Simple String EnCrypt + DeCrypt function

Sometimes you need some simple way to avoid stuff is read by someone else.
Some texts you want to keep private.
Can be if you save information in files, at a server with limited options for file protection.

If your need of security is not that high,
this script makes it a bit more difficult to get to your information.
Most people would never be able to decode your text.
If you have stuff that needs high security, you should use other tools.
Sure is possible to add more complicated operations,
but I wanted to keep it small, fast and simple.

This little function will use a Secret Key to encrypt text.
And you would have to use same Key to decrypt it back.
There is only one function for both encrypt/decrypt.
And you call it the same way always.

Script below will output:

Code:
Key: mysecretkey
To be or not to be, that is the question
Yv3gf2jf+kvy9gj#p`8+qqlm3lp2q|n%hx|`qj}k
To be or not to be, that is the question

I think it is easy to see how to use this function.
Here is my code:

PHP Code:

<?php
// String EnCrypt + DeCrypt function
// Author: halojoy, July 2006
function convert($str,$ky=''){
if(
$ky=='')return $str;
$ky=str_replace(chr(32),'',$ky);
if(
strlen($ky)<8)exit('key error');
$kl=strlen($ky)<32?strlen($ky):32;
$k=array();for($i=0;$i<$kl;$i++){
$k[$i]=ord($ky{$i})&0x1F;}
$j=0;for($i=0;$i<strlen($str);$i++){
$e=ord($str{$i});
$str{$i}=$e&0xE0?chr($e^$k[$j]):chr($e);
$j++;$j=$j==$kl?0:$j;}
return
$str;
}
///////////////////////////////////

// Secret key to encrypt/decrypt with
$key=‘mysecretkey’; // 8-32 characters without spaces

// String to encrypt
$string1=‘To be or not to be, that is the question’;

// EnCrypt string
$string2=convert($string1,$key);

// DeCrypt back
$string3=convert($string2,$key);

// Test output
echo ‘<span style=”font-family:Courier”>’.“\n”;

Quoted from: halojoy @ phpbuilder.com

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PHP: Encrypt and Decrypt

<?PHP
/*
Description : A function with a very simple but powerful xor method to encrypt
and/or decrypt a string with an unknown key. Implicitly the key is
defined by the string itself in a character by character way.
There are 4 items to compose the unknown key for the character
in the algorithm
1.- The ascii code of every character of the string itself
2.- The position in the string of the character to encrypt
3.- The length of the string that include the character
4.- Any special formula added by the programmer to the algorithm
to calculate the key to use
*/
FUNCTION ENCRYPT_DECRYPT($Str_Message) {
//Function : encrypt/decrypt a string message v.1.0  without a known key
//Author   : Aitor Solozabal Merino (spain)
//Email    : aitor-3@euskalnet.net
//Date     : 01-04-2005
$Len_Str_Message=STRLEN($Str_Message);
$Str_Encrypted_Message=””;
FOR ($Position = 0;$Position<$Len_Str_Message;$Position++){
// long code of the function to explain the algoritm
//this function can be tailored by the programmer modifyng the formula
//to calculate the key to use for every character in the string.
$Key_To_Use = (($Len_Str_Message+$Position)+1); // (+5 or *3 or ^2)
//after that we need a module division because can´t be greater than 255
$Key_To_Use = (255+$Key_To_Use) % 255;
$Byte_To_Be_Encrypted = SUBSTR($Str_Message, $Position, 1);
$Ascii_Num_Byte_To_Encrypt = ORD($Byte_To_Be_Encrypted);
$Xored_Byte = $Ascii_Num_Byte_To_Encrypt ^ $Key_To_Use;  //xor operation
$Encrypted_Byte = CHR($Xored_Byte);
$Str_Encrypted_Message .= $Encrypted_Byte;//short code of  the function once explained
//$str_encrypted_message .= chr((ord(substr($str_message, $position, 1))) ^ ((255+(($len_str_message+$position)+1)) % 255));
}
RETURN $Str_Encrypted_Message;
} //end function
?>

sample use of the function

$Str_Test=”This function is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation in any version
of the License.”.”<br>”.”This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.”.”<br>”.”Hello Aitor, Wellcome Home”.”<br>”;
ECHO $Str_Test.”<br>”;
$Str_Test2 = ENCRYPT_DECRYPT($Str_Test);
ECHO $Str_Test2.”<br><br>”;
$Str_Test3 = ENCRYPT_DECRYPT($Str_Test2);
ECHO “<br>”.$Str_Test3.”<br>”;
?>

Quoted from: weberdev.com