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

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, PublicKey, PrivateKey, Prng, Ecc;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
prngClient: HCkPrng;
eccClient: HCkEcc;
privKeyClient: HCkPrivateKey;
pubKeyClient: HCkPublicKey;
prngServer: HCkPrng;
eccServer: HCkEcc;
privKeyServer: HCkPrivateKey;
pubKeyServer: HCkPublicKey;
pubKeyFromServer: HCkPublicKey;
sharedSecret1: PWideChar;
pubKeyFromClient: HCkPublicKey;
sharedSecret2: PWideChar;

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 := CkPrng_Create();
eccClient := CkEcc_Create();
privKeyClient := CkEcc_GenEccKey(eccClient,'secp256r1',prngClient);
if (CkEcc_getLastMethodSuccess(eccClient) <> True) then
  begin
    Memo1.Lines.Add(CkEcc__lastErrorText(eccClient));
    Exit;
  end;
pubKeyClient := CkPrivateKey_GetPublicKey(privKeyClient);
CkPublicKey_SavePemFile(pubKeyClient,False,'qa_output/eccClientPub.pem');
CkPublicKey_Dispose(pubKeyClient);

// -----------------------------------------------------------------
// (Server-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
prngServer := CkPrng_Create();
eccServer := CkEcc_Create();
privKeyServer := CkEcc_GenEccKey(eccServer,'secp256r1',prngServer);
if (CkEcc_getLastMethodSuccess(eccServer) <> True) then
  begin
    Memo1.Lines.Add(CkEcc__lastErrorText(eccServer));
    Exit;
  end;
pubKeyServer := CkPrivateKey_GetPublicKey(privKeyServer);
CkPublicKey_SavePemFile(pubKeyServer,False,'qa_output/eccServerPub.pem');
CkPublicKey_Dispose(pubKeyServer);

// -----------------------------------------------------------------
// (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 := CkPublicKey_Create();
CkPublicKey_LoadFromFile(pubKeyFromServer,'qa_output/eccServerPub.pem');
sharedSecret1 := CkEcc__sharedSecretENC(eccClient,privKeyClient,pubKeyFromServer,'base64');
CkPrivateKey_Dispose(privKeyClient);

// -----------------------------------------------------------------
// (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 := CkPublicKey_Create();
CkPublicKey_LoadFromFile(pubKeyFromClient,'qa_output/eccClientPub.pem');
sharedSecret2 := CkEcc__sharedSecretENC(eccServer,privKeyServer,pubKeyFromClient,'base64');
CkPrivateKey_Dispose(privKeyServer);

// ---------------------------------------------------------
// 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);

CkPrng_Dispose(prngClient);
CkEcc_Dispose(eccClient);
CkPrng_Dispose(prngServer);
CkEcc_Dispose(eccServer);
CkPublicKey_Dispose(pubKeyFromServer);
CkPublicKey_Dispose(pubKeyFromClient);

end;