Adler-32 Hash
Technical details, regex signatures, and cracking commands for the Adler-32 algorithm.
What is Adler-32?
Adler-32 is a lightweight checksum algorithm introduced in 1996 by Mark Adler as part of the zlib compression library, designed to provide a fast, fixed-size 32-bit hash for data integrity verification. Structurally, it operates as a non-cryptographic hash function by maintaining two 16-bit sums: one tracking the cumulative sum of input bytes (A) and the other the cumulative sum of these sums (B). The final hash is computed as `(A % 65521) << 16 | (B % 65521)`, where the modulo operation ensures values remain within the 16-bit range. Unlike cryptographic hashes, Adler-32 lacks collision resistance and was never intended for security applications; instead, it serves as a quick integrity check for compressed files, network protocols (e.g., HTTP checksums), and simple data validation tasks where computational efficiency outweighs security concerns.
The vulnerability of Adler-32 stems from its design trade-offs for speed. Its linear complexity (O(n)) and lack of cryptographic properties make it susceptible to brute-force collisions—two distinct inputs can produce the same hash with high probability due to its small output space (2³² possible values). The absence of a salt or keyed component eliminates resistance to precomputation attacks, while its simplicity enables GPU/CPU optimizations (e.g., SIMD vectorization) to generate hash collisions at scale. Additionally, its reliance on simple arithmetic operations allows adversaries to exploit patterns in input data to craft deliberate collisions, rendering it unsuitable for any context requiring integrity or authenticity guarantees.
Identifying Adler-32 Hashes
Identifying a hash blindly is often difficult because multiple algorithms can output strings of the exact same length. For example, a standard 32-character hexadecimal string could be MD5, NTLM, MD4, or LM. To definitively identify Adler-32, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.
How to Crack Adler-32
If you need to recover the plaintext password for a Adler-32 hash during a penetration test or forensics investigation, you must supply the correct module ID to your cracking software. Use the exact commands provided at the top of this page to target the hash successfully.