Delphi <> PHP XOR Encryption

Question

I am trying to do encryption and decryption between PHP and Delphi.

My PHP code is;

<?php
error_reporting(E_ALL);
$key = "5y';syhl0ngl4st1ngdfvt5tt";

function decrypt1($string, $key){

    $y = 1;
    for ($x = 1;$i < strlen($string); $i++) {
        $a = (ord($string[$x]) and 0x0f) ^ (ord($key[$y]) and 0x0f);
        $string[$x] = chr((ord($string[$x]) and 0xf0) + $a);

        $y++;
        if ($y > strlen($key)) $y = 1;
    }
    return $string;
}

echo decrypt1(base64_decode("cWx0fw=="),$key);
?>

My Delphi is;

function Decrypt1(Str : String; Key: string): AnsiString;
var
  X, Y : Integer;
  A : Byte;
begin
  Y := 1;
  for X := 1 to Length(Str) do
  begin
    A := (ord(Str[X]) and $0f) xor (ord(Key[Y]) and $0f);
    Str[X] := char((ord(Str[X]) and $f0) + A);

    Inc(Y);
    If Y > length(Key) then Y := 1;
  end;
  Result := Str;
end;

function Encrypt(Str : String; Key: string): String;
begin
result:= Decrypt1(str,key);
result:= EncodeBase64(result);
end;

The encryption / decryption doesn't work. When attempting to decode encoded value from Delphi in PHP, I get a load of rubbish.

I have a feeling it might be something to do with the character encoding?

Delphi works with Ansi or since D2009 with UTF16 and PHP with UTF8. You have to ensure to work on the same encoding. — Sir Rufo
– Sir Rufo, Commented Aug 18, 2014 at 22:46
Step 1 is to stop using strings to hold byte arrays. Use TBytes. This is the single biggest misapprehension that we encounter regarding encryption. Encryption operates on binary data and not text. — David Heffernan
– David Heffernan, Commented Aug 19, 2014 at 5:43

David Heffernan · Accepted Answer · 2014-08-19 15:04:53Z

4

There are a few problems here:

String indexing in PHP is zero-based and not one-based as your code assumes.
Delphi strings (well, in modern Delphi) are UTF-16 encoded. Your code assumes some unspecified 8 bit encoding.
Encryption/decryption operates on binary data rather than text and you fail to recognise this.

You should encrypt like this:

Encode the text in a specific, well-defined encoding. For instance, UTF-8. This gives a byte array. In Delphi that is TBytes.
Encrypt this byte array to yield another byte array.
Encode that byte array using base64 to get a text representation.

Decryption simply reverses these steps. The key thing to absorb is that encryption/decryption operates on binary data rather than text.

answered Aug 19, 2014 at 15:04

David Heffernan

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Comments

Community · Accepted Answer · 2017-05-23 12:20:51Z

1

I'm going to take a guess here and say you're using a Delphi version where string is a UnicodeString. PHP generally uses some ANSI encoding, which can be configured. The best way to deal with this is to have your Delphi code save to UTF-8 and load from UTF-8, and make sure your PHP loads from UTF-8. Standardize on one encoding across the board and then issues like this won't happen.

edited May 23, 2017 at 12:20

CommunityBot

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answered Aug 18, 2014 at 22:48

Mason Wheeler

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8 Comments

Jake Evans Over a year ago

I'm actually using Delphi XE6, so I would assume it's Ansi?

Mason Wheeler Over a year ago

@Tom: Anything D2009 or later (including the entire XE line) is Unicode.

Jake Evans Over a year ago

So how would I make Delphi and PHP encoding's compatible?

Mason Wheeler Over a year ago

@Tom: By doing exactly what I said. Use a standard encoding. When you're writing data out, use a UTF8String instead of a string, for example.

Jake Evans Over a year ago

I've tried that, I am still getting a different result when doing it in PHP

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