ISO/IEC 18014-3:2004 describes time-stamping services producing linked tokens, that is, tokens that are cryptographically bound to other tokens produced by these time-stamping services. It describes a general model for time-stamping services of this type and the basic components used to construct a time-stamping service of this type, it defines the data structures and protocols used to interact with a time-stamping service of this type, and it describes specific instances of such time-stamping services.
The usage of linking operations reduces the level of trust required in the time-stamping service. The trustworthiness of linked tokens depends on the integrity of the linking operations carried out by the time-stamping service. The integrity of the linking operations performed by the time-stamping service can be verified algorithmically. A time-stamping service producing linked tokens may publish values derived from the linking operations into widely available media to further bind the issued tokens to widely-witnessed events and provide additional assurance of integrity. A time-stamping service producing linked tokens may also use aggregation operations to bind multiple token requests together, thus providing higher throughput through the use of co-operating processes. Algorithms applicable to linking, aggregation and publishing operations are covered.