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

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Demonstrates how to validate an RSA Signature against the string 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
sb: TChilkatStringBuilder;
crlfLineEnding: Integer;
i: Integer;
base64_rsa_sig: WideString;
pubKey: TPublicKey;
success: Integer;
rsa: TChilkatRsa;
signedString: WideString;

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

sb := TChilkatStringBuilder.Create(Self);
crlfLineEnding := 1;

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