For online payment security, bothconfidentiality(protection of data) andnonrepudiation(ensuring the sender cannot deny a transaction) are essential.

Option A (Incorrect):DES is outdatedandinsecurefor modern encryption needs. It has been replaced by stronger algorithms.

Option B (Incorrect):AES provides strong encryption(confidentiality) but does not handlenonrepudiationon its own.

Option C (Correct):PKI (Public Key Infrastructure)is the best solution because it providesencryption for confidentialityanddigital signatures for nonrepudiation, ensuring bothsecuretransactions andauthenticationof parties involved.

Option D (Incorrect):AVPN secures network traffic, but it does not address nonrepudiation, which is critical in online payments.