A digital envelope combines the strengths of symmetric and asymmetric cryptography. The message itself is encrypted using a fast symmetric algorithm. The session key used for symmetric encryption is then encrypted using the recipient's public key. This ensures efficiency (large data encrypted quickly with symmetric keys) and security (session key securely transmitted using asymmetric encryption). Options A, C, and D describe other cryptographic processes (compression, hashing, or digital signatures) but do not correctly represent a digital envelope. ISACA training materials and CISA manuals highlight this hybrid approach as the standard method for secure data transmission.
References (ISACA): CISA Review Manual - Cryptography Concepts; ISACA Glossary.