How can I convert this XOR-encryption function from Delphi to C#?

Question

The following Delphi routine is originally from a long-ago CompuServe posting, and is used to encrypt various information in our database. Below are both the Delphi 2007 and (thanks to some SO help with the Unicode differences) Delphi XE versions.

We have been trying to convert this to C#, and have gotten close-ish, but we're missing something somewhere. Unfortunately, our Delphi guy (me) doesn't know C#, and the C# guy is new to Delphi. C# doesn't (appear to) have the concept of AnsiString, so the solution will probably involve byte or char arrays?

We'd greatly appreciate any help in converting this to C#.

Delphi 2007 Version (ASCII)

function EncodeDecode(Str: string): string;
const
  Hash: string = '^%12hDVjED1~~#29afdmSD`6ZvUY@hbkDBC3fn7Y7euF|R7934093*7a-|-  Q`';
var
  I: Integer;
begin
  for I := 1 to Length (Str) do
    Str[I] := chr (ord (Str[I]) xor not (ord (Hash[I mod Length (Hash) + 1])));
  Result := Str;
end;

Delphi XE Version (Unicode)

function TfrmMain.EncodeDecode(Str: AnsiString): AnsiString;
const
  Hash: string = '^%12hDVjED1~~#29afdmSD`6ZvUY@hbkDBC3fn7Y7euF|R7934093*7a-|-  Q`';
var
  I: Integer;
begin
  Result := Str;
  for I := 1 to Length (Result) do
    Result[I] := AnsiChar (ord (Result[I]) xor not (Ord (Hash[I mod Length (Hash) + 1])));
end;

Just a note: Since now your encryption method including the key (this is your "Hash" string) is fully public, you should change this string as soon as possible, otherwise your data is not safe at all against attackers. But then you can switch to a better algorithm altogether. — Paŭlo Ebermann
Thanks Paŭlo - I mangled the key before posting here. Our actual key is much different. — Eric S.

David Heffernan David Heffernan · Accepted Answer · 2011-07-20T20:32:37

I don't know C# either, so this is probably seriously non-idiomatic.

static string EncodeDecode(string str)
{
    byte[] hash = new byte[63] { 94, 37, 49, 50, 104, 68, 86, 106, 69, 68, 49, 126, 
        126, 35, 50, 57, 97, 102, 100, 109, 83, 68, 96, 54, 90, 118, 85, 89, 64, 
        104, 98, 107, 68, 66, 67, 51, 102, 110, 55, 89, 55, 101, 117, 70, 124, 82, 
        55, 57, 51, 52, 48, 57, 51, 42, 55, 97, 45, 124, 45, 32, 32, 81, 96 };

    Encoding ANSI = Encoding.GetEncoding(1252);
    byte[] input = ANSI.GetBytes(str);
    byte[] output = new byte[input.Length];
    for (int i = 0; i < input.Length; i++)
        output[i] = (byte)(input[i] ^ ~hash[(i + 1) % hash.Length]);
    return ANSI.GetString(output);
}

I have assumed that your ANSI strings are encoded with Windows 1252, but it you happen to have encoded your legacy data with a different code page it is obvious enough how to change it.

Since C# doesn't have the equivalent of Delphi's 8 bit string types, I personally would be sorely tempted to use byte[] rather than string.

Done that way it looks like this:

static byte[] EncodeDecode(byte[] input)
{
    byte[] hash = new byte[63] { 94, 37, 49, 50, 104, 68, 86, 106, 69, 68, 49, 126, 
        126, 35, 50, 57, 97, 102, 100, 109, 83, 68, 96, 54, 90, 118, 85, 89, 64, 
        104, 98, 107, 68, 66, 67, 51, 102, 110, 55, 89, 55, 101, 117, 70, 124, 82, 
        55, 57, 51, 52, 48, 57, 51, 42, 55, 97, 45, 124, 45, 32, 32, 81, 96 };

    byte[] output = new byte[input.Length];
    for (int i = 0; i < input.Length; i++)
        output[i] = (byte)(input[i] ^ ~hash[(i + 1) % hash.Length]);
    return output;
}

@Groo makes the excellent point that the hash can be initialised more cleanly list this:

byte[] hash = ANSI.GetBytes(@"^%12hDVjED1~~#29afdmSD`6ZvUY@hbkDBC3fn7Y7euF|R7934093*7a-|-  Q`");

How can I convert this XOR-encryption function from Delphi to C#?

2 Answers