Provided by: tcllib_1.19-dfsg-2_all 
NAME
aes - Implementation of the AES block cipher
SYNOPSIS
package require Tcl 8.5
package require aes ?1.2.1?
::aes::aes ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv vector? ?-hex? ?-out channel?
?-chunksize size? [ -in channel | ?--? data ]
::aes::Init mode keydata iv
::aes::Encrypt Key data
::aes::Decrypt Key data
::aes::Reset Key iv
::aes::Final Key
________________________________________________________________________________________________________________
DESCRIPTION
This is an implementation in Tcl of the Advanced Encryption Standard (AES) as published by the U.S.
National Institute of Standards and Technology [1]. AES is a 128-bit block cipher with a variable key
size of 128, 192 or 256 bits. This implementation supports ECB and CBC modes.
COMMANDS
::aes::aes ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv vector? ?-hex? ?-out channel?
?-chunksize size? [ -in channel | ?--? data ]
Perform the aes algorithm on either the data provided by the argument or on the data read from the
-in channel. If an -out channel is given then the result will be written to this channel.
The -key option must be given. This parameter takes a binary string of either 16, 24 or 32 bytes
in length and is used to generate the key schedule.
The -mode and -dir options are optional and default to cbc mode and encrypt respectively. The
initialization vector -iv takes a 16 byte binary argument which defaults to all zeros. See MODES
OF OPERATION for more about available modes and their uses.
AES is a 128-bit block cipher. This means that the data must be provided in units that are a
multiple of 16 bytes.
PROGRAMMING INTERFACE
Internal state is maintained in an opaque structure that is returned from the Init function. In ECB mode
the state is not affected by the input but for CBC mode some input dependent state is maintained and may
be reset by calling the Reset function with a new initialization vector value.
::aes::Init mode keydata iv
Construct a new AES key schedule using the specified key data and the given initialization vector.
The initialization vector is not used with ECB mode but is important for CBC mode. See MODES OF
OPERATION for details about cipher modes.
::aes::Encrypt Key data
Use a prepared key acquired by calling Init to encrypt the provided data. The data argument should
be a binary array that is a multiple of the AES block size of 16 bytes. The result is a binary
array the same size as the input of encrypted data.
::aes::Decrypt Key data
Decipher data using the key. Note that the same key may be used to encrypt and decrypt data
provided that the initialization vector is reset appropriately for CBC mode.
::aes::Reset Key iv
Reset the initialization vector. This permits the programmer to re-use a key and avoid the cost of
re-generating the key schedule where the same key data is being used multiple times.
::aes::Final Key
This should be called to clean up resources associated with Key. Once this function has been
called the key may not be used again.
MODES OF OPERATION
Electronic Code Book (ECB)
ECB is the basic mode of all block ciphers. Each block is encrypted independently and so identical
plain text will produce identical output when encrypted with the same key. Any encryption errors
will only affect a single block however this is vulnerable to known plaintext attacks.
Cipher Block Chaining (CBC)
CBC mode uses the output of the last block encryption to affect the current block. An
initialization vector of the same size as the cipher block size is used to handle the first block.
The initialization vector should be chosen randomly and transmitted as the first block of the
output. Errors in encryption affect the current block and the next block after which the cipher
will correct itself. CBC is the most commonly used mode in software encryption. This is the
default mode of operation for this module.
EXAMPLES
% set nil_block [string repeat \\0 16]
% aes::aes -hex -mode cbc -dir encrypt -key $nil_block $nil_block
66e94bd4ef8a2c3b884cfa59ca342b2e
set Key [aes::Init cbc $sixteen_bytes_key_data $sixteen_byte_iv]
append ciphertext [aes::Encrypt $Key $plaintext]
append ciphertext [aes::Encrypt $Key $additional_plaintext]
aes::Final $Key
REFERENCES
[1] "Advanced Encryption Standard", Federal Information Processing Standards Publication 197, 2001
(http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf)
AUTHORS
Thorsten Schloermann, Pat Thoyts
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please
report such in the category aes of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can be made by
going to the Edit form of the ticket immediately after its creation, and then using the left-most button
in the secondary navigation bar.
SEE ALSO
blowfish(3tcl), des(3tcl), md5(3tcl), sha1(3tcl)
KEYWORDS
aes, block cipher, data integrity, encryption, security
CATEGORY
Hashes, checksums, and encryption
COPYRIGHT
Copyright (c) 2005, Pat Thoyts <patthoyts@users.sourceforge.net> Copyright (c) 2012-2014, Andreas Kupries <andreas_kupries@users.sourceforge.net>