(Java) 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.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // 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) {
        System.out.println(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) {
        System.out.println(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.
    // ---------------------------------------------------------
    System.out.println(sharedSecret1);
    System.out.println(sharedSecret2);
  }
}