Pascal (Lazarus/Delphi)

About RSA Public/Private Keys

See more RSA Examples

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.PrivateKey,
  Chilkat.PublicKey,
  Chilkat.Cert;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  cert: TCert;
  pubKey: TPublicKey;
  privKey: TPrivateKey;

begin
  success := False;

  cert := TCert.Create;

  //  Load a digital certificate.
  success := cert.LoadFromFile('digitalCert.cer');
  if (success = False) then
    begin
      WriteLn(cert.LastErrorText);
      Exit;
    end;

  //  A .cer file does not contain the private key.  It should contain
  //  the public key...
  pubKey := TPublicKey.Create;
  cert.GetPublicKey(pubKey);

  //  Let's have a look at it (in XML format).
  WriteLn('Public Key from Certificate:');
  WriteLn(pubKey.GetXml());

  //  An RSA public key consists of a modulus and exponent.

  //  An RSA private key includes both the modulus and exponent,
  //  as well as other "big" numbers: P, Q, D, etc.

  //  Let's load an RSA private key from a DER-encoded file:
  privKey := TPrivateKey.Create;

  success := privKey.LoadAnyFormatFile('PrivateKey.key','');
  if (success <> True) then
    begin
      WriteLn(privKey.LastErrorText);
      Exit;
    end;

  //  If this private key is the matching half to the public key from
  //  the certificate, then the modulus and exponent should
  //  be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
  WriteLn('Private Key from DER:');
  WriteLn(privKey.GetXml());


  cert.Free;
  pubKey.Free;
  privKey.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.