It's 3:12 PM. You just emailed a file named Q3-Financials-CONFIDENTIAL.xlsx to your auditor. You set a password. You hit Send. You breathe. Then your colleague asks: 'Wait — is that file *really* encrypted? Or just locked?' You pause. You're not sure.
Quick Answer
Yes — but only if you used File > Info > Protect Workbook > Encrypt with Password. That applies AES-128 or AES-256 encryption. Passwords set via Review > Protect Sheet or Protect Workbook (structure only) do not encrypt — they just prevent editing or structural changes. The underlying data remains readable by tools that bypass Excel’s UI.
All the Methods
| Method | Steps | Best For | Limitations |
|---|---|---|---|
| File-level encryption | File > Info > Protect Workbook > Encrypt with Password | Securing full file contents from unauthorized access | Password recovery is impossible if lost |
| Sheet protection | Review > Protect Sheet > enter password | Preventing accidental edits to formulas or formatting | Zero encryption — cell values visible in Formula Bar, XML extraction, or VBA |
| Workbook structure protection | Review > Protect Workbook > check 'Structure' > enter password | Stopping sheet adds/deletes/renames | No encryption — raw XML still fully accessible |
| VBA project password | Alt + F11 > Tools > VBAProject Properties > Protection tab | Hiding macro logic from casual users | Not encryption — VBA password can be removed with hex editors or free tools |
| Password-protected ZIP wrapper | Save as .xlsx > compress into ZIP > set ZIP password | Adding a second layer outside Excel | Requires recipient to unzip first — breaks Excel auto-opening and cloud sync |
Method 1 Deep Dive
This is the only method that truly encrypts your data. When you choose Encrypt with Password, Excel rewrites the entire file using AES encryption before saving. No cell value — not even hidden ones in column Z or buried in array formulas — is readable without the key.
Try it now with real sample data:
| A1 | B1 | C1 | D1 |
|---|---|---|---|
| Sarah Chen | Acme Corp | $45,200 | 2024-03-15 |
| Marcus Lee | Veridian Solutions | $62,800 | 2024-04-02 |
| Priya Nair | Nexus Labs | $38,150 | 2024-04-11 |
| Diego Ruiz | Stellar Dynamics | $51,900 | 2024-04-18 |
| Anya Petrova | Orion Group | $73,400 | 2024-05-03 |
Select File > Info > Protect Workbook > Encrypt with Password. Enter AlphaQ3!2024. Save. Close. Reopen — you’ll see the password prompt before anything loads. Open that same file in Notepad++ or VS Code? You’ll see only gibberish — no names, no dollar amounts, no dates. That’s real encryption.
Pro tip: Excel defaults to AES-128 on older versions, but if you’re on Microsoft 365 or Excel 2019+, it uses AES-256 automatically — provided you’re saving as .xlsx or .xlsb, not legacy .xls. And yes — this works for files stored in SharePoint or OneDrive. The encryption stays intact.
Method 2 Deep Dive
Now try protecting just the sheet. Select Review > Protect Sheet. Enter SheetLock2024. Click OK. You’ll notice something odd: you can still select cells A1:D5. You can copy them. Paste them elsewhere. You can even view formulas in the Formula Bar — unless you previously hid them (Format Cells > Protection > Hidden, then protected). But here’s what most people miss:
If you change the file extension from .xlsx to .zip, extract it, and open xl/worksheets/sheet1.xml in any text editor — you’ll see every value in plain text:
<c r="A1"><v>45200</v></c> <c r="B1"><v>Acme Corp</v></c>
No encryption. Just obfuscation. Even worse: open the same file in LibreOffice Calc — it opens instantly, no password prompt. Why? Because LibreOffice ignores Excel’s sheet-protection flag entirely. (Trust me, I learned this the hard way during a vendor audit.)
This method has its place — locking down a dashboard so interns don’t break pivot tables — but never use it for sensitive PII, salaries, or contract terms. If your company policy says “all confidential data must be encrypted”, sheet protection alone fails that test.
Cheat Sheet
| Task | Exact Steps | Shortcut | Verification Tip |
|---|---|---|---|
| Apply real encryption | File > Info > Protect Workbook > Encrypt with Password → enter & confirm | None (no Alt sequence) | File size increases ~10–15%. Opening shows password prompt *before* any content renders. |
| Check current protection | File > Info > Permissions > See who can access → look for 'Encrypted' | Alt+F+I | If it says 'Protected' but not 'Encrypted', it’s only sheet/workbook structure protection. |
| Remove weak protection | Review > Unprotect Sheet (if password known) or Review > Unprotect Workbook | Alt+R+U+S (sheet), Alt+R+U+W (workbook) | After removal, verify no 'Locked' icon appears in the status bar. |
| Test encryption strength | Rename file to .zip → extract → try opening xl/sharedStrings.xml | None | If you see readable text: NOT encrypted. If you see binary garbage or 'Invalid ZIP': encryption is active. |
