1.3.3 Encryption
Password-protected documents can be created by using one of four mechanisms:
40-bit RC4 encryption.
Cryptographic Application Programming Interface (CAPI) or CryptoAPI encryption.
ECMA-376 document encryption [ECMA-376], which can include one of three approaches:
Standard encryption: This approach uses a binary EncryptionInfo structure. It uses Advanced Encryption Standard (AES) as an encryption algorithm and SHA-1 as a hashing algorithm.
Agile encryption: This approach uses an XML EncryptionInfo structure. The encryption and hashing algorithms are specified in the structure and can be for any encryption supported on the host computer.
Extensible encryption: This approach uses an extensible mechanism to allow arbitrary cryptographic modules to be used.