(Android™) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkCrypt2 crypt = new CkCrypt2();

    crypt.put_EncodingMode("hex");
    crypt.put_HashAlgorithm("sha-1");

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when 
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    String hashStr = crypt.hashFileENC("hamlet.xml");

    CkDsa dsa = new CkDsa();

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.
    String pemPrivateKey;
    pemPrivateKey = dsa.loadText("dsa_priv.pem");
    boolean success = dsa.FromPem(pemPrivateKey);
    if (success != true) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.VerifyKey();
    if (success != true) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

    // Load the hash to be signed into the DSA object:
    success = dsa.SetEncodedHash("hex",hashStr);
    if (success != true) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    success = dsa.SignHash();
    if (success != true) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    String hexSig = dsa.getEncodedSignature("hex");
    Log.i(TAG, "Signature:");
    Log.i(TAG, hexSig);

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    CkDsa dsa2 = new CkDsa();

    // Load the DSA public key to be used for verification:
    String pemPublicKey;
    pemPublicKey = dsa2.loadText("dsa_pub.pem");
    success = dsa2.FromPublicPem(pemPublicKey);
    if (success != true) {
        Log.i(TAG, dsa2.lastErrorText());
        return;
        }

    // Load the hash to be verified against the signature.
    success = dsa2.SetEncodedHash("hex",hashStr);
    if (success != true) {
        Log.i(TAG, dsa2.lastErrorText());
        return;
        }

    // Load the signature:
    success = dsa2.SetEncodedSignature("hex",hexSig);
    if (success != true) {
        Log.i(TAG, dsa2.lastErrorText());
        return;
        }

    // Verify:
    success = dsa2.Verify();
    if (success != true) {
        Log.i(TAG, dsa2.lastErrorText());
        }
    else {
        Log.i(TAG, "DSA Signature Verified!");
        }


  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}