C++

How to Generate an Elliptic Curve Shared Secret

See more ECC Examples

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. C++

#include <CkPrng.h>
#include <CkEcc.h>
#include <CkPrivateKey.h>
#include <CkPublicKey.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  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...

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

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

    //  -----------------------------------------------------------------
    //  (Server-Side) Generate an ECC key, save the public part to a file.
    //  -----------------------------------------------------------------
    CkPrng prngServer;
    CkEcc eccServer;
    CkPrivateKey privKeyServer;
    eccServer.GenKey("secp256r1",prngServer,privKeyServer);

    CkPublicKey pubKeyServer;
    privKeyServer.ToPublicKey(pubKeyServer);
    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;
    pubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem");
    const char *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;
    pubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem");
    const char *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.
    //  ---------------------------------------------------------
    std::cout << sharedSecret1 << "\r\n";
    std::cout << sharedSecret2 << "\r\n";
    }