Delphi ActiveX

DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature. 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;
crypt: TChilkatCrypt2;
hashStr: WideString;
dsa: TChilkatDsa;
pemPrivateKey: WideString;
asnSig: WideString;
asn: TChilkatAsn;
xml: TChilkatXml;
r: WideString;
s: WideString;
dsa2: TChilkatDsa;
pemPublicKey: WideString;

begin
success := 0;

// 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';

hashStr := crypt.HashFileENC('qa_data/hamlet.xml');
Memo1.Lines.Add('hash to sign: ' + hashStr);

dsa := TChilkatDsa.Create(Self);

pemPrivateKey := dsa.LoadText('qa_data/dsa/dsaPrivKey2.pem');
success := dsa.FromPem(pemPrivateKey);
if (success = 0) 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 = 0) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// Sign the hash.
success := dsa.SignHash();
if (success = 0) then
  begin
    Memo1.Lines.Add(dsa.LastErrorText);
    Exit;
  end;

// Get the ASN.1 signature.
asnSig := dsa.GetEncodedSignature('base64');
Memo1.Lines.Add('Signature: ' + asnSig);

// Examine the details of the ASN.1 signature.
// We want to get the r,s values as hex strings..
asn := TChilkatAsn.Create(Self);
success := asn.LoadEncoded(asnSig,'base64');
if (success = 0) then
  begin
    Memo1.Lines.Add(asn.LastErrorText);
    Exit;
  end;

// Get the ASN.1 as XML.
xml := TChilkatXml.Create(Self);
success := xml.LoadXml(asn.AsnToXml());
Memo1.Lines.Add('Signature as XML: ');
Memo1.Lines.Add(xml.GetXml());

// Sample XML shown here.
// The r and s values are the two hex strings in the XML.

// <?xml version="1.0" encoding="utf-8"?>
// <sequence>
//     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
//     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
// </sequence>

// Pretend we're starting with r,s
r := '2C187F3AB6E47A66497B86CE97BB39E2133810F5';
s := '588E53D3F7B69636B48FD7175E99A3961BD7D775';

// Build the XML that will be converted to ASN.1
xml.Clear();
xml.Tag := 'sequence';
xml.NewChild2('int',r);
xml.NewChild2('int',s);

// Convert the XML to ASN.1
success := asn.LoadAsnXml(xml.GetXml());

// Emit the signature as DER encoded ASN.1 (base64)
asnSig := asn.GetEncodedDer('base64');

// --------------------------------------------------------------------
// Verify the signature using the asnSig we built from the r,s values
// --------------------------------------------------------------------

dsa2 := TChilkatDsa.Create(Self);

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

pemPublicKey := dsa2.LoadText('qa_data/dsa/dsaPubKey2.pem');
success := dsa2.FromPublicPem(pemPublicKey);
if (success = 0) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Load the hash to be verified.
success := dsa2.SetEncodedHash('hex',hashStr);
if (success = 0) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Load the ASN.1 signature:
success := dsa2.SetEncodedSignature('base64',asnSig);
if (success = 0) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
    Exit;
  end;

// Verify:
success := dsa2.Verify();
if (success = 0) then
  begin
    Memo1.Lines.Add(dsa2.LastErrorText);
  end
else
  begin
    Memo1.Lines.Add('DSA Signature Verified!');
  end;
end;