Nonrepudiation

Definition

The security quality subfactor, nonrepudiation, is the degree to a party to an interaction (e.g., message, transaction, transmission of data) is prevented from successfully repudiating (i.e., denying) any aspect of the interaction.

Measurement

Nonrepudiation is typically measured in terms of:

• The [number/percentage] of parties that are successfully prevented from repudiating an interaction [of a specific type] [during a given unit of time].

Requirements

See nonrepudiation requirements.

Mechanisms

Typical mechanisms for implementing support for nonrepudiation include:

• Digital signatures (to identify the parties)
• Timestamps (to capture dates and times)
• Encryption and decryption (to protect the information)
• Hash functions (to ensure that the information has not been changed)
• Storage of records with a third-party “nortary” system
• “Certified mail” receipt of successful delivery of message

Guidelines

The following guidelines have been found to be useful with respect to nonrepudiation:

• Nonrepudiation primarily deals with ensuring that adequate tamper-proof records are kept. It is not sufficient to merely make records; these records must be:
  • Complete.
  • Tamper-proof.
• Nonrepudiation typically involves the storage of a significant amount of information about each interaction including:
  • The authenticated identity of all parties involved in the transaction.
  • The date and time that the interaction was sent, received, and acknowledged (if relevant).
  • The significant information that is passed during the interaction.
• Although nonrepudiation may imply that a record is kept of the fact that the receiver received the message from the sender, it may (or may not) mean that the receiver has both read and understood the message (e.g., by requiring an explicit acknowledgement).