lib/bcrypt
1
0
Fork 0
mirror of https://github.com/rg3/libbcrypt.git synced 2026-10-23 12:08:58 +03:00
Code Releases Activity

implemented time safe string comparison

Browse Source
This commit is contained in:
Alex Young
2015-05-16 10:08:49 +01:00
parent 7a5bc2a2ae
commit e27fcc3d4b
2 changed files with 29 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

30
bcrypt.c
View File

@@ -61,6 +61,23 @@ static int try_read(int fd, char *out, size_t count)
return 0;
}
/*
* Time taken only varies with the length of str1. Because user input is hashed
* with bcrypt_hashpw(passwd, hashed, outhash) beforehand and the length of
* hashed is constant the time taken to execute this function will be constant.
*/
static int timing_safe_strcmp(const char *str1, const char *str2)
{
int i, str1len, str2len, rv = 0;
str1len = strlen(str1);
str2len = strlen(str2);
for (i = 0; i < str1len; i++) {
rv |= str1[i] ^ str2[i];
}
rv |= str1len ^ str2len; // lengths must match
return rv;
}
int bcrypt_gensalt(int factor, char salt[BCRYPT_HASHSIZE])
{
int fd;
@@ -101,7 +118,7 @@ int bcrypt_checkpw(const char *passwd, const char hashed[BCRYPT_HASHSIZE])
char outhash[BCRYPT_HASHSIZE];
ret = bcrypt_hashpw(passwd, hashed, outhash);
if (ret == 0 && strcmp(hashed, outhash) == 0)
if (ret == 0 && timing_safe_strcmp(hashed, outhash) == 0)
{
return 1;
}
@@ -145,8 +162,17 @@ int main()
assert(ret == 0);
printf("Second hash check: %s\n", (strcmp(hash2, hash) == 0)?"OK":"FAIL");
printf("First hash check w/ bcrypt_checkpw: %s\n", (bcrypt_checkpw(pass, hash))?"OK":"FAIL");
before = clock();
printf("First hash check w/ bcrypt_checkpw: %s\n", (bcrypt_checkpw(pass, hash1))?"OK":"FAIL");
after = clock();
printf("Time taken: %f seconds\n",
(float)(after - before) / CLOCKS_PER_SEC);
before = clock();
printf("Second hash check w/ bcrypt_checkpw: %s\n", (bcrypt_checkpw(pass, hash2))?"OK":"FAIL");
after = clock();
printf("Time taken: %f seconds\n",
(float)(after - before) / CLOCKS_PER_SEC);
return 0;
}

1
bcrypt.h
View File

@@ -48,6 +48,7 @@ int bcrypt_hashpw(const char *passwd, const char salt[BCRYPT_HASHSIZE],
/*
* This function expects a password and a hash to verify the password against.
* String comparisons in this function are constant time.
*
* The return value is zero if the password verification failed and nonzero
* otherwise.