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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](https://131002.net/siphash/siphashdos_29c3_slides.pdf).
It is now used in the hash tables implementation of Python, Ruby, Perl
5, etc.
SipHash was designed by [Jean-Philippe Aumasson](https://131002.net) and
[Daniel J. Bernstein](http://cr.yp.to).
Usage
-----
Running
```sh
make
```
will build sanity checks (test vectors) for SipHash-2-4, the default
version of SipHash:
```C
./siphash24_test
```
verifies 64 test vectors, and
```C
./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
```C
#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
```sh
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](https://creativecommons.org/publicdomain/zero/1.0/), 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](https://131002.net/siphash) includes
* a list of third-party implementations and modules
* a list of projects using SipHash
* references to cryptanalysis results
|
