MURMUR3A hash

 

About MURMUR3A hash

MurmurHash is a family of non-cryptographic hash functions developed by Austin Appleby. Murmur3 is a specific variant within this family known for its speed and efficiency, especially in generating well-distributed hash values. Murmur3 has two main variants: Murmur3A and Murmur3B. Here, I'll focus on Murmur3A.

Characteristics of Murmur3A

  1. Output Size:

    • Murmur3A produces a fixed-length output of 32 bits (4 bytes) or 64 bits (8 bytes), depending on the implementation.

  2. Initialization Values:

    • Murmur3A uses an initial seed value (seed) to start the hash computation. This seed can be any arbitrary value chosen by the user.

  3. Hash Calculation:

    • Murmur3A processes the input data in blocks of 4 bytes (32-bit) or 8 bytes (64-bit), depending on the chosen output size.
    • For each block of data:
      • Mixes the bits using a series of bitwise rotations, XOR operations, and multiplications with a constant prime number.
      • Updates the hash state based on the processed data block and the current hash value.

  4. Finalization:

    • After processing all data blocks, Murmur3A applies finalization steps to ensure good distribution and avalanche effect in the hash output.

  5. Properties:

    • Murmur3A is designed for fast computation of hash values with good dispersion properties.
    • It is deterministic and produces the same hash value for identical input data and seed.
    • Murmur3A is widely used in applications requiring fast and reliable hash functions, such as hash tables, hash-based lookups, and non-cryptographic data integrity checks.

Usage

  • Applications: Murmur3A is suitable for applications where speed and good distribution of hash values are crucial. It is commonly used in databases, caching systems, and distributed systems for partitioning data.

  • Implementation: Implementing Murmur3A is straightforward and efficient, making it a popular choice in software libraries and frameworks.

Example Calculation

Given a sequence of bytes data and an initial seed seed, the Murmur3A hash Murmur3A(data, seed) is calculated as follows:

  • Initialize the hash value hash with the seed value.
  • Process each 4-byte (or 8-byte) block of data using specific mixing operations.
  • Finalize the hash value to ensure good dispersion and avalanche effect.
  • The final Murmur3A hash value after processing all data blocks is returned.

Security Considerations

  • Murmur3A is not suitable for cryptographic purposes due to its vulnerability to collision attacks and its predictable nature.
  • It should only be used in scenarios where data integrity verification and distribution of hash values are the primary concerns.

Summary

Murmur3A is a fast and efficient non-cryptographic hash function used for generating hash values with good dispersion properties. It is suitable for applications requiring quick computation of hash values and is widely used in various software applications and systems. However, it should not be relied upon for cryptographic security purposes.