confidentialstring.php

<?php
namespace phpsec;



/**
 * Parent Exception
 */
class FileExceptions extends \Exception {}



/**
 * Child Exceptions
 */
class FileNotWritable extends FileExceptions {}     //The file does not have write permissions in it



class Encryption
{



    /**
     * Cipher to be used for encryption.
     * @var string      Name of the cipher
     */
    private static $cipher = MCRYPT_RIJNDAEL_256;



    /**
     * Key to be used for encryption/decryption.
     * @var string      The key for encryption/decryption
     */
    private static $key = "qgyXyjD5YpF";



    /**
     * Mode to be used for encryption/decryption such as "ebc", "cbc" etc.
     * @var string      Mode for encryption/decryption
     */
    private static $mode = "cbc";



    /**
     * IV to be used for modes other than "ebc".
     * @var string      The initial vector for encryption/decryption
     */
    private static $iv = "12345678901234567890123456789012";



    /**
     * Function to get the value of cipher.
     * @return string   Returns the name/value of the cipher in use
     */
    public static function getCipher()
    {
        return Encryption::$cipher;
    }



    /**
     * Function to get the value of key.
     * @return string   Returns the key of the cipher in use
     */
    public static function getKey()
    {
        return Encryption::$key;
    }



    /**
     * Function to get the value of encryption/decryption mode such as "ebc", "cbc" etc.
     * @return string   Returns of the mode used in cipher
     */
    public static function getMode()
    {
        return Encryption::$mode;
    }



    /**
     * Function to get the value of IV.
     * @return string   Returns the IV used for the current cipher
     */
    public static function getIV()
    {
        return Encryption::$iv;
    }
}



/**
 * Function to encrypt the sensitive data on its first run. For rest of the run, this function decrypts the encrypted data for use.
 * @return string       The string in plain-text
 * @throws FileNotWritable  Thrown when the file is not writable
 */
function confidentialString()
{
    $trace = debug_backtrace(); //get the trace of this function call.

    //From this trace, find the proper sub-array which contains this function call. That call would be when the array's function parameter would contain this __FUNCTION__ value.
    $arraySlot = null;
    foreach ($trace as $count => $oncCall) {
        if ($oncCall['function'] == __FUNCTION__) {
            $arraySlot = $count;
            break;
        }
    }

    //If no value is passed to this function, then there is nothing to protect. Hence exit.
    if (count($trace[$arraySlot]['args']) == 0) {
        return "";
    }


    //Every encrypted string will contain ":" in the beginning. If this character is found in the string, then this is an encrypted string.
    if ($trace[$arraySlot]['args'][0][0] == ":") {
        $decodedString = substr($trace[$arraySlot]['args'][0], 1); //remove the ":" character form the string.
        $decodedString = base64_decode($decodedString); //the string was base64 encoded. Hence decode it back.

        $decryptedString = mcrypt_decrypt(Encryption::getCipher(), Encryption::getKey(), $decodedString, Encryption::getMode(), Encryption::getIV()); //decrypt the string.

        return unserialize(rtrim($decryptedString, "\0")); //return the decrypted string.
    }
    else //This is the first run of this function for this string. We know this because this string is not encrypted.
    {
        $origString = $trace[$arraySlot]['args'][0]; //store the original value.

        $encryptedString = mcrypt_encrypt(Encryption::getCipher(), Encryption::getKey(), serialize($origString), Encryption::getMode(), Encryption::getIV()); //encrypt the value.
        $encryptedString = base64_encode($encryptedString); //base 64 encode it.
        $encryptedString = ":" . $encryptedString; //append ":" at the beginning of the encrypted string.

        $fileData = file($trace[$arraySlot]['file']); //get file contents as an array.

        $prevLine = $fileData[(int)$trace[$arraySlot]['line'] - 1]; //get the line that needs to be replaced i.e. the string that contains the plain-text sensitive data.
        $functionName = str_replace(__NAMESPACE__ . "\\", '', __FUNCTION__); //calculate the function name of this function (without any namespace).
        $pos = strpos($prevLine, $functionName); //find the position of this function-name in the original string.
        $endPos = strpos($prevLine, ")", $pos); //search where this function ends, but start the search from the start of the function.

        $newLine = substr($prevLine, 0, $pos) . $functionName . "('{$encryptedString}')"; //generate the new line i.e. with encrypted String.

        $fileData[(int)$trace[$arraySlot]['line'] - 1] = $newLine . substr($prevLine, $endPos + 1); //replace the old line with the new line.
        $fileData = implode("", $fileData); //get the data from the array.

        //check if file is writable or not.
        if (!is_writable($trace[$arraySlot]['file'])) {
            throw new FileNotWritable("ERROR: This file is not Writable!!");
        }

        //write this new data to file.
        $fp = fopen($trace[$arraySlot]['file'], 'w');
        fwrite($fp, $fileData);
        fclose($fp);

        //return the un-encrypted string for use.
        return $origString;
    }
}