Encrypting and decrypting passwords in PHP

Question

I am wanting to encrypt a password and decrypt a password using PHP. Is this a safe method?

$pass = "password"
//encrypt password
$salt = strtr(base64_encode(mcrypt_create_iv(16, MCRYPT_DEV_URANDOM)), '+', '.');
$salt = sprintf("2ドルa$%02d$", 10) . $salt;
$hash = crypt($pass, $salt);
//decryption in second program
if(crypt($pass, $hash) == $hash){
 echo "you are in";
}

• user69075: You should NEVER encrypt passwords. Hash them.
• D.W.: 1. Don't use a fast hash; it's important to use a slow hash function. 2. security.stackexchange.com/q/211/971 covers the considerations pretty well.

Answer 1

As KIKO Software and the documentation for crypt said, password_hash() is encouraged. It's safer (it applies multiple rounds of hashing, thus increasing the time it takes to decrypt the hash), and it will manage salts for you, which means that your code will be simpler.

If for some reason you do not want to use password_hash, note the warning from the crypt documentation:

Warning When validating passwords, a string comparison function that isn't vulnerable to timing attacks should be used

You are not doing that, you are just using ==. hash_equals would be one such timing safe function.

• KIKO Software: Good point about timing attacks.

Answer 2

The name of the function crypt() is somewhat misleading, but you're not encrypting and decrypting. You create a hash and you check it, that's it.

It's not the best I have seen, but it is not uncommon to do it this way.

In the PHP crypt() documentation it says: Use of password_hash() is encouraged. You didn't see that? It allows you to choose an algorihtm. The PASSWORD_BCRYPT algorithm should be used. See: http://codahale.com/how-to-safely-store-a-password

I also see that you're not really using a salt in the traditional manner. Here's a nice introduction: http://www.martinstoeckli.ch/hash/en/index.php

So you're not using a salt on a per-password basis. See: http://blog.codinghorror.com/youre-probably-storing-passwords-incorrectly

There's much to say about this topic. Password security is a hot topic.

One of the mistakes most programmers make is that they rely on the user to select a password. In general users are just plain bad at choosing a secure password. You can try and force them to choose one, which is probably secure, but by doing that you will only annoy the hell out of the user. The solution is quite simple: You choose the password for the user. For a site where security is not that paramount you can use simple password. A random five digit number, in combination with a email address and brute force protection, is already reasonable secure; there are a million different possible combinations. Most developers however stick to what they know.