RijndaelOpenSSL.php

<?php

class RijndaelOpenSSL
{
    const METHOD = 'aes-256-cbc';

    private $pbkdfBase = '';
    private $pbkdfExtra = '';
    private $pbkdfExtracount = 0;
    private $pbkdfHashno = 0;
    private $pbkdfState = 0;
    private $iterations = 100;

    public function reset()
    {
        $this->pbkdfBase = '';
        $this->pbkdfExtra = '';
        $this->pbkdfExtracount = 0;
        $this->pbkdfHashno = 0;
        $this->pbkdfState = 0;
    }

    public function decrypt($inputText, $password)
    {
        $this->reset();
        $salt = (string) mb_strlen($password);
        $key = $this->pbkdf1($password, $salt, 32);
        $iv = $this->pbkdf1($password, $salt, 16);
        $decrypted = openssl_decrypt(base64_decode($inputText), self::METHOD, $key, OPENSSL_RAW_DATA, $iv);
        return mb_convert_encoding($decrypted, 'UTF-8', 'UTF-16LE');
    }

    public function encrypt($inputText, $password)
    {
        $this->reset();
        $salt = (string) mb_strlen($password);
        $key = $this->pbkdf1($password, $salt, 32);
        $iv = $this->pbkdf1($password, $salt, 16);
        $textUTF = mb_convert_encoding($inputText, 'UTF-16LE');
        $encrypted = openssl_encrypt($textUTF, self::METHOD, $key, OPENSSL_RAW_DATA, $iv);
        return base64_encode($encrypted);
    }

    /**
     * This code is not mine. It is based on: https://stackoverflow.com/questions/36511731/decrypting-string-encrypted-in-c-sharp-with-rijndaelmanaged-class-using-php
     */
    private function pbkdf1($pass, $salt, $countBytes)
    {
        if ($this->pbkdfState == 0) {
            $this->pbkdfHashno = 0;
            $this->pbkdfState = 1;

            $key = $pass . $salt;
            $this->pbkdfBase = sha1($key, true);
            for ($i = 2; $i < $this->iterations; $i++) {
                $this->pbkdfBase = sha1($this->pbkdfBase, true);
            }
        }

        $result = '';

        if ($this->pbkdfExtracount > 0) {
            $rlen = strlen($this->pbkdfExtra) - $this->pbkdfExtracount;
            if ($rlen >= $countBytes) {
                $result = substr($this->pbkdfExtra, $this->pbkdfExtracount, $countBytes);
                if ($rlen > $countBytes) {
                    $this->pbkdfExtracount += $countBytes;
                } else {
                    $this->pbkdfExtra = null;
                    $this->pbkdfExtracount = 0;
                }
                return $result;
            }
            $result = substr($this->pbkdfExtra, $rlen, $rlen);
        }

        $current = '';
        $clen = 0;
        $remain = $countBytes - strlen($result);
        while ($remain > $clen) {
            if ($this->pbkdfHashno == 0) {
                $current = sha1($this->pbkdfBase, true);
            } else if ($this->pbkdfHashno < 1000) {
                $num = sprintf('%d', $this->pbkdfHashno);
                $tmp = $num . $this->pbkdfBase;
                $current .= sha1($tmp, true);
            }
            $this->pbkdfHashno++;
            $clen = strlen($current);
        }

        // $current now holds at least as many bytes as we need
        $result .= substr($current, 0, $remain);

        // Save any left over bytes for any future requests
        if ($clen > $remain) {
            $this->pbkdfExtra = $current;
            $this->pbkdfExtracount = $remain;
        }

        return $result;
    }
}