(Delphi DLL) 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 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, Dsa, Crypt2;

...

procedure TForm1.Button1Click(Sender: TObject);
var
crypt: HCkCrypt2;
hashStr: PWideChar;
dsa: HCkDsa;
pemPrivateKey: PWideChar;
success: Boolean;
hexSig: PWideChar;
dsa2: HCkDsa;
pemPublicKey: PWideChar;

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

crypt := CkCrypt2_Create();

CkCrypt2_putEncodingMode(crypt,'hex');
CkCrypt2_putHashAlgorithm(crypt,'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 := CkCrypt2__hashFileENC(crypt,'hamlet.xml');

dsa := CkDsa_Create();

// 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 := CkDsa__loadText(dsa,'dsa_priv.pem');
success := CkDsa_FromPem(dsa,pemPrivateKey);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa));
    Exit;
  end;

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

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

// Now that the DSA object contains both the private key and hash,
// it is ready to create the signature:
success := CkDsa_SignHash(dsa);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa));
    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 := CkDsa__getEncodedSignature(dsa,'hex');
Memo1.Lines.Add('Signature:');
Memo1.Lines.Add(hexSig);

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

dsa2 := CkDsa_Create();

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

pemPublicKey := CkDsa__loadText(dsa2,'dsa_pub.pem');
success := CkDsa_FromPublicPem(dsa2,pemPublicKey);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa2));
    Exit;
  end;

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

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

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

CkCrypt2_Dispose(crypt);
CkDsa_Dispose(dsa);
CkDsa_Dispose(dsa2);

end;