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. * *
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.
*
* @author Li Gong
* @see java.io.OutputStream
* @see java.io.FilterOutputStream
* @see javax.crypto.Cipher
* @see javax.crypto.CipherInputStream
*
* @since 1.4
*/
public class CipherOutputStream extends FilterOutputStream {
// the cipher engine to use to process stream data
private Cipher cipher;
// the underlying output stream
private OutputStream output;
/* the buffer holding one byte of incoming data */
private byte[] ibuffer = new byte[1];
// the buffer holding data ready to be written out
private byte[] obuffer;
/**
*
* 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.
*
* @param os the OutputStream object
* @param c an initialized Cipher object
*/
public CipherOutputStream(OutputStream os, Cipher c) {
super(os);
output = os;
cipher = c;
};
/**
* 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.
*
* @param os the OutputStream object
*/
protected CipherOutputStream(OutputStream os) {
super(os);
output = os;
cipher = new NullCipher();
}
/**
* Writes the specified byte to this output stream.
*
* @param b the byte.
* @exception IOException if an I/O error occurs.
* @since JCE1.2
*/
public void write(int b) throws IOException {
ibuffer[0] = (byte) b;
obuffer = cipher.update(ibuffer, 0, 1);
if (obuffer != null) {
output.write(obuffer);
obuffer = null;
}
};
/**
* 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.
*
* @param b the data.
* @exception NullPointerException if b is null.
* @exception IOException if an I/O error occurs.
* @see javax.crypto.CipherOutputStream#write(byte[], int, int)
* @since JCE1.2
*/
public void write(byte b[]) throws IOException {
write(b, 0, b.length);
}
/**
* Writes len bytes from the specified byte array
* starting at offset off to this output stream.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @exception IOException if an I/O error occurs.
* @since JCE1.2
*/
public void write(byte b[], int off, int len) throws IOException {
obuffer = cipher.update(b, off, len);
if (obuffer != null) {
output.write(obuffer);
obuffer = null;
}
}
/**
* 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.
*
* @exception IOException if an I/O error occurs.
* @since JCE1.2
*/
public void flush() throws IOException {
if (obuffer != null) {
output.write(obuffer);
obuffer = null;
}
output.flush();
}
/**
* 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.
*
* @exception IOException if an I/O error occurs.
* @since JCE1.2
*/
public void close() throws IOException {
try {
obuffer = cipher.doFinal();
} catch (IllegalBlockSizeException e) {
obuffer = null;
} catch (BadPaddingException e) {
obuffer = null;
}
try {
flush();
} catch (IOException ignored) {}
out.close();
}
}