/**
* Pads the input according to the RSASSA-PSS algorithm, the result is placed in output. The input
* should be 20-byte SHA1 hash of the message to be signed. This method *does not* do signing
* (encrypting) itself. Due to the randomness of this algorithm the subsequent signing may fail
* (when the result of this method is larger than the key modulus) in which case the padding
* should be attempted again.
*/
private void pssPad(
byte[] input,
short inOffset,
short hashLen,
byte[] output,
short outputOffset,
short emLen,
byte firstKeyByte)
throws CryptoException {
do {
short hLen = hashLen;
short outOffset = outputOffset;
if (hLen != SHA1_LEN
|| (short) (inOffset + hLen) > input.length
|| (short) (outOffset + emLen) > output.length) {
CryptoException.throwIt(CryptoException.ILLEGAL_VALUE);
}
short sLen = SHA1_LEN;
short psLen = (short) (emLen - sLen - hLen - 2);
Util.arrayFillNonAtomic(output, outOffset, emLen, (byte) 0x00);
md.update(output, outOffset, (short) 8);
md.update(input, inOffset, hLen);
rd.generateData(output, (short) (outOffset + psLen + 1), sLen);
md.doFinal(output, (short) (outOffset + psLen + 1), sLen, tmp, TMP_HASH_OFFSET);
output[(short) (outOffset + psLen)] = (byte) 0x01;
Util.arrayFillNonAtomic(output, outOffset, psLen, (byte) 0x00);
short hOffset = (short) (outOffset + emLen - hLen - 1);
Util.arrayCopyNonAtomic(tmp, TMP_HASH_OFFSET, output, hOffset, hLen);
output[(short) (outOffset + emLen - 1)] = (byte) 0xbc;
tmp[(short) (TMP_C_OFFSET + C_LEN - 1)] = 0;
while (outOffset < hOffset) {
md.update(output, hOffset, hLen);
md.doFinal(tmp, TMP_C_OFFSET, C_LEN, tmp, TMP_HASH_OFFSET);
if ((short) (outOffset + hLen) > hOffset) {
hLen = (short) (hOffset - outOffset);
}
for (short i = 0; i < hLen; i++) {
output[outOffset++] ^= tmp[(short) (TMP_HASH_OFFSET + i)];
}
tmp[(short) (TMP_C_OFFSET + C_LEN - 1)]++;
}
} while (firstKeyByte <= tmp[TMP_OFFSET]);
}
