xjava.security

Class CipherOutputStream

java.lang.Object

java.io.OutputStream

java.io.FilterOutputStream

xjava.security.CipherOutputStream

All Implemented Interfaces:

java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable

public class CipherOutputStream
extends java.io.FilterOutputStream

A FilterOutputStream that encrypts or decrypts the data passing through it.

This class has a constructor that takes a Cipher and an output stream as arguments. The cipher is used to encrypt or decrypt all data supplied via calls to one of the write methods. The encryption/decryption result is written to the output stream.

For block ciphers, a buffer is used for receiving the data to be encrypted or decrypted. The maximum number of bytes that may be buffered at any given time is given by the getBufferSize method. For byte-oriented stream ciphers, no buffering is done (and getBufferSize() returns 0).

To supply the bytes that need to be encrypted/decrypted, make one or more calls to one of the write methods. After you have supplied all the data, call close() to ensure final processing is done.

Note: JavaSoft's JCE required calling flush for final processing, rather than close. However, if you call flush and then write more data, there will not be sufficient information available when reading in the stream (e.g. using CipherInputStream), to determine when the flush happened. Unpadding can only work correctly if no further data is written after the final processing, which means that close is the right method to trigger this processing. I'm not sure whether JavaSoft's implementation works if only close is called, but calling flush followed by close should work in both implementations.

With a cipher in the ENCRYPT state, the number of bytes not yet encrypted and written to the stream is kept between 0 and cipher.getPlaintextBlockSize()-1 inclusive. When close is called, the final data is padded, encrypted, and the result written to the output stream. If the cipher's padding scheme is NONE and the final data does not comprise a complete plaintext block, an IllegalBlockSizeException is thrown.

With a cipher in the DECRYPT state, [DOCUMENT ME]. When close is called, an exact number of ciphertext blocks should be in the buffer (otherwise an IllegalBlockSizeException is thrown). Those blocks are decrypted, unpadded, and written to the output stream.

Note: calling methods of a cipher while it is being used by a CipherInputStream (apart from methods that have no side-effects, like getAlgorithm(), get*BlockSize(), etc.) will probably result in incorrect or unexpected output.

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

$Revision: 1.6 $

See Also:

java.security.Cipher, java.security.Cipher#getInputBlockSize, java.security.Cipher#getOutputBlockSize, java.security.CipherInputStream

Field Summary

Fields inherited from class java.io.FilterOutputStream

out

Constructor Summary

Constructors

Constructor and Description
CipherOutputStream(java.io.OutputStream os, Cipher cipher) Constructs an output stream using a cipher that must be initialized for either encryption or decryption, that is, a cipher whose state is either ENCRYPT or DECRYPT.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the output stream.
void	flush() Flushes the underlying output stream.
void	write(byte[] in, int offset, int length) Supplies bytes to be used for encryption or decryption, depending on the cipher state.
void	write(int b) Supplies a byte to be used for encryption or decryption, depending on the cipher state.

Methods inherited from class java.io.FilterOutputStream

write

Methods inherited from class java.lang.Object

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

Constructor Detail

CipherOutputStream

public CipherOutputStream(java.io.OutputStream os,
                          Cipher cipher)

Constructs an output stream using a cipher that must be initialized for either encryption or decryption, that is, a cipher whose state is either ENCRYPT or DECRYPT.

Parameters:

os - the output stream.

cipher - an initialized cipher.

Throws:

java.lang.NullPointerException - if os == null || cipher == null

Method Detail

write

public void write(byte[] in,
                  int offset,
                  int length)
           throws java.io.IOException

Supplies bytes to be used for encryption or decryption, depending on the cipher state.

Overrides:

write in class java.io.FilterOutputStream

Parameters:

in - the buffer containing the bytes to be used for encryption or decryption.

offset - the offset into in indicating the location of the first byte to be used.

length - the number of bytes to read from in, starting at offset offset.

Throws:

java.lang.ArrayIndexOutOfBoundsException - if (long)offset + length > in.length

java.io.IOException - if an error occurs, or the stream has already been closed.

write

public void write(int b)
           throws java.io.IOException

Supplies a byte to be used for encryption or decryption, depending on the cipher state.

Overrides:

write in class java.io.FilterOutputStream

Parameters:

b - the byte to be used for encryption or decryption.

Throws:

java.io.IOException - if an error occurs.

flush

public void flush()
           throws java.io.IOException

Flushes the underlying output stream. Unlike JavaSoft's implementation, this never writes any further data to the stream. To make sure that all data has been written, call close().

Specified by:

flush in interface java.io.Flushable

Overrides:

flush in class java.io.FilterOutputStream

Throws:

java.io.IOException - if an error occurs.

close

public void close()
           throws java.io.IOException

Closes the output stream. Before it is closed, buffered data is processed, taking into account padding, and the result is written to the stream.

For an encrypter stream, any buffered data is encrypted and the result written to the output stream. If the padding scheme is not "NONE", the data is padded before encryption. If the padding scheme is "NONE" and the final data does not comprise a complete block, an IllegalBlockSize exception is thrown.

For a decrypter stream, when close is called, exactly one block should be in the buffer. It is decrypted, unpadded, and written out.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Overrides:

close in class java.io.FilterOutputStream

Throws:

java.io.IOException - if an error occurs.