Excel Password Recovery by Version

At-a-Glance Comparison

Candidate throughput varies with the file parameters, implementation, hardware, and attack design. Treat any benchmark as an environment-specific estimate, not a recovery promise.

Why old Excel files can be finite-key candidates

Microsoft released Excel 97 in 1996. Back then, US export regulations restricted strong cryptography, so Microsoft shipped Excel with a deliberately weak 40-bit RC4 cipher. A 40-bit key has roughly one trillion (2^40) possible values. On a modern GPU, you can try all one trillion keys in a few hours. Recovery does not even involve passwords — the service searches the key space directly and decrypts the file once the correct key is found.

That makes some password-protected .xls files from Excel 97, 2000, XP or 2003 candidates for finite-key analysis. The analyzer still has to confirm the exact variant and validate the result before any release is quoted.

The 2007 Generational Leap

Excel 2007 introduced the .xlsx format — an XML-based Office Open XML container — and replaced 40-bit RC4 with real AES-128. Instead of searching a one-trillion-key space, an attacker now has to guess the original password and derive the key from it using SHA-1 at 50,000 iterations.

The 2007 derivation is cheaper to test than later variants, but the useful question is whether the password falls inside a justified candidate set. Hardware throughput and candidate ordering vary, so a large leaked corpus is not a universal estimate of coverage or time.

The 2010 hardening

Excel 2010 changed the derivation parameters and makes each candidate more expensive to test. The practical route shifts from broad guessing toward targeted wordlists and owner-provided patterns.

2013 and Later — Same Spec, Stronger Reality

From a pure cryptography standpoint, Excel 2013, 2016, 2019 and Microsoft 365 are identical: AES-128 with SHA-512 at 100,000 iterations. Microsoft did not bump iteration count again because the attack ecosystem shifted: modern GPUs still churn through 140k/s, so adding iterations would have hurt honest users (slow file open) without stopping motivated attackers.

So why are odds progressively worse? Three reasons:

• Password managers became mainstream. Excel 2007 files are often from an era when people typed pet names. Excel 2019 files are more likely protected with a 16-character random string from a password manager.
• UI nudges toward stronger passwords. Newer Excel versions show real-time strength meters, complain about short passwords, and default to stricter policies in corporate deployments.
• User awareness. High-profile data breaches of the last decade trained business users to use unique passwords they do not reuse.

What About Sheet Protection?

None of the encryption above applies to Excel sheet protection, which is a soft lock stored as XML. Sheet protection can be removed in minutes without any password — see our step-by-step unprotect Excel sheet guide. This page is specifically about the file-open password that Excel requires before it displays anything.

How to Tell Which Version Saved Your File

Three quick checks, in order of reliability:

1. Extension — .xls means Excel 97-2003 regardless of when you think the file was created. .xlsx means Excel 2007 or later.
2. Encryption header — open the file in a hex editor. Excel 97-2003 files start with D0 CF 11 E0 (OLE compound). Excel 2007+ .xlsx files start with 50 4B 03 04 (ZIP). An encrypted .xlsx is wrapped in an OLE container so it also shows D0 CF 11 E0 — unzip-like tools will refuse.
3. Internal version string — for unencrypted .xlsx, the app name lives in docProps/app.xml. For encrypted files you need a dedicated parser; recovery services detect this automatically on upload.

Conditional outcomes — three examples

Frequently Asked Questions