MS Office 2016 - SheetProtection Hash

What is MS Office 2016 - SheetProtection?

The **MS Office 2016 SheetProtection hash format** is a proprietary cryptographic scheme introduced to secure Excel workbook sheets via password protection, leveraging a modified variant of the **MD5-based hashing mechanism** embedded within the XML-based Office Open XML (OOXML) file structure. Originating from Microsoft’s internal encryption framework for Office 2016 (and later iterations), this format encodes the password hash within the `sheetProtection` element of the workbook’s `xl/workbook.xml` file. The structure consists of a **32-byte MD5 digest** (derived from the password via a non-standardized key derivation process) concatenated with a **4-byte salt** (hardcoded as `0x00000000` in early versions) and additional XML metadata. Unlike traditional password hashes, this format lacks iterative hashing (e.g., PBKDF2) or adaptive work factors, relying instead on a single MD5 pass, making it vulnerable to brute-force attacks. Its primary use-case was to enforce read/write restrictions on protected sheets, but its reliance on legacy cryptographic primitives rendered it obsolete for security-sensitive applications.

The **vulnerability of this hash format stems from its fundamental design flaws**, primarily its **lack of salting, collision susceptibility, and computational inefficiency**. The hardcoded zero-salt (`0x00000000`) allows attackers to precompute rainbow tables targeting the predictable prefix, drastically reducing the effort required to crack passwords. Additionally, MD5’s **128-bit output space** enables practical collision attacks when combined with the fixed salt, enabling adversaries to forge valid hashes for arbitrary passwords. The absence of a **key stretching mechanism** (e.g., HMAC-based iterations) allows modern GPUs and FPGA clusters to perform **brute-force attacks at speeds exceeding 10^9 hashes per second**, rendering the scheme effectively broken within minutes for short passwords. Furthermore, the **lack of a pepper or context-specific salt** in the OOXML structure means the same hash can be reused across different workbooks, further exacerbating exposure. Optimizations like **parallelized GPU-based MD5 cracking** (e.g., via tools like Hashcat) exploit the format’s linear complexity, making recovery trivial for passwords under 8 characters.

Identifying MS Office 2016 - SheetProtection 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 MS Office 2016 - SheetProtection, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack MS Office 2016 - SheetProtection

If you need to recover the plaintext password for a MS Office 2016 - SheetProtection 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.