private void gCTRBlock(byte[] block, byte[] out, int outOff) {
byte[] tmp = getNextCounterBlock();
GCMUtil.xor(tmp, block);
System.arraycopy(tmp, 0, out, outOff, BLOCK_SIZE);
gHASHBlock(S, forEncryption ? tmp : block);
totalLength += BLOCK_SIZE;
}
private void gCTRPartial(byte[] buf, int off, int len, byte[] out, int outOff) {
byte[] tmp = getNextCounterBlock();
GCMUtil.xor(tmp, buf, off, len);
System.arraycopy(tmp, 0, out, outOff, len);
gHASHPartial(S, forEncryption ? tmp : buf, 0, len);
totalLength += len;
}
private void gHASHPartial(byte[] Y, byte[] b, int off, int len) {
GCMUtil.xor(Y, b, off, len);
multiplier.multiplyH(Y);
}
private void gHASHBlock(byte[] Y, byte[] b) {
GCMUtil.xor(Y, b);
multiplier.multiplyH(Y);
}
@Override
public int doFinal(byte[] out, int outOff)
throws IllegalStateException, InvalidCipherTextException {
if (totalLength == 0) {
initCipher();
}
int extra = bufOff;
if (forEncryption) {
if (out.length < (outOff + extra + macSize)) {
throw new OutputLengthException("Output buffer too short");
}
} else {
if (extra < macSize) {
throw new InvalidCipherTextException("data too short");
}
extra -= macSize;
if (out.length < (outOff + extra)) {
throw new OutputLengthException("Output buffer too short");
}
}
if (extra > 0) {
gCTRPartial(bufBlock, 0, extra, out, outOff);
}
atLength += atBlockPos;
if (atLength > atLengthPre) {
/*
* Some AAD was sent after the cipher started. We determine the difference b/w the hash value
* we actually used when the cipher started (S_atPre) and the final hash value calculated
* (S_at). Then we carry this difference forward by multiplying by H^c, where c is the number
* of (full or partial) cipher-text blocks produced, and adjust the current hash.
*/
// Finish hash for partial AAD block
if (atBlockPos > 0) {
gHASHPartial(S_at, atBlock, 0, atBlockPos);
}
// Find the difference between the AAD hashes
if (atLengthPre > 0) {
GCMUtil.xor(S_at, S_atPre);
}
// Number of cipher-text blocks produced
long c = ((totalLength * 8) + 127) >>> 7;
// Calculate the adjustment factor
byte[] H_c = new byte[16];
if (exp == null) {
exp = new Tables1kGCMExponentiator();
exp.init(H);
}
exp.exponentiateX(c, H_c);
// Carry the difference forward
GCMUtil.multiply(S_at, H_c);
// Adjust the current hash
GCMUtil.xor(S, S_at);
}
// Final gHASH
byte[] X = new byte[BLOCK_SIZE];
Pack.longToBigEndian(atLength * 8, X, 0);
Pack.longToBigEndian(totalLength * 8, X, 8);
gHASHBlock(S, X);
// T = MSBt(GCTRk(J0,S))
byte[] tag = new byte[BLOCK_SIZE];
cipher.processBlock(J0, 0, tag, 0);
GCMUtil.xor(tag, S);
int resultLen = extra;
// We place into macBlock our calculated value for T
this.macBlock = new byte[macSize];
System.arraycopy(tag, 0, macBlock, 0, macSize);
if (forEncryption) {
// Append T to the message
System.arraycopy(macBlock, 0, out, outOff + bufOff, macSize);
resultLen += macSize;
} else {
// Retrieve the T value from the message and compare to calculated one
byte[] msgMac = new byte[macSize];
System.arraycopy(bufBlock, extra, msgMac, 0, macSize);
if (!Arrays.constantTimeAreEqual(this.macBlock, msgMac)) {
throw new InvalidCipherTextException("mac check in GCM failed");
}
}
reset(false);
return resultLen;
}
