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lc4.py
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@ -54,8 +54,10 @@ import argparse
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version = "v2.8.1 (2018-07-24)"
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# define alphabet
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letters6 = "#_23456789abcdefghijklmnopqrstuvwxyz"
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letters7 = "_abcdefghijklmnopqrstuvwxyz.0123456789,-+*/:?!'()"
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letters6 = "#_23456789abcdefghijklmnopqrstuvwxyz"
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letters6card = "#abcdefghijklmnopqrstuvwxyz_23456789"
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letters7 = "_abcdefghijklmnopqrstuvwxyz.0123456789,-+*/:?!'()"
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letters7card = "0abcdefghijklmnopqrstuvwxyz_.,-+*/:?!'()123456789"
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def missing_letters(s,t):
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@ -149,9 +151,11 @@ def rotate_marker_down(m, col, n):
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return ((m[0] + n) % size, m[1])
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def derive_key(password):
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def derive_key(password, one_indexed):
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i = 0
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k = letters
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# if using one-indexed arrays, moves the zero element to the end
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if one_indexed: k = k[1:]+k[0]
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for c in password:
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(row, col) = find_ix(c)
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k = rotate_down(rotate_right(k, i, col), i, row)
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@ -293,7 +297,7 @@ def test1(size, fixednonce):
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else:
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keyword = 's3cret_p4ssw0rd/31337'
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szkeyword = keyword # This statement needed to show keyword in printinfo() [don't change args.keywordstring within test1()!]
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key = derive_key(keyword)
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key = derive_key(keyword, false)
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else:
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key = letters
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initialkey = key
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@ -333,6 +337,8 @@ if __name__ == '__main__':
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mgroup1.add_argument("-6", "--lc4", help="use ElsieFour cipher (6x6 table) (default)", action="store_true")
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mgroup1.add_argument("-7", "--ls47", help="use LS47 cipher (7x7 table)", action="store_true")
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parser.add_argument("-pc", "--playingcard", help="Use the \"playing card\" character tables (default: standard tables)", action="store_true")
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mgroup2 = parser.add_mutually_exclusive_group()
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mgroup2.add_argument("-ks", "--keystring", metavar="STRING", help="use STRING as key")
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mgroup2.add_argument("-kf", "--keyfile", metavar="FILE", help="read key from FILE")
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@ -375,10 +381,16 @@ if __name__ == '__main__':
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if args.ls47:
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size = 7
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letters = letters7
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if args.playingcard:
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letters = letters7card
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else:
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letters = letters7
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else:
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size = 6
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letters = letters6
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if args.playingcard:
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letters = letters6card
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else:
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letters = letters6
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tiles = list(zip(letters, [(x // size, x % size) for x in range(size * size)]))
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@ -423,7 +435,7 @@ if __name__ == '__main__':
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if args.keywordfile: args.keywordstring = open(args.keywordfile, 'r').read().rstrip('\r\n')
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if args.keywordstring:
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szkeyword = args.keywordstring
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key = derive_key(args.keywordstring)
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key = derive_key(args.keywordstring, args.playingcard)
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if args.keyfile: args.keystring = open(args.keyfile, 'r').read().rstrip('\r\n')
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if args.keystring: key = args.keystring;
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