How to use (un) padded hash to verify signature

Question

Hi,
Thanks to the person that posted the code for padding a Hash in the topic http://forum.java.sun.com/thread.jspa?forumID=9&threadID=657241
It helped a lot !
Now, I want to do the reverse. I want to verify that the signature created matches the calculated hash in the file.
This is my code to create the signature file assuming that I have the hash of the file to be signed:
  public void signHash( byte[] bHash, String szSignHashFile )
         Cipher rsaCipher = Cipher.getInstance("RSA/ECB/NoPadding","BC");
          rsaCipher.init(Cipher.ENCRYPT_MODE, privKey);   
         byte[] bPaddedHash =  padHash (bHash, (RSAPrivateKey) privKey);
         byte[] enc = rsaCipher.doFinal(bPaddedHash);
         ByteBuffer bbuf = ByteBuffer.allocate(enc.length).put(enc);
         bbuf.flip();
         File fOutput = new File(szSignHashFile);
         // FileReader frInput = new FileReader(fInput);
         // FileWriter fwOutput = new FileWriter(fOutput);
         FileChannel wChannel = new FileOutputStream(fOutput, false).getChannel();
         wChannel.write( bbuf );
         wChannel.close();now, I need a verifyHash ( byte[] bHash, String szSignHashFile ) function that reads the file with the signature, decrypts the signature with the RSAPublicKey and compares the result with the passed hash to verify if the file has been tampered with. The problem is that I don't know how to unpad the byte array created when I call rsaCipher.doFinal(bSignatureByteArray) in DECRYPT MODE to give me the 20bytes of the original hash so I can compare them. Can somebody help with the unpadding hash function?
Thanks,
Juan C.

Answer 1

Thank you for this post and for the other posts. They have been very helpful.