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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.hash-pbkdf2" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>hash_pbkdf2</refname>
<refpurpose>Generate a PBKDF2 key derivation of a supplied password</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>string</type><methodname>hash_pbkdf2</methodname>
<methodparam><type>string</type><parameter>algo</parameter></methodparam>
<methodparam><modifier role="attribute">#[\SensitiveParameter]</modifier><type>string</type><parameter>password</parameter></methodparam>
<methodparam><type>string</type><parameter>salt</parameter></methodparam>
<methodparam><type>int</type><parameter>iterations</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>length</parameter><initializer>0</initializer></methodparam>
<methodparam choice="opt"><type>bool</type><parameter>binary</parameter><initializer>&false;</initializer></methodparam>
<methodparam choice="opt"><type>array</type><parameter>options</parameter><initializer>[]</initializer></methodparam>
</methodsynopsis>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>algo</parameter></term>
<listitem>
<para>
Name of selected hashing algorithm (e.g. <literal>"sha256"</literal>).
For a list of supported algorithms see <function>hash_hmac_algos</function>.
<note>
<para>
Non-cryptographic hash functions are not allowed.
</para>
</note>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>password</parameter></term>
<listitem>
<para>
The password to use for the derivation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>salt</parameter></term>
<listitem>
<para>
The salt to use for the derivation. This value should be generated randomly.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>iterations</parameter></term>
<listitem>
<para>
The number of internal iterations to perform for the derivation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>length</parameter></term>
<listitem>
<para>
The length of the output string. If <parameter>binary</parameter>
is &true; this corresponds to the byte-length of the derived key, if
<parameter>binary</parameter> is &false; this corresponds to twice the
byte-length of the derived key (as every byte of the key is returned as
two hexits).
</para>
<para>
If <literal>0</literal> is passed, the entire output of the supplied
algorithm is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>binary</parameter></term>
<listitem>
<para>
When set to &true;, outputs raw binary data. &false; outputs lowercase
hexits.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>options</parameter></term>
<listitem>
<para>
An array of options for the various hashing algorithms.
Currently, only the <literal>"seed"</literal> key is
supported by the MurmurHash variants.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues"><!-- {{{ -->
&reftitle.returnvalues;
<para>
Returns a string containing the derived key as lowercase hexits unless
<parameter>binary</parameter> is set to &true; in which case the raw
binary representation of the derived key is returned.
</para>
</refsect1><!-- }}} -->
<refsect1 role="errors"><!-- {{{ -->
&reftitle.errors;
<para>
Throws a <classname>ValueError</classname> exception if the algorithm is
unknown, the <parameter>iterations</parameter> parameter is less than or
equal to <literal>0</literal>, the <parameter>length</parameter> is less
than <literal>0</literal> or the <parameter>salt</parameter> is too long
(greater than <constant>INT_MAX</constant><literal> - 4</literal>).
</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>8.0.0</entry>
<entry>
Now throws a <classname>ValueError</classname> exception on error.
Previously, &false; was returned and an <constant>E_WARNING</constant>
message was emitted.
</entry>
</row>
<row>
<entry>7.2.0</entry>
<entry>Usage of non-cryptographic hash functions (adler32, crc32, crc32b, fnv132, fnv1a32, fnv164, fnv1a64, joaat) was disabled.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>hash_pbkdf2</function> example, basic usage</title>
<programlisting role="php">
<![CDATA[
<?php
$password = "password";
$iterations = 600000;
// Generate a cryptographically secure random salt using random_bytes()
$salt = random_bytes(16);
$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 20);
var_dump($hash);
// for raw binary, the $length needs to be halved for equivalent results
$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 10, true);
var_dump(bin2hex($hash));?>
]]>
</programlisting>
&example.outputs.similar;
<screen>
<![CDATA[
string(20) "120fb6cffcf8b32c43e7"
string(20) "120fb6cffcf8b32c43e7"
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<caution>
<para>
The PBKDF2 method can be used for hashing passwords for storage. However, it
should be noted that <function>password_hash</function> or
<function>crypt</function> with <constant>CRYPT_BLOWFISH</constant> are
better suited for password storage.
</para>
</caution>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>password_hash</function></member>
<member><function>hash_hkdf</function></member>
<member><function>sodium_crypto_pwhash</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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