[aes/model] Add basic C model of AES unit and example application
This model targets functional verification of the AES unit during the
design phase as well as later design verification. It also comes with
an example application that showing how to use it and check the results
versus the output of the BoringSSL/OpenSSL library.
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+AES Model
+=========
+
+This directory contains a basic C model of the AES unit targeting functional
+verfication of the AES unit during the design phase as well as later design
+verification.
+
+Besides the actual model, this directory also contains an example application
+that:
+- Shows how to interface the C model.
+- Allows printing of intermediate results for debugging.
+- Checks the output of the model versus the exptected results.
+- Checks the output of the model versus the output of the BoringSSL/OpenSSL
+ library.
+
+How to build and run the example
+--------------------------------
+
+Open the makefile and update the variable BORING_SSL_PATH pointing to the
+BoringSSL directory on your machine. If make cannot find the crypto library
+in that directory, the example is automatically linked to OpenSSL instead
+of BoringSSL.
+
+Simply execute
+
+ ```make```
+
+to build the example and
+
+ ```./aes_example KEY_LEN_BYTES```
+
+to run the example. The optional argument KEY_LEN_BYTES determines the key
+length in bytes and is either 16, 24, or 32 for AES-128, 192 or 256,
+respectively. By default, a key length of 16 Bytes is used (AES-128).
+
+Details of the model
+--------------------
+
+- aes.c/h: contains the C model of the AES unit
+- crypto.c/h: contains BoringSSL/OpenSSL library interface functions
+- aes_example.c/h: contains the example application including test
+ input and expected output
