The string itself has his own different key for every character
FUNCTION ENCRYPT_DECRYPT($Str_Message) {
//Function : encrypt/decrypt a string message v.1.0 without a known key
$Len_Str_Message=STRLEN($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."."
"."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."."
"."Hello Aitor, Wellcome Home"."
";
ECHO $Str_Test."
";
$Str_Test2 = ENCRYPT_DECRYPT($Str_Test);
ECHO $Str_Test2."
";
$Str_Test3 = ENCRYPT_DECRYPT($Str_Test2);
ECHO "
".$Str_Test3."
";
?>