Office 365 vs Office 2021 — Password Protection Differences

Encryption Is Identical at the File Level

The good news: there is no difference in file encryption between Microsoft 365 and Office 2021. Both use the same ECMA-376 Standard Encryption with AES-256 and the SHA-512 key derivation function at 100,000 iterations (hashcat mode 9600). A file encrypted in Office 2021 opens in Microsoft 365 with the same password, and vice versa.

The file format (.xlsx, .docx, .pptx) is identical between editions. The encryption metadata (salt, verifier hash, encrypted key, CSP name) is stored in the same XML structure inside the ZIP container. There is no edition-specific encryption header or algorithm.

This means that from a password recovery perspective, there is no distinction between files created in Office 365 vs Office 2021. The hashcat mode is 9600 for both (or 9400/9500 for older formats). The recovery speed and feasibility are identical for the same password strength.

Where They Differ: Feature Coverage

Despite the identical encryption engine, the two editions differ in surrounding features that affect how password protection is applied and managed:

Sensitivity Labels — Microsoft 365 Only

The most significant difference between the two editions is Sensitivity Labels (part of Microsoft Information Protection, formerly Azure Information Protection). Microsoft 365 subscribers can apply labels like "Confidential — Internal" or "Highly Restricted" to documents. These labels encrypt the document with an Azure Rights Management (Azure RMS) key rather than a password-derived key.

Office 2021 can open sensitivity-labelled documents (if the user has a Microsoft 365 account with the appropriate rights), but it cannot create or edit labels. The label management UI is a Microsoft 365 exclusive feature.

AutoSave and Version History — A Double-Edged Sword

Microsoft 365's AutoSave feature (enabled by default for OneDrive/SharePoint files) continuously saves changes as you work. For password-protected files, this creates an important side effect: every AutoSave snapshot is an independently encrypted version of the file, each requiring the same password to decrypt.

In practice, this means that if you edited a password-protected file over several days in Microsoft 365, OneDrive stores 25+ encrypted versions in version history. Each version uses the same password (the one you entered when first opening the file), so the password is not multiplied — but the encrypted payloads are different (different salts per save). This does not make recovery harder per se, but it means that if you used different passwords at different times, you need to crack each version's password separately.

Office 2021 does not support AutoSave or OneDrive version history. Files are saved locally with a single encryption pass. This eliminates the version-history complexity but also means no cloud backup and no rollback capability.

Co-Authoring and Password Protection

Microsoft 365 supports real-time co-authoring — multiple people editing the same document simultaneously. However, co-authoring is disabled for password-protected files, regardless of whether you use Microsoft 365 or Office 2021. The reason is technical: co-authoring requires the server to read and merge concurrent edits, which is impossible when the file is encrypted with a user-supplied password that the server does not have.

If you need both protection and collaboration, Microsoft 365 offers a workaround: use Sensitivity Labels instead of file passwords. Labels let the server hold the decryption key and apply it per-user, enabling co-authoring while still restricting access. Office 2021 users do not have this option — they must choose between password protection and collaboration.

Future-Proofing: Encryption Updates

Microsoft 365 receives continuous updates, including potential encryption enhancements. Office 2024 introduced SHA-512 with 200,000 iterations (mode 96100) and optional Argon2ID (mode 96200). While Office 2021 does not support these new modes, Microsoft 365 subscribers may receive them in a future update if Microsoft decides to raise the encryption baseline.

The practical implication: if you save a file encrypted in Microsoft 365 after a future encryption update, that file may not be openable in Office 2021. This is already true for Office 2024-created files — they use a new header format that Office 2021 cannot parse. Microsoft 365 users should be aware that their latest-saved encrypted files may drift out of compatibility with perpetual-license editions over time.

For now (2026), both editions use mode 9600. But Microsoft 365 users who want maximum future compatibility should keep a copy saved without encryption, or document the password in a password manager.

Practical Recommendations

• If you use Microsoft 365: Be aware that AutoSave creates multiple encrypted versions. If you might forget your password, disable AutoSave for encrypted files, or use a password manager. Consider Sensitivity Labels for collaborative environments instead of file passwords.
• If you use Office 2021: Your encrypted files are simpler (single-version, local-only) but you miss out on Sensitivity Labels and co-authoring. For maximum security, pair Office 2021 encryption with an external backup strategy.
• If you share encrypted files between editions: Both use mode 9600, so files are interchangeable. But if the Microsoft 365 user saves in a future updated format, the Office 2021 user may not be able to open it.
• Password recovery is identical for both editions: Hashcat mode 9600, same speed benchmarks, same feasibility profiles. The choice between editions does not affect recovery odds.

Frequently Asked Questions