Which of the following is the PRIMARY type of cryptography required to support non-repudiation of a digitally signed document?

Message digest (MD) algorithms like MD5 produce a fixed-length hash of data but do not involve key pairs or identity binding, so they cannot alone provide non-repudiation.

Asymmetric cryptography uses a mathematically linked key pair - a private key (kept secret by the signer) and a public key (shared openly). When a document is signed with the signer's private key, any recipient can verify it with the corresponding public key, proving only that individual could have created the signature. This binding of identity to action is the foundation of non-repudiation, as the signer cannot credibly deny signing without claiming their private key was compromised.

Symmetric cryptography uses a single shared secret key known to multiple parties, meaning any party with the key could have created the message, making it impossible to uniquely attribute authorship and thus it cannot support non-repudiation.

Hashing is a one-way function used to verify data integrity (e.g., confirming a document hasn't changed), but without a private key to bind the hash to a specific identity, it does not provide non-repudiation on its own.