Date: Mon, 23 May 2011 03:27:57 +0400 From: Solar Designer <solar@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: "excessive partial hash collisions detected" for mskrb5 magnum, Dhiru - On Sun, May 22, 2011 at 11:47:21PM +0200, magnum wrote: > True, I have no binary_hash() or get_hash() functions. As far as I can > tell, there's just no way to implement them for this format. I think you > could say it's implemented as "salt only". After crypt_all() I have a > partial decrypt of the input, that will contain known plaintext if the > key was correct. This means a get_hash() function has no chance of > producing anything that a binary_hash() could produce too. This sounds right. > If not, maybe there should be a way to tell john that it should not emit > that warning for this format (and possibly some others)? Maybe just the > fact that I'm also using fmt_default_binary()? I think we can add a check for zero binary_size to loader.c - and not print the warning if so. Your use of fmt_default_binary() does not tell as much. This function simply returns the ASCII ciphertext unmodified, which some format could be using (including in its hash functions). You could move from decryption (resulting in known plaintext) to encryption (of the known plaintext), then you could compare partial ciphertexts and compute hashes of those. Moreover, you'd get rid of salts, for a huge speedup (when there's more than one of these non-hashes to crack). But this might not be possible in your specific case (I haven't checked whether it is). I think it depends on things such as block cipher mode used (should be possible for ECB, but not for chaining modes if plaintext for the preceding blocks is not known). Disclaimer: I haven't yet looked at your code, sorry. My response is about issues of this kind in general. I think it might be relevant to Dhiru's work as well. Thanks, Alexander
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