Lazarus Pascal Requires Chilkat v11.0.0+

Verify an RSA Signature Against the Signed String

See more Apple Keychain Examples

Demonstrates how to validate an RSA Signature against the string that was signed. Lazarus Pascal

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.StringBuilder,
  Chilkat.Rsa,
  Chilkat.PublicKey;

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

procedure RunDemo;
var
  success: Boolean;
  sb: TStringBuilder;
  crlfLineEnding: Boolean;
  i: Integer;
  base64_rsa_sig: string;
  pubKey: TPublicKey;
  rsa: TRsa;
  signedString: string;

begin
  success := False;

  //  Create the same string we previously signed in this example: 
  //  RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

  sb := TStringBuilder.Create;
  crlfLineEnding := True;

  for i := 0 to 10 do
    begin
      sb.AppendLine('This is a test.',crlfLineEnding);
    end;

  base64_rsa_sig := 'gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==';

  //  Get the public key to be used for signature verification.
  pubKey := TPublicKey.Create;
  success := pubKey.LoadFromFile('rsaKeys/chilkat-rsa-2048.pem');
  if (success = False) then
    begin
      WriteLn(pubKey.LastErrorText);
      Exit;
    end;

  rsa := TRsa.Create;
  success := rsa.UsePublicKey(pubKey);
  if (success = False) then
    begin
      WriteLn(rsa.LastErrorText);
      Exit;
    end;

  //  Verify the string against the signature.
  //  We signed the utf-8 byte representation of the string, so we must indicate
  //  to also validate against the utf-8 byte representation.
  rsa.Charset := 'utf-8';
  rsa.EncodingMode := 'base64';
  signedString := sb.GetAsString();
  success := rsa.VerifyStringENC(signedString,'sha256',base64_rsa_sig);

  if (success = False) then
    begin
      WriteLn(rsa.LastErrorText);
      WriteLn('Signature invalid.');
    end
  else
    begin
      WriteLn('Signature valid.');
    end;


  sb.Free;
  pubKey.Free;
  rsa.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.