(Android™) How to Generate an Elliptic Curve Shared Secret

Demonstrates how to generate an ECC (Elliptic Curve Cryptography) shared secret. Imagine a cilent has one ECC private key, the server has another. A shared secret is computed by each side providing it's public key to the other. The private keys are kept private.

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.

    // This example includes both client-side and server-side code.
    // Each code segment is marked as client-side or server-side.
    // Imagine these segments are running on separate computers...

    boolean success;

    // -----------------------------------------------------------------
    // (Client-Side) Generate an ECC key, save the public part to a file.
    // -----------------------------------------------------------------
    CkPrng prngClient = new CkPrng();
    CkEcc eccClient = new CkEcc();
    CkPrivateKey privKeyClient = eccClient.GenEccKey("secp256r1",prngClient);
    if (eccClient.get_LastMethodSuccess() != true) {
        Log.i(TAG, eccClient.lastErrorText());
        return;
        }

    CkPublicKey pubKeyClient = privKeyClient.GetPublicKey();
    pubKeyClient.SavePemFile(false,"qa_output/eccClientPub.pem");

    // -----------------------------------------------------------------
    // (Server-Side) Generate an ECC key, save the public part to a file.
    // -----------------------------------------------------------------
    CkPrng prngServer = new CkPrng();
    CkEcc eccServer = new CkEcc();
    CkPrivateKey privKeyServer = eccServer.GenEccKey("secp256r1",prngServer);
    if (eccServer.get_LastMethodSuccess() != true) {
        Log.i(TAG, eccServer.lastErrorText());
        return;
        }

    CkPublicKey pubKeyServer = privKeyServer.GetPublicKey();
    pubKeyServer.SavePemFile(false,"qa_output/eccServerPub.pem");

    // -----------------------------------------------------------------
    // (Client-Side) Generate the shared secret using our private key, and the other's public key.
    // -----------------------------------------------------------------

    // Imagine that the server sent the public key PEM to the client.
    // (This is simulated by loading the server's public key from the file.
    CkPublicKey pubKeyFromServer = new CkPublicKey();
    pubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem");
    String sharedSecret1 = eccClient.sharedSecretENC(privKeyClient,pubKeyFromServer,"base64");

    // -----------------------------------------------------------------
    // (Server-Side) Generate the shared secret using our private key, and the other's public key.
    // -----------------------------------------------------------------

    // Imagine that the client sent the public key PEM to the server.
    // (This is simulated by loading the client's public key from the file.
    CkPublicKey pubKeyFromClient = new CkPublicKey();
    pubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem");
    String sharedSecret2 = eccServer.sharedSecretENC(privKeyServer,pubKeyFromClient,"base64");

    // ---------------------------------------------------------
    // Examine the shared secrets.  They should be the same.
    // Both sides now have a secret that only they know.
    // ---------------------------------------------------------
    Log.i(TAG, sharedSecret1);
    Log.i(TAG, sharedSecret2);

  }

  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."
  }
}