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package javax.crypto;
import java.io.*;
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 overridden 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 Also: Since: 1.4
/**
* 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.
*
* <p> For example, if the cipher is initialized for encryption, the
* CipherOutputStream will attempt to encrypt data before writing out the
* encrypted data.
*
* <p> 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.
*
* <p> It is crucial for a programmer using this class not to use
* methods that are not defined or overridden 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;
// stream status
private boolean closed = false;
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.
Params: - os – the OutputStream object
- c – an initialized Cipher object
/**
*
* Constructs a CipherOutputStream from an OutputStream and a
* Cipher.
* <br>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.
Params: - os – the OutputStream object
/**
* Constructs a CipherOutputStream from an OutputStream without
* specifying a Cipher. This has the effect of constructing a
* CipherOutputStream using a NullCipher.
* <br>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.
Params: - b – the
byte.
Throws: - IOException – if an I/O error occurs.
/**
* Writes the specified byte to this output stream.
*
* @param b the <code>byte</code>.
* @exception IOException if an I/O error occurs.
*/
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.
Params: - b – the data.
Throws: - NullPointerException – if
b is null. - IOException – if an I/O error occurs.
See Also:
/**
* Writes <code>b.length</code> bytes from the specified byte array
* to this output stream.
* <p>
* The <code>write</code> method of
* <code>CipherOutputStream</code> calls the <code>write</code>
* method of three arguments with the three arguments
* <code>b</code>, <code>0</code>, and <code>b.length</code>.
*
* @param b the data.
* @exception NullPointerException if <code>b</code> is null.
* @exception IOException if an I/O error occurs.
* @see javax.crypto.CipherOutputStream#write(byte[], int, int)
*/
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.
Params: - 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.
/**
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> 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.
*/
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.
Throws: - IOException – if an I/O error occurs.
/**
* Flushes this output stream by forcing any buffered output bytes
* that have already been processed by the encapsulated cipher object
* to be written out.
*
* <p>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 <code>write</code> methods is less than
* the cipher's block size, no bytes will be written out.
*
* @exception IOException if an I/O error occurs.
*/
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.
Throws: - IOException – if an I/O error occurs.
/**
* Closes this output stream and releases any system resources
* associated with this stream.
* <p>
* This method invokes the <code>doFinal</code> 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
* <code>flush</code> method of this output stream.
* <p>
* This method resets the encapsulated cipher object to its initial state
* and calls the <code>close</code> method of the underlying output
* stream.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {
if (closed) {
return;
}
closed = true;
try {
obuffer = cipher.doFinal();
} catch (IllegalBlockSizeException | BadPaddingException e) {
obuffer = null;
}
try {
flush();
} catch (IOException ignored) {}
out.close();
}
}