By default Excel 2003 encrypts password protected excel files using trivial security.
In order to use RSA or AES encryption, you must have Office 2003 service pack 1 or better and even then, only 128 bit encryption is supported. We need to expressly set the encryption type of the file before we save it.
- Open the Excel file to be encrypted
- From the tools menu select ‘.’Options’
- In the resulting window, select the ‘Security’ tab
- Enter a password in the ‘Password to Open:’ box
- Click the ‘Advanced…’ button
- In the resulting window select the Microsoft Enhanced RSA and AES Cryptographic Provider
- Verify that the key length is 128 and click OK
- Click OK
- You will be prompted to rekey the password for the file
- Enter the password and click OK
- Save the file