Timestamp request with file hash already generated in client

Question

I need to make a timpestamp request to a tsa of a large data file and so i am generating hash in client using javscript crypto-js.

The problem comes when later in java i try to make the request. Apparently the method TimeStampRequestGenerator.generate needs a byte[] parameter that in examples i can se that is a MessageDigest object generated from the content of the file and i can't find the way to use only the hash already generated.

Is it possible to make a request using only the hash of the file already generated ?

Thanks

Answer 1

After hard testing, i have found the solution.

The SHA-256 hash generated in javascript can be used directly in bouncyclaste after some type conversion as follows:

byte[] decodedHex = Hex.decodeHex(digest.toCharArray());

so you can use it as a normal

java.security.MessageDigest

when they are both converted to

byte[]

full code here:

// Get hash code as hexadecimal string (generated by crypto-js)
String digest = servletRequest.getParameter("digest");

// hexadecimal to string decoder
byte[] decodedHex = Hex.decodeHex(digest.toCharArray());

// Timestamp request
TimeStampRequestGenerator reqgen = new TimeStampRequestGenerator();
TimeStampRequest req = reqgen.generate(TSPAlgorithms.SHA256, decodedHex);
byte request[] = req.getEncoded();
...