Non-repudiation is "Assurance the sender of the data is provided with proof of delivery and the recipient is provided with proof of the sender\'s identity, so neither can later deny having processed the data." Smart cards and digital signatures support non-repudiation. DoD has recently implemented smart cards called the Common Access Card. These cards use Public Key Infrastructure, or PKI, for authentication and encryption. You can find out more about PKI through the Defense Information Systems Agency course catalog.