ADLER32 hash

 

About ADLER32 hash

Adler-32 is a simple checksum algorithm used for error-checking in data transmission and storage. It was invented by Mark Adler in 1995 and named after him. Adler-32 is not a cryptographic hash function but rather a checksum algorithm, which means it's designed to quickly detect errors in data but does not provide strong collision resistance or other security properties required of cryptographic hashes.

Characteristics of Adler-32

  1. Output Size:

    • Adler-32 produces a 32-bit checksum, typically represented as a single integer value.

  2. Input Handling:

    • Adler-32 operates on a sequence of bytes or data blocks. It processes the input data in chunks and calculates the checksum iteratively.

  3. Checksum Calculation:

    • The algorithm uses two 16-bit integers, A and B, initialized to 1 and 0 respectively.
    • For each byte of data in the input, A is updated by adding the byte value, and B is updated by adding the current value of A.
    • After processing all bytes, the checksum is formed by combining B (shifted left by 16 bits) with A.

  4. Properties:

    • Adler-32 is designed for speed and simplicity in error-checking rather than cryptographic security.
    • It is efficient in terms of computational resources and can quickly calculate the checksum for large amounts of data.

  5. Usage:

    • Adler-32 checksums are commonly used in file formats (like PNG) and network protocols (like zlib-compressed data) to verify data integrity.
    • They are also used in software libraries and utilities for error detection and prevention.

Example Calculation

For a sequence of bytes, the Adler-32 checksum Adler32(data) is calculated as follows:

  • Initialize A = 1 and B = 0.
  • Process each byte data[i]:
    • Update A = (A + data[i]) % 65521.
    • Update B = (B + A) % 65521.
  • The Adler-32 checksum is B * 65536 + A.

Security Considerations

  • Adler-32 is not suitable for cryptographic purposes because it is vulnerable to intentional modifications (due to its linearity and limited output size).
  • It may detect accidental errors in data transmission but cannot prevent deliberate tampering or forgery.

Summary

Adler-32 is a checksum algorithm designed for quick error detection in data transmission and storage. It calculates a 32-bit checksum that is efficient to compute and widely used in various applications for verifying data integrity. However, it should not be used for cryptographic purposes where stronger security guarantees are required.