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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.6.
package org.bouncycastle.crypto.modes.gcm;
import org.bouncycastle.crypto.util.Pack;
abstract class GCMUtil
{
static int[] asInts(byte[] bs)
{
int[] us = new int[4];
us[0] = Pack.bigEndianToInt(bs, 0);
us[1] = Pack.bigEndianToInt(bs, 4);
us[2] = Pack.bigEndianToInt(bs, 8);
us[3] = Pack.bigEndianToInt(bs, 12);
return us;
}
// P is the value with only bit i=1 set
static void multiplyP(int[] x)
{
boolean lsb = (x[3] & 1) != 0;
shiftRight(x);
if (lsb)
{
// R = new int[]{ 0xe1000000, 0, 0, 0 };
// xor(v, R);
x[0] ^= 0xe1000000;
}
}
static void multiplyP8(int[] x)
{
for (int i = 8; i != 0; --i)
{
multiplyP(x);
}
}
static void shiftRight(byte[] block)
{
int i = 0;
int bit = 0;
for (;;)
{
int b = block[i] & 0xff;
block[i] = (byte) ((b >>> 1) | bit);
if (++i == 16)
break;
bit = (b & 1) << 7;
}
}
static void shiftRight(int[] block)
{
int i = 0;
int bit = 0;
for (;;)
{
int b = block[i];
block[i] = (b >>> 1) | bit;
if (++i == 4) break;
bit = b << 31;
}
}
static void xor(byte[] block, byte[] val)
{
for (int i = 15; i >= 0; --i)
{
block[i] ^= val[i];
}
}
static void xor(int[] block, int[] val)
{
for (int i = 3; i >= 0; --i)
{
block[i] ^= val[i];
}
}
}