gnu.crypto.mode
Interface IMode

All Superinterfaces:

java.lang.Cloneable, IBlockCipher

All Known Implementing Classes:

BaseMode

public interface IMode

extends IBlockCipher

The basic visible methods of any block cipher mode.

Block ciphers encrypt plaintext in fixed size n-bit blocks. For messages larger than n bits, the simplest approach is to segment the message into n-bit blocks and process (encrypt and/or decrypt) each one separately (Electronic Codebook or ECB mode). But this approach has disadvantages in most applications. The block cipher modes of operations are one way of working around those disadvantages.

A Mode always employs an underlying block cipher for processing its input. For all intents and purposes, a Mode appears to behave as any other block cipher with the following differences:

• Depending on the specifications of the mode, the block size may be different that that of the underlying cipher.
• While some modes of operations allow operations on block sizes that can be 1-bit long, this library will only deal with sizes that are multiple of 8 bits. This is because the byte is the smallest, easy to handle, primitive type in Java.
• Some modes need an Initialisation Vector (IV) to be properly initialised.

Possible additional initialisation values for an instance of that type are:

• The block size in which to operate this mode instance. This value is optional, if unspecified, the underlying block cipher's configured block size shall be used.
• Whether this mode will be used for encryption or decryption. This value is mandatory and should be included in the initialisation parameters. If it isn't, a IllegalStateException will be thrown if any method, other than reset() is invoked on the instance.
• The byte array containing the initialisation vector, if required by this type of mode.

Version:

$Revision: 1.2 $

Field Summary

static int	DECRYPTION Constant indicating the instance is being used for decryption.
static int	ENCRYPTION Constant indicating the instance is being used for encryption.
static java.lang.String	IV Property name of the initialisation vector to use, if required, with this instance.
static java.lang.String	MODE_BLOCK_SIZE Property name of the block size in which to operate this mode.
static java.lang.String	STATE Property name of the state in which to operate this mode.

Fields inherited from interface gnu.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Method Summary

void	update(byte[] in, int inOffset, byte[] out, int outOffset) A convenience method.

Methods inherited from interface gnu.crypto.cipher.IBlockCipher

blockSizes, clone, currentBlockSize, decryptBlock, defaultBlockSize, defaultKeySize, encryptBlock, init, keySizes, name, reset, selfTest

Field Detail

STATE

public static final java.lang.String STATE

Property name of the state in which to operate this mode. The value associated to this property name is taken to be an Integer which value is either ENCRYPTION or DECRYPTION.

See Also:

Constant Field Values

MODE_BLOCK_SIZE

public static final java.lang.String MODE_BLOCK_SIZE

Property name of the block size in which to operate this mode. The value associated with this property name is taken to be an Integer. If it is not specified, the value of the block size of the underlying block cipher, used to construct the mode instance, shall be used.

See Also:

Constant Field Values

IV

public static final java.lang.String IV

Property name of the initialisation vector to use, if required, with this instance. The value associated with this property name is taken to be a byte array. If the concrete instance needs such a parameter, and it has not been specified as part of the initialissation parameters, an all-zero byte array of the appropriate size shall be used.

See Also:

Constant Field Values

ENCRYPTION

public static final int ENCRYPTION

Constant indicating the instance is being used for encryption.

See Also:

Constant Field Values

DECRYPTION

public static final int DECRYPTION

Constant indicating the instance is being used for decryption.

See Also:

Constant Field Values

Method Detail

update

public void update(byte[] in,
                   int inOffset,
                   byte[] out,
                   int outOffset)
            throws java.lang.IllegalStateException

A convenience method. Effectively invokes the encryptBlock() or decryptBlock() method depending on the operational state of the instance.

Parameters:

in - the plaintext.

inOffset - index of in from which to start considering data.

out - the ciphertext.

outOffset - index of out from which to store result.

Throws:

java.lang.IllegalStateException - if the instance is not initialised.