diff options
Diffstat (limited to 'bcprov/src/main/java/org/bouncycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java')
-rw-r--r-- | bcprov/src/main/java/org/bouncycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java b/bcprov/src/main/java/org/bouncycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java new file mode 100644 index 0000000..a051208 --- /dev/null +++ b/bcprov/src/main/java/org/bouncycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java @@ -0,0 +1,57 @@ +package org.bouncycastle.crypto.modes.gcm; + +import java.util.Vector; + +import org.bouncycastle.util.Arrays; + +public class Tables1kGCMExponentiator implements GCMExponentiator +{ + // A lookup table of the power-of-two powers of 'x' + // - lookupPowX2[i] = x^(2^i) + private Vector lookupPowX2; + + public void init(byte[] x) + { + if (lookupPowX2 != null && Arrays.areEqual(x, (byte[])lookupPowX2.elementAt(0))) + { + return; + } + + lookupPowX2 = new Vector(8); + lookupPowX2.addElement(Arrays.clone(x)); + } + + public void exponentiateX(long pow, byte[] output) + { + byte[] y = GCMUtil.oneAsBytes(); + int bit = 0; + while (pow > 0) + { + if ((pow & 1L) != 0) + { + ensureAvailable(bit); + GCMUtil.multiply(y, (byte[])lookupPowX2.elementAt(bit)); + } + ++bit; + pow >>>= 1; + } + + System.arraycopy(y, 0, output, 0, 16); + } + + private void ensureAvailable(int bit) + { + int count = lookupPowX2.size(); + if (count <= bit) + { + byte[] tmp = (byte[])lookupPowX2.elementAt(count - 1); + do + { + tmp = Arrays.clone(tmp); + GCMUtil.multiply(tmp, tmp); + lookupPowX2.addElement(tmp); + } + while (++count <= bit); + } + } +} |