Lazarus Pascal

Example: Hash Text in Chunks

Shows how to generate a final hash, like SHA-256, for a large text by processing it in chunks. 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.BinData,
  Chilkat.Crypt2;

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

procedure RunDemo;
var
  success: Boolean;
  crypt: TCrypt2;
  bd: TBinData;
  s: string;
  i: Integer;
  encodedHash: string;

begin
  success := False;

  crypt := TCrypt2.Create;
  crypt.HashAlgorithm := 'sha256';
  crypt.Charset := 'utf-8';

  bd := TBinData.Create;

  s := 'The quick brown fox jumped over the lazy dog.' + #13#10;

  //  Accumulate the text in a StringBuilder.  We'll demonstrate hashing the text in chunks,
  //  and then also hashing the entire text at once to show the results are the same.

  bd.AppendString(s,'utf-8');
  success := crypt.HashBeginString(s);

  i := 0;
  while i < 200 do
    begin
      bd.AppendString(s,'utf-8');
      crypt.HashMoreString(s);
      i := i + 1;
    end;

  //  Get the hash in base64 format.
  crypt.EncodingMode := 'base64';

  encodedHash := crypt.HashFinalENC();
  WriteLn('Hash computed in chunks: ' + encodedHash);

  //  Let's alternatively compute the hash of the entire amount of data at once,
  //  to show the hash computation is the same:
  encodedHash := crypt.HashBdENC(bd);
  WriteLn('Hash computed in 1 step: ' + encodedHash);

  //  Output:

  //  Hash computed in chunks: unwkVff61k40roRIJizaknreScHaL6frWe37kydXbZQ=
  //  Hash computed in 1 step: unwkVff61k40roRIJizaknreScHaL6frWe37kydXbZQ=


  crypt.Free;
  bd.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.