ファイルの簡単な暗号化なら、これつかえ。
function XOR(InFile, OutFile:string);
var
　P:Byte;
　InStream, OutStream: TFileStream;
begin
　InStream := TFileStream.Create;
　OutStream := TFileStream.Create;

　InStream.LoadFromFile( InFile );
　while InStream.Position < InStream.Size do begin
　　InStream.ReadBuffer( P, 1 );
　　OutStream.WriteBuffer( P xor $FF, 1 );
　end;

　OutStream.SaveToFile( OutFile );

　InStream.Free;
　OutStream.Free;
end;