phc-discussions - pufferfish

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Date: Sun, 23 Mar 2014 07:59:48 -0700
From: Jeremi Gosney <epixoip@...dshell.nl>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: pufferfish

I've pushed code to a public repository for the candidate I will be
submitting, pufferfish. This repository will be frantically updated over
the coming week as I prepare my submission, but I wanted to get some
initial feedback before the cutoff.

https://github.com/epixoip/pufferfish

As the name implies, pufferfish is an improvement upon bcrypt, and ergo
blowfish. Concisely stated, pufferfish modifies the blowfish algorithm
to use 64-bit words, a 128-bit block size, and dynamic s-boxes. The
reference implementation uses a fixed key size of 256 bits, simply
because for these purposes there is no need to support different key
lengths.

The dynamic s-boxes are of course the biggest differentiating factor
between pufferfish and blowfish. The s-box generation is as follows:

1. Hash the raw salt as sha512
2. hmac-sha512 the password using the hashed salt as the key
3. hmac-sha512 the password again, using the output of the hmac
operation in step 2 as the key
4. These two hmac hashes are concatenated to initialize the 1024-bit state
5. The four s-boxes are each filled with m_cost / 4 / sizeof (uint64_t)
words by iterating over the internal state with a variant of chacha8

The state is then iterated 64 more times with chacha8 to generate a
third hmac key, which is used to hmac-sha512 the password one more time
to generate the inital encryption key.

The rest of the construction is largely identical to bcrypt, using the
same eksblowfish algorithm. However, to support variable output lengths,
the 256-bit ciphertext is hashed with sha512 after being repeatedly
encrypted before being written to the output buffer.

I elected to use this design because I really like bcrypt, and I really
like the idea of being memory hard while using as little memory as
possible. And I believe that the modifications I have made increase the
effectiveness and extend the longevity of the original bcrypt design.

The reference code is clear, concise, and extensively commented, so it
should easy to read, especially if you are already familiar with
blowfish and/or bcrypt. I welcome your feedback.

- epixoip