Lazarus Pascal

ECDSA Sign and Verify

See more ECC Examples

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. Lazarus Pascal

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Asn,
  Chilkat.Prng,
  Chilkat.BinData,
  Chilkat.PrivateKey,
  Chilkat.PublicKey,
  Chilkat.Xml,
  Chilkat.Crypt2,
  Chilkat.Ecc;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  privKey: TPrivateKey;
  bd: TBinData;
  crypt: TCrypt2;
  hashStr: string;
  ecdsa: TEcc;
  prng: TPrng;
  sig: string;
  asn: TAsn;
  xml: TXml;
  r: string;
  s: string;
  pubKey: TPublicKey;
  ecc2: TEcc;
  result: Integer;
  xml2: TXml;
  asn2: TAsn;
  encodedSig: string;

begin
  success := False;

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

  //  First load an ECDSA private key to be used for signing.
  privKey := TPrivateKey.Create;
  success := privKey.LoadEncryptedPemFile('qa_data/ecc/secp256r1-key-pkcs8-secret.pem','secret');
  if (success = False) then
    begin
      WriteLn(privKey.LastErrorText);
      Exit;
    end;

  //  Sign the SHA256 hash of some data.
  bd := TBinData.Create;
  success := bd.LoadFile('qa_data/hamlet.xml');
  if (success = False) then
    begin
      WriteLn('Failed to load file to be hashed.');
      Exit;
    end;

  crypt := TCrypt2.Create;
  crypt.HashAlgorithm := 'sha256';
  crypt.EncodingMode := 'base64';
  hashStr := crypt.HashBdENC(bd);

  ecdsa := TEcc.Create;
  prng := TPrng.Create;
  //  Returns ASN.1 signature as a base64 string.
  sig := ecdsa.SignHashENC(hashStr,'base64',privKey,prng);
  WriteLn('sig = ' + sig);

  //  The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
  //  SEQUENCE (2 elem)
  //    INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
  //    INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

  //  If you wish, you can get the r and s components of the signature like this:
  asn := TAsn.Create;
  asn.LoadEncoded(sig,'base64');
  xml := TXml.Create;
  xml.LoadXml(asn.AsnToXml());

  WriteLn(xml.GetXml());

  //  We now have this:
  //  <?xml version="1.0" encoding="utf-8"?>
  //  <sequence>
  //      <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
  //      <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
  //  </sequence>

  //  Get the "r" and "s" as hex strings
  r := xml.GetChildContentByIndex(0);
  s := xml.GetChildContentByIndex(1);

  WriteLn('r = ' + r);
  WriteLn('s = ' + s);

  //  --------------------------------------------------------------------
  //  Now verify against the hash of the original data.

  //  Get the corresponding public key.
  pubKey := TPublicKey.Create;
  success := pubKey.LoadFromFile('qa_data/ecc/secp256r1-pub.pem');
  if (success = False) then
    begin
      WriteLn(pubKey.LastErrorText);
      Exit;
    end;

  //  We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
  ecc2 := TEcc.Create;
  result := ecc2.VerifyHashENC(hashStr,sig,'base64',pubKey);
  if (result <> 1) then
    begin
      WriteLn(ecc2.LastErrorText);
      Exit;
    end;

  WriteLn('Verified!');

  //  Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
  xml2 := TXml.Create;
  xml2.Tag := 'sequence';
  xml2.NewChild2('int',r);
  xml2.NewChild2('int',s);

  asn2 := TAsn.Create;
  asn2.LoadAsnXml(xml2.GetXml());
  encodedSig := asn2.GetEncodedDer('base64');
  WriteLn('encoded DSS signature: ' + encodedSig);

  //  You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
  //  You will see the ASN.1 such as this:

  //  SEQUENCE (2 elem)
  //    INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
  //    INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...


  privKey.Free;
  bd.Free;
  crypt.Free;
  ecdsa.Free;
  prng.Free;
  asn.Free;
  xml.Free;
  pubKey.Free;
  ecc2.Free;
  xml2.Free;
  asn2.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.