(Delphi ActiveX) 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.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat for Delphi Downloads Chilkat ActiveX DLL for Delphi Chilkat non-ActiveX DLL for Delphi * The examples here use the ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Integer;
prngClient: TChilkatPrng;
eccClient: TChilkatEcc;
privKeyClient: TPrivateKey;
pubKeyClient: TPublicKey;
prngServer: TChilkatPrng;
eccServer: TChilkatEcc;
privKeyServer: TPrivateKey;
pubKeyServer: TPublicKey;
pubKeyFromServer: TPublicKey;
sharedSecret1: WideString;
pubKeyFromClient: TPublicKey;
sharedSecret2: WideString;

begin
// 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 := TChilkatPrng.Create(Self);
eccClient := TChilkatEcc.Create(Self);
privKeyClient := TPrivateKey.Create(Self);
success := eccClient.GenKey('secp256r1',prngClient.ControlInterface,privKeyClient.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(eccClient.LastErrorText);
    Exit;
  end;
pubKeyClient := TPublicKey.Create(Self);
privKeyClient.ToPublicKey(pubKeyClient.ControlInterface);
pubKeyClient.SavePemFile(0,'qa_output/eccClientPub.pem');

// -----------------------------------------------------------------
// (Server-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
prngServer := TChilkatPrng.Create(Self);
eccServer := TChilkatEcc.Create(Self);
privKeyServer := TPrivateKey.Create(Self);
eccServer.GenKey('secp256r1',prngServer.ControlInterface,privKeyServer.ControlInterface);

pubKeyServer := TPublicKey.Create(Self);
privKeyServer.ToPublicKey(pubKeyServer.ControlInterface);
pubKeyServer.SavePemFile(0,'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 := TPublicKey.Create(Self);
pubKeyFromServer.LoadFromFile('qa_output/eccServerPub.pem');
sharedSecret1 := eccClient.SharedSecretENC(privKeyClient.ControlInterface,pubKeyFromServer.ControlInterface,'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 := TPublicKey.Create(Self);
pubKeyFromClient.LoadFromFile('qa_output/eccClientPub.pem');
sharedSecret2 := eccServer.SharedSecretENC(privKeyServer.ControlInterface,pubKeyFromClient.ControlInterface,'base64');

// ---------------------------------------------------------
// Examine the shared secrets.  They should be the same.
// Both sides now have a secret that only they know.
// ---------------------------------------------------------
Memo1.Lines.Add(sharedSecret1);
Memo1.Lines.Add(sharedSecret2);
end;