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.

Download Chilkat DSA ActiveX

Download Chilkat Crypt ActiveX

uses
    Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
    Dialogs, StdCtrls,
    CHILKATCRYPT2Lib_TLB,
    CHILKATDSALib_TLB,
    OleCtrls;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Integer;
crypt: TChilkatCrypt2;
hashStr: String;
dsa: TChilkatDsa;
pemPrivateKey: String;
hexSig: String;
dsa2: TChilkatDsa;
pemPublicKey: String;

begin


//  Use Chilkat Crypt to hash the contents of a file.
crypt := TChilkatCrypt2.Create(Self);
success := crypt.UnlockComponent('Anything for 30-day trial.');
if (success <> 1) then
  begin
    ShowMessage(crypt.LastErrorText);
    Exit;
  end;

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);

//  The Chilkat Crypt and Chilkat DSA components are separate
//  products.  To license both, it's least expensive to purchase
//  the "Chilkat Bundle" which provides licenses to all the
//  Chilkat components.
success := dsa.UnlockComponent('Anything for 30-day trial');
if (success <> 1) then
  begin
    ShowMessage(dsa.LastErrorText);
    Exit;
  end;

//  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
    ShowMessage(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
    ShowMessage(dsa.LastErrorText);
    Exit;
  end;

//  Load the hash to be signed into the DSA object:
success := dsa.SetEncodedHash('hex',hashStr);
if (success <> 1) then
  begin
    ShowMessage(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
    ShowMessage(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
    ShowMessage(dsa2.LastErrorText);
    Exit;
  end;

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

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

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


end;