Encrypting Excel Files
Microsoft Excel (97 - 2007) enables you to encrypt and password protect your spreadsheets. It uses algorithms provided by a cryptographic service provider, or CSP, a set of cryptographic algorithms with different properties. The default CSP is ‘Office 97/2000 Compatible’ or ‘Weak Encryption (XOR)’. It’s important to choose the proper encryption key length. Some CSPs don’t support more than 40 or 56 bits. That’s considered to be weak encryption. For strong encryption, a minimum key length of 128 bits is required. Microsoft Windows contains CSPs that offer strong encryption types as well, for example the ‘Microsoft Strong Cryptographic Provider’. To give you an idea, 128 bits encryption is what banks use to encrypt the connection with their Internet Banking systems.
Aspose.Cells allows you to encrypt and password protect Microsoft Excel files with your desired encryption type.
Using Microsoft Excel
To set file encryption settings in Microsoft Excel (here Microsoft Excel 2003):
- From the Tools menu, select Options. A dialog will appear.
- Select the Security tab.
- Input a password and click Advanced
- Choose the encryption type and confirm the password.
Encryption with Aspose.Cells
The following example shows how to encrypt and password protect an excel file using the Aspose.Cells API.
Specifying Password to modify Option
The following example shows how to set the Password to modify Microsoft Excel option for an existing file using the Aspose.Cells API.
Verify the password of the encrypted file
To verify the password of the encrypted file, Aspose.Cells for .NET provides the VerifyPassword method. These methods accept two parameters, the file stream and the password that needs to be verified. The following code snippet demonstrates the use of the VerifyPassword method to verify whether the provided password is valid or not.
Encryption/Decryption of ODS file with Aspose.Cells
Aspose.Cells allows to encrypt and decrypt ODS file. Decrypted ODS file can be opened both in Excel and OpenOffice, however encrypted ODS file can only be opened by OpenOffice after providing the password. Excel cannot open the encrypted ODS file and may raise warning message. The Encryption options are not applicable for ODS file unlike other file types. For encrypting an ODS file, load the file and set the WorkbookSettings.Password value to the actual password before saving it. The output encrypted ODS file can be opened in OpenOffice only.
For decrypting an ODS file, load the file by providing a password in the LoadOptions.Password. Once the file is loaded, call function Workbook.Unprotect() with actual password as an argument and finally set the WorkbookSettings.Password string to null.