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Date: Fri, 5 Oct 2012 14:08:17 +0400
From: Solar Designer <>
Subject: Password hashing at scale (for Internet companies with millions of users) - YaC 2012 slides


The slides for my YaC 2012 talk "Password hashing at scale" are now online:

In this talk, I have focused on approaches to and challenges with
setting up better password hashing for Internet companies with millions
of users.  Some of the topics covered are possible use of HSMs (and
YubiHSM as a specific example), how much password stretching can be
afforded, different password hash types (including what's wrong with
PBKDF2, bcrypt, scrypt, possible revisions of scrypt), trade-offs with
using memory-hard KDFs in general, possible defensive use of GPUs,
Xeon Phi coprocessor, FPGAs.

SHA-3 is deliberately not mentioned on the slides yet.  I briefly
thought of retroactively adding a few mentions of it (YaC 2012 was a day
too early), but decided not to.  SHA-3 should be similar to DES (read:
very good) in context of possible defensive use of FPGAs.  As to
PBKDF2-HMAC-SHA-3, things are less clear, although it's probably weaker
than PBKDF2-HMAC-SHA-512 (is it also weaker than -SHA-256? than -SHA-1?
not sure).  (In this context, "weaker" means it allows for even more
efficient attack-optimized implementations than the other hash type,
resulting in higher passwords tested per second rate for the same
processing cost of defensive use.)  I prefer to keep only fairly
reliable information on the slides, and not speculate on important
issues there (but I do speculate here, as you can see).  Those of you
who follow @solardiz on Twitter probably already know a bit more on my
expectations and reasoning for throughput-optimized parallelized
implementations of SHA-3, due to the too-many-tweet conversation I had
with @marshray. ;-)


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