Date: Fri, 26 Jun 2015 10:56:24 +0300 From: Aleksey Cherepanov <lyosha@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: precomputed attacks for john: rainbow tables and other ways On Thu, Jun 25, 2015 at 05:09:16PM -0400, Matt Weir wrote: > Side note, to back up what Aleksey said, Rainbow Tables, (or Hellman > Tables), don't have to be charset based. As long as you have a fast > indexing function you can create dictionary based rainbow tables too. The > method described by Aleksy is very much like the PRINCE attack. If you want > to look at some of the issues with other rule based rainbow tables you > might want to check out Chapter 4 of my dissertation where I did some > research on the subject. > > https://sites.google.com/site/reusablesec/Home/presentations-and-papers/Weir_C_Dissertation_2010.pdf > > The biggest issue is by going to a dictionary based approach you can > introduce collisions in the index_to_plain function which isn't a problem > in character based RTs. Collisions in Rainbow Tables are much worse than > collisions in a normal cracking session so it helps to put extra thought in > how to avoid those. Do you mean that rules for reject make gaps in numbering that we need to map somewhere that produces uneven distribution that reduces candidate count per space efficiency of tables? Thanks! -- Regards, Aleksey Cherepanov
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