Patent ID: 7484098

Claim:
A method of operating a terminal to provide non-repudiation in respect of data exchanged between the terminal and at least one other terminal, the data exchanged on a data exchange timescale via a link operable to provide a first link mode in which at least a portion of the exchanged data may be lost, the method comprising the steps of: (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 comprising both the data determined to have been received at the other terminal and the data indicated to have been received at the terminal, establishing non-repudiation in respect of only the data determined to have been received at the other terminal and the data indicated to have been received at the terminal, wherein said method steps being carried out on a timescale different from the data exchange timescale.