1.3.3 Encryption

Password-protected documents can be created by using one of four mechanisms:

  • XOR obfuscation.

  • 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.