Cisco-ASA(MD5) Hash

What is Cisco-ASA(MD5)?

The **Cisco-ASA(MD5)** hash format is a proprietary variant of the widely deployed **MD5 (Message-Digest algorithm, version 5)** cryptographic hash function, originally designed by **Ron Rivest in 1991** as a general-purpose hash for data integrity verification. While MD5 was standardized as an open-source algorithm (RFC 1321), Cisco’s implementation in its **Adaptive Security Appliance (ASA) firewalls** introduced a non-standardized twist: it appends a **fixed-length salt** (a 16-byte Cisco-specific prefix) to the input data before hashing, producing a **32-byte (256-bit) hexadecimal digest** (32 characters long). This format was primarily used for **password storage in Cisco ASA devices**, particularly in older firmware versions (pre-8.4), where MD5 served as a lightweight alternative to stronger algorithms like SHA-256. The structure ensures a consistent output length but lacks cryptographic rigor, as the salt is not dynamically derived from the password or user context—only a static Cisco-derived value.

The **Cisco-ASA(MD5)** format is highly vulnerable to cracking due to **three critical weaknesses**: (1) **Lack of salt randomness**—the fixed salt enables **rainbow table precomputation**, allowing attackers to reverse-engineer passwords offline with minimal computational overhead; (2) **MD5’s inherent collision susceptibility**—the algorithm’s 128-bit output space is prone to **birthday attacks**, with practical collision generation now feasible (e.g., via **Frey-Rück’s attack** or **SHA-3 collisions**), undermining its integrity guarantees; and (3) **GPU/ASIC optimizations**—modern hardware (e.g., **FPGA-based crackers like Hashcat**) can brute-force MD5 hashes at **terahashes per second**, rendering brute-force attacks on short passwords trivial. Additionally, the **absence of key stretching** (e.g., no iterative hashing or work factor) means password hashes resist only trivial computational effort, making this format **catastrophically insecure** for modern security standards.

Identifying Cisco-ASA(MD5) 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 Cisco-ASA(MD5), security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack Cisco-ASA(MD5)

If you need to recover the plaintext password for a Cisco-ASA(MD5) 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.