Moved alternative board to a new "modifications" section
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Trevor Terris
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README.md
114
README.md
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@ -63,62 +63,6 @@ To run (hand-run) the encryption/decryption, you will also need some kind of a
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marker (e.g. a small shiny stone, bolt nut or similar kind of well-shaped
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marker (e.g. a small shiny stone, bolt nut or similar kind of well-shaped
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trash).
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trash).
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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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0 a b c d e f
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g h i j k l m
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n o p q r s t
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u v w x y z _
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. , - + * / :
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? ! ' ( ) 1 2
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3 4 5 6 7 8 9
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```
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With this layout, 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 LC4, the following board could be used:
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```
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# a b c d e
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f g h i j k
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l m n o p q
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r s t u v w
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x y z _ 2 3
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4 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 10♠ and A♠, respectively.
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## How-To
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## How-To
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You may as well see the paper [1], there are also pictures. This is somewhat more concentrated:
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You may as well see the paper [1], there are also pictures. This is somewhat more concentrated:
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@ -198,6 +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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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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### Key expansion from a password
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Remembering 49-position random permutation that includes weird characters is
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Remembering 49-position random permutation that includes weird characters is
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@ -252,6 +198,62 @@ 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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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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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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0 a b c d e f
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g h i j k l m
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n o p q r s t
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u v w x y z _
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. , - + * / :
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? ! ' ( ) 1 2
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3 4 5 6 7 8 9
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```
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With this layout, 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 LC4, the following board could be used:
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```
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# a b c d e
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f g h i j k
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l m n o p q
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r s t u v w
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x y z _ 2 3
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4 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 10♠ and A♠, respectively.
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## References
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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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