Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1 Hash

What is Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1?

The **Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1** hash format is a proprietary cryptographic scheme derived from legacy Office file encryption (e.g., `.doc`, `.xls`, `.ppt` files created before 2004), where document-level permissions and password protection relied on a hybrid hashing mechanism. Structurally, it combines **SHA-1** for initial data hashing with **RC4** in a stream cipher mode to encrypt the derived key, though the exact implementation deviates from standard RC4 usage. The primary use-case was to secure file access via a password, where the plaintext password was hashed via SHA-1, then used as a key for RC4 to encrypt a symmetric key stored in the file’s header. This symmetric key was subsequently employed to decrypt the actual file contents. The format lacks standardized documentation, relying instead on reverse-engineering efforts (e.g., from tools like `libpff` or `ofcrack`) to expose its inner workings, which include a fixed-length salt (the file’s unique identifier) and no iterative key stretching, making it vulnerable to targeted attacks.

This scheme is critically flawed due to its reliance on **SHA-1’s known collision vulnerabilities**, combined with **RC4’s susceptibility to bias and weak key schedules**. The absence of a cryptographic salt (beyond the file’s UUID) allows attackers to precompute or reuse hashes across multiple files, enabling **rainbow table attacks** or **brute-force acceleration** via GPU-optimized SHA-1 implementations (e.g., CUDA-accelerated hashing). Additionally, RC4’s deterministic output, when seeded with a SHA-1 hash, fails to resist **differential cryptanalysis** or **chosen-plaintext attacks** in collider-mode, where identical hashes can be forced across different inputs. Modern hardware (e.g., FPGA/ASIC clusters) can crack such hashes at rates exceeding **millions per second**, rendering the scheme effectively broken for password recovery. The lack of key stretching exacerbates this, as weak passwords (common in legacy systems) are cracked in seconds, while stronger candidates benefit from **gpu-optimized SHA-1+RC4 simulators** (e.g., `hashcat` modes 13600+).

Identifying Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1 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 Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1

If you need to recover the plaintext password for a Microsoft Office ≤ 2003 (SHA1+RC4) collider-mode #1 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.