aes

Based on the old aes128 project of mine (https://github.com/pauljoohyunkim/aes128). This project will also be obsolete, and will be absorbed into a larger project, in a more cleanly-structured way.

Encrypted File Format

Suppose "inputfile" contains some bytes "$$$$$$$$$$$$$$$$" and its cipher text is some "????????????????". The generated encrypted file will follow the following format.

"APF[16d][32p][32f]????????????????"

where

• A represents the format of the AES used. ("\x01" for AES-128, "\x02" for AES-192, and "\x03" for AES-256)
• P represents the flag for not allowing password checks. ("\x01" for skipping password checks.)
• F represents the flag for not allowing file integrity check after decryption.
• [16d] represents the 16 byte IV (initialization vector).
• [32p] represents the 32 byte SHA256 hash of the password file with IV as salt. (This will be missing if P is set to 1.)
• [32f] represents the 32 byte SHA256 hash of the file with the password as salt. (This will be missing if F is set to 1.)
• Salting is done by XOR-ing the salt with the file in the first "salt-len" bytes.

Build Instruction

Unix

To build on a Unix environment that supports <pthread.h>, simply run the following command

mkdir build

cd build

../configure

make

[optional] make check

make install

Should the "make" line causes an error, navigate to the root directory of the project and run "automake --add-missing", and try it again.

You can check if the program functions as expected by running "make check". There are 48 tests in total, and each test should take between 2 seconds to 5 seconds (depending on how fast your machine is.)

To build on other systems, navigate to the src/aes directory, and build using

gcc aes_enc.c -o aes_enc -pthread

gcc aes_dec.c -o aes_dec -pthread

If for some reason the compilation fails due to the -pthread option, try again with -lpthread flag instead.

Windows

If you are building on a platform that does not natively support pthread.h, such as Windows, you can build manually without the -pthread flag.

gcc aes_enc.c -o aes_enc

gcc aes_dec.c -o aes_dec

Option (-h)

aes_enc

Usage: aes_enc -t (AES type) -i (input file) -k (key file) [other options]

Required options:

  -t <AES type>: AES bit mode (1:128bit, 2:192bit, 3:256bit)
  -i <input file>: name of the file you wish to encrypt
  -k <key file>: file containing your key.

Common options:

  -o <output file>: specify the output file. (default: <input file>.aes)
  (Warning: Do not set the output file to be equal to the input file.)
  -u <positive integer>: status update frequency. (default: 5)     [ORIGINALLY UNIX-BASED ENVIORNMENT EXCLUSIVE]
  -q: disable status update during encryption.			 [ORIGINALLY UNIX-BASED ENVIRONMENT EXCLUSIVE]
  -s: disable password check when decrypting.
  -f: disable file integrity check after decryption.

Note that you can use any file as a key file, whether it is a text file, image file, etc, as long as you keep it secret.

Example)

aes_enc -t1 -i secret_file.txt -k super_secret_key

Encrypts using AES128-CTR the file "secret_file.txt" using "super_secret_key" file as key file.

aes_dec

Usage: aes_dec -i (encrypted file) -k (key file) [other options]

Required options:

  -i <encrypted file>: name of the file you wish to encrypt
  -k <key file>: file containing your key.

Common options:

  -o <output file>: specify the output file. (default: <encrypted file>.decrypted)
  (Warning: Do not set the output file to be equal to the encrypted file.)
  -u <positive integer>: status update frequency. (default: 5)     [ORIGINALLY UNIX-BASED ENVIORNMENT EXCLUSIVE]
  -q: disable status update during encryption.			 [ORIGINALLY UNIX-BASED ENVIRONMENT EXCLUSIVE]

Override options: -s: disable password check (even if password hash is included.) -f: disable file integrity check after decryption (even if file integrity hash is included.)