8.1. Auxiliary Authenticated Application Information

8.1. Auxiliary Authenticated Application Information

HPKE has two places at which applications can specify auxiliary authenticated information: (1) during context construction via the Setup info parameter, and (2) during Context operations, i.e., with the aad parameter for Open() and Seal(), and the exporter_context parameter for Export(). Application information applicable to multiple operations on a single Context should use the Setup info parameter. This avoids redundantly processing this information for each Context operation. In contrast, application information that varies on a per-message basis should be specified via the Context APIs (Seal(), Open(), or Export()).

Applications that only use the single-shot APIs described in Section 6 should use the Setup info parameter for specifying auxiliary authenticated information. Implementations which only expose single-shot APIs should not allow applications to use both Setup info and Context aad or exporter_context auxiliary information parameters.