Tiny AES128 in C

This is a small and portable implementation of the AES128 ECB encryption algorithm implemented in C.

The API is very simple and looks like this (I am using C99/<stdint.h>-style annotated types):

void AES128_ECB_encrypt(uint8_t* input, uint8_t* key, uint8_t *output);
void AES128_ECB_decrypt(uint8_t* input, uint8_t* key, uint8_t *output);

The module uses just a bit more than 200 bytes of RAM and 2.5K ROM when compiled for ARM (~2K for Thumb but YMMV).

It is the smallest implementation in C I've seen yet, but do contact me if you know of something smaller (or have improvements to the code here).

I've successfully used the code on 64bit x86, 32bit ARM and 8 bit AVR platforms.

GCC size output when compiled for ARM:

$ arm-none-eabi-gcc -Os -c aes.c
$ size aes.o
   text    data     bss     dec     hex filename
   2515       0     204    2719     a9f aes.o

.. and when compiling for the THUMB instruction set, we end up around 2K in code size.

$ arm-none-eabi-gcc -mthumb -Os -c aes.c
$ size aes.o
   text    data     bss     dec     hex filename
   1883       0     204    2087     827 aes.o

I am using Mentor Graphics free ARM toolchain:

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 4.8.3 20131129 (release) [ARM/embedded-4_8-branch revision 205641]
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The implementation is verified against the data in:

National Institute of Standards and Technology Special Publication 800-38A 2001 ED Appendix F: Example Vectors for Modes of Operation of the AES.