There is a definitional distinction between the legal use of the term "non-repudiation" and the common use that has taken hold within IT. In legal terminology an alleged signatory to a document is at all times able to repudiate a signature that has been attributed to him or her. The basis for a repudiation of a traditional signature may include:
- The signature is a forgery;
- The signature is not a forgery, but was obtained via:
- Unconscionable conduct by a party to a transaction;
- Fraud instigated by a third party;
- Undue influence exerted by a third party.
The universal rule of evidence is that if an individual denies a signature (or the creation of a transaction), then it falls upon the party that is relying on the signature to prove that the signature is truly that of the person who has denied it. In legal terminology, the terms "deny" and "repudiate" are synonymous.
The common law trust mechanism developed to prevail over a false claim of non-repudiation is known as witnessing. Witnessing occurs at the time the signature is being affixed. An independent witness to the signing of a document reduces the ability of the signatory to successfully deny the signature as a forgery at a later date through the provision of contradictory evidence.
From organizational perspective the aim is not to remove the ability for an individual to deny a transaction, but rather to ensure that sufficient evidence exists to enable the organization to successfully prove that the transaction or signature was created by the party who were supposed to have created. In order to support non-repudiation, an organization needs to consider the following technical controls:
- Digital signatures
- Secure timestamps
- Secure audit logs