MD5哈希无法处理大字符串

Question

I'm making a MD5 hash of a response, and then signing it with a shared secret.

For most calls this works, but strangely fails (Generates a MD5 hash different from the client) on the only two calls that bring a lot of content in the body.

Can this be because of the size of the body? or maybe because those calls return the content chunked ?

Any idea will be appreciated. Thanks a lot.

The hashing code (note that algorithm == MD5 and ENCODING == 'UTF-8' ):

private static byte[] hash(String toHash, String algorithm){
      try{
      MessageDigest dg = MessageDigest.getInstance(algorithm);
      dg.update(toHash.getBytes(ENCODING));
      return dg.digest();
    }catch(Exception e){
      throw new ApiInternalException("Error while hashing string: " + toHash,e);
    }
    }

Answer 1

It'd be great if you included your code. Without that, I can only guess what the problem is. Anyway, here's the correct way to create an MD5 hash in Java. If your code differs from this, then you have a problem.

String plainString = "Hash me please";
String md5Hash = "NOTHASHED";
try {
     MessageDigest md5Digest = MessageDigest.getInstance("MD5");
     md5String = new String(md5Digest.digest(plainString.getBytes()));
} catch (NoSuchAlgorithmException nsae) {
     // MD5 is included in all versions of Java, this can never happen
}

Of course, this will return something that looks like: ǚ ; f &fu If you want it to be human readable, it's usually suggested that you Bas64 encode it, in which case just use the line:

new String(Base64Encoder.encode((md5Digest.digest(DESKTOP_STRING.getBytes()))));

Which will give you something that looks like: ssea19zwO6Jm3AiF4SZmdQ==

Keeping in mind that you will need to unencode it later before using it as an md5 hash.

Answer 2

Either explanation is plausible. Other possible explanation include:

• something (maybe a proxy server) is altering content in transit,
• there is a mismatch in the way that character encoding / decoding is being dealt with
• it is actually the MD5 hashes that are being damaged.

You need to gather more information to figure out which it is. I suggest that you modify your client and server sides to capture the data being sent / received into files, move them to the same machine and do a byte-wise comparison. Other things you could try include turning off chunking and dumping / comparing the MD5 checksums at both ends.

EDIT : It would also help us help you if you posted the code that does the MD5 checksum calculation at both ends, and the code that encodes / decodes the checksums for transmission (eg using hexadecimal, base64 or whatever).