Timing safe string compare function #778
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The implementation for `CompareStrings` function initially used strcmp, which is not timing safe, i.e. it breaks at the first non-equal character which allows information to be extracted about the prefix that is matching, which is know as the timing attack. To avoid that, we use the modified `CompareStrings`, that will iterate over all the character until the very end of the supplied password only. So, in this way all operations will happen exactly the length of supplied string s1 times.
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See the discussion about why this is unnecessary in bcrypt |
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Hi @agathver , yes, practically brcypt isn't affected by timing attacks because of the part that it hashes the input before comparing which will always generate a string string of constant length. Unless you have the exact string whose hashes will match exactly, it's equivalent to traversing the whole string space. Thanks for taking a look at it. I will be closing this PR. |
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The implementation for
CompareStringsfunction initially usedstrcmp, which is not timing safe, i.e. it breaks at the first non-equal character which allows information to be extracted about the prefix that is matching. This could allow to guess the number of chars matching or the size of the hash.To avoid that, we use the modified
CompareStrings, that will iterate over all the character until the very end of the supplied string only. So, in this way all operations will happen exactly the length of supplied strings1times, so no information gets leaked about the number of characters matched and the length of the unknown strings2.