diff --git a/README.md b/README.md index d3a2a5c..284f39e 100644 --- a/README.md +++ b/README.md @@ -66,46 +66,43 @@ 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]. This could be -more innocuous and easily explainable to the secret police than a set of -peculiar numbered tiles. +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 +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) | +| **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 is calculated from the index with the usual modular -arithmetic: `x = index % 7` and `y = index / 7`. +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`. -Note that the offset can be easily calculated from a given card: take the -order of the suit (0-3), multiply by 13, and add the card number (11-13 for -face cards, 1 for the Ace) to get the index. The offset can then be calculated -from the index. - -Alphanumeric characters can be easily mapped to cards as well, with letters -mapping to Diamonds or Clubs, and numbers mapping to Spades (and optionally -a Joker). 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 +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: @@ -119,8 +116,9 @@ x y z _ 2 3 4 5 6 7 8 9 ``` -The "Hearts" suit would be ommitted from the card mappin table. `#` and `_` -would map to the Joker/10♠ and A♠, respectively. +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 @@ -257,5 +255,5 @@ text after several characters. ## References -[1] *Kaminsky, Alan. "ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication." IACR Cryptology ePrint Archive 2017 (2017): 339.* -[2] *Schneier, Bruce. ["The Solitaire Encryption Algorith"](https://www.schneier.com/academic/solitaire/). +[1] *Kaminsky, Alan. "ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication." IACR Cryptology ePrint Archive 2017 (2017): 339.* +[2] *Schneier, Bruce. ["The Solitaire Encryption Algorithm"](https://www.schneier.com/academic/solitaire/).*