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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