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cryptix.jce.provider.cipher
Class ModeOpenpgpCFB  

java.lang.Object
  cryptix.jce.provider.cipher.Mode
      cryptix.jce.provider.cipher.ModeCFB
          cryptix.jce.provider.cipher.ModeOpenpgpCFB

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class ModeOpenpgpCFB

extends ModeCFB

This mode implements the special CFB mode used by the OpenPGP standard (RFC 2440)

Due to the design of the JCE, it is not completely the OpenPGP CFB mode though. OpenPGP specifies that blocksize+2 bytes need to be prefixed to the encrypted data, consisting of blocksize bytes of random data and then repeating the last two bytes of this random data to make it possible to check whether we're decrypting with the right key.

Now the question is, where should this data be added and thus also where should this check be done. Inside this mode object would be the obvious choice, such that applications need not to bother themselves with this quirk. However there's no way to throw an Exception if the check fails. The only possibility is a RuntimeException and that's not really how it should work.

So the application needs to do the check, which means the application has to pass in this random data on encryption and it needs to retrieve it back on decryption. For passing it in on encryption, JCE has so called AlgorithmParameterSpec objects which would be perfect for this job. However, there is no way for the application to retrieve it again at decryption time and therefore no way to check it.

So the only way to do this is if the application handles the prefix. This mode then only takes care of the resynchronization at blocksize+2 bytes. It's not ideal and not how is should work, but it's the only thing possible within the JCE.

Version:

$Revision: 1.2 $

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Field Summary
protected  int	bufCount           How many bytes the buffer holds
protected  long	byteCount           How many bytes we have processed.
protected  BlockCipher	cipher           Underlying block cipher
protected  int	CIPHER_BLOCK_SIZE           Block size of underlying cipher
private  long	extraCrankCount           Holds byteCount where the OpenPGP CFB extra crank is required.

 

Constructor Summary
(package private)	ModeOpenpgpCFB(BlockCipher cipher)

 

Method Summary
(package private)  byte[]	coreGetIV()
(package private)  int	coreGetOutputSize(int inputLen)
(package private)  java.security.spec.AlgorithmParameterSpec	coreGetParamSpec()
(package private)  void	coreInit(boolean decrypt, java.security.Key key, java.security.spec.AlgorithmParameterSpec params, java.security.SecureRandom random)
(package private)  int	coreUpdate(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset)
protected  byte[]	extractIV(java.security.spec.AlgorithmParameterSpec params)
protected  byte[]	generateIV()
(package private)  int	getBlockSize()
(package private)  int	getBufSize()
(package private) static Mode	getInstance(java.lang.String mode, BlockCipher cipher)
(package private)  byte[]	getIV()
(package private)  int	getOutputSize(int inputLen)
(package private)  java.security.spec.AlgorithmParameterSpec	getParamSpec()
(package private)  void	init(boolean decrypt, java.security.Key key, java.security.spec.AlgorithmParameterSpec params, java.security.SecureRandom random)
protected  boolean	needCrank()           Sync policy, can be overridden in subclasses.
(package private)  boolean	needsPadding()
(package private)  int	update(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset)

 

Methods inherited from class java.lang.Object

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

 

Field Detail

extraCrankCount

private final long extraCrankCount

Holds byteCount where the OpenPGP CFB extra crank is required. OpenPGP CFB mode specifies that an extra shift register encryption (crank) occurs at CIPHER_BLOCK_SIZE+2 bytes.

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byteCount

protected long byteCount

How many bytes we have processed. Used to determine when to 'sync'.

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cipher

protected final BlockCipher cipher

Underlying block cipher

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CIPHER_BLOCK_SIZE

protected final int CIPHER_BLOCK_SIZE

Block size of underlying cipher

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bufCount

protected int bufCount

How many bytes the buffer holds

Constructor Detail

ModeOpenpgpCFB

ModeOpenpgpCFB(BlockCipher cipher)

Method Detail

needCrank

protected boolean needCrank()

Description copied from class: ModeCFB

Sync policy, can be overridden in subclasses.

Overrides:

needCrank in class ModeCFB

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coreGetOutputSize

final int coreGetOutputSize(int inputLen)

Specified by:

coreGetOutputSize in class Mode

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coreInit

void coreInit(boolean decrypt,
              java.security.Key key,
              java.security.spec.AlgorithmParameterSpec params,
              java.security.SecureRandom random)
        throws java.security.InvalidKeyException,
               java.security.InvalidAlgorithmParameterException

Specified by:

coreInit in class Mode

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coreUpdate

int coreUpdate(byte[] input,
               int inputOffset,
               int inputLen,
               byte[] output,
               int outputOffset)

Specified by:

coreUpdate in class Mode

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coreGetIV

final byte[] coreGetIV()

Specified by:

coreGetIV in class Mode

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coreGetParamSpec

final java.security.spec.AlgorithmParameterSpec coreGetParamSpec()

Specified by:

coreGetParamSpec in class Mode

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needsPadding

final boolean needsPadding()

Specified by:

needsPadding in class Mode

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getInstance

static Mode getInstance(java.lang.String mode,
                        BlockCipher cipher)
                 throws java.security.NoSuchAlgorithmException

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init

void init(boolean decrypt,
          java.security.Key key,
          java.security.spec.AlgorithmParameterSpec params,
          java.security.SecureRandom random)
    throws java.security.InvalidKeyException,
           java.security.InvalidAlgorithmParameterException

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getIV

final byte[] getIV()

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getParamSpec

final java.security.spec.AlgorithmParameterSpec getParamSpec()

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getOutputSize

final int getOutputSize(int inputLen)

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getBlockSize

final int getBlockSize()

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update

final int update(byte[] input,
                 int inputOffset,
                 int inputLen,
                 byte[] output,
                 int outputOffset)

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getBufSize

final int getBufSize()

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generateIV

protected byte[] generateIV()

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extractIV

protected final byte[] extractIV(java.security.spec.AlgorithmParameterSpec params)
                          throws java.security.InvalidAlgorithmParameterException

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> cryptix >> jce >> provider >> [ cipher overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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