AES

Introduction

The aes egg implements the AES / Rijndael cryptosystem.

It does not provide any higher-level operations such as encryption 'modes'; it just provides two procedures per variant of the algorithm, which take a key (as a blob of the correct length) and return a procedure that maps 16-byte blobs to 16-byte blobs - one for encryption, one for decryption.

Rather conflating the purpose of the egg but usefully for writing tests, there are also procedures provided for converting between blobs and hexadecimal strings.

Examples

 
(import aes)
(import crypto-tools) ; for the hexstring functions
(define encryptor (make-aes128-encryptor (hexstring->blob "00010203050607080A0B0C0D0F101112")))
(define decryptor (make-aes128-decryptor (hexstring->blob "00010203050607080A0B0C0D0F101112")))
(define encrypted (encryptor (hexstring->blob "506812A45F08C889B97F5980038B8359")))
(define decrypted (decryptor encrypted))

(blob->hexstring encrypted)
 => "d8f532538289ef7d06b506a4fd5be9c9"

(blob->hexstring decrypted)
 => "506812a45f08c889b97f5980038b8359"

Library functions

[procedure] (make-aes128-encryptor BLOB) => PROCESSOR
[procedure] (make-aes128-decryptor BLOB) => PROCESSOR
[procedure] (make-aes192-encryptor BLOB) => PROCESSOR
[procedure] (make-aes192-decryptor BLOB) => PROCESSOR
[procedure] (make-aes256-encryptor BLOB) => PROCESSOR
[procedure] (make-aes256-decryptor BLOB) => PROCESSOR

Using the supplied blob as a raw key, return a procedure that maps 16-byte blobs to 16-byte blobs, either encrypting or decrypting them with the specified key. The key is not modified in any way; if you just split your data into blocks (with padding) and encrypt each, you will merely be operating in ECB mode, which isn't very secure.

128-bit keys must be 16 bytes long, 192-bit keys 24 bytes, and 256-bit keys 32 bytes. Otherwise, an error will be signalled. Likewise, passing a blob of other than 16 bytes to a `PROCESSOR` will result in an error.

Authors

Alaric B. Snell-Pym, based on public domain code from http://www.efgh.com/software/rijndael.htm.

My modifications extend no further than pasting it together and putting static modifiers on all the functions.

The author of the original code is "Philip J. Erdelsky <pje@efgh.com>", who based it on code by Vincent Rijmen vincent.rijmen@esat.kuleuven.ac.be, Antoon Bosselaers antoon.bosselaers@esat.kuleuven.ac.be, and Paulo Barreto paulo.barreto@terra.com.br

Repository

This egg is hosted on the CHICKEN Subversion repository:

https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/aes

If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.

License

The C code is based on public-domain code.

However, the Scheme wrapper is subject to the following license:

 Copyright (c) 2003-2009, Warhead.org.uk Ltd
 All rights reserved.
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
 Redistributions in binary form must reproduce the above copyright
 notice, this list of conditions and the following disclaimer in the
 documentation and/or other materials provided with the distribution.
 Neither the names of Warhead.org.uk Ltd, Snell Systems, nor Kitten
 Technologies, nor the names of their contributors may be used to
 endorse or promote products derived from this software without
 specific prior written permission.
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.

Requirements

The C implementation of the AES code is entirely embedded in the egg.

Version History