Repudiation is the denial of having been a part of a data exchange. This repudiation might be to avoid responsibility for an action. Nonrepudiation is a security feature that helps ensure that data has been sent and received by the parties claiming to have sent and received it. Nonrepudiation guarantees that the sender of a message can’t later deny (repudiate) having sent the message. Similarly, the recipient can’t deny having received the message.

Methods for implementing nonrepudiation include the following:

• Digital signatures Unique identifier for an individual, much like a written signature

• Confirmation services The message transfer agent creates digital receipts indicating messages were sent and/or received

• Timestamps The date and time a document was composed, proving a document existed at a certain time