This also adds the MAC length constraint on imported HMAC keys. HMAC doesn't work without this constraint at the moment. Bug: 18088752 Change-Id: I8613f58f5d2a84df00bcf6179d13e30619440330
This currently supports AES and HMAC with SHA-256. Bug: 18088752 Change-Id: Ife55438cf4129b895295681bb35091cd37eb73fb