SipHash Hash

What is SipHash?

SipHash is a cryptographic hash function designed in 2012 by Jean-Philippe Aumasson and Daniel J. Bernstein to mitigate **rainbow table attacks** and **GPU/ASIC acceleration** of hash functions like MD5, SHA-1, or even SHA-256 in password storage scenarios. Structurally, SipHash is a **low-digest-size hash function** (typically 8 or 16 bytes) that prioritizes **resistance to brute-force and hardware optimization** over collision resistance or preimage resistance. It employs a **fixed, simple compression function** composed of modular additions, XORs, and bit rotations, iterated in a carefully designed sequence to obfuscate input patterns while maintaining computational efficiency. Unlike traditional hash functions, SipHash avoids complex operations like modular exponentiation or large-word multiplications, instead relying on **lightweight, branchless operations** that are hard to parallelize on modern hardware. Its primary use-case stems from its **memory-hardness**—it forces attackers to process each byte of input sequentially, making it impractical to exploit with GPU/FPGA acceleration, which is critical for securing password hashes in high-throughput systems like web applications.

Despite its strengths, SipHash exhibits critical vulnerabilities rooted in its **deterministic structure and lack of salt**. Its **compression function’s predictability** allows for **precomputation attacks** when used without a unique salt per password, enabling adversaries to precompute hashes for common inputs (e.g., dictionary words) offline. Additionally, its **low output size (8–16 bytes)** increases collision probability, though this is less critical than in traditional hashing. More critically, SipHash’s **iterative design**—while resistant to GPU optimization—can be **optimized on CPUs with careful instruction scheduling**, reducing its theoretical advantage. Furthermore, its **lack of adaptive iteration count** (unlike Argon2 or bcrypt) means performance remains constant regardless of input length, making it susceptible to **timing attacks** if not implemented with constant-time comparisons. Finally, its **simplicity** has led to **side-channel vulnerabilities**, where power analysis or cache timing can leak partial information about the input, particularly in embedded or constrained environments.

Identifying SipHash 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 SipHash, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack SipHash

If you need to recover the plaintext password for a SipHash 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.