Date: Tue, 28 Jul 2015 14:57:02 +0300 From: Aleksey Cherepanov <lyosha@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: multiformats, (ab)use of salt in 'gost' format On Sun, Jul 19, 2015 at 01:56:12PM +0300, Aleksey Cherepanov wrote: > Recently I discovered that 'gost' format has salt. Using it, it > differentiates regular gost and cryptpro gost. These can be viewed as > 2 formats with 1 algo and different sboxes. There are 2 format tags: > > #define FORMAT_TAG "$gost$" > #define FORMAT_TAG_CP "$gost-cp$" > > So the 'salt' shows sboxes to use. > > It can be generalized to multiformats: such formats that handle hashes > of different formats as 1 format (even without any similarities > between algorithms). > > Multiformats may be interesting during contests to attack all fast > hashes in 1 command (the idea is not mine, Solar Designer shared this > idea after last hash runner). It would be something like --format=fast > > Solar Designer pointed out to me that formats can assume that, when > their init() is called, other formats are done(), so 2 formats can't > be init()'ed in parallel. > > Another approach to multiformats would be a wrapper that calls john > several times. > > Other ideas? Salt is interesting: if we have hashes of both types, then we can go ahead and hash each password by 2 algos claiming that we "generate" a candidate. Alexander Cherepanov just gave an awesome idea: having sha1($p) and sha1(sha1($p), we can avoid separate computation of sha1($p). It applies to all formats with similar beginning. Having sha1($p), sha1(sha1($p)), md5($p), md5(md5($p), sha1(md5($p)) and md5(sha1($p)), we can reduce 10 raw hashing ops to 6 raw hashing ops. Thanks! -- Regards, Aleksey Cherepanov
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