(Delphi ActiveX) Verify an RSA Signature Against the Signed Hash

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Demonstrates how to validate an RSA Signature against the hash that was signed.

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
bd: TChilkatBinData;
i: Integer;
sha256_base64: WideString;
base64_rsa_sig: WideString;
pubKey: TPublicKey;
success: Integer;
rsa: TChilkatRsa;

begin
bd := TChilkatBinData.Create(Self);

for i := 0 to 100 do
  begin
    bd.AppendEncoded('000102030405060708090A0B0C0D0E0F','hex');
  end;

sha256_base64 := bd.GetHash('sha256','base64');
Memo1.Lines.Add('sha256 hash in base64 format: ' + sha256_base64);

base64_rsa_sig := 'AwF2BbOvL6jA5DwmMAc9n6J2Cc8PI6Rj5W079+aKJcIEtPWRzHor0Bvc3aftGM3Jbgj6SXlIC3M3RYS7UZOnfiHKFNZgbxaNT5WwsWooK42ZkC8DBZl0p7OunBUKd5SciUo+TKilioeUkriN3L1Zl9hwi3HVDVqgVo3XXskwIftSqLSFlepTLTmOWj9Y93dp8J4D9RyLtNgFQBc0WB22tyJTsuY56mLcWe1AMF3LizB9OrbwjynF2u16xWlrJdugccz795fJBUV9aQSD+8S3KeqwQhoi8RK1uhD68aGCyaSpBq0NZ8COAkn7MXaF4POxrAAt8udfHM+PRfSOptcH/w==';

// Get the public key to be used for signature verification.
pubKey := TPublicKey.Create(Self);
success := pubKey.LoadFromFile('rsaKeys/chilkat-rsa-2048.pem');
if (success = 0) then
  begin
    Memo1.Lines.Add(pubKey.LastErrorText);
    Exit;
  end;

rsa := TChilkatRsa.Create(Self);
rsa.ImportPublicKeyObj(pubKey.ControlInterface);

// Verify the hash against the signature.
rsa.EncodingMode := 'base64';
success := rsa.VerifyHashENC(sha256_base64,'sha256',base64_rsa_sig);

if (success = 0) then
  begin
    Memo1.Lines.Add(rsa.LastErrorText);
    Memo1.Lines.Add('Signature invalid.');
  end
else
  begin
    Memo1.Lines.Add('Signature valid.');
  end;
end;