In a TA context, which concept is used to provide non-repudiation by signing data with a private key?

• A. Encryption transforms plaintext to ciphertext.
• B. Hashing produces a fixed digest for data integrity.
• C. Digital Signatures provide non-repudiation of data.
• D. Symmetric key management secures data at rest.

Answer: (C)

Digital signatures provide non-repudiation by tying the data to the signer through a private key. The signer creates a signature on the data (typically on a hash of the data) using their private key, and anyone with the corresponding public key can verify that signature. Because the private key is kept secret, a valid signature proves that the signer originated the data and cannot credibly deny it later. This also protects integrity, since any alteration would cause verification to fail. Encrypted data shows confidentiality, not who signed it. Hashing ensures data hasn’t changed but doesn’t prove who produced it. Symmetric key approaches rely on shared secrets, which doesn’t support non-repudiation because both parties could have produced the same MAC.