Date: Tue, 27 Mar 2012 12:52:46 +0400 From: Solar Designer <solar@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: Working on DES format on CUDA On Mon, Mar 26, 2012 at 06:11:31AM +0800, myrice wrote: > I am currently working on DES and will first implement it on CUDA. I will > track my progress and ask questions in this post. OK, although this is relatively difficult or at least time-consuming stuff for someone who hasn't been into DES and bitslicing before, whereas a non-bitslice GPU implementation will likely be ridiculously slow (you can try, though - at least to learn from this). > Here are some of my questions(Tried but not get the answer :( ) > > 1) How can I debug the JtR. I add -g to CFLAGS in Makefile. But gdb still > can not find the symbols Already answered by magnum - you also need to remove -s from LDFLAGS. > 2) I read the code in DES_fmt.c, it seems that it is a DES-Based algorithm. > Now I do not clear about how the salt is obtained. The only available > information I found about salt on DES is old unix /etc/passwd. They add 2 > characters at the front of the encrypted password. However, > the DES_raw_get_salt is more complex. Is there any document about this? You may read about the traditional DES-based crypt(3) in many places, e.g. in Wikipedia: http://en.wikipedia.org/wiki/Crypt_(Unix)#Traditional_DES-based_scheme There are 25 iterations of salt-modified DES (the E expansion table is modified when the salt value is non-zero). > I think I will implement original DES algorithm first. Does that okay? That's up to you. There are JtR formats that build upon the original DES as well (without the E table modification). To understand bitslicing, you'll need to read Eli Biham's paper. http://en.wikipedia.org/wiki/Bit_slicing#Modern_use http://www.cs.technion.ac.il/users/wwwb/cgi-bin/tr-info.cgi?1997/CS/CS0891 To be sincere, I fully expect that you won't have anything convincing by the student selection deadline if you go with this project (I mean focusing on DES) - so your chances of being selected are low. On the other hand, if you do succeed this quickly, that will boost your chances a lot. This is similar to the bcrypt stuff in this regard - low chances for success with the project in the available time, but if the student does succeed, it means a lot. If you're brave enough or if you just want to learn (great!), then go for it. :-) Alexander
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