SipHash family of pseudo random functions implemented in Crystal
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Crystal implementation of SipHash and HalfSipHash, a family of pseudorandom functions optimized for short inputs.

See for more information on the algorithms.


You may choose how many compression-rounds and finalization-rounds to execute. Be wary about your use cases; SipHash(2, 4) has been verified to be cryptographically secure for example, whereas SipHash(1, 3) is faster but not verified, and should only be used when the result is never disclosed (e.g. for table hashing).

require "secure_random"
require "siphash"

key = uninitialized SipHash::Key

# generate a 64-bit hash:
hash = SipHash(2, 4).siphash("some data", key)
# => UInt64

# generate a 128-bit hash:
hash =
SipHash(2, 4).siphash("some data", hash, key)

You may alternatively hash a streaming input as you read it. This implies a slight performance hit, and may only generate 64-bit hashes. This is still useful when you don't know the complete input beforehand, or the input is scaterred from different places.

require "secure_random"
require "siphash/siphash64"

key = uninitialized SipHash64::Key

hasher = SipHash64(2, 4).new(key)
hasher.update("some data")
hash = # => UInt64


An alternative SipHash pseudorandom function that uses a 64-bit key and generates 32-bit or 64-bit hashes, meant for 32-bit platforms. On 64-bit platform we advise to use SipHash instead.

While SipHash(2, 4) has been analyzed and verified to be cryptographically secure, HalfSipHash has not, and isn't expected to be. Results from the hasher should never be disclosed (e.g. use for table hashing on 32-bit).

require "secure_random"
require "siphash/halfsiphash"

key = uninitialized HalfSipHash::Key

# generate a 32-bit hash:
hash = HalfSipHash(2, 4).siphash("some data", key)
# => UInt32

# generate a 64-bit hash:
hash =
HalfSipHash(2, 4).siphash("some data", hash, key)

A streaming version is also available, limited to 32-bit hashes:

require "secure_random"
require "siphash/halfsiphash32"

key = uninitialized HalfSipHash32::Key

hasher = HalfSipHash32(2, 4).new(key)
hasher.update("some data")
hash = # => UInt32


Distributed under the Apache 2.0 license.


Created by:

  • Jean-Philippe Aumasson
  • Daniel J. Bernstein

Ported by:

  • Julien Portalier