org.bouncycastle.crypto.engines
Class IDEAEngine

java.lang.Object
  org.bouncycastle.crypto.engines.IDEAEngine

All Implemented Interfaces:

BlockCipher

public class IDEAEngine
extends java.lang.Object
implements BlockCipher

A class that provides a basic International Data Encryption Algorithm (IDEA) engine.

This implementation is based on the "HOWTO: INTERNATIONAL DATA ENCRYPTION ALGORITHM" implementation summary by Fauzan Mirza (F.U.Mirza@sheffield.ac.uk). (baring 1 typo at the end of the mulinv function!).

It can be found at ftp://ftp.funet.fi/pub/crypt/cryptography/symmetric/idea/

Note: This algorithm is patented in the USA, Japan, and Europe including at least Austria, France, Germany, Italy, Netherlands, Spain, Sweden, Switzerland and the United Kingdom. Non-commercial use is free, however any commercial products are liable for royalties. Please see www.mediacrypt.com for further details. This announcement has been included at the request of the patent holders.

Field Summary

private static int	BASE
protected static int	BLOCK_SIZE
private static int	MASK
private int[]	workingKey

Constructor Summary

IDEAEngine()
standard constructor.

Method Summary

(package private) int	addInv(int x) Return the additive inverse of x.
private int	bytesToWord(byte[] in, int inOff)
private int[]	expandKey(byte[] uKey) The following function is used to expand the user key to the encryption subkey.
private int[]	generateWorkingKey(boolean forEncryption, byte[] userKey)
java.lang.String	getAlgorithmName() Return the name of the algorithm the cipher implements.
int	getBlockSize() Return the block size for this cipher (in bytes).
private void	ideaFunc(int[] workingKey, byte[] in, int inOff, byte[] out, int outOff)
void	init(boolean forEncryption, CipherParameters params) initialise an IDEA cipher.
private int[]	invertKey(int[] inKey) The function to invert the encryption subkey to the decryption subkey.
private int	mul(int x, int y) return x = x * y where the multiplication is done modulo 65537 (0x10001) (as defined in the IDEA specification) and a zero input is taken to be 65536 (0x10000).
private int	mulInv(int x) This function computes multiplicative inverse using Euclid's Greatest Common Divisor algorithm.
int	processBlock(byte[] in, int inOff, byte[] out, int outOff) Process one block of input from the array in and write it to the out array.
void	reset() Reset the cipher.
private void	wordToBytes(int word, byte[] out, int outOff)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

BLOCK_SIZE

protected static final int BLOCK_SIZE

See Also:

Constant Field Values

workingKey

private int[] workingKey

MASK

private static final int MASK

See Also:

Constant Field Values

BASE

private static final int BASE

See Also:

Constant Field Values

Constructor Detail

IDEAEngine

public IDEAEngine()

standard constructor.

Method Detail

init

public void init(boolean forEncryption,
                 CipherParameters params)

initialise an IDEA cipher.

Specified by:

init in interface BlockCipher

Parameters:

forEncryption - whether or not we are for encryption.

params - the parameters required to set up the cipher.

Throws:

java.lang.IllegalArgumentException - if the params argument is inappropriate.

getAlgorithmName

public java.lang.String getAlgorithmName()

Description copied from interface: BlockCipher

Return the name of the algorithm the cipher implements.

Specified by:

getAlgorithmName in interface BlockCipher

Returns:

the name of the algorithm the cipher implements.

getBlockSize

public int getBlockSize()

Description copied from interface: BlockCipher

Return the block size for this cipher (in bytes).

Specified by:

getBlockSize in interface BlockCipher

Returns:

the block size for this cipher in bytes.

processBlock

public int processBlock(byte[] in,
                        int inOff,
                        byte[] out,
                        int outOff)

Description copied from interface: BlockCipher

Process one block of input from the array in and write it to the out array.

Specified by:

processBlock in interface BlockCipher

Parameters:

in - the array containing the input data.

inOff - offset into the in array the data starts at.

out - the array the output data will be copied into.

outOff - the offset into the out array the output will start at.

Returns:

the number of bytes processed and produced.

reset

public void reset()

Description copied from interface: BlockCipher

Reset the cipher. After resetting the cipher is in the same state as it was after the last init (if there was one).

Specified by:

reset in interface BlockCipher

bytesToWord

private int bytesToWord(byte[] in,
                        int inOff)

wordToBytes

private void wordToBytes(int word,
                         byte[] out,
                         int outOff)

mul

private int mul(int x,
                int y)

return x = x * y where the multiplication is done modulo 65537 (0x10001) (as defined in the IDEA specification) and a zero input is taken to be 65536 (0x10000).

Parameters:

x - the x value

y - the y value

Returns:

x = x * y

ideaFunc

private void ideaFunc(int[] workingKey,
                      byte[] in,
                      int inOff,
                      byte[] out,
                      int outOff)

expandKey

private int[] expandKey(byte[] uKey)

The following function is used to expand the user key to the encryption subkey. The first 16 bytes are the user key, and the rest of the subkey is calculated by rotating the previous 16 bytes by 25 bits to the left, and so on until the subkey is completed.

mulInv

private int mulInv(int x)

This function computes multiplicative inverse using Euclid's Greatest Common Divisor algorithm. Zero and one are self inverse.

i.e. x * mulInv(x) == 1 (modulo BASE)

addInv

int addInv(int x)

Return the additive inverse of x.

i.e. x + addInv(x) == 0

invertKey

private int[] invertKey(int[] inKey)

The function to invert the encryption subkey to the decryption subkey. It also involves the multiplicative inverse and the additive inverse functions.

generateWorkingKey

private int[] generateWorkingKey(boolean forEncryption,
                                 byte[] userKey)