The goal of the Non-repudiation service is to generate, collect, maintain, make available and validate evidence concerning a claimed event or action in order to resolve disputes about the occurrence or non occurrence of the event or action. This part of ISO/IEC 13888 describes a model for non-repudiation mechanisms providing evidence based on cryptographic techniques. Non-repudiation mechanisms generic to the various non- repudiation services are first described and then applied to a selection of specific non-repudiation services such as:
- non-repudiation of origin,
- non-repudiation of delivery,
- non-repudiation of submission,
- non-repudiation of transport.
Non-repudiation services establish evidence: evidence establishes accountability regarding a particular event or action. The entity responsible for the action, or associated with the event, with regard to which evidence is generated, is known as the evidence subject. There are two main types of evidence the nature of which depends on cryptographic techniques employed:
- Secure Envelopes generated by an evidence generating authority using symmetric cryptographic techniques,
- Digital signatures generated by an evidence generator or an evidence generating authority using asymmetric cryptographic techniques.
Non-repudiation mechanisms provide protocols for the exchange of non-repudiation tokens specific to each non-repudiation service. Non-repudiation tokens consist of Secure Envelopes and/or digital signatures and, optionally, of additional data. Non- repudiation tokens may be stored as non-repudiation information that may be used subsequently by disputing parties or by an adjudicator to arbitrate in disputes.
Depending on the non-repudiation policy in effect for a specific application, and the legal environment within which the application operates, additional information may be required to complete the non-repudiation information, e.g.,
- evidence including a trusted time stamp provided by a Time Stamping Authority,
- evidence provided by a notary which provides assurance about data created or the action or event performed by one or more entities.
Non-repudiation can only be provided within the context of a clearly defined security policy for a particular application and its legal environment. Non-repudiation policies are described in ISO/IEC 10181-4.
This part of ISO/IEC 13888 serves as a general model for subsequent parts specifying non-repudiation mechanisms using cryptographic techniques. ISO/IEC 13888 provides non-repudiation mechanisms for the following phases of non-repudiation:
- evidence generation,
- evidence transfer, storage and retrieval, and
- evidence verification.
Dispute arbitration is outside the scope of ISO/IEC 13888.