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Date: Mon, 31 Jan 2011 16:13:33 +0100 (CET)
From: "M. Sprengers" <m.sprengers@...dent.ru.nl>
To: john-users@...ts.openwall.com
Subject: FreeBSD crypt() / MD5-crypt implementation question

Hi all,

I am writing to this mailing list to inquire some more information about the MD5-crypt implementation in John the Ripper. I am currently writing my master thesis which is titled 'On the Security of Password Hashing Schemes regarding Advances in Graphic Processing Units' and I am doing research to see if password hashing schemes like MD5-crypt can be implemented efficiently on GPU hardware to see if the security of those schemes is still preserved when performing exhaustive search on the password input space.

I used Poul-Hennig Kamp's code to produce a CUDA compatible implementation of MD5-crypt that can perform exhaustive search on GPU's (which already performs 30 times faster than an equally priced CPU). However, when I tried to unravel the FreeBSD MD5 implementation in John the Ripper (more specifically, 'void MD5_std_crypt()' in MD5_std.c), I could not determine why you only need 500 iterations (instead of 1000) to calculate the final hash. I searched for some design/implementation documents/comments in this mailing list, but without success. Can somebody explain this to me? 

Thank you!

Kind regards,
Martijn Sprengers
Master student 'Computer Security' at the Kerckhoffs Institute
Radboud University Nijmegen
The Netherlands

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