SharedModelTypeProcessor (SMTP) maintains one encryption key per model type, it is stored in ModelTypeState.

When encryption key is changed by remote client SMTP reencrypts all the entities it maintains (SharedModelTypeProcessor::RecommitAllForEncryption). Typically though by the time the client gets to reencryption all the entities are already encrypted with new key.
This process will repeat once per client resulting in redundant commit traffic to the server.

Processor needs to remember with which key each entity was encrypted. Encryption key name should be stored in EntityMetadata.