FNV1A64 hash

 

About FNV1A64 hash

FNV-1a 64-bit (Fowler-Noll-Vo version 1a with a 64-bit output) is a hash function known for its simplicity and speed in computing hash values. It extends the FNV-1a algorithm to produce a 64-bit hash value, offering improved dispersion and reduced collision rates compared to its 32-bit counterpart.

Characteristics of FNV-1a 64-bit

  1. Output Size:

    • FNV-1a 64-bit produces a fixed-length output of 64 bits (8 bytes).

  2. Initialization Value:

    • The initial hash value (hash) for FNV-1a 64-bit is typically set to 0xcbf29ce484222325. This value is chosen to help ensure good dispersion of hash values across the output space.

  3. Prime and XOR Constants:

    • FNV-1a 64-bit uses specific constants for its hash calculation:
      • Prime: The prime number used in FNV-1a 64-bit is 0x100000001b3.
      • XOR: Each byte of the input data is XORed into the hash value before multiplying by the prime.

  4. Hash Calculation:

    • For each byte data[i] in the input data:
      • Update the hash value using the formula: hash = (hash ^ data[i]) * Prime.
    • After processing all bytes, the hash value is the final 64-bit FNV-1a hash.

  5. Properties:

    • FNV-1a 64-bit is designed for fast computation of hash values with improved dispersion compared to its 32-bit counterpart.
    • It is deterministic and produces the same hash value for identical input data.
    • Like FNV-1a 32-bit, FNV-1a 64-bit is not suitable for cryptographic purposes due to its vulnerability to collision attacks and its predictable nature.

Usage

  • Applications: FNV-1a 64-bit is commonly used in applications where a larger hash output size is required for data integrity checks, hash tables, and some non-critical hash-based operations.

  • Implementation: It is efficient in terms of computational resources and straightforward to implement, making it suitable for scenarios requiring rapid computation of 64-bit hash values.

Example Calculation

Given a sequence of bytes data, the FNV-1a 64-bit hash FNV1a_64(data) is calculated as follows:

  • Initialize the hash value hash to 0xcbf29ce484222325.
  • For each byte data[i] in the input data:
    • XOR hash with data[i].
    • Multiply hash by the prime number 0x100000001b3.
  • The final FNV-1a 64-bit hash value after processing all bytes is hash.

Security Considerations

  • FNV-1a 64-bit, like its 32-bit counterpart, is not designed for cryptographic purposes and should not be used where strong security guarantees are required.
  • It is susceptible to collision attacks and should only be used in scenarios where data integrity verification is the primary concern rather than security against malicious attacks.

Summary

FNV-1a 64-bit is an extension of the FNV-1a hash function that provides a larger 64-bit hash output. It is suitable for applications requiring a larger hash size with moderate integrity checking capabilities. However, it is not suitable for cryptographic purposes due to its predictable nature and vulnerability to attacks.