Short-input hashing

Example

var key = ShortHash.GenerateKey(); //16 byte key
var message = "This is an easy example";

//returns a 8 byte hash
var shorthash = ShortHash.Hash(message, key);

Purpose

Many applications and programming language implementations were recently found to be vulnerable to denial-of-service attacks when a hash function with weak security guarantees, such as Murmurhash 3, was used to construct a hash table.

In order to address this, libsodium-net provides the Sodium.ShortHash function, which outputs short but unpredictable (without knowing the secret key) values suitable for picking a list in a hash table for a given key.

This function is optimized for short inputs.

The output of this function is only 64 bits. Therefore, it should not be considered collision-resistant.

Use cases:

• Hash tables
• Probabilistic data structures such as Bloom filters
• Integrity checking in interactive protocols

Random Helpers

public static byte[] GenerateKey()

Namespace: Sodium.ShortHash

Uses Sodium.SodiumCore.GetRandomBytes() to generate a 16 byte key.

Usage

public static byte[] Hash(byte[] message, byte[] key)

//there exists some overloaded versions:
public static byte[] Hash(string message, byte[] key)
public static byte[] Hash(string message, string key)

This is the .NET equivalent of crypto_shorthash.

Namespace: Sodium.ShortHash

The Hash() method computes a 8 byte fingerprint for the message, using a 16 byte key.

The key must be 16 bytes, otherwise the method throws a KeyOutOfRangeException.

The same message hashed with the same key will always produce the same output.

Algorithm details

SipHash-2-4