phc-discussions - On the Test Results (paper from Milan Broz)

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Date: Mon, 30 Mar 2015 19:26:11 +0200 (CEST)
From: Stefan.Lucks@...-weimar.de
To: discussions@...sword-hashing.net
Subject: On the Test Results (paper from Milan Broz)

Dear Milan,

>  https://github.com/mbroz/PHCtest/blob/master/output/phc_round2.pdf

thank you for your work!

We (the Catena team) have two comments, a minor one and a major one.

1. The minor one is that the output length for Cartena *appears* to be 
limited to 64 bytes. But, if you really need longer outputs, it would be 
straightforward to employ Catena-KG, the key generation variant of Catena. 
Apart from key generation, we cannot think of any reason why one would 
want to use longer password hashes, but there is nothing so special about 
key generation, that you cannot use it for ordinary password hashing, if 
you want to.

2. The major concern is about your test for the KDF mode.

In our design document, we have been very specific that we suggest to use 
Catena-Butterfly, for the case that the defender's memory is quite 
limited, and the defender desires to push back all attackers with even 
less memory (per core). On the other hand, we explicitly recommend 
Catena-Butterfly if the defender is going to use plenty of memory, 
definitively with 100 MB or more.

Using the Catena-Axungia tool,

   https://github.com/medsec/catena-axungia

we measured the following values:

 		1MB     100MB   1G
Dragonfly	0.008   0.20    3.14
Butterfly	0.034   1.78    33.7

Our values for Catena-Butterfly are slightly faster than the one you 
measured. This is not an issue. We guess, our machine is 5--10% faster 
than the one you used.

But unfortunately, you didn't benchmark Catena-Dragonfly, even though that 
is the variant we recommend for big memory.

As the results show, Catena-Dragonfly can easily allocate and use the 
required memory while maintaining a speed of <<1 second (for 100 MB) or 
<<20 seconds (for 1 GB).

So long

Stefan

------  I  love  the  taste  of  Cryptanalysis  in  the morning!  ------
uni-weimar.de/de/medien/professuren/mediensicherheit/people/stefan-lucks
--Stefan.Lucks (at) uni-weimar.de, Bauhaus-Universität Weimar, Germany--