/**
* computes digest hash using specified algorithm
*
* @param message base from which the digest will be computed (i.e. file to be stamped)
* @param messageDigest algorithm used to calculate the digest
* @return calculated digest
*/
protected byte[] calculateMessageDigest(byte[] message, ExtendedDigest messageDigest) {
messageDigest.update(message, 0, message.length); // offset - '0' means start from the beginning
// digest obviously has to be computed from whole message
byte[] digest = new byte[messageDigest.getDigestSize()];
int size = messageDigest.doFinal(digest, 0); // offset - '0' means start from the beginning
// return only valid part of digest (can be shorter than maximum digest size)
return Arrays.copyOfRange(digest, 0, size); // offset - '0' means start from the beginning
}
/**
* Main method for stamping given file. It serves as an example of whole process in one go.
*
* @param filename
* @param is
* @return
* @throws java.io.IOException
* @throws org.bouncycastle.tsp.TSPException
*/
public byte[] stamp(String filename, InputStream is) throws IOException, TSPException {
logger.entry();
logger.info("File to be stamped: {}", filename);
byte[] file = getBytesFromInputStream(is);
ExtendedDigest digestAlgorithm = new SHA256Digest(); // select hash algorithm
ASN1ObjectIdentifier requestAlgorithm;
try {
requestAlgorithm = getHashObjectIdentifier(digestAlgorithm.getAlgorithmName());
} catch (IllegalArgumentException e) {
logger.catching(e);
throw e;
}
logger.info("Selected algorithm: {}", digestAlgorithm.getAlgorithmName());
// create request
byte[] digest = calculateMessageDigest(file, digestAlgorithm);
TimeStampRequest tsq = getTSRequest(digest, requestAlgorithm);
logger.debug("TS request generated");
// send request and receive response
TimeStampResponse tsr;
try {
tsr = getTSResponse(tsq, server);
} catch (IOException | TSPException e) {
logger.catching(e);
throw e;
}
logger.debug("TSA response received");
// log reason of failure
if (tsr.getFailInfo() != null) {
logFailReason(tsr.getFailInfo().intValue());
return null;
}
// log response
logResponse(tsr);
logger.exit();
return tsr.getEncoded();
}