Setting Strong Encryption Type

Microsoft Excel (97-2007/2010) enables you to encrypt and password‑protect spreadsheets. It uses algorithms provided by a Crypto Service Provider. A Crypto Service Provider (or CSP) is a set of cryptographic algorithms with different properties. The default CSP is “Office 97/2000 Compatible”. This is a CSP with some publicly known security issues. Spreadsheets that are secured with the “weak encryption (XOR)” or with the “Office 97/2000 Compatible” encryption type can be cracked easily.

To overcome this problem, use one of the strong encryption types provided by Microsoft Excel. You can change the encryption type to the strongest available CSP. For strong encryption, a minimum key length of 128 bits is required, for example, Microsoft Strong Cryptographic Provider.

You can also encrypt and password‑protect Excel files with a strong encryption type using the Aspose.Cells API.

Applying Encryption with Microsoft Excel

To implement file encryption in Microsoft Excel (for example, 2007):

1. From the Tools menu, select Options.
2. Select the Security tab.
3. Enter a value for the Password to open field.
4. Click Advanced.
5. Choose the encryption type and confirm the password.

Applying Encryption with Aspose.Cells

The code examples below apply strong encryption to a file and set a password.