password-hash.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.password-hash" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>password_hash</refname>
  <refpurpose>Creates a password hash</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>password_hash</methodname>
   <methodparam><modifier role="attribute">#[\SensitiveParameter]</modifier><type>string</type><parameter>password</parameter></methodparam>
   <methodparam><type class="union"><type>string</type><type>int</type><type>null</type></type><parameter>algo</parameter></methodparam>
   <methodparam choice="opt"><type>array</type><parameter>options</parameter><initializer>[]</initializer></methodparam>
  </methodsynopsis>
  <para>
   <function>password_hash</function> creates a new password hash using a strong one-way hashing
   algorithm.
  </para>
  <simpara>
   The following algorithms are currently supported:
  </simpara>
  <para>
   <itemizedlist>
    <listitem>
     <simpara>
      <constant>PASSWORD_DEFAULT</constant> - Use the bcrypt algorithm (default as of PHP 5.5.0).
      Note that this constant is designed to change over time as new and stronger algorithms are added
      to PHP. For that reason, the length of the result from using this identifier can change over
      time. Therefore, it is recommended to store the result in a database column that can expand
      beyond 60 bytes (255 bytes would be a good choice).
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <constant>PASSWORD_BCRYPT</constant> - Use the bcrypt algorithm to
      create the hash. This will produce a standard <function>crypt</function> compatible hash using
      the <literal>$2y$</literal> identifier.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <constant>PASSWORD_ARGON2I</constant> - Use the Argon2i hashing algorithm to create the hash.
      This algorithm is only available if PHP has been compiled with Argon2 support.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <constant>PASSWORD_ARGON2ID</constant> - Use the Argon2id hashing algorithm to create the hash.
      This algorithm is only available if PHP has been compiled with Argon2 support.
     </simpara>
    </listitem>
   </itemizedlist>
  </para>
  <simpara>
   Supported options for <constant>PASSWORD_BCRYPT</constant>:
  </simpara>
  <para>
   <itemizedlist>
    <listitem>
     <para>
      <literal>salt</literal> (<type>string</type>) - to manually provide a salt to use when hashing the password.
      Note that this will override and prevent a salt from being automatically generated.
     </para>
     <para>
      If omitted, a random salt will be generated by <function>password_hash</function> for
      each password hashed. This is the intended mode of operation.
     </para>
     <warning>
      <para>
       The salt option is deprecated. It is now
       preferred to simply use the salt that is generated by default.
       As of PHP 8.0.0, an explicitly given salt is ignored.
      </para>
     </warning>
    </listitem>
    <listitem>
     <para>
      <literal>cost</literal> (<type>int</type>) - which denotes the algorithmic cost that should be used. 
      Examples of these values can be found on the <function>crypt</function> page.
     </para>
     <para>
      If omitted, a default value of <literal>12</literal> will be used. This is a good
      baseline cost, but it should be adjusted depending on hardware used.
     </para>
    </listitem>
   </itemizedlist>
  </para>
  <simpara>
   Supported options for <constant>PASSWORD_ARGON2I</constant>
   and <constant>PASSWORD_ARGON2ID</constant>:
  </simpara>
  <para>
   <itemizedlist>
    <listitem>
     <para>
      <literal>memory_cost</literal> (<type>int</type>) - Maximum memory (in kibibytes) that may 
      be used to compute the Argon2 hash. Defaults to <constant>PASSWORD_ARGON2_DEFAULT_MEMORY_COST</constant>.
     </para>
    </listitem>
    <listitem>
     <para>
      <literal>time_cost</literal> (<type>int</type>) - Maximum amount of time it may 
      take to compute the Argon2 hash. Defaults to <constant>PASSWORD_ARGON2_DEFAULT_TIME_COST</constant>.
     </para>
    </listitem>
    <listitem>
     <para>
      <literal>threads</literal> (<type>int</type>) - Number of threads to use for computing 
      the Argon2 hash. Defaults to <constant>PASSWORD_ARGON2_DEFAULT_THREADS</constant>.
     </para>
     <warning>
      <para>
        Only available when PHP uses libargon2, not with libsodium implementation.
      </para>
     </warning>
    </listitem>
   </itemizedlist>
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>password</parameter></term>
    <listitem>
     <para>
      &password.parameter.password;
     </para>
      <caution>
       <para>
        Using the <constant>PASSWORD_BCRYPT</constant> as the
        algorithm, will result
        in the <parameter>password</parameter> parameter being truncated to a
        maximum length of 72 bytes.
       </para>
      </caution>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>algo</parameter></term>
    <listitem>
     <para>
      &password.parameter.algo;
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>options</parameter></term>
    <listitem>
     <para>
      &password.parameter.options;
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the hashed password.
  </para>
  <para>
   The used algorithm, cost and salt are returned as part of the hash. Therefore,
   all information that's needed to verify the hash is included in it. This allows
   the <function>password_verify</function> function to verify the hash without
   needing separate storage for the salt or algorithm information.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>8.4.0</entry>
       <entry>
        The default value of the <literal>cost</literal> option of the
        <constant>PASSWORD_BCRYPT</constant> algorithm was increased from
        <literal>10</literal> to <literal>12</literal>.
       </entry>
      </row>
      <row>
       <entry>8.3.0</entry>
       <entry>
        <function>password_hash</function> now sets the underlying
        <exceptionname>Random\RandomException</exceptionname> as the
        <property>Exception::$previous</property> exception when a
        <exceptionname>ValueError</exceptionname> is thrown due to a failure
        in the salt generation.
       </entry>
      </row>
      <row>
       <entry>8.0.0</entry>
       <entry>
        <function>password_hash</function> no longer returns &false; on failure, instead a
        <classname>ValueError</classname> will be thrown if the password hashing algorithm
        is not valid, or an <classname>Error</classname> if the password hashing failed
        for an unknown error.
       </entry>
      </row>
      <row>
       <entry>8.0.0</entry>
       <entry>
        The <parameter>algo</parameter> parameter is nullable now.
       </entry>
      </row>
      <row>
       <entry>7.4.0</entry>
       <entry>
        The <parameter>algo</parameter> parameter expects a &string; now, but still accepts
        &integer;s for backward compatibility.
       </entry>
      </row>
      <row>
       <entry>7.4.0</entry>
       <entry>
        The sodium extension provides an alternative implementation for Argon2 passwords.
       </entry>
      </row>
      <row>
       <entry>7.3.0</entry>
       <entry>
        Support for Argon2id passwords using <constant>PASSWORD_ARGON2ID</constant> was added.
       </entry>
      </row>
      <row>
       <entry>7.2.0</entry>
       <entry>
        Support for Argon2i passwords using <constant>PASSWORD_ARGON2I</constant> was added.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>password_hash</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
echo password_hash("rasmuslerdorf", PASSWORD_DEFAULT);
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
$2y$12$4Umg0rCJwMswRw/l.SwHvuQV01coP0eWmGzd61QH2RvAOMANUBGC.
]]>
    </screen>
   </example>
  </para> 
  <para>
   <example>
    <title><function>password_hash</function> example setting cost manually</title>
    <programlisting role="php">
<![CDATA[
<?php
$options = [
    // Increase the bcrypt cost from 12 to 13.
    'cost' => 13,
];
echo password_hash("rasmuslerdorf", PASSWORD_BCRYPT, $options);
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
$2y$13$xeDfQumlmdm0Sco.4qmH1OGfUUmOcuRmfae0dPJhjX1Bq0yYhqbNi
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title><function>password_hash</function> example finding a good cost</title>
    <simpara>
     This code will benchmark the machine to determine how high of a cost can be used
     without deteriorating user experience. It is recommended to set the highest cost
     that does not slow down other operations the machine needs to perform. 11 is a
     good baseline, and more is better if the machine is fast enough. The code below
     aims for ≤ 350 milliseconds stretching time, which is an appropriate delay for
     systems handling interactive logins.
    </simpara>
    <programlisting role="php">
<![CDATA[
<?php
$timeTarget = 0.350; // 350 milliseconds

