Session keys are supported by the AES, GHASH, and CHACHA engine.
Before starting a cryptographic operation using a session key, the desired key value must be written in clear-text by the CPU into the write-only key registers of the corresponding engine. One session key can be overwritten by another as long as the write order of the write-only key registers are respected. Please refer to the corresponding chapter of each cryptographic engine for more information about write order.
The AES engine supports 128/192/256 bits session keys, GHASH engine supports 128 bits session keys, and CHACHA engine supports 128/256 bits session keys.
The last written session key for each engine is retained until CRYPTOCELL is disabled, the engine is reset, or the device is reset.