/**
* Resets the cipher object to its original state. This is used when doFinal is called in the
* Cipher class, so that the cipher can be reused (with its original key and iv).
*/
void reset() {
if (aadBuffer == null) {
aadBuffer = new ByteArrayOutputStream();
} else {
aadBuffer.reset();
}
if (gctrPAndC != null) gctrPAndC.reset();
if (ghashAllToS != null) ghashAllToS.reset();
processed = 0;
sizeOfAAD = 0;
if (ibuffer != null) {
ibuffer.reset();
}
}
/**
* Initializes the cipher in the specified mode with the given key and iv.
*
* @param decrypting flag indicating encryption or decryption
* @param algorithm the algorithm name
* @param key the key
* @param iv the iv
* @param tagLenBytes the length of tag in bytes
* @exception InvalidKeyException if the given key is inappropriate for initializing this cipher
*/
void init(boolean decrypting, String algorithm, byte[] keyValue, byte[] ivValue, int tagLenBytes)
throws InvalidKeyException {
if (keyValue == null || ivValue == null) {
throw new InvalidKeyException("Internal error");
}
// always encrypt mode for embedded cipher
this.embeddedCipher.init(false, algorithm, keyValue);
this.subkeyH = new byte[AES_BLOCK_SIZE];
this.embeddedCipher.encryptBlock(new byte[AES_BLOCK_SIZE], 0, this.subkeyH, 0);
this.iv = ivValue.clone();
preCounterBlock = getJ0(iv, subkeyH);
byte[] j0Plus1 = preCounterBlock.clone();
increment32(j0Plus1);
gctrPAndC = new GCTR(embeddedCipher, j0Plus1);
ghashAllToS = new GHASH(subkeyH);
this.tagLenBytes = tagLenBytes;
if (aadBuffer == null) {
aadBuffer = new ByteArrayOutputStream();
} else {
aadBuffer.reset();
}
processed = 0;
sizeOfAAD = 0;
if (decrypting) {
ibuffer = new ByteArrayOutputStream();
}
}
/** Restores the content of this cipher to the previous saved one. */
void restore() {
processed = processedSave;
sizeOfAAD = sizeOfAADSave;
if (aadBuffer != null) {
aadBuffer.reset();
if (aadBufferSave != null) {
aadBuffer.write(aadBufferSave, 0, aadBufferSave.length);
}
}
if (gctrPAndC != null) gctrPAndC.restore();
if (ghashAllToS != null) ghashAllToS.restore();
if (ibuffer != null) {
ibuffer.reset();
ibuffer.write(ibufferSave, 0, ibufferSave.length);
}
}
/**
* 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;
}
