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





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



  

  
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.

  

  
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(n), des(n), md5(n), sha1(n)






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>








  

    1.2.1
    tcllib