Siemens-S7 Hash

What is Siemens-S7?

The Siemens S7 cryptographic hash format originates from the proprietary security mechanisms embedded in Siemens’ industrial automation systems, particularly the S7-300, S7-400, and S7-1200 PLC (Programmable Logic Controller) families, which were first widely deployed in the late 1990s and early 2000s. Structurally, it does not adhere to standard cryptographic conventions like SHA or MD5 but instead employs a custom hash scheme tied to the device’s firmware and communication protocols, primarily within the **S7 Communication Protocol (S7CP)** and **S7 Data Link Protocol (S7DP)**. The format typically involves a 16-byte (128-bit) hash value derived from concatenated data segments—such as user credentials, device identifiers (e.g., CPU serial number), and session-specific tokens—processed through a non-public, deterministic algorithm. This hash is used to authenticate and authorize communication between master stations (e.g., PCS7 or WinCC) and PLCs, ensuring integrity and preventing unauthorized access to PLC memory or configuration data. Unlike modern cryptographic hashes, the Siemens S7 hash lacks formal specification transparency, relying instead on Siemens’ internal documentation and reverse-engineered implementations to maintain compatibility.

The Siemens S7 hash format is highly vulnerable to cracking due to its inherent design flaws and computational inefficiencies. Primarily, the algorithm lacks cryptographic salt or peppering, rendering it susceptible to **rainbow table attacks** and **precomputed hash lookups**, as identical inputs (e.g., default passwords) consistently produce the same hash. Additionally, the deterministic nature of the hash—combining fixed device identifiers with user inputs—creates predictable patterns, allowing attackers to brute-force credentials by iterating through plausible password combinations and verifying hashes against known PLC behaviors. Modern hardware acceleration (e.g., GPU-based cracking tools like **Hashcat**) further exacerbates the risk, as the algorithm’s simplicity enables parallelized attacks at high speeds (often exceeding **100,000 hashes per second**). Finally, the absence of collision resistance—due to its small output size (128 bits)—makes it trivial to generate false positives, enabling **birthday attack** scenarios where two distinct inputs produce the same hash, undermining integrity checks. These vulnerabilities were exacerbated by Siemens’ historical practice of embedding weak default credentials (e.g., "OPEN" or "PASSWORD") in unpatched firmware, creating a vast attack surface for industrial espionage or sabotage.

Identifying Siemens-S7 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 Siemens-S7, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack Siemens-S7

If you need to recover the plaintext password for a Siemens-S7 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.