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3.1 The IMode Interface

The IMode interface is similar to the IBlockCipher interface, except modes have a state associated with them, e.g. whether the instance is used for encryption or decryption. The IMode interface is usually the one that is used when encrypting or decrypting; IBlockCipher is used when the lowest level—the cipher function itself—needs to be accessed. IMode extends IBlockCipher interface, and thus all methods specified in that interface are implemented in modes, and have the same meaning. The properties passed to the init method of IBlockCipher may also be passed to the init mehtod of IMode, along with the following property names.

diagrams/mode_class_diag.png

Figure 2: Modes class diagram
— Variable: java.lang.String STATE

The property name for the mode's state, as passed to the init method. Values for this property are an java.lang.Integer containing either the ENCRYPTION constant or the DECRYPTION constant.

— Variable: int ENCRYPTION

The value passed for the STATE property, wrapped in a java.lang.Integer, which indicates that the instance is to be used for encryption.

— Variable: int DECRYPTION

The value passed for the STATE property, wrapped in a java.lang.Integer, which indicates that the instance is to be used for decryption.

— Variable: java.lang.String MODE_BLOCK_SIZE

The property name for the block size of this mode. The value for this propery should be a java.lang.Integer of the block size. If omitted, the underlying cipher's block size is used.

— Variable: java.lang.String IV

The property name for the initialization vector to initialize this mode with, if required. The value should be a byte array equal in size to the MODE_BLOCK_SIZE property. If omitted a byte array consisting of zeros is used.

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

Transforms the block in in starting at inOffset into the block in out starting at outOffset. Encryption or decryption is performed depending upon the value passed along with the state property given to the init method. A java.lang.IllegalStateException is thrown if this instance has not been initialized, and it is up to the programmer to ensure that there is one full block in in starting at inOffset, and enough space for one full block in out starting at outOffset. Since modes can have states, and may require that the be used in a particular sequence, using this method is preferred over the encryptBlock and decryptBlock methods of IBlockCipher.