README.md

SipHash

Reference implementation of SipHash, a family of pseudorandom functions optimized for speed on short messages.

SipHash was designed as a mitigation to hash-flooding DoS attacks. It is now used in the hash tables implementation of Python, Ruby, Perl 5, etc.

SipHash was designed by Jean-Philippe Aumasson and Daniel J. Bernstein.

Usage

Running

  make

will build sanity checks (test vectors) for SipHash-2-4, the default version of SipHash:

  ./siphash24_test

verifies 64 test vectors, and

  ./siphash24_debug

does the same and prints intermediate values.

The code can be adapted to implement SipHash-c-d, the version of SipHash with c compression rounds and d finalization rounds, by tweaking the lines

#define cROUNDS 2
#define dROUNDS 4

Obviously, if the number of rounds is modified then the test vectors won't verify.

128-bit tags (experimental)

In addition to the original SipHash, which returns 64-bit tags, this reference code implements an experimental mode to return 128-bit tags. This mode is enabled when the constant DOUBLE is defined.

Running

  make double

will build siphash24_test_double and siphash24_debug_double.

SipHash with 128-bit tags targets PRF security with 128-bit key and 128-bit tags. In particular, any attack trying up to 2^s should succeed with probability at most 2^(s - 128).

The 128-bit mode is experimental, use at your own risk.

Intellectual property

The SipHash reference code is released under CC0 license, a public domain-like licence.

We aren't aware of any patents or patent applications relevant to SipHash, and we aren't planning to apply for any.

References

The SipHash page includes

• a list of third-party implementations and modules
• a list of projects using SipHash
• references to cryptanalysis results