Mega Code Archive
PHP Function to EncryptDecrypt a string without a known key
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The string itself has his own different key for every character
<?PHP
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."."<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>";
?>
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