Pascal (Lazarus/Delphi)

RSA Signature/Verify with .key and .cer

See more RSA Examples

Demonstrates how to use a .key file (private key) and digital certificate (.cer, public key) to create and verify an RSA signature. 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.PublicKey,
  Chilkat.PrivateKey,
  Chilkat.Rsa,
  Chilkat.Cert;

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

procedure RunDemo;
var
  success: Boolean;
  privKey: TPrivateKey;
  rsa: TRsa;
  strData: string;
  hexSig: string;
  cert: TCert;
  pubKey: TPublicKey;
  rsa2: TRsa;

begin
  success := False;

  //  This example assumes the Chilkat API to have been previously unlocked.
  //  See Global Unlock Sample for sample code.

  privKey := TPrivateKey.Create;

  //  Load the private key from an RSA .key file:
  success := privKey.LoadPemFile('privateKey.key');
  if (success = False) then
    begin
      WriteLn(privKey.LastErrorText);
      Exit;
    end;

  rsa := TRsa.Create;

  //  Import the private key into the RSA component:
  success := rsa.UsePrivateKey(privKey);
  if (success = False) then
    begin
      WriteLn(rsa.LastErrorText);
      Exit;
    end;

  //  Create the signature as a hex string:
  rsa.EncodingMode := 'hex';

  strData := 'This is the string to be signed.';

  //  Sign the string using the sha256 hash algorithm.
  //  Other valid choices are "md2", "sha1", "sha384",
  //  "sha512", and "md5".
  hexSig := rsa.SignStringENC(strData,'sha256');

  WriteLn(hexSig);

  //  Load a digital certificate from a .cer file:
  cert := TCert.Create;

  success := cert.LoadFromFile('myCert.cer');
  if (success = False) then
    begin
      WriteLn(cert.LastErrorText);
      Exit;
    end;

  pubKey := TPublicKey.Create;
  cert.GetPublicKey(pubKey);

  //  Now verify using a new instance of the RSA object:
  rsa2 := TRsa.Create;

  //  Import the public key into the RSA object:
  success := rsa2.UsePublicKey(pubKey);
  if (success = False) then
    begin
      WriteLn(rsa2.LastErrorText);
      Exit;
    end;

  //  The signature is a hex string, so make sure the EncodingMode is correct:
  rsa2.EncodingMode := 'hex';

  //  Verify the signature:
  success := rsa2.VerifyStringENC(strData,'sha256',hexSig);
  if (success = False) then
    begin
      WriteLn(rsa2.LastErrorText);
      Exit;
    end;

  WriteLn('Success.');


  privKey.Free;
  rsa.Free;
  cert.Free;
  pubKey.Free;
  rsa2.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.