(Android™) Create ECSDA Signature using Raw r and s Format (not ASN.1)

See more ECC Examples

Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

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.

    // To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    // is signed.

    CkStringBuilder sb = new CkStringBuilder();
    sb.Append("The quick brown fox jumps over the lazy dog");
    String hash = sb.getHash("sha256","base64","utf-8");

    // Load the ECDSA key to be used for signing.
    CkPrivateKey privKey = new CkPrivateKey();
    boolean success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != true) {
        Log.i(TAG, privKey.lastErrorText());
        return;
        }

    CkPrng prng = new CkPrng();
    CkEcc ecdsa = new CkEcc();

    // Produce a signature that is not ASN.1, but is instead the concatenation
    // of the raw r and s signature parts.
    // This feature was added in Chilkat v9.5.0.97
    ecdsa.put_AsnFormat(false);

    String ecdsaSigBase64 = ecdsa.signHashENC(hash,"base64",privKey,prng);
    if (ecdsa.get_LastMethodSuccess() != true) {
        Log.i(TAG, ecdsa.lastErrorText());
        return;
        }

    Log.i(TAG, "ECDSA signature = " + ecdsaSigBase64);

    // -----------------------------------------------------------
    // Now let's verify the signature using the public key.

    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem");
    if (success != true) {
        Log.i(TAG, pubKey.lastErrorText());
        return;
        }

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    int result = ecdsa.VerifyHashENC(hash,ecdsaSigBase64,"base64",pubKey);
    if (result == 1) {
        Log.i(TAG, "Signature is valid.");
        return;
        }

    if (result == 0) {
        Log.i(TAG, "Signature is invalid.");
        return;
        }

    if (result < 0) {
        Log.i(TAG, ecdsa.lastErrorText());
        Log.i(TAG, "The VerifyHashENC method call failed.");
        return;
        }


  }

  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."
  }
}