In ATAES132A datasheet on pages 112, 113 and 114 we have described process of Mac generation, Encryption and Decryption.
In this explanation there are used two modes of encryption/decryption - CBC and CTR.
I'm facing ATAES132A with uC using my own AES C library. Now after Auth Command(Outbound Only Authentication) or EncRead I would like to retrieve data on uC. To do this things I need a couple of input's which I don't know how to get, starting from the end (decryption):
- A counter block (Initialization Vector for CTR).
- A nonce computer by chip (one way to know the nonce I think is to provide it by Nonce command from the uC).
- A Initilization vector for CBC mode for decryption.
Also I don't know how is constructed Counter Block for CTR - how many bytes are used by Nonce and how many bytes are used for counter.
I was reading many times specifications of AES, modes of operation and CCM specification but I have know idea how to connect all these informations with ATAES132A.
I know I missing something simple, but I don't know what is this.
I'm counting for any help or hint.
Thanks in advance, Daniel.