(C# UWP/WinRT) 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 Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// 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.
// -----------------------------------------------------------------
Chilkat.Prng prngClient = new Chilkat.Prng();
Chilkat.Ecc eccClient = new Chilkat.Ecc();
Chilkat.PrivateKey privKeyClient = eccClient.GenEccKey("secp256r1",prngClient);
if (eccClient.LastMethodSuccess != true) {
    Debug.WriteLine(eccClient.LastErrorText);
    return;
}

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

// -----------------------------------------------------------------
// (Server-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
Chilkat.Prng prngServer = new Chilkat.Prng();
Chilkat.Ecc eccServer = new Chilkat.Ecc();
Chilkat.PrivateKey privKeyServer = eccServer.GenEccKey("secp256r1",prngServer);
if (eccServer.LastMethodSuccess != true) {
    Debug.WriteLine(eccServer.LastErrorText);
    return;
}

Chilkat.PublicKey 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.
Chilkat.PublicKey pubKeyFromServer = new Chilkat.PublicKey();
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.
Chilkat.PublicKey pubKeyFromClient = new Chilkat.PublicKey();
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.
// ---------------------------------------------------------
Debug.WriteLine(sharedSecret1);
Debug.WriteLine(sharedSecret2);