PHP加密/解密与恢复代码

我尝试重新构建这里解释的加密流

$password = 'pass123456';  //user password
$message = 'Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.';
$Ku = openssl_random_pseudo_bytes(256 / 8); //user-specific symmetric key
$Ru = openssl_random_pseudo_bytes(256 / 8); //recovery code
$Su = openssl_random_pseudo_bytes(256 / 8); //user salt ###STORED ON SERVER###
$hash = hash_pbkdf2('sha256', $password, $Su, 5000, 256 / 8, true);
$split = str_split($hash, 16);
$Vu = $split[0]; //password verification token ###STORED ON SERVER###
$Ek = $split[1]; //key to encrypt Ku

$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
$Eu = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $Ek, $Ku, MCRYPT_MODE_CBC, $iv); ###STORED ON SERVER###
$Fu = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $Ru, $Ku, MCRYPT_MODE_CBC, $iv); ###STORED ON SERVER###
$encryptedMessage = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $Ku, $message, MCRYPT_MODE_CBC, $iv);

$hash = hash_pbkdf2('sha256', ###ENTERED PASSWORD###, ###STORED Su###, 5000, 256 / 8, true);
$split = str_split($hash, 16);
$Vu = $split[0];
$Ek = $split[1];

if($Vu != ###STORED Vu###) {
   => wrong password
} else {
   => correct password
}

$Ku = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $EK, ###STORED Eu###, MCRYPT_MODE_CBC, ###STORED iv###);
$message = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $Ku, $encryptedMessage, MCRYPT_MODE_CBC, ###STORED iv###);

如果我丢失了我的密码，我可以恢复"Ku":

$Ku = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, ###REVOVERY KEY###, ###STORED Fu###, MCRYPT_MODE_CBC, ###STORED iv###);

上面的代码安全吗?openssl_random_pseudo_bytes是否足够随机，或者是否有更好的可能性，即使用鼠标移动来生成初始化数?

应该如何"初始化向量"为mcrypt处理?这是正确的吗?