NAME
     idea - encrypt and decrypt using IDEA

SYNOPSIS
     idea [ -e | -d ] [ -r ] [ -ecb | -cbcN | -cfbN | -ofbN ]
          ( -k keyString | -K keyHexString )
          [ inputFile [ ouputFile ] ]

     idea [ -h | -H ] [ -tan | -abr ]
          [ -k keyString | -K keyHexString ]
          [ inputFile [ [ ouputFile ] hashvalFile ]

DESCRIPTION
     Idea reads inputFile and writes  the  en/decrypted  data  to
     outputFile or writes the hash value to hashvalFile.  If file
     name is not given in command line, idea uses standard  input
     or  output.   If  the  input file name is given as '-', idea
     reads from the standard input.

     IDEA (International Data Encryption Algorithm)  is  a  block
     cipher  developed  by  Dr.  Xuejia  Lai  and Prof. Dr. J. L.
     Massey at the Swiss Federal Institute of Technology.

OPTIONS
     -e   Encrypt data. (default)

     -d   Decrypt data.

     -r   InputFile is a raster-file.

     -k   Key is specified with keyString.

     -K   Key and initial values are specified with keyHexString.

     -h   Compute a 128 bit hash value from the input  data.  The
          hash  value is written to hashvalFile (or standard out-
          put).

     -H   Compute a 128 bit hash value from the input  data.  The
          input  is copied to outputFile (or standard output) and
          the hash value is written to hashvalFile  (or  standard
          error).

     Notation:
          N           = interleave factor (1 is default)
          z           = 128 bit key
          x[i]        = 64 bit plaintext block
          y[i]        = 64 bit ciphertext block
          x[1]..x[L]  = plaintext  (last  block  is  filled  with
                        zeros)
          x[L+1]      = length of plaintext in bits
          y[1]..y[L+1]= ciphertext
          IDEA(z, .)  = encryption function
          IIDEA(z, .) = decryption function
          x = IIDEA(z, IDEA(z ,x))

     Encryption / Decrypion Modes:

     -ecb electronic code book mode
          y[i] = IDEA(z, x[i])
          x[i] = IIDEA(z, y[i])

     -cbc cipher block chaining mode (cbc1 is default)
          y[i] = IDEA(z, x[i] ^ y[i-N])
          x[i] = IIDEA(z, y[i]) ^ y[i-N]

     -cfb ciphertext feedback mode
          y[i] = x[i] ^ IDEA(z, y[i-N])
          x[i] = y[i] ^ IDEA(z, y[i-N])

     -ofb output feedback mode
          h[i] = IDEA(z, h[i-N])
          y[i] = x[i] ^ h[i]
          x[i] = y[i] ^ h[i]

     Hash Functions:
          If no key is given, idea uses the all zero key.
          hash value = h[L+1] * 2**64 + g[L+1]
          h[0] = z / 2**64
          g[0] = z % 2**64

     -tan tandem DM-scheme (default)
          w = IDEA(g[i-1] * 2**64 + x[i], h[i-1])
          h[i] = h[i-1] ^ w
          g[i] = g[i-1] ^ IDEA(x[i] * 2**64 + w, g[i-1])

     -abr abreast DM-scheme
          h[i] = h[i-1] ^ IDEA(g[i-1] * 2**64 + x[i], h[i-1])
          g[i] = g[i-1] ^ IDEA(x[i] * 2**64 + h[i-1], ~ g[i-1])

     Key Formats:
          keyHexString = { '0'..'9' | 'a'..'f' | 'A'..'F' | ':' }
          keyHexString = z:y[1-N]:y[2-N]:y[3-N]..
          keyString = { '!'..'~' } = z

EXAMPLES
     To encrypt and decrypt a file in cipher block chaining  mode
     with an interleave factor of 8:

          idea -e -cbc8 -K 12345:67:89::ab:cDEf data data.cr
          idea -d -cbc8 -K 12345:67:89::ab:cDef data.cr data.ori
          data and data.ori are identical

     To compute the hash value with tandem DM-scheme:

          idea -h data

     To compute the hash value and encrypt the data in one step:

          idea -Hk "k e y" data | idea -K 123:9a::eF - data.cr

PATENT
     IDEA is registered as the international patent  WO  91/18459
     "Device for Converting a Digital Block and the Use thereof".
     For commercial use of IDEA, one should contact

     ASCOM TECH AG
     Freiburgstrasse 370
     CH-3018 Bern, Switzerland

AUTHOR
     Richard De Moliner (demoliner@isi.ee.ethz.ch)
     Signal and Information Processing Laboratory
     Swiss Federal Institute of Technology
     CH-8092 Zurich, Switzerland

BUGS
     This program is at most as strong as  IDEA  itself.  So,  we
     urge  the user to use this program only after he has assured
     himself that IDEA is strong  enough  AND  he  has  read  the
     source  code  of  this  program and its libraries AND he has
     compiled the program himself with a troyan-free compiler. WE
     DO  NOT  GUARANTEE  THAT THIS PROGRAM IS A DECENT ENCRYPTION
     PROGRAM.