Date: Fri, 19 Jun 2015 17:33:11 +0300 From: Aleksey Cherepanov <lyosha@...nwall.com> To: john-dev@...ts.openwall.com Subject: continuous feeding (for data driven branching) Just to document a discussion behind an idea... When there is a data driven branching we may want to pack intermediate results into several queues. For example, sunmd5 does it after "coin flip". Currently we get a lot of candidates, separate them into 2 packs and, oops, packs may be sub-optimal: for instance, we got 8 candidates and based on "coin flip" (or other factor), we got packs with intermediate results for 3 and 5 candidates while we would like to have 4 and 4 for our sse code. Continuous feeding: format reads N candidates, separate them and if it needs more input to fill up buffers optimally then it asks for them. Problem 1: format's interface needs changes. Changes can be minimal: currently crypt_all() can hold back some candidates, use them on next call and report them as newly generated. The only changes needed: call crypt_all() in the end with count=0 as a signal for crypt_all() that it needs to flush all candidates at any cost because john finishes. (As a modification: call with count=0 only if the last call had count == MAX_KEYS_PER_CRYPT .) Such change was proposed by Solar Designer and may be good for asynchronous calls too (to support FPGAs). Problem 2: holding candidate (worst case: password) for too long: for instance, 1 our queue got 1 candidate that is password but we don't hash it because 1 is not optimal, all other candidates go to other queue by a coincidence, so format waits for the finish to hash that 1 candidate and user instead of 5 minutes has to wait long hours/days/months/years. So format has to do something to not hold candidates more than N minutes. Problem 3: partial hashing and holding back would give inaccurate speed reports. Thanks! -- Regards, Aleksey Cherepanov
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