From 2076f1b57b95b00807c8b00020227527bd6fd063 Mon Sep 17 00:00:00 2001
From: Trevor Terris <tterris@redhat.com>
Date: Thu, 22 Apr 2021 18:58:23 -0400
Subject: [PATCH] Change indexing to make card ordering more intuitive

Update the indexing so that the table starts at "1". This way the ordered card layout (used for key generation) starts with the Ace of Diamonds and proceeds through the cards and suits as normal. This seems cleaner than awkwardly prepending the 10 of Spades. However, it involves a slight tweak to the key key_derive function to support the change in card order.
---
 README.md | 29 +++++++++++++++--------------
 lc4.py    |  8 +++++---
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/README.md b/README.md
index 1568b5f..9487cfb 100644
--- a/README.md
+++ b/README.md
@@ -206,16 +206,17 @@ 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
+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 0
 ```
 
-With this layout, the following mapping to playing cards is used:
+**This board uses a 1-based index**, so `a=1`, `b=2`, and so on. With this layout, 
+the following mapping to playing cards is used:
 
 | **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index | **Character** | Card | Index  |
 |-----------|------|-------|-----------|------|-------|-----------|------|-------|-----------|------|--------|
@@ -242,12 +243,12 @@ 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
+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
diff --git a/lc4.py b/lc4.py
index 5a2785f..fea2f7a 100644
--- a/lc4.py
+++ b/lc4.py
@@ -151,9 +151,11 @@ def rotate_marker_down(m, col, n):
         return ((m[0] + n) % size, m[1])
 
 
-def derive_key(password):
+def derive_key(password, one_indexed):
     i = 0
     k = letters
+    # if using one-indexed arrays, moves the zero element to the end
+    if one_indexed: k = k[1:]+k[0]
     for c in password:
         (row, col) = find_ix(c)
         k = rotate_down(rotate_right(k, i, col), i, row)
@@ -295,7 +297,7 @@ def test1(size, fixednonce):
         else:
             keyword = 's3cret_p4ssw0rd/31337'
         szkeyword = keyword # This statement needed to show keyword in printinfo() [don't change args.keywordstring within test1()!]
-        key = derive_key(keyword)
+        key = derive_key(keyword, false)
     else:
         key = letters
     initialkey = key
@@ -433,7 +435,7 @@ if __name__ == '__main__':
     if args.keywordfile: args.keywordstring = open(args.keywordfile, 'r').read().rstrip('\r\n')
     if args.keywordstring:
         szkeyword = args.keywordstring
-        key = derive_key(args.keywordstring)
+        key = derive_key(args.keywordstring, args.playingcard)
 
     if args.keyfile: args.keystring = open(args.keyfile, 'r').read().rstrip('\r\n')
     if args.keystring: key = args.keystring;