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Use hash_equals instead of StringUtils::equals #6231

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Feb 7, 2016
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Use hash_equals instead of StringUtils::equals #6231

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25 changes: 11 additions & 14 deletions components/security/secure_tools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -5,21 +5,25 @@ The Symfony Security component comes with a collection of nice utilities
related to security. These utilities are used by Symfony, but you should
also use them if you want to solve the problem they address.

.. note::

The functions described in this article were introduced in PHP 5.6 or 7.
For older PHP versions, a polyfill is provided by the
`Symfony Polyfill Component`_.
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We need a component section for the polyfills to which we can link instead where explain that you should rather install the polyfill packages you need instead of the big meta package imo (see #6052).

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Yes, I agree.


Comparing Strings
~~~~~~~~~~~~~~~~~

The time it takes to compare two strings depends on their differences. This
can be used by an attacker when the two strings represent a password for
instance; it is known as a `Timing attack`_.

Internally, when comparing two passwords, Symfony uses a constant-time
algorithm; you can use the same strategy in your own code thanks to the
:class:`Symfony\\Component\\Security\\Core\\Util\\StringUtils` class::

use Symfony\Component\Security\Core\Util\StringUtils;
When comparing two passwords, you should use the :phpfunction:`hash_equals`
function::

// is some known string (e.g. password) equal to some user input?
$bool = StringUtils::equals($knownString, $userInput);
if (hash_equals($knownString, $userInput)) {
// ...
}

Generating a Secure Random String
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Expand Down Expand Up @@ -49,12 +53,5 @@ use the :phpfunction:`random_int` function::

$random = random_int(1, 10);

.. note::

PHP 7 and up provide the ``random_bytes()`` and ``random_int()`` functions
natively, for older versions of PHP a polyfill is provided by the
`Symfony Polyfill Component`_ and the `paragonie/random_compat package`_.

.. _`Timing attack`: https://en.wikipedia.org/wiki/Timing_attack
.. _`Symfony Polyfill Component`: https://github.com/symfony/polyfill
.. _`paragonie/random_compat package`: https://github.com/paragonie/random_compat