(Delphi DLL) Duplicate openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

1. Creates a SHA256 digest of the contents of the input file.
2. Verifies the SHA256 digest using the public key.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, BinData, Rsa, PublicKey;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
pubKey: HCkPublicKey;
bdFileData: HCkBinData;
bdSig: HCkBinData;
rsa: HCkRsa;

begin
success := False;

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

pubKey := CkPublicKey_Create();

// Load the public key from an PEM file:
success := CkPublicKey_LoadFromFile(pubKey,'pubKey.pem');
if (success = False) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey));
    Exit;
  end;

// Load the data of the original file that was signed.
bdFileData := CkBinData_Create();
success := CkBinData_LoadFile(bdFileData,'in.dat');

// Load the signature.
bdSig := CkBinData_Create();
success := CkBinData_LoadFile(bdSig,'signature.sig');

rsa := CkRsa_Create();

// Import the public key into the RSA component:
success := CkRsa_UsePublicKey(rsa,pubKey);
if (success = False) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Exit;
  end;

// OpenSSL uses big-endian.
CkRsa_putLittleEndian(rsa,False);

success := CkRsa_VerifyBd(rsa,bdFileData,'sha256',bdSig);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Memo1.Lines.Add('The signature was invalid.');
    Exit;
  end;

Memo1.Lines.Add('The signature was verified.');

CkPublicKey_Dispose(pubKey);
CkBinData_Dispose(bdFileData);
CkBinData_Dispose(bdSig);
CkRsa_Dispose(rsa);

end;