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246 lines
8.6 KiB
XML
246 lines
8.6 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://docbook.org/ns/docbook" xml:id="function.crypt">
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<refnamediv>
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<refname>crypt</refname>
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<refpurpose>One-way string hashing</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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¬e.not-bin-safe;
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</refsynopsisdiv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>string</type><methodname>crypt</methodname>
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<methodparam><modifier role="attribute">#[\SensitiveParameter]</modifier><type>string</type><parameter>string</parameter></methodparam>
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<methodparam><type>string</type><parameter>salt</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>crypt</function> will return a hashed string using the
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standard Unix <abbrev>DES</abbrev>-based algorithm or
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alternative algorithms. <function>password_verify</function> is
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compatible with <function>crypt</function>. Therefore, password
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hashes created by <function>crypt</function> can be used with
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<function>password_verify</function>.
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</para>
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<para>
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Prior to PHP 8.0.0, the <parameter>salt</parameter> parameter was optional. However, <function>crypt</function> creates a weak hash without the <parameter>salt</parameter>, and raises an <constant>E_NOTICE</constant> error without it. Make sure to specify a strong enough salt for better security.
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</para>
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<para>
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<function>password_hash</function> uses a strong hash, generates a strong salt, and applies proper rounds automatically. <function>password_hash</function> is a simple <function>crypt</function> wrapper and compatible with existing password hashes. Use of <function>password_hash</function> is encouraged.
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</para>
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<para>
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The hash type is triggered by the salt argument.
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If no salt is provided, PHP will
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auto-generate either a standard two character (DES) salt, or a twelve
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character (MD5), depending on the availability of MD5 crypt(). PHP sets a
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constant named <constant>CRYPT_SALT_LENGTH</constant> which indicates the
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longest valid salt allowed by the available hashes.
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</para>
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<para>
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The standard DES-based <function>crypt</function> returns the
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salt as the first two characters of the output. It also only uses the
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first eight characters of <parameter>string</parameter>, so longer strings
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that start with the same eight characters will generate the same result
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(when the same salt is used).
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</para>
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<simpara>
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The following hash types are supported:
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</simpara>
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<itemizedlist>
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<listitem>
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<simpara>
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<constant>CRYPT_STD_DES</constant> - Standard DES-based hash with a two character salt
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from the alphabet "./0-9A-Za-z". Using invalid characters in the salt will cause
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crypt() to fail.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>CRYPT_EXT_DES</constant> - Extended DES-based hash. The "salt" is a
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9-character string consisting of an underscore followed by 4 characters of iteration count
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and 4 characters of salt. Each of these 4-character strings encode 24 bits, least significant
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character first. The values <literal>0</literal> to <literal>63</literal> are encoded as
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<literal>./0-9A-Za-z</literal>. Using invalid characters in the salt will cause crypt() to fail.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>CRYPT_MD5</constant> - MD5 hashing with a twelve character salt starting with
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$1$
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>CRYPT_BLOWFISH</constant> - Blowfish hashing with a salt as
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follows: "$2a$", "$2x$" or "$2y$", a two digit cost parameter, "$", and
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22 characters from the alphabet "./0-9A-Za-z". Using characters outside of
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this range in the salt will cause crypt() to return a zero-length string.
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The two digit cost parameter is the base-2 logarithm of the iteration
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count for the underlying Blowfish-based hashing algorithm and must be
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in range 04-31, values outside this range will cause crypt() to fail.
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"$2x$" hashes are potentially weak; "$2a$" hashes are compatible and
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mitigate this weakness. For new hashes, "$2y$" should be used.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>CRYPT_SHA256</constant> - SHA-256 hash with a sixteen character salt
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prefixed with $5$. If the salt string starts with 'rounds=<N>$', the numeric value of N
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is used to indicate how many times the hashing loop should be executed, much like the cost
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parameter on Blowfish. The default number of rounds is 5000, there is a minimum of
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1000 and a maximum of 999,999,999. Any selection of N outside this range will be truncated to
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the nearest limit.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<constant>CRYPT_SHA512</constant> - SHA-512 hash with a sixteen character salt
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prefixed with $6$. If the salt string starts with 'rounds=<N>$', the numeric value of N
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is used to indicate how many times the hashing loop should be executed, much like the cost
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parameter on Blowfish. The default number of rounds is 5000, there is a minimum of
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1000 and a maximum of 999,999,999. Any selection of N outside this range will be truncated to
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the nearest limit.
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</simpara>
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</listitem>
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</itemizedlist>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>string</parameter></term>
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<listitem>
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<para>
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The string to be hashed.
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</para>
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<caution>
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<para>
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Using the <constant>CRYPT_BLOWFISH</constant> algorithm, will result
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in the <parameter>string</parameter> parameter being truncated to a
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maximum length of 72 bytes.
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</para>
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</caution>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>salt</parameter></term>
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<listitem>
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<para>
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A salt string to base the hashing on. If not provided, the
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behaviour is defined by the algorithm implementation and can lead to
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unexpected results.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns the hashed string or a string that is shorter than 13 characters
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and is guaranteed to differ from the salt on failure.
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</para>
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<warning>
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<simpara>
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When validating passwords, a string comparison function that isn't
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vulnerable to timing attacks should be used to compare the output of
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<function>crypt</function> to the previously known hash. PHP
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provides <function>hash_equals</function> for this purpose.
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</simpara>
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</warning>
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</refsect1>
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<refsect1 role="changelog">
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&reftitle.changelog;
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>8.0.0</entry>
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<entry>
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The <parameter>salt</parameter> is no longer optional.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title><function>crypt</function> examples</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$user_input = 'rasmuslerdorf';
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$hashed_password = '$6$rounds=1000000$NJy4rIPjpOaU$0ACEYGg/aKCY3v8O8AfyiO7CTfZQ8/W231Qfh2tRLmfdvFD6XfHk12u6hMr9cYIA4hnpjLNSTRtUwYr9km9Ij/';
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// Validate an existing crypt() hash in a way that is compatible with non-PHP software.
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if (hash_equals($hashed_password, crypt($user_input, $hashed_password))) {
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echo "Password verified!";
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}
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</refsect1>
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<refsect1 role="notes">
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&reftitle.notes;
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<note>
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<simpara>
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There is no decrypt function, since <function>crypt</function> uses a
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one-way algorithm.
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</simpara>
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</note>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>hash_equals</function></member>
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<member><function>password_hash</function></member>
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<member>The Unix man page for your crypt function for more information</member>
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</simplelist>
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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