$cost = 11;
do {
    $cost++;
    $start = microtime(true);
    password_hash("test", PASSWORD_BCRYPT, ["cost" => $cost]);
    $end = microtime(true);
} while (($end - $start) < $timeTarget);

echo "Appropriate Cost Found: " . $cost - 1;
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
Appropriate Cost Found: 13
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title><function>password_hash</function> example using Argon2i</title>
    <programlisting role="php">
<![CDATA[
<?php
echo 'Argon2i hash: ' . password_hash('rasmuslerdorf', PASSWORD_ARGON2I);
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
Argon2i hash: $argon2i$v=19$m=1024,t=2,p=2$YzJBSzV4TUhkMzc3d3laeg$zqU/1IN0/AogfP4cmSJI1vc8lpXRW9/S0sYY2i2jHT0
]]>
    </screen>
   </example>
  </para>
 </refsect1>
 
 <refsect1 role="notes">
  &reftitle.notes;
  <caution>
   <para>
    It is strongly recommended not to provide an explicit salt for this function.
    A secure salt will automatically be created if no salt is specified.
   </para>
   <para>
    As noted above, providing the <literal>salt</literal> option in PHP 7.0.0
    will generate a deprecation warning. Support for providing a salt explicitly
    has been removed in PHP 8.0.0.
   </para>
  </caution>
  <note>
   <para>
    It is recommended to test this function on the machine used, adjusting the cost parameter(s)
    so that execution of the function takes less than 350 milliseconds for interactive logins.
    The script in the above example will help choosing an appropriate bcrypt cost for the given
    machine.
   </para>
  </note>
  <note>
   <simpara>
    Updates to supported algorithms by this function (or changes to the default one) must follow 
    the following rules:
   </simpara>
   <para>
    <itemizedlist>
     <listitem>
      <simpara>
      Any new algorithm must be in core for at least 1 full release of PHP
      prior to becoming default. So if, for example, a new algorithm is added
      in 7.5.5, it would not be eligible for default until 7.7 (since 7.6
      would be the first full release). But if a different algorithm was added
      in 7.6.0, it would also be eligible for default at 7.7.0.
      </simpara>
     </listitem>
     <listitem>
      <simpara>
       The default should only change in a full release (7.3.0, 8.0.0, etc)
       and not in a revision release.  The only exception to this is in an
       emergency when a critical security flaw is found in the current
       default.
      </simpara>
     </listitem>
    </itemizedlist>
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>password_verify</function></member>
    <member><function>password_needs_rehash</function></member>
    <member><function>crypt</function></member>
    <member><function>sodium_crypto_pwhash_str</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->