(C++) 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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#include <CkPrng.h>
#include <CkEcc.h>
#include <CkPrivateKey.h>
#include <CkPublicKey.h>

void ChilkatSample(void)
    {
    // 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...

    bool success;

    // -----------------------------------------------------------------
    // (Client-Side) Generate an ECC key, save the public part to a file.
    // -----------------------------------------------------------------
    CkPrng prngClient;
    CkEcc eccClient;
    CkPrivateKey *privKeyClient = eccClient.GenEccKey("secp256r1",prngClient);
    if (eccClient.get_LastMethodSuccess() != true) {
        std::cout << eccClient.lastErrorText() << "\r\n";
        return;
    }

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

    // -----------------------------------------------------------------
    // (Server-Side) Generate an ECC key, save the public part to a file.
    // -----------------------------------------------------------------
    CkPrng prngServer;
    CkEcc eccServer;
    CkPrivateKey *privKeyServer = eccServer.GenEccKey("secp256r1",prngServer);
    if (eccServer.get_LastMethodSuccess() != true) {
        std::cout << eccServer.lastErrorText() << "\r\n";
        return;
    }

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

    // -----------------------------------------------------------------
    // (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;
    pubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem");
    const char *sharedSecret1 = eccClient.sharedSecretENC(*privKeyClient,pubKeyFromServer,"base64");
    delete privKeyClient;

    // -----------------------------------------------------------------
    // (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;
    pubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem");
    const char *sharedSecret2 = eccServer.sharedSecretENC(*privKeyServer,pubKeyFromClient,"base64");
    delete privKeyServer;

    // ---------------------------------------------------------
    // Examine the shared secrets.  They should be the same.
    // Both sides now have a secret that only they know.
    // ---------------------------------------------------------
    std::cout << sharedSecret1 << "\r\n";
    std::cout << sharedSecret2 << "\r\n";
    }