Non-Repudiation Using Symmetric Techniques

Non-repudiation is, by definition, rather an ‘asymmetric’ requirement. It demands a capability linked to a specific entity and not one shared with another entity (unlike confidentiality, for example). It should not, therefore, be a surprise that digital signature schemes are normally provided using techniques associated with public-key cryptography. That said, there are several special circumstances in which symmetric techniques based on MACs can be used to provide non-repudiation.

Arbitrated digital signature schemes

The first case arises when there exists a trusted third party, the arbitrator, who participates in the transfer of data and generates evidence that can be used to settle disputes. Both the signer and verifier trust the arbitrator. Disputes are settled based on the premise that a statement is true if the arbitrator says it is true.