This is a small and portable implementation of the AES128 ECB and CBC encryption algorithms written 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, const uint8_t* key, uint8_t* output);
void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t* output);
void AES128_CBC_encrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv);
void AES128_CBC_decrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv);You can choose to use one or both of the modes-of-operation, by defining the symbols CBC and ECB. See the header file for clarification.
Additionally, there are two variants of the CBC functions that operate on the buffer "in-place"
uint8_t AES128_CBC_encrypt_inplace( uint8_t* data, size_t length, const uint8_t* key, const uint8_t* iv);
uint8_t AES128_CBC_decrypt_inplace( uint8_t* data, size_t length, const uint8_t* key, uint8_t* iv);These have their own restrictions, see the header file for details.
The module uses around 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 ECB mode is compiled for ARM:
$ arm-none-eabi-gcc -Os -c aes.c -DCBC=0
$ size aes.o
text data bss dec hex filename
2323 0 184 2507 9cb 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 -DCBC=0
$ size aes.o
text data bss dec hex filename
1775 0 184 1959 7a7 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) 4.8.4 20140526 (release) [ARM/embedded-4_8-branch revision 211358]
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.
This 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.
All material in this repository is in the public domain.
Modifications made to test using the NovaProva C testing framework