I Am Groot I Am Groot - 5 months ago 23
PHP Question

Double password_hash php

I was wondering if it was possible/wise to use password_hash twice for my users passwords on my website.

So let's say this:

  • User registers on my site, they enter a password, we will call this

  • During account creation, their password is
    $firstHash =
    password_hash($input, PASSWORD_BCRYPT)
    (For example sake, lets say
    this hashes to "thisFirstHash"

  • Once their password is hashed, it is hashed again
    $firstHash =
    password_hash($firstHash, PASSWORD_BCRYPT)
    (For example sake, lets
    say this hashes to "thisSecondHash")

  • This second hash is what is stored to the database, so now when they
    log in, the server has to decrypt a hashed hash.

  • When the user logs in, they enter their password again, we will again
    call this

  • the server then has to reencrypt the input to compare with the saved
    $loginHash1 = password_hash($input, PASSWORD_BCRYPT)

  • The server compares the new
    variable with the saved

  • If the first hash matches, compare the second hash

  • password_verify($input,"thisFirstHash")

I couldn't quite get this to work properly in my small testing environment, I suspect it has something to do with the randomized salt being different during the login phase when rehashing the input.

So my questions are,

  1. Is it possible to do this?

  2. Is it beneficial to do this?


The whole point of the password hashing API is to make it simple to implement secure hashing. Adding complexity as you are will not add any security, and it makes your code more difficult to debug. Use one password_hash and one password_verify. PHP's PASSWORD_DEFAULT is chosen to be very strong already:

To hash

$hash = password_hash($cleartext, PASSWORD_DEFAULT)

To verify

$isCorrect = password_verify($cleartext, $hash);

If you're not happy with PHP's very strong defaults, you can look into the cost setting. But it's really not needed. The docs say:

password_hash() uses a strong hash, generates a strong salt, and applies proper rounds automatically. password_hash() is a simple crypt() wrapper and compatible with existing password hashes. Use of password_hash() is encouraged.