Delphi DLL

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 DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Asn, Xml, Dsa, Crypt2;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
crypt: HCkCrypt2;
hashStr: PWideChar;
dsa: HCkDsa;
pemPrivateKey: PWideChar;
asnSig: PWideChar;
asn: HCkAsn;
xml: HCkXml;
r: PWideChar;
s: PWideChar;
dsa2: HCkDsa;
pemPublicKey: PWideChar;

begin
success := False;

// 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');

hashStr := CkCrypt2__hashFileENC(crypt,'qa_data/hamlet.xml');
Memo1.Lines.Add('hash to sign: ' + hashStr);

dsa := CkDsa_Create();

pemPrivateKey := CkDsa__loadText(dsa,'qa_data/dsa/dsaPrivKey2.pem');
success := CkDsa_FromPem(dsa,pemPrivateKey);
if (success = False) 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 = False) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa));
    Exit;
  end;

// Sign the hash.
success := CkDsa_SignHash(dsa);
if (success = False) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa));
    Exit;
  end;

// Get the ASN.1 signature.
asnSig := CkDsa__getEncodedSignature(dsa,'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 := CkAsn_Create();
success := CkAsn_LoadEncoded(asn,asnSig,'base64');
if (success = False) then
  begin
    Memo1.Lines.Add(CkAsn__lastErrorText(asn));
    Exit;
  end;

// Get the ASN.1 as XML.
xml := CkXml_Create();
success := CkXml_LoadXml(xml,CkAsn__asnToXml(asn));
Memo1.Lines.Add('Signature as XML: ');
Memo1.Lines.Add(CkXml__getXml(xml));

// 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
CkXml_Clear(xml);
CkXml_putTag(xml,'sequence');
CkXml_NewChild2(xml,'int',r);
CkXml_NewChild2(xml,'int',s);

// Convert the XML to ASN.1
success := CkAsn_LoadAsnXml(asn,CkXml__getXml(xml));

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

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

dsa2 := CkDsa_Create();

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

pemPublicKey := CkDsa__loadText(dsa2,'qa_data/dsa/dsaPubKey2.pem');
success := CkDsa_FromPublicPem(dsa2,pemPublicKey);
if (success = False) then
  begin
    Memo1.Lines.Add(CkDsa__lastErrorText(dsa2));
    Exit;
  end;

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

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

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

CkCrypt2_Dispose(crypt);
CkDsa_Dispose(dsa);
CkAsn_Dispose(asn);
CkXml_Dispose(xml);
CkDsa_Dispose(dsa2);

end;