(Android™) DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature.

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");

    String hashStr = crypt.hashFileENC("qa_data/hamlet.xml");
    Log.i(TAG, "hash to sign: " + hashStr);

    CkDsa dsa = new CkDsa();

    String pemPrivateKey;
    pemPrivateKey = dsa.loadText("qa_data/dsa/dsaPrivKey2.pem");
    boolean success = dsa.FromPem(pemPrivateKey);
    if (success == false) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

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

    // Sign the hash.
    success = dsa.SignHash();
    if (success == false) {
        Log.i(TAG, dsa.lastErrorText());
        return;
        }

    // Get the ASN.1 signature.
    String asnSig = dsa.getEncodedSignature("base64");
    Log.i(TAG, "Signature: " + asnSig);

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    CkAsn asn = new CkAsn();
    success = asn.LoadEncoded(asnSig,"base64");
    if (success == false) {
        Log.i(TAG, asn.lastErrorText());
        return;
        }

    // Get the ASN.1 as XML.
    CkXml xml = new CkXml();
    success = xml.LoadXml(asn.asnToXml());
    Log.i(TAG, "Signature as XML: ");
    Log.i(TAG, xml.getXml());

    // Sample XML shown here.
    // The r and s values are the two hex strings in the XML.

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
    //     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
    // </sequence>

    // Pretend we're starting with r,s
    String r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5";
    String s = "588E53D3F7B69636B48FD7175E99A3961BD7D775";

    // Build the XML that will be converted to ASN.1
    xml.Clear();
    xml.put_Tag("sequence");
    xml.NewChild2("int",r);
    xml.NewChild2("int",s);

    // Convert the XML to ASN.1
    success = asn.LoadAsnXml(xml.getXml());

    // Emit the signature as DER encoded ASN.1 (base64)
    asnSig = asn.getEncodedDer("base64");

    // --------------------------------------------------------------------
    // Verify the signature using the asnSig we built from the r,s values
    // --------------------------------------------------------------------

    CkDsa dsa2 = new CkDsa();

    // Load the DSA public key to be used for verification:
    String pemPublicKey;
    pemPublicKey = dsa2.loadText("qa_data/dsa/dsaPubKey2.pem");
    success = dsa2.FromPublicPem(pemPublicKey);
    if (success == false) {
        Log.i(TAG, dsa2.lastErrorText());
        return;
        }

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

    // Load the ASN.1 signature:
    success = dsa2.SetEncodedSignature("base64",asnSig);
    if (success == false) {
        Log.i(TAG, dsa2.lastErrorText());
        return;
        }

    // Verify:
    success = dsa2.Verify();
    if (success == false) {
        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."
  }
}