RACF Hash

What is RACF?

The **RACF (Resource Access Control Facility) hash format** originates from IBM’s legacy mainframe security infrastructure, specifically within the z/OS operating system, where it was introduced in the 1970s to secure user passwords and system credentials. Structurally, RACF hashes are **fixed-length (16-byte) binary representations** derived from a proprietary password-encryption scheme that combines a **DES-like cipher** (based on IBM’s early symmetric encryption) with a **non-standardized iteration count** (typically 256 iterations). Unlike modern hash functions, RACF does not employ salting by default, relying instead on a **static key derivation process** tied to the system’s internal cryptographic seed. Its primary use-case was authentication within IBM’s z/OS environment, where it served as the de facto standard for password storage until superseded by more secure alternatives like **RACF’s SHA-256-based hashes (introduced in later versions)**. The format lacks standardized documentation, as its implementation was tightly coupled with IBM’s proprietary hardware and software stack, leaving it susceptible to reverse-engineering and exploitation.

RACF hashes are highly vulnerable to cracking due to **predictable iteration patterns, absence of salting, and optimizable cipher structure**. The fixed iteration count (often 256 rounds) can be brute-forced efficiently using **GPU-accelerated tools** like Hashcat, as the cipher’s linear nature allows for parallelized decryption. Additionally, the **lack of per-password salting** means identical passwords across systems produce identical hashes, enabling **rainbow table attacks** and precomputed crack databases. The underlying cipher’s reliance on **early DES-like block operations** (e.g., Feistel networks with weak key schedules) also makes it prone to **differential cryptanalysis**, while modern hardware optimizations (e.g., AVX/SSE instructions) further accelerate offline cracking. Finally, the **absence of collision resistance**—a hallmark of modern hashes—means RACF hashes can be forged or inverted with relative ease, rendering them unsuitable for contemporary security standards.

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

How to Crack RACF

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