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Date: Sun, 13 Sep 2015 00:51:21 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Judy array

Sayantan, all -

I just had a very interesting e-mail conversation with Fred Wang, the
author of MDXfind:

https://hashes.org/mdxfind.php

MDXfind has very impressive performance when targeting large lists of
saltless hashes (such as tens of million or more), beating JtR and
*hashcat, while also using less RAM.  MDXfind also has many unique
features such as matching against partial or rotated hash encodings,
as prompted by this thread:

http://forum.insidepro.com/viewtopic.php?t=20963

Fred suggested that we look into using Judy, which he uses in MDXfind,
along with a Bloom filter ("but Judy is the key", in his words).

https://en.wikipedia.org/wiki/Judy_array

Fred also confirmed my understanding that while needing exactly two
lookups with perfect hash tables is very nice, it's just not good enough
on its own for this application - we (also) have to optimize for the
common case of a miss, and thus achieve a little higher than one lookup
per hash computed on average (MDXfind does).

Alexander

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