Delphi ActiveX

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. Delphi ActiveX

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
success: Integer;
pubKey: TPublicKey;
rsa: TChilkatRsa;
bdHash: TChilkatBinData;
bdSig: TChilkatBinData;
enc: WideString;

begin
success := 0;

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

// Let's say you have a file containing the 32-bytes of a SHA256 hash,
// and a file that is an RSA signature of those 32 bytes.
// Here's how you verify using the RSA public key found in a PEM.

pubKey := TPublicKey.Create(Self);
success := pubKey.LoadFromFile('rsaPubKey.pem');
if (success = 0) then
  begin
    Memo1.Lines.Add(pubKey.LastErrorText);
    Exit;
  end;

rsa := TChilkatRsa.Create(Self);

// Get the public key.
success := rsa.UsePublicKey(pubKey.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(rsa.LastErrorText);
    Exit;
  end;

// Get the 32-byte SHA256 hash.
bdHash := TChilkatBinData.Create(Self);
success := bdHash.LoadFile('myHash.sha256');
if (success = 0) then
  begin
    Memo1.Lines.Add('Failed to load SHA256 hash.');
    Exit;
  end;

// Get the RSA signature to be validated.
bdSig := TChilkatBinData.Create(Self);
success := bdSig.LoadFile('mySig.sig');
if (success = 0) then
  begin
    Memo1.Lines.Add('Failed to load RSA signature.');
    Exit;
  end;

// Verify the signature against the SHA256 hash.
enc := 'base64';
rsa.EncodingMode := enc;
success := rsa.VerifyHashENC(bdHash.GetEncoded(enc),'sha256',bdSig.GetEncoded(enc));
if (success = 0) then
  begin
    Memo1.Lines.Add(rsa.LastErrorText);
    Exit;
  end;

Memo1.Lines.Add('Signature validated.');
end;