Apart from Encrypt/Decrypt of external data, what use is the VolatileKey register?
Is anybody using it? What would you Auth with it?
As the data sheet states:
The VolatileKey can never be used to read or write the User Memory or to increment the Counters.
VolatileKey can only be used to perform authentication operations and to encrypt or decrypt external data.
See Section VolatileKey Configuration for the VolatileKey usage restrictions.
A side from Encryption and Decryption, you can use a VolatileKey for Authorization (as you stated). Suppose you have the following scenario and configure the device as follows:
Key05 can be configured to be require to do EncReads and EncWrites for Zone 00. To use Key05, you can require pre-auth with the VolatileKey (0xFF). In order to load the the VolatileKey, you need to use the KeyLoad or KeyCreate. To do this, both commands require another key and a MAC. In my opinion, it's another way to obscure your data and enhance your security. One of the cool features of the device is allowing you to daisy chain key Authorization.
"When all else fails, read the directions"
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