xjava.security
public class CipherInputStream extends FilterInputStream
This class has a constructor that takes an input stream and a Cipher as arguments. The cipher is used to encrypt or decrypt all data read through the stream.
The data is encrypted or decrypted, depending on the initialisation
state of the Cipher. To get the encryption/decryption result bytes,
make one or more calls to the read
methods. One
read
method, with no arguments,
returns the next result byte. The other
read
method returns
multiple result bytes at once.
For block ciphers, some buffering of the data received from the input stream is done. The buffer length is calculated as follows:
buffer length = cipher.getInputBlockSize() + (cipher.isPaddingBlockCipher() && cipher.getState() == Cipher.DECRYPT) ? 1 : 0Each read operation will attempt to completely fill the buffer. The maximum number of bytes that can remain unprocessed after each
read
call
is one less than the buffer length. In the case of a padding block cipher in
DECRYPT mode, this means that one full ciphertext block may remain
unprocessed, because it is necessary to read an extra byte in order to
determine whether this is the last block of the stream. (It would be
incorrect to process a block without making this check, since it may have
padding bytes that need to be stripped out.)
When EOF is reached for a padding/unpadding cipher in DECRYPT mode, the the decryption result is unpadded. If EOF is encountered part-way through a block, an IllegalBlockSizeException is thrown.
When EOF is reached for a padding/unpadding cipher in ENCRYPT mode, the last block is padded before encryption. If the cipher does not support padding and the last block is incomplete, an IllegalBlockSizeException is thrown.
For stream ciphers, that is, ciphers capable of encrypting or decrypting a byte at a time, no buffering is necessary.
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: 1.10 $
Since: IJCE 1.0.0
See Also: java.security.Cipher java.security.Cipher#getInputBlockSize java.security.Cipher#getOutputBlockSize java.security.CipherOutputStream
Constructor Summary | |
---|---|
CipherInputStream(InputStream is, Cipher cipher)
Constructs an input stream using a cipher that must be
initialised for either encryption or decryption, that is, a
cipher whose state is either ENCRYPT or
DECRYPT .
|
Method Summary | |
---|---|
int | available()
Returns the number of bytes that can be guaranteed to be read from this
input stream without blocking.
|
void | close()
Closes the input stream.
|
void | mark(int readlimit)
Does nothing, since this class does not support mark/reset. |
boolean | markSupported()
Tests if this input stream supports the mark and
reset methods of InputStream, which it does not.
|
int | read(byte[] out, int offset, int length)
Fills up the specified bytes of the out array with the next
len encrypted or decrypted bytes (depending on the cipher state).
|
int | read()
Returns the next encrypted or decrypted byte, depending on the
cipher state.
|
void | reset()
Always throws an IOException, since this class does not support mark/reset. |
long | skip(long n)
Skips over and discards n bytes of data from the
input stream. |
ENCRYPT
or
DECRYPT
.
Parameters: in the input stream. cipher an initialised cipher.
Throws: NullPointerException if is == null || cipher == null IllegalStateException if cipher.getState() == UNINITIALIZED
See Also: java.security.Cipher
Throws: IOException if an I/O error occurs.
Throws: IOException if an error occurs.
mark
and
reset
methods of InputStream, which it does not.
Returns: false
, since this class does not support the
mark
and reset
methods.
Parameters: out the byte array into which the encrypted or decrypted bytes will be read. offset the offset into out indicating where the first encrypted or decrypted byte should be read. length the number of encrypted/decrypted bytes to read.
Returns: the number of bytes read into out, or -1 if no encrypted or decrypted bytes remained.
Throws: IOException if an error occurs.
See Also: java.security.Cipher#ENCRYPT java.security.Cipher#DECRYPT java.security.Cipher#getState
Returns: the next encrypted or decrypted byte, or -1 if the last encrypted/decrypted byte was already returned.
Throws: IOException if an error occurs.
See Also: java.security.Cipher#ENCRYPT java.security.Cipher#DECRYPT java.security.Cipher#getState
skip
method may, for a variety of
reasons, end up skipping over some smaller number of bytes,
possibly 0. The actual number of bytes skipped is returned.
Parameters: n the number of bytes to be skipped.
Returns: the actual number of bytes skipped.
Throws: IOException if an I/O error occurs.