Class CipherOutputStream

java.lang.Object
- java.io.OutputStream
- - java.io.FilterOutputStream
  - - javax.crypto.CipherOutputStream

All Implemented Interfaces:: Closeable, Flushable, AutoCloseable

public class CipherOutputStream
extends FilterOutputStream

A CipherOutputStream is composed of an OutputStream and a Cipher so that write() methods first process the data before writing them out to the underlying OutputStream. The cipher must be fully initialized before being used by a CipherOutputStream.

For example, if the cipher is initialized for encryption, the CipherOutputStream will attempt to encrypt data before writing out the encrypted data.

This class adheres strictly to the semantics, especially the failure semantics, of its ancestor classes java.io.OutputStream and java.io.FilterOutputStream. This class has exactly those methods specified in its ancestor classes, and overrides them all. Moreover, this class catches all exceptions that are not thrown by its ancestor classes. In particular, this class catches BadPaddingException and other exceptions thrown by failed integrity checks during decryption. These exceptions are not re-thrown, so the client will not be informed that integrity checks failed. Because of this behavior, this class may not be suitable for use with decryption in an authenticated mode of operation (e.g. GCM) if the application requires explicit notification when authentication fails. Such an application can use the Cipher API directly as an alternative to using this class.

It is crucial for a programmer using this class not to use methods that are not defined or overriden in this class (such as a new method or constructor that is later added to one of the super classes), because the design and implementation of those methods are unlikely to have considered security impact with regard to CipherOutputStream.

Since:: 1.4
See Also:: OutputStream, FilterOutputStream, Cipher, CipherInputStream

Field Summary

Fields declared in class java.io.FilterOutputStream

out

Constructor Summary

Constructors
Modifier	Constructor	Description
`protected`	`CipherOutputStream(OutputStream os)`	Constructs a CipherOutputStream from an OutputStream without specifying a Cipher.
	`CipherOutputStream(OutputStream os, Cipher c)`	Constructs a CipherOutputStream from an OutputStream and a Cipher.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`close()`	Closes this output stream and releases any system resources associated with this stream.
`void`	`flush()`	Flushes this output stream by forcing any buffered output bytes that have already been processed by the encapsulated cipher object to be written out.
`void`	`write(byte[] b)`	Writes `b.length` bytes from the specified byte array to this output stream.
`void`	`write(byte[] b, int off, int len)`	Writes `len` bytes from the specified byte array starting at offset `off` to this output stream.
`void`	`write(int b)`	Writes the specified byte to this output stream.

Methods declared in class java.io.OutputStream

nullOutputStream

Methods declared in class java.lang.Object

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

Constructor Detail

CipherOutputStream

public CipherOutputStream(OutputStream os,
                          Cipher c)

Constructs a CipherOutputStream from an OutputStream and a Cipher.
Note: if the specified output stream or cipher is null, a NullPointerException may be thrown later when they are used.

Parameters:: os - the OutputStream object; c - an initialized Cipher object

CipherOutputStream

protected CipherOutputStream(OutputStream os)

Constructs a CipherOutputStream from an OutputStream without specifying a Cipher. This has the effect of constructing a CipherOutputStream using a NullCipher.
Note: if the specified output stream is null, a NullPointerException may be thrown later when it is used.

Parameters:: os - the OutputStream object

Method Detail

write

public void write(int b)
           throws IOException

Writes the specified byte to this output stream.

Overrides:: write in class FilterOutputStream
Parameters:: b - the byte.
Throws:: IOException - if an I/O error occurs.

write

public void write(byte[] b)
           throws IOException

Writes b.length bytes from the specified byte array to this output stream.

The write method of CipherOutputStream calls the write method of three arguments with the three arguments b, 0, and b.length.

Overrides:: write in class FilterOutputStream
Parameters:: b - the data.
Throws:: NullPointerException - if b is null.; IOException - if an I/O error occurs.
See Also:: write(byte[], int, int)

write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException

Writes len bytes from the specified byte array starting at offset off to this output stream.

Overrides:: write in class FilterOutputStream
Parameters:: b - the data.; off - the start offset in the data.; len - the number of bytes to write.
Throws:: IOException - if an I/O error occurs.
See Also:: FilterOutputStream.write(int)

flush

public void flush()
           throws IOException

Flushes this output stream by forcing any buffered output bytes that have already been processed by the encapsulated cipher object to be written out.

Any bytes buffered by the encapsulated cipher and waiting to be processed by it will not be written out. For example, if the encapsulated cipher is a block cipher, and the total number of bytes written using one of the write methods is less than the cipher's block size, no bytes will be written out.

Specified by:: flush in interface Flushable
Overrides:: flush in class FilterOutputStream
Throws:: IOException - if an I/O error occurs.
See Also:: FilterOutputStream.out

close

public void close()
           throws IOException

Closes this output stream and releases any system resources associated with this stream.

This method invokes the doFinal method of the encapsulated cipher object, which causes any bytes buffered by the encapsulated cipher to be processed. The result is written out by calling the flush method of this output stream.

This method resets the encapsulated cipher object to its initial state and calls the close method of the underlying output stream.

Specified by:: close in interface AutoCloseable
Specified by:: close in interface Closeable
Overrides:: close in class FilterOutputStream
Throws:: IOException - if an I/O error occurs.
See Also:: FilterOutputStream.flush(), FilterOutputStream.out