* UMacGenerator requires an index parameter
* (initialisation parameter gnu.crypto.prng.umac.kdf.index taken
* to be an instance of {@link Integer} with a value between 0 and
* 255). Using the same key, but different indices, generates
* different pseudorandom outputs.
*
* This implementation generalises the definition of the
* UmacGenerator algorithm to allow for other than the AES
* symetric key block cipher algorithm (initialisation parameter
* gnu.crypto.prng.umac.cipher.name taken to be an instance of
* {@link String}). If such a parameter is not defined/included in the
* initialisation Map, then the "Rijndael" algorithm is used.
* Furthermore, if the initialisation parameter
* gnu.crypto.cipher.block.size (taken to be a instance of
* {@link Integer}) is missing or undefined in the initialisation
* Map, then the cipher's default block size is used.
*
* NOTE: Rijndael is used as the default symmetric key block cipher * algorithm because, with its default block and key sizes, it is the AES. Yet * being Rijndael, the algorithm offers more versatile block and key sizes which * may prove to be useful for generating "longer" key streams. *
* References: *
index value to use in this
* instance. The value is taken to be an {@link Integer} less than
* 256.
*/
public static final String INDEX = "gnu.crypto.prng.umac.index";
/** The name of the underlying symmetric key block cipher algorithm. */
public static final String CIPHER = "gnu.crypto.prng.umac.cipher.name";
/** The generator's underlying block cipher. */
private IBlockCipher cipher;
/** Trivial 0-arguments constructor. */
public UMacGenerator()
{
super(Registry.UMAC_PRNG);
}
public void setup(Map attributes)
{
boolean newCipher = true;
String cipherName = (String) attributes.get(CIPHER);
if (cipherName == null)
if (cipher == null) // happy birthday
cipher = CipherFactory.getInstance(Registry.RIJNDAEL_CIPHER);
else // we already have one. use it as is
newCipher = false;
else
cipher = CipherFactory.getInstance(cipherName);
// find out what block size we should use it in
int cipherBlockSize = 0;
Integer bs = (Integer) attributes.get(IBlockCipher.CIPHER_BLOCK_SIZE);
if (bs != null)
cipherBlockSize = bs.intValue();
else
{
if (newCipher) // assume we'll use its default block size
cipherBlockSize = cipher.defaultBlockSize();
// else use as is
}
// get the key material
byte[] key = (byte[]) attributes.get(IBlockCipher.KEY_MATERIAL);
if (key == null)
throw new IllegalArgumentException(IBlockCipher.KEY_MATERIAL);
int keyLength = key.length;
// ensure that keyLength is valid for the chosen underlying cipher
boolean ok = false;
for (Iterator it = cipher.keySizes(); it.hasNext();)
{
ok = (keyLength == ((Integer) it.next()).intValue());
if (ok)
break;
}
if (! ok)
throw new IllegalArgumentException("key length");
// ensure that remaining params make sense
int index = -1;
Integer i = (Integer) attributes.get(INDEX);
if (i != null)
{
index = i.intValue();
if (index < 0 || index > 255)
throw new IllegalArgumentException(INDEX);
}
// now initialise the underlying cipher
Map map = new HashMap();
if (cipherBlockSize != 0) // only needed if new or changed
map.put(IBlockCipher.CIPHER_BLOCK_SIZE, Integer.valueOf(cipherBlockSize));
map.put(IBlockCipher.KEY_MATERIAL, key);
try
{
cipher.init(map);
}
catch (InvalidKeyException x)
{
throw new IllegalArgumentException(IBlockCipher.KEY_MATERIAL);
}
buffer = new byte[cipher.currentBlockSize()];
buffer[cipher.currentBlockSize() - 1] = (byte) index;
try
{
fillBlock();
}
catch (LimitReachedException impossible)
{
}
}
public void fillBlock() throws LimitReachedException
{
cipher.encryptBlock(buffer, 0, buffer, 0);
}
}