Date: Wed, 3 Oct 2012 21:09:14 +0200 From: magnum <john.magnum@...hmail.com> To: john-dev@...ts.openwall.com Subject: Non-hash dupe suppression (was: o5logon format hacks) On 3 Oct, 2012, at 19:37 , magnum <john.magnum@...hmail.com> wrote: > On 3 Oct, 2012, at 19:12 , Dhiru Kholia <dhiru.kholia@...il.com> wrote: > >> On Wed, Oct 3, 2012 at 10:21 PM, magnum <john.magnum@...hmail.com> wrote: >>> On 3 Oct, 2012, at 18:45 , magnum <john.magnum@...hmail.com> wrote: >>> >>>> ...here's how I *think* we could do to all non-hash formats in order to get proper dupe detection and no warnings. >>>> >>>> 1. Use a short binary size (eg. 4) so we don't waste too much memory. >>>> >>>> 2. Write a simple mockup binary() that just returns a 4-byte hash of the full ciphertext. This could be standard crc32 or something else, but it should use all of the ciphertext. >>>> >>>> 3. Use standard binary_hash() functions just like the ones you used now. >>> >>> Small correction: We should probably use 8 bytes and crc64 in order to be reasonably safe against hash collisions. >> >> Looking forward for these changes. > > I could try this in the office formats and see how it works out. If this turns out OK, you can copy that changes to all your non-hash formats if you like. Unfortunately my idea does not fly. Core changes are needed. After just doing the above, the self-test complains that get_hash() does not produce the same hash as binary_hash() since the former just use the fmt_default. I should have expected that :) I see no way to do this without changing core. With a core change, we could instead do something like this: All non-hash formats just use a BINARY_SIZE of 0 and fmt_default_binary etc. And loader.c could detect this situation and do the dupe supression all by itself by crc64'ing the ciphertexts. I *think* this could be a fairly easy fix but I won't touch that until Solar talks. magnum
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