BSDi Crypt Hash

What is BSDi Crypt?

BSDi Crypt, derived from the classic Unix password hashing scheme, emerged in the early 1990s as an evolution of the DES-based crypt(5) algorithm used in Berkeley Software Distribution (BSD) systems. Structurally, it retains the core principles of its predecessor—iterative hashing with a fixed-length output—but introduces a key modification: the incorporation of a **modular exponentiation** step (via the `modulus` parameter) to slow down brute-force attacks. The format is encoded as a string prefixed with `$2y$`, followed by a cost parameter (e.g., `10`), a salt (base64-encoded), and the hashed password. Unlike earlier schemes, BSDi Crypt leverages the **Blowfish cipher** in a key-stretching manner, where the password is iteratively hashed with a dynamically adjusted modulus (default: `2^31 - 2`) to resist timing attacks and improve resistance to parallel cracking. Its primary use-case was securing password storage in Unix-like systems, particularly in BSD derivatives and Linux distributions adopting the OpenBSD `crypt` implementation, though it has since been superseded by more robust schemes like Argon2 or bcrypt.

The vulnerability of BSDi Crypt stems from its **suboptimal cryptographic design choices**, particularly its reliance on a **fixed modulus** and **predictable iteration count**. Early versions (pre-2004) suffered from **insufficient salt entropy** and **low iteration counts** (e.g., `1` or `2`), making them susceptible to **GPU/ASIC-based cracking** via tools like Hashcat. While later iterations increased the cost parameter, the **modular exponentiation step** remains computationally inefficient for modern hardware, enabling **optimized side-channel attacks** (e.g., power analysis or fault injection). Additionally, the algorithm’s **lack of adaptive resistance**—where iteration counts are tied to hardware performance—means that even high-cost parameters can be bypassed with **parallelized cracking** (e.g., via FPGA clusters). Finally, the **output length (22 characters)** and **base64 encoding** introduce predictable patterns, aiding in **rainbow table precomputation** for weaker salts. These flaws render BSDi Crypt obsolete for modern security standards, despite its historical role in Unix password hashing.

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

How to Crack BSDi Crypt

If you need to recover the plaintext password for a BSDi Crypt 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.