(Delphi ActiveX) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

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
crypt: TChilkatCrypt2;
hashStr: WideString;
dsa: TChilkatDsa;
pemPrivateKey: WideString;
success: Integer;
hexSig: WideString;
dsa2: TChilkatDsa;
pemPublicKey: WideString;

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

crypt := TChilkatCrypt2.Create(Self);

crypt.EncodingMode := 'hex';
crypt.HashAlgorithm := 'sha-1';

// Return the SHA-1 hash of a file.  The file may be any size.
// The Chilkat Crypt component will stream the file when 
// computing the hash, keeping the memory usage constant
// and reasonable.
// The 20-byte SHA-1 hash is returned as a hex-encoded string.
hashStr := crypt.HashFileENC('hamlet.xml');

dsa := TChilkatDsa.Create(Self);

// Load a DSA private key from a PEM file.  Chilkat DSA
// provides the ability to load and save DSA public and private
// keys from encrypted or non-encrypted PEM or DER.
// The LoadText method is for convenience only.  You may
// use any means to load the contents of a PEM file into
// a string.

pemPrivateKey := dsa.LoadText('dsa_priv.pem');
success := dsa.FromPem(pemPrivateKey);
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// You may optionally verify the key to ensure that it is a valid
// DSA key.
success := dsa.VerifyKey();
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// Load the hash to be signed into the DSA object:
success := dsa.SetEncodedHash('hex',hashStr);
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// Now that the DSA object contains both the private key and hash,
// it is ready to create the signature:
success := dsa.SignHash();
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// If SignHash is successful, the DSA object contains the
// signature.  It may be accessed as a hex or base64 encoded
// string.  (It is also possible to access directly in byte array form via
// the "Signature" property.)
hexSig := dsa.GetEncodedSignature('hex');
Memo1.Lines.Add('Signature:');
Memo1.Lines.Add(hexSig);

// -----------------------------------------------------------
// Step 2: Verify the DSA Signature
// -----------------------------------------------------------

dsa2 := TChilkatDsa.Create(Self);

// Load the DSA public key to be used for verification:

pemPublicKey := dsa2.LoadText('dsa_pub.pem');
success := dsa2.FromPublicPem(pemPublicKey);
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Load the hash to be verified against the signature.
success := dsa2.SetEncodedHash('hex',hashStr);
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Load the signature:
success := dsa2.SetEncodedSignature('hex',hexSig);
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Verify:
success := dsa2.Verify();
if (success <> 1) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
  end
else
  begin
    Memo1.Lines.Add('DSA Signature Verified!');
  end;
end;