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Moved alternative board to a new "modifications" section

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Trevor Terris 2021-04-22 08:51:04 -04:00
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@ -63,62 +63,6 @@ To run (hand-run) the encryption/decryption, you will also need some kind of a
marker (e.g. a small shiny stone, bolt nut or similar kind of well-shaped
trash).
#### Alternative playing-card-compatible board
The following board can be used so that characters and offsets can be easily
mapped to playing cards, similar to the Solitaire cipher [2]. Using playing
cards could be more innocuous and easily explainable to the secret police than
a set of peculiar numbered tiles.
```
0 a b c d e f
g h i j k l m
n o p q r s t
u v w x y z _
. , - + * / :
? ! ' ( ) 1 2
3 4 5 6 7 8 9
```
With this layout, the following mapping to playing cards is used:
| **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index |
|-----------|------|-------|-----------|------|-------|-----------|------|-------|-----------|------|--------|
| a | A♦ | 1 | n | A♣ | 14 | _ | A♥ | 27 | 1 | A♠ | 40 |
| b | 2♦ | 2 | o | 2♣ | 15 | . | 2♥ | 28 | 2 | 2♠ | 41 |
| c | 3♦ | 3 | p | 3♣ | 16 | , | 3♥ | 29 | 3 | 3♠ | 42 |
| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
| j | 10♦ | 10 | w | 10♣ | 23 | ! | 10♥ | 39 | 7 | 7♠ | 46 |
| k | J♦ | 11 | x | J♣ | 24 | ' | J♥ | 39 | 8 | 8♠ | 47 |
| l | Q♦ | 12 | y | Q♣ | 25 | ( | Q♥ | 39 | 9 | 9♠ | 48 |
| m | K♦ | 13 | z | K♣ | 26 | ) | K♥ | 39 | 0 | 10♠ | 49 (0) |
The (x, y) offset can be calculated by first determining the index: take the
number of the suit (0-3), multiply by 13, and add the card number (using 1 for
the Ace, 11-13 for face cards). Then, determine the offset from the index
using the usual modular arithmetic: `x = index % 7` and `y = index / 7`.
Alphanumeric characters can be easily mapped to cards, with letters mapping to
Diamonds or Clubs and numbers mapping to Spades (note that Spades face cards
are ommitted). All of the special characters are mapped to the Hearts, though
coming up with a mnemonic for the mapping of each special character to each
Heart is left as an exercise for the reader.
For LC4, the following board could be used:
```
# a b c d e
f g h i j k
l m n o p q
r s t u v w
x y z _ 2 3
4 5 6 7 8 9
```
The "Hearts" suit would be ommitted from the card mapping table, and the index
of each of the Spades would be decreased by 13 to compensate. `#` and `_`
would map to 10♠ and A♠, respectively.
## How-To
You may as well see the paper [1], there are also pictures. This is somewhat more concentrated:
@ -198,6 +142,8 @@ stays the same.
Grab a bag full of tiles and randomly draw them one by one. Key is the 49-item permutation of them.
## Modifications
### Key expansion from a password
Remembering 49-position random permutation that includes weird characters is
@ -252,6 +198,62 @@ This works because the cipher output is message-dependent: Having a wrong bit
somewhere in the middle causes avalanche effect and erases any meaning from the
text after several characters.
### Alternative playing-card-compatible board
The following board can be used so that characters and offsets can be easily
mapped to playing cards, similar to the Solitaire cipher [2]. Using playing
cards could be more innocuous and easily explainable to the secret police than
a set of peculiar numbered tiles.
```
0 a b c d e f
g h i j k l m
n o p q r s t
u v w x y z _
. , - + * / :
? ! ' ( ) 1 2
3 4 5 6 7 8 9
```
With this layout, the following mapping to playing cards is used:
| **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index |
|-----------|------|-------|-----------|------|-------|-----------|------|-------|-----------|------|--------|
| a | A♦ | 1 | n | A♣ | 14 | _ | A♥ | 27 | 1 | A♠ | 40 |
| b | 2♦ | 2 | o | 2♣ | 15 | . | 2♥ | 28 | 2 | 2♠ | 41 |
| c | 3♦ | 3 | p | 3♣ | 16 | , | 3♥ | 29 | 3 | 3♠ | 42 |
| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
| j | 10♦ | 10 | w | 10♣ | 23 | ! | 10♥ | 39 | 7 | 7♠ | 46 |
| k | J♦ | 11 | x | J♣ | 24 | ' | J♥ | 39 | 8 | 8♠ | 47 |
| l | Q♦ | 12 | y | Q♣ | 25 | ( | Q♥ | 39 | 9 | 9♠ | 48 |
| m | K♦ | 13 | z | K♣ | 26 | ) | K♥ | 39 | 0 | 10♠ | 49 (0) |
The (x, y) offset can be calculated by first determining the index: take the
number of the suit (0-3), multiply by 13, and add the card number (using 1 for
the Ace, 11-13 for face cards). Then, determine the offset from the index
using the usual modular arithmetic: `x = index % 7` and `y = index / 7`.
Alphanumeric characters can be easily mapped to cards, with letters mapping to
Diamonds or Clubs and numbers mapping to Spades (note that Spades face cards
are ommitted). All of the special characters are mapped to the Hearts, though
coming up with a mnemonic for the mapping of each special character to each
Heart is left as an exercise for the reader.
For LC4, the following board could be used:
```
# a b c d e
f g h i j k
l m n o p q
r s t u v w
x y z _ 2 3
4 5 6 7 8 9
```
The "Hearts" suit would be ommitted from the card mapping table, and the index
of each of the Spades would be decreased by 13 to compensate. `#` and `_`
would map to 10♠ and A♠, respectively.
## References
[1] *Kaminsky, Alan. "ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication." IACR Cryptology ePrint Archive 2017 (2017): 339.*