___________ can verify the authenticity of the sender and enforce nonrepudiation to prove that the sender is who she/he claims to be and cannot deny sending it.

• A. Symmetric encryption
• B. Asymmetric encryption
• C. Hashing
• D. Digital signatures

Answer: (A)

Authenticating the sender and enforcing nonrepudiation is achieved through digital signatures. A digital signature signs a hash of the message with the sender’s private key, and others verify it using the sender’s public key. This proves the signer’s identity and that the message hasn’t been altered, and because the private key is kept secret, the signer cannot later deny having sent it. Symmetric encryption can protect confidentiality but does not tie actions to a single, verifiable identity nor provide nonrepudiation, since anyone with the shared key could produce the same result. Hashing alone only ensures data integrity and does not verify who sent the data or prevent denial of origin.