(PHP Extension) 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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<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

// 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.
// -----------------------------------------------------------------
$prngClient = new CkPrng();
$eccClient = new CkEcc();
// privKeyClient is a CkPrivateKey
$privKeyClient = $eccClient->GenEccKey('secp256r1',$prngClient);
if ($eccClient->get_LastMethodSuccess() != true) {
    print $eccClient->lastErrorText() . "\n";
    exit;
}

// pubKeyClient is a CkPublicKey
$pubKeyClient = $privKeyClient->GetPublicKey();
$pubKeyClient->SavePemFile(false,'qa_output/eccClientPub.pem');

// -----------------------------------------------------------------
// (Server-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
$prngServer = new CkPrng();
$eccServer = new CkEcc();
// privKeyServer is a CkPrivateKey
$privKeyServer = $eccServer->GenEccKey('secp256r1',$prngServer);
if ($eccServer->get_LastMethodSuccess() != true) {
    print $eccServer->lastErrorText() . "\n";
    exit;
}

// pubKeyServer is a 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.
$pubKeyFromServer = new CkPublicKey();
$pubKeyFromServer->LoadFromFile('qa_output/eccServerPub.pem');
$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.
$pubKeyFromClient = new CkPublicKey();
$pubKeyFromClient->LoadFromFile('qa_output/eccClientPub.pem');
$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.
// ---------------------------------------------------------
print $sharedSecret1 . "\n";
print $sharedSecret2 . "\n";

?>