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100 lines
3.5 KiB
XML
100 lines
3.5 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<book xml:id="book.hash" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<?phpdoc extension-membership="core" ?>
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<title>HASH Message Digest Framework</title>
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<titleabbrev>Hash</titleabbrev>
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<!-- {{{ preface -->
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<preface xml:id="intro.hash">
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&reftitle.intro;
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<para>
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This extension provides functions that can be used for direct or
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incremental processing of arbitrary length messages using a variety of
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hashing algorithms, including the generation of <acronym>HMAC</acronym>
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values and key derivations including <acronym>HKDF</acronym> and
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<acronym>PBKDF2</acronym>.
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</para>
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<para>
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There are roughly three categories of hashing algorithms, and a complete list of
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algorithms can be found in the documentation for <function>hash_algos</function>.
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<itemizedlist>
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<listitem>
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<simpara>
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Checksum algorithms (such as <literal>"crc32b"</literal> or <literal>"adler32"</literal>):
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These are used to calculate checksums, useful in situations such as when
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transmission errors are to be detected. They are often very fast. These
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algorithms often generate values that are easily "guessable" or can be manipulated
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to create collisions, so they are entirely unsuitable for cryptographic use.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Non-cryptographic algorithms (such as the xxHash family):
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These are often used to calculate hash values for hash tables, as they are
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designed to yield a good distribution over arbitrary string inputs. They
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are also generally fast, but also not suitable for cryptographic use.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Cryptographic algorithms (such as the SHA-2 family):
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These are designed to yield hash values that are representative of their
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inputs but are not guessable nor prone to collisions. Performance is often
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a secondary concern, but modern hardware often supports special handling
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for these algorithms that PHP tries to use when available.
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</simpara>
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<simpara>
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The Computer Security Resource Center of the <acronym>NIST</acronym> has
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<link xlink:href="&url.hash.nist-hash-functions;">explanation of the algorithms
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currently approved by United States Federal Information Processing
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Standards</link>.
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</simpara>
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<caution>
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<para>
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Some of the early cryptographic algorithms, such as <literal>"md4"</literal>,
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<literal>"md5"</literal>, and <literal>"sha1"</literal>, have been proven
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to be prone to collision attacks and it is generally recommended to no
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longer use these for cryptographic applications.
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</para>
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</caution>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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See also the <link linkend="faq.passwords">FAQ on Safe Password Hashing</link>
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for information on best practices for using hash functions in handling
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passwords.
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</para>
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</preface>
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<!-- }}} -->
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&reference.hash.setup;
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&reference.hash.constants;
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&reference.hash.hashcontext;
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&reference.hash.reference;
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</book>
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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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