Unicode 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. Unicode C++

#include <CkPrngW.h>
#include <CkEccW.h>
#include <CkPrivateKeyW.h>
#include <CkPublicKeyW.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.
    // -----------------------------------------------------------------
    CkPrngW prngClient;
    CkEccW eccClient;
    CkPrivateKeyW privKeyClient;
    success = eccClient.GenKey(L"secp256r1",prngClient,privKeyClient);
    if (success == false) {
        wprintf(L"%s\n",eccClient.lastErrorText());
        return;
    }

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

    // -----------------------------------------------------------------
    // (Server-Side) Generate an ECC key, save the public part to a file.
    // -----------------------------------------------------------------
    CkPrngW prngServer;
    CkEccW eccServer;
    CkPrivateKeyW privKeyServer;
    eccServer.GenKey(L"secp256r1",prngServer,privKeyServer);

    CkPublicKeyW pubKeyServer;
    privKeyServer.ToPublicKey(pubKeyServer);
    pubKeyServer.SavePemFile(false,L"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.
    CkPublicKeyW pubKeyFromServer;
    pubKeyFromServer.LoadFromFile(L"qa_output/eccServerPub.pem");
    const wchar_t *sharedSecret1 = eccClient.sharedSecretENC(privKeyClient,pubKeyFromServer,L"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.
    CkPublicKeyW pubKeyFromClient;
    pubKeyFromClient.LoadFromFile(L"qa_output/eccClientPub.pem");
    const wchar_t *sharedSecret2 = eccServer.sharedSecretENC(privKeyServer,pubKeyFromClient,L"base64");

    // ---------------------------------------------------------
    // Examine the shared secrets.  They should be the same.
    // Both sides now have a secret that only they know.
    // ---------------------------------------------------------
    wprintf(L"%s\n",sharedSecret1);
    wprintf(L"%s\n",sharedSecret2);
    }