Abstract: Non-repudiation of two-party data is provided by operating a terminal to provide non-repudiation in respect of data exchanged between the terminal and at least one other terminal. The data is exchanged via a link operable to provide a first link mode in which at least a portion of the exchanged data may be lost. The process involves: (a) determining which data sent from the terminal was received at the other terminal; (b) indicating to the other terminal, which data sent from the other terminal was received at the terminal; (c) receiving a digital signature from the other terminal; and (d) in the event that the terminal determines that the digital signature was created utilizing a private cryptographic key associated with the other terminal and data including both the determined data and the indicated data, establishing non-repudiation in respect thereof.

Abstract: The present invention relates to a method of and apparatus for two-party data non-repudiation. An abiding concern in the history of communication techniques is the worry that messages or conversations, whilst purporting to come from or be with a particular party might in fact have been made up by another (malicious) party. Cryptographic techniques have been used to address the problem of so-called non-repudiation. In one problem field, an application might, for example, produce a stream of messages each carrying data such as a portion of a voice conversation between two parties. Non-repudiation of both transmission and receipt would then be desirable to provide for the possibility of proof of who had said what in the conversation and who had heard it. These voice messages may suitably be carried in the form of packets. For applications which have a (near) real-time operation however, the slowness engendered by the straightforward cryptographic signing of messages may well be intolerable.