Date: Thu, 3 Apr 2014 02:17:45 -0400
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Yarn issues

Just kidding.  Evgeny, did the title scare you at all?

The last PHS submission I read (because of it's position in the
alphabet) was Yarn.  He didn't submit his code with the PHS prototype,
which annoyed me, because I'm trying to compile it.  There's no
Makefile, no main function, indentation by tab (one keystroke) and
there's not one freaking comment in his code.  Grr...

I could see from the code we've got another super-genius involved, so
I Googled him, and sure enough he's the winner of some programming
contest I never heard of.  There may be huge issues with it, but I
didn't see any in a quick read of the code.  He's basically using AES
instructions to build a fast memory-hard PHS, similar to some others.
His 280-ish lines of code is impressively small, but when you see that
it includes a full-up copy of both Blake2b and AES in that file...
nice.

What are the odds that he messed up on his Blake2b or AES
implementations, which seem to be written in his style, so I'm
guessing he wrote them from scratch?  I'm not going to take that
bet...  I did check his initial key derivation.  I'd say at least
1/3rd of the entries have obvious input collisions, mostly from doing
H(password || salt), which allows trivial collisions by moving the
boundary between password and salt.

If I am not mistaken, he has input collisions on both salt, and a
parameter called "pers".  Both are padded with 0's to 8 bytes, and
XOR-ed onto Blake2b state, so adding additional 0's up to a total
length of 8 doesn't change the output.  The password is free of such
collisions, so this isn't a critical issue.  He also has a spelling
error on the last line of his README :-)

Bill

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