If anyone has this same problem in the future, the solution is to replace the strlen($var) function calls with mb_strlen($var, ‘latin1’). This will cause mb_strlen to act like the original strlen function. You also need to do it to a few of the substr calls also as the 4th parameter. Here is my code:
/**
* Decrypt using Mcrypt
*
* @access public
* @param string
* @param string
* @return string
*/
function mcrypt_decode($data, $key)
{
$data = $this->_remove_cipher_noise($data, $key);
$init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());
if ($init_size > mb_strlen($data, 'latin1'))
{
return FALSE;
}
$init_vect = mb_substr($data, 0, $init_size, 'latin1');
$data = mb_substr($data, $init_size, mb_strlen($data, 'latin1'), 'latin1');
return rtrim(mcrypt_decrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), "\0");
}
// --------------------------------------------------------------------
/**
* Adds permuted noise to the IV + encrypted data to protect
* against Man-in-the-middle attacks on CBC mode ciphers
* http://www.ciphersbyritter.com/GLOSSARY.HTM#IV
*
* Function description
*
* @access private
* @param string
* @param string
* @return string
*/
function _add_cipher_noise($data, $key)
{
$keyhash = $this->hash($key);
$keylen = strlen($keyhash);
$str = '';
for ($i = 0, $j = 0, $len = mb_strlen($data, 'latin1'); $i < $len; ++$i, ++$j)
{
if ($j >= $keylen)
{
$j = 0;
}
$str .= chr((ord($data[$i]) + ord($keyhash[$j])) % 256);
}
return $str;
}
// --------------------------------------------------------------------
/**
* Removes permuted noise from the IV + encrypted data, reversing
* _add_cipher_noise()
*
* Function description
*
* @access public
* @param type
* @return type
*/
function _remove_cipher_noise($data, $key)
{
$keyhash = $this->hash($key);
$keylen = mb_strlen($keyhash, 'latin1');
$str = '';
for ($i = 0, $j = 0, $len = mb_strlen($data, 'latin1'); $i < $len; ++$i, ++$j)
{
if ($j >= $keylen)
{
$j = 0;
}
$temp = ord($data[$i]) - ord($keyhash[$j]);
if ($temp < 0)
{
$temp = $temp + 256;
}
$str .= chr($temp);
}
return $str;
}
