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

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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 mul-
              tiple 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.

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/publica-
              tions/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://sourceforge.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)