Imported from aspose-cells/agentic-net-examples (encryption-and-protection/AGENTS.md). Install upstream with npx skills add aspose-cells/agentic-net-examples --skill encryption-and-protection. Copyright stays with the author.

--- name: Aspose.Cells Encryption and Protection Agent category: encryption-and-protection product: Aspose.Cells for .NET language: C# parent: ../AGENTS.md version: 3.0 last_reviewed: 2026-08-21 primary_intent: Encrypt Excel files and protect workbooks, worksheets, cells, VBA projects, and signatures in C# primary_apis: [Worksheet.Protect, Worksheet.Unprotect, ProtectionType, WorkbookSettings, EncryptionType, WriteProtection] related_categories: [../open-workbook/, ../save-workbook/, ../macro-project/, ../document-properties/]

Encryption and Protection Agent Instructions

Mission and security boundary

Create secure, accurate Aspose.Cells for .NET examples that clearly distinguish access control, workbook/worksheet protection, write protection, file encryption, and digital signatures. Follow ../AGENTS.md.

These features are not interchangeable:

Never claim worksheet protection encrypts workbook contents or provides strong confidentiality.

Scope

In scope: protect/unprotect workflows, locked/unlocked cells, workbook structure, open passwords, encryption providers/types, password-to-modify, signatures, certificate handling, protection verification, and security audits.

Use macro-project for VBA editing, open-workbook for general loading, and document-properties for ordinary metadata.

Hard rules

• Use placeholder passwords from environment/configuration in production-oriented examples; never hard-code real secrets.
• Keep demonstration passwords obviously synthetic and warn that they are not production credentials.
• Do not print passwords, private keys, certificate secrets, or decrypted content.
• Use a format that supports the requested protection/encryption feature.
• Validate by reopening with the correct password and, where safe, confirming failure with an incorrect password.
• Explain what attackers are and are not prevented from doing.
• Never weaken encryption silently to maximize compatibility.
• Do not use a password hint that reveals the password.

Canonical worksheet pattern

Workbook workbook = new Workbook();
Worksheet worksheet = workbook.Worksheets[0];
worksheet.Cells["A1"].PutValue("Protected content");

worksheet.Protect(ProtectionType.All, "ExampleOnly-Password", null);
workbook.Save("protected-worksheet.xlsx");

For file encryption, use the package-version-supported load/save encryption APIs rather than repurposing worksheet protection.

Example contract

Each example must name the protected asset, threat/intent, mechanism, format, credential source, allowed operations, and verification. Use explicit types and synthetic data. Prefer filenames such as encrypt-xlsx-with-open-password.cs or protect-excel-worksheet-in-csharp.cs.

Signature examples must identify whether they add a visible signature line or a cryptographic signature. Certificate examples must use a test certificate and never assume access to a machine certificate store in CI.

Enterprise validation

• Verify APIs and algorithms against the installed package and current product documentation.
• Build and run without exposing secrets.
• Reopen with valid credentials and verify protected flags/content.
• Test invalid credentials only when failure can be asserted safely.
• Confirm the saved format retains the intended control.
• For signatures, verify signature validity after save and detect post-sign modification.

Reject examples that confuse protection with encryption, contain real credentials, depend silently on Windows-only certificate state, or claim compliance/certification without evidence.

SEO, GEO, and AEO

Target one direct question: "password protect Excel in C#," "encrypt XLSX without Excel," "lock cells," or "digitally sign an Excel file." The opening comment must identify the asset and mechanism. Use precise security language over marketing claims.

Related knowledge

• Category overview
• Open workbook
• Macro projects
• Official protection and encryption documentation

Definition of done

The example is done when the security objective, mechanism, limitation, credential handling, format support, and verification are explicit and correct.