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aes(n)                               Advanced Encryption Standard (AES)                               aes(n)



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NAME
       aes - Implementation of the AES block cipher

SYNOPSIS
       package require Tcl  8.2

       package require aes  ?1.0.1?

       ::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 iden-tical identical
              tical plain text will produce identical output when encrypted with the same key.  Any  encryp-tion encryption
              tion  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 initial-ization initialization
              ization  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.


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   SF   Trackers   [http://source-
       forge.net/tracker/?group_id=12883].   Please  also report any ideas for enhancements you may have for
       either package and/or documentation.

SEE ALSO
       blowfish(n), des(n), md5(n), sha1(n)

KEYWORDS
       aes, block cipher, data integrity, encryption, security

COPYRIGHT
       Copyright (c) 2005, Pat Thoyts <patthoyts@users.sourceforge.net>




aes                                                 1.0.1                                             aes(n)