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 output).

-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.