AnsweredAssumed Answered

AES encryption/decryption

Question asked by Todd Kiefer on Dec 1, 2016
Latest reply on Dec 2, 2016 by Todd Kiefer

I'm working with the MCF52259 processor which includes the CAU (Cryptographic Acceleration Unit).

I wish to implement a simple AES256 decryption.  In reading the NXP document (AN4307) "Using the CAU and mmCAU in ColdFire, ColdFire+, and Kinetis", section 2.3 specifically states that the crypto algorithms are executed in Cipher-block chaining (CBC) modes.

NXP document (AN4234) "Using the Cryptographic Service Engine (CSE)", section 1.2 discusses the Electronic Codebook (ECB) and the Cipher-block chaining (CBC).  This document does not indicate which mode is used in the CAU, nor does it indicate if there is any ability to specify the mode.

When I read the NXP document "Colfire/ColdFire+ CAU and Kinetis mmCAU Software Library" user guide, revision 2.3, there are only 3 library commands associated with the AES encryption/decryption methodology; cau_aes_set_key, cau_aes_encrypt, and cau_aes_decrypt.  If the AES methodolgy implemented in the CAU does indeed use the CBC mode, then there must be some manner in which I can provide the "initialization value" (commonly listed in AES documentation as IV), in addition to the key.  I guess the other possibility is that the CBC mode is not really being used, but rather the ECB mode, which does not require the IV value.

Can anyone shed a little light on this for me?

Outcomes