/**
* Performs decryption operation for the last time.
*
* <p>NOTE: For cipher feedback modes which does not perform special handling for the last few
* blocks, this is essentially the same as <code>encrypt(...)</code>. Given most modes do not do
* special handling, the default impl for this method is to simply call <code>decrypt(...)</code>.
*
* @param in the input buffer with the data to be decrypted
* @param inOfs the offset in <code>cipher</code>
* @param len the length of the input data
* @param out the buffer for the decryption result
* @param outOfs the offset in <code>plain</code>
* @return the number of bytes placed into the <code>out</code> buffer
*/
int decryptFinal(byte[] in, int inOfs, int len, byte[] out, int outOfs)
throws IllegalBlockSizeException, AEADBadTagException, ShortBufferException {
if (len < tagLenBytes) {
throw new AEADBadTagException("Input too short - need tag");
}
if (out.length - outOfs < ((ibuffer.size() + len) - tagLenBytes)) {
throw new ShortBufferException("Output buffer too small");
}
processAAD();
if (len != 0) {
ibuffer.write(in, inOfs, len);
}
// refresh 'in' to all buffered-up bytes
in = ibuffer.toByteArray();
inOfs = 0;
len = in.length;
ibuffer.reset();
byte[] tag = new byte[tagLenBytes];
// get the trailing tag bytes from 'in'
System.arraycopy(in, len - tagLenBytes, tag, 0, tagLenBytes);
len -= tagLenBytes;
if (len > 0) {
doLastBlock(in, inOfs, len, out, outOfs, false);
}
byte[] lengthBlock = getLengthBlock(sizeOfAAD * 8, processed * 8);
ghashAllToS.update(lengthBlock);
byte[] s = ghashAllToS.digest();
byte[] sOut = new byte[s.length];
GCTR gctrForSToTag = new GCTR(embeddedCipher, this.preCounterBlock);
gctrForSToTag.doFinal(s, 0, s.length, sOut, 0);
for (int i = 0; i < tagLenBytes; i++) {
if (tag[i] != sOut[i]) {
throw new AEADBadTagException("Tag mismatch!");
}
}
return len;
}
/**
* Performs encryption operation for the last time.
*
* @param in the input buffer with the data to be encrypted
* @param inOfs the offset in <code>in</code>
* @param len the length of the input data
* @param out the buffer for the encryption result
* @param outOfs the offset in <code>out</code>
* @return the number of bytes placed into the <code>out</code> buffer
*/
int encryptFinal(byte[] in, int inOfs, int len, byte[] out, int outOfs)
throws IllegalBlockSizeException, ShortBufferException {
if (out.length - outOfs < (len + tagLenBytes)) {
throw new ShortBufferException("Output buffer too small");
}
processAAD();
if (len > 0) {
doLastBlock(in, inOfs, len, out, outOfs, true);
}
byte[] lengthBlock = getLengthBlock(sizeOfAAD * 8, processed * 8);
ghashAllToS.update(lengthBlock);
byte[] s = ghashAllToS.digest();
byte[] sOut = new byte[s.length];
GCTR gctrForSToTag = new GCTR(embeddedCipher, this.preCounterBlock);
gctrForSToTag.doFinal(s, 0, s.length, sOut, 0);
System.arraycopy(sOut, 0, out, (outOfs + len), tagLenBytes);
return (len + tagLenBytes);
}
// Utility to process the last block; used by encryptFinal and decryptFinal
void doLastBlock(byte[] in, int inOfs, int len, byte[] out, int outOfs, boolean isEncrypt)
throws IllegalBlockSizeException {
// process data in 'in'
gctrPAndC.doFinal(in, inOfs, len, out, outOfs);
processed += len;
byte[] ct;
int ctOfs;
if (isEncrypt) {
ct = out;
ctOfs = outOfs;
} else {
ct = in;
ctOfs = inOfs;
}
int lastLen = len % AES_BLOCK_SIZE;
if (lastLen != 0) {
ghashAllToS.update(ct, ctOfs, len - lastLen);
byte[] padded = expandToOneBlock(ct, (ctOfs + len - lastLen), lastLen);
ghashAllToS.update(padded);
} else {
ghashAllToS.update(ct, ctOfs, len);
}
}