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## cryptix.provider.cipher
Class DES_EDE3

    java.lang.Object
      |
      +--java.security.IJCE_Traceable
            |
            +--java.security.Cipher
                  |
                  +--cryptix.provider.cipher.DES_EDE3

public class DES_EDE3
extends Cipher
implements SymmetricCipher

This class implements Triple DES EDE encryption with three independent keys. DES-EDE3 acts as a block cipher with an 8 byte block size.

The encoded form of the Triple DES key should be a 24-byte array, consisting of three 8-byte single DES keys in order - K1, K2 and K3. Encryption and decryption are done as follows:

- C = EK3(DK2(EK1(P)))
- P = DK1(EK2(DK3(C)))

The alternating encryption and decryption was designed by IBM to enable compatibility with single DES, when all three keys are equal (although it is now rare for Triple DES to be used in that way).

When DES-EDE3 is used with the CBC mode class (algorithm name "DES-EDE3/CBC"), the result is Outer-CBC, and only one IV is used.

DES was written by IBM and first released in 1976. The algorithm is freely usable for both single and triple encryption.

References:

1. Bruce Schneier, "Chapter 12 Data Encryption Standard," and "Section 15.2 Triple Encryption," Applied Cryptography, 2nd edition, John Wiley & Sons, 1996

2. R.C. Merkle and M. Hellman, "On the Security of Multiple Encryption," Communications of the ACM, vol. 24 no. 7, 1981, pages 465-467.

3. P Karn, P Metzger, W A Simpson "The ESP Triple DES Transform," Internet Draft, draft-simpson-esp-des3-x-01.txt

Copyright © 1997 Systemics Ltd on behalf of the Cryptix Development Team.
All rights reserved.

$Revision: 1.5 $

Since:
  Cryptix 2.2.2
Author:
  David Hopwood

Fields inherited from class java.security.Cipher
`DECRYPT, ENCRYPT, UNINITIALIZED`

Constructor Summary
`DES_EDE3()` Constructs a DES-EDE3 cipher object, in the UNINITIALIZED state.

Method Summary
`int` | `engineBlockSize()` SPI: Returns the length of an input block, in bytes.
`protected void` | `engineInitDecrypt(Key key)` SPI: Initializes this cipher for decryption, using the specified key.
`void` | `engineInitEncrypt(Key key)` SPI: Initializes this cipher for encryption, using the specified key.
`protected int` | `engineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset)` SPI: This is the main engine method for updating data.

Methods inherited from class java.security.Cipher
`blockSize, clone, crypt, crypt, crypt, doFinal, doFinal, doFinal, doFinal, engineCiphertextBlockSize, engineCrypt, engineGetParameter, engineInBufferSize, engineOutBufferSize, enginePlaintextBlockSize, engineSetPaddingScheme, engineSetParameter, getAlgorithm, getAlgorithms, getAlgorithms, getCiphertextBlockSize, getInputBlockSize, getInstance, getInstance, getInstance, getMode, getOutputBlockSize, getPadding, getPaddingScheme, getParameter, getPlaintextBlockSize, getProvider, getState, inBufferSize, inBufferSizeFinal, initDecrypt, initEncrypt, isPaddingBlockCipher, outBufferSize, outBufferSizeFinal, setParameter, toString, update, update, update, update`

Methods inherited from class java.lang.Object
`equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

### DES_EDE3

    public DES_EDE3()

  Constructs a DES-EDE3 cipher object, in the UNINITIALIZED state. This calls the Cipher constructor with implBuffering false, implPadding false and the provider set to "Cryptix".

Method Detail

### engineBlockSize

    public int engineBlockSize()

  SPI: Returns the length of an input block, in bytes.
  Overrides:
    engineBlockSize in class Cipher
  Returns:
    the length in bytes of an input block for this cipher.

### engineInitEncrypt

    public void engineInitEncrypt(Key key)
                           throws KeyException

  SPI: Initializes this cipher for encryption, using the specified key.
  Overrides:
    engineInitEncrypt in class Cipher
  Parameters:
    `key` - the key to use for encryption.
  Throws:
    KeyException - if one of the following occurs:
    - key.getEncoded() == null;
    - The length of the user key array is invalid.

### engineInitDecrypt

    protected void engineInitDecrypt(Key key)
                              throws KeyException

  SPI: Initializes this cipher for decryption, using the specified key.
  Overrides:
    engineInitDecrypt in class Cipher
  Parameters:
    `key` - the key to use for decryption.
  Throws:
    KeyException - if one of the following occurs:
    - key.getEncoded() == null;
    - The length of the user key array is invalid.

### engineUpdate

    protected int engineUpdate(byte[] in,
                               int inOffset,
                               int inLen,
                               byte[] out,
                               int outOffset)

  SPI: This is the main engine method for updating data.

  in and out may be the same array, and the input and output regions may overlap.

  Overrides:
    engineUpdate in class Cipher
  Parameters:
    `in` - the input data.
    `inOffset` - the offset into in specifying where the data starts.
    `inLen` - the length of the subarray.
    `out` - the output array.
    `outOffset` - the offset indicating where to start writing into the out array.
  Returns:
    the number of bytes written.
  Throws:
    CryptixException - if the native library is being used, and it reports an error.

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Copyright (C) 1995-2000 The Cryptix Foundation Ltd. All rights reserved.