Java Digital Signature different to C#

Question

I have the following c# code to generate a digital signature from a private key:

    static string Sign(string text, string certificate)
    {

        X509Certificate2 cert = new X509Certificate2(certificate, "TestPassword", X509KeyStorageFlags.Exportable);
        RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)cert.PrivateKey;
        // Hash the data
        SHA1Managed sha1 = new SHA1Managed();
        ASCIIEncoding encoding = new ASCIIEncoding();
        byte[] data = encoding.GetBytes(text);
        byte[] hash = sha1.ComputeHash(data);
        // Sign the hash
        return System.Convert.ToBase64String(rsa.SignHash(hash, CryptoConfig.MapNameToOID("SHA1")));            
    }

I then created what I thought was the equivalent java code:

public static String signData(String dataToSign, String keyFile) { 
  FileInputStream keyfis = null;
  try {
    keyfis = new FileInputStream(fileName);
    KeyStore store = KeyStore.getInstance("PKCS12");
    store.load(keyfis, "TestPassword".toCharArray());
    KeyStore.PrivateKeyEntry pvk = (KeyStore.PrivateKeyEntry)store.
          getEntry("testkey", 
          new KeyStore.PasswordProtection("TestPassword".toCharArray()));
    PrivateKey privateKey = (PrivateKey)pvk.getPrivateKey();
    byte[] data = dataToSign.getBytes("US-ASCII");
    MessageDigest md = MessageDigest.getInstance("SHA1");
    byte[] hashed = md.digest(data);
    Signature rsa = Signature.getInstance("SHA1withRSA");
    rsa.initSign(privateKey);
    rsa.update(data);
    return Base64.encode(rsa.sign());
  } catch (Exception ex) {
    Logger.getLogger(this.getClass().getName()).log(Level.SEVERE, null, ex);
  } finally {
    if ( keyfis != null ) {
      try { keyfis.close() } catch (Exception ex) { keyfis = null; }
    }
  }
  return null;
}

Unfortunately the digital signatures do not match.

Any assistance will be greatly appreciated. Thanks in advance.

EDIT: If I remove the MessageDigest from the java code then the output is the same. Why? I thought hashing is needed.

Regards, Eugene

Answer 1

The Java sign method does hashing and signing based on the algorithms provided in getInstance method of the Signature class, so basically you were hashing twice in Java.