Delphi DLL

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. Delphi 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;
rsa: HCkRsa;
bdHash: HCkBinData;
bdSig: HCkBinData;
enc: PWideChar;

begin
success := False;

// 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 := CkPublicKey_Create();
success := CkPublicKey_LoadFromFile(pubKey,'rsaPubKey.pem');
if (success = False) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey));
    Exit;
  end;

rsa := CkRsa_Create();

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

// Get the 32-byte SHA256 hash.
bdHash := CkBinData_Create();
success := CkBinData_LoadFile(bdHash,'myHash.sha256');
if (success = False) then
  begin
    Memo1.Lines.Add('Failed to load SHA256 hash.');
    Exit;
  end;

// Get the RSA signature to be validated.
bdSig := CkBinData_Create();
success := CkBinData_LoadFile(bdSig,'mySig.sig');
if (success = False) then
  begin
    Memo1.Lines.Add('Failed to load RSA signature.');
    Exit;
  end;

// Verify the signature against the SHA256 hash.
enc := 'base64';
CkRsa_putEncodingMode(rsa,enc);
success := CkRsa_VerifyHashENC(rsa,CkBinData__getEncoded(bdHash,enc),'sha256',CkBinData__getEncoded(bdSig,enc));
if (success = False) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Exit;
  end;

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

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

end;