AES is the most widely adopted symmetric encryption standard nowadays. This repository contains an implementation in C of the AES-128 algorithm. The program takes two arguments: a 32-bytes hexadecimal string representing the 128-bit input block, and another 32-bytes hexadecimal string representing the 128-bit key. It then outputs the corresponding ciphertext in hexadecimal form.

AES Reference: https://doi.org/10.6028/NIST.FIPS.197-upd1

Screenshot taken after building the project with the build.bat file.

Installation

First make sure you have installed the GCC compiler v8.1.0 or above.
The gcc --version command should output:

gcc (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0
Copyright (C) 2018 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.

Then, clone this repository in any location on your computer and double-click on build.bat.
You should now see the following program's output:

CIPHERTEXT: 732281c0a0aab8f7a54a0c67a0c45ecf

The corresponding plaintext and key to obtain this ciphertext are encoded within the build.bat file.

Usage and test vectors

The program takes two arguments: a 32-bytes hexadecimal string representing the 128-bit input block, and another 32-bytes hexadecimal string representing the 128-bit key. It then outputs the corresponding ciphertext in hexadecimal form.
You can find some test vectors on the official NIST website on this page.

For example, with the following sample data set:

KEY = 00000000000000000000000000000000
PLAINTEXT = 6a84867cd77e12ad07ea1be895c53fa3

The program should output:

CIPHERTEXT: 732281c0a0aab8f7a54a0c67a0c45ecf

To check this output, build the project and then execute this command:

main.exe 6a84867cd77e12ad07ea1be895c53fa3 00000000000000000000000000000000

You should now see the ciphertext 732281c0a0aab8f7a54a0c67a0c45ecf.

Future work

A few ideas to improve this project:

Add decryption part.
Test the implementation in ECB or CBC block cipher modes.
Rewrite the key expansion function in a cleaner way.
Add features for file encryption.

License

This work is shared under the MIT license.

The AES S-Box initialization function has not been written by me and have been taken from:
https://en.wikipedia.org/wiki/Rijndael_S-box (Accessed on March 21, 2025)
Original licence: CC BY-SA 4.0