1 package org.bouncycastle.crypto.modes.gcm; 2 3 import java.util.Vector; 4 5 import org.bouncycastle.util.Arrays; 6 7 public class Tables1kGCMExponentiator implements GCMExponentiator 8 { 9 // A lookup table of the power-of-two powers of 'x' 10 // - lookupPowX2[i] = x^(2^i) 11 private Vector lookupPowX2; 12 13 public void init(byte[] x) 14 { 15 int[] y = GCMUtil.asInts(x); 16 if (lookupPowX2 != null && Arrays.areEqual(y, (int[])lookupPowX2.elementAt(0))) 17 { 18 return; 19 } 20 21 lookupPowX2 = new Vector(8); 22 lookupPowX2.addElement(y); 23 } 24 25 public void exponentiateX(long pow, byte[] output) 26 { 27 int[] y = GCMUtil.oneAsInts(); 28 int bit = 0; 29 while (pow > 0) 30 { 31 if ((pow & 1L) != 0) 32 { 33 ensureAvailable(bit); 34 GCMUtil.multiply(y, (int[])lookupPowX2.elementAt(bit)); 35 } 36 ++bit; 37 pow >>>= 1; 38 } 39 40 GCMUtil.asBytes(y, output); 41 } 42 43 private void ensureAvailable(int bit) 44 { 45 int count = lookupPowX2.size(); 46 if (count <= bit) 47 { 48 int[] tmp = (int[])lookupPowX2.elementAt(count - 1); 49 do 50 { 51 tmp = Arrays.clone(tmp); 52 GCMUtil.multiply(tmp, tmp); 53 lookupPowX2.addElement(tmp); 54 } 55 while (++count <= bit); 56 } 57 } 58 } 59
