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References: <87iowuuof9.fsf@gmail.com>
Date: Fri, 18 Oct 2013 16:58:27 -0700
Message-ID: <CAAS2fgQ1uYvNxZu6DOKZ2k9qj2kYhGpHxxzsZdsqb-Oi2uSKmw@mail.gmail.com>
From: Gregory Maxwell <gmaxwell@gmail.com>
To: jan <jan.marecek@gmail.com>
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Cc: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] BIP39 word list
Precedence: list

some fairly old wordlist solver code of mine:

https://people.xiph.org/~greg/wordlist.visual.py

it has a 52x52 letter visual similarity matrix in it (along with a citation)

On Fri, Oct 18, 2013 at 4:52 PM, jan <jan.marecek@gmail.com> wrote:
>
> The words 'public', 'private' and 'secret' could be confusing when
> encoding public and private keys. eg. a private key that begins with
> the word 'public'.
>
> I think avoiding words that could look similar when written down would
> be a good idea aswell. I searched for words that only differ by the
> letters c & e, g & y, u & v and found the following:
>
> car ear
> cat eat
> gear year
> value valve
>
> Other combinations could potentially be problematic depending on the
> handwriting style: ft, ao, ij, vy, possibly even lt and il?
>
> I've included the search utility I used below.
>
>
> #include <stdbool.h>
> #include <string.h>
> #include <stdio.h>
>
> char *similar_char_pairs[] = { "ce", "gy", "uv", NULL };
>
> bool is_similar_char(char c1, char c2)
> {
>   char **pairs = similar_char_pairs;
>   do {
>     char *p = *pairs;
>     if ((c1 == p[0] && c2 == p[1]) ||
>         (c1 == p[1] && c2 == p[0]))
>       return true;
>   } while (*++pairs);
>
>   return false;
> }
>
> bool print_words_if_similar(char *word1, char *word2)
> {
>   /* reject words of different lengths */
>   if (strlen(word1) != strlen(word2))
>     return false;
>
>   size_t i, similarcount = 0;
>
>   for (i = 0; i < strlen(word1); i++) {
>     /* skip identical letters */
>     if (word1[i] == word2[i])
>       continue;
>
>     /* reject words that don't match */
>     if (is_similar_char(word1[i], word2[i]) == false)
>       return false;
>
>     similarcount++;
>   }
>
>   /* reject words with more than 1 different letter */
>   //if (similarcount > 1)
>   //  return false;
>
>   printf("%s %s\n", word1, word2);
>
>   return true;
> }
>
> int main(void)
> {
>   /* english.txt is assumed to exist in the working directory
>      download from:
>      https://github.com/trezor/python-mnemonic/blob/master/mnemonic/wordlist/english.txt */
>   FILE* f = fopen("english.txt", "r");
>   if (!f) {
>     fprintf(stderr, "failed to open english.txt\n");
>     return 1;
>   }
>
>   /* read in word list, assumes one word per line */
>   #define MAXWORD 16
>   char wordlist[2048][MAXWORD];
>   int word = 0;
>   while (fgets(wordlist[word], MAXWORD, f)) {
>     /* strip trailing whitespace, assumes no leading whitespace */
>     char *ch = strpbrk(wordlist[word], " \n\t");
>     if (ch)
>       *ch = '\0';
>     word++;
>   }
>
>   if (word != 2048) {
>     fprintf(stderr, "word list incorrect length\n");
>     return 1;
>   }
>
>   /* check each word for similarity against every other word */
>   int i, j, count = 0;
>   for (i = 0; i < 2048; i++) {
>     for (j = i+1; j < 2048; j++) {
>       if (print_words_if_similar(wordlist[i], wordlist[j]))
>         count++;
>     }
>   }
>
>   printf("%d matches\n", count);
>
>   return 0;
> }
>
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