php-doc-en/reference/mcrypt/constants.xml

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<appendix xml:id="mcrypt.constants" xmlns="http://docbook.org/ns/docbook">
 &reftitle.constants;
 &extension.constants;
 <para>
  Mcrypt can operate in four block cipher modes (<literal>CBC</literal>,
  <literal>OFB</literal>, <literal>CFB</literal>, and
  <literal>ECB</literal>). If linked against libmcrypt-2.4.x or higher the
  functions can also operate in the block cipher mode <literal>nOFB</literal>
  and in <literal>STREAM</literal> mode. Below you find a list with all
  supported encryption modes together with the constants that are
  defined for the encryption mode.  For a more complete reference and
  discussion see &book.applied.cryptography;.
  <itemizedlist>
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_ECB</constant> (<literal>electronic
     codebook</literal>) is a block cipher mode that is generally
     unsuitable for most purposes. The use of this mode is not recommended.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_CBC</constant> (<literal>cipher block
     chaining</literal>) is a block cipher mode that is significantly
     more secure than <literal>ECB</literal> mode.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_CFB</constant> (<literal>cipher
     feedback, in 8-bit mode</literal>) is a stream cipher mode.
     It is recommended to use <literal>NCFB</literal> mode rather
     than <literal>CFB</literal> mode.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_OFB</constant> (<literal>output feedback, in
     8-bit mode</literal>) is a stream cipher mode comparable to <literal>CFB</literal>, but
     can be used in applications where error propagation cannot
     be tolerated.
     It is recommended to use <literal>NOFB</literal> mode rather
     than <literal>OFB</literal> mode.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_NOFB</constant> (<literal>output feedback,
     in n-bit mode</literal>) is comparable to <literal>OFB</literal> mode,
     but operates on the full block size of the algorithm.
    </simpara>
   </listitem> 
   <listitem>
    <simpara>
     <constant>MCRYPT_MODE_STREAM</constant> is an extra mode to include
     some stream algorithms like <literal>"WAKE"</literal> or <literal>"RC4"</literal>.
    </simpara>
   </listitem> 
  </itemizedlist>
 </para>
 
 <para>
  Mcrypt supports some other modes of operation for which there are no predefined constants.
  They can be utilised by passing a string in place of the missing constants.
  <itemizedlist>
   <listitem>
    <simpara>
     <constant>"ctr"</constant> (<literal>counter mode</literal>) is a stream cipher mode.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     <constant>"ncfb"</constant> (<literal>cipher feedback,
     in n-bit mode</literal>) is comparable to <literal>CFB</literal> mode, 
     but operates on the full block size of the algorithm.
    </simpara>
   </listitem>
  </itemizedlist>
 </para>

 <para>
  Some other mode and random device constants:
  <variablelist>
   <varlistentry xml:id="constant.mcrypt-encrypt">
    <term>
     <constant>MCRYPT_ENCRYPT</constant> 
     (<type>int</type>)
    </term>
    <listitem>
     <simpara>
      
     </simpara>
    </listitem>
   </varlistentry>
   <varlistentry xml:id="constant.mcrypt-decrypt">
    <term>
     <constant>MCRYPT_DECRYPT</constant> 
     (<type>int</type>)
    </term>
    <listitem>
     <simpara>
      
     </simpara>
    </listitem>
   </varlistentry>
   <varlistentry xml:id="constant.mcrypt-dev-random">
    <term>
     <constant>MCRYPT_DEV_RANDOM</constant> 
     (<type>int</type>)
    </term>
    <listitem>
     <simpara>
      
     </simpara>
    </listitem>
   </varlistentry>
   <varlistentry xml:id="constant.mcrypt-dev-urandom">
    <term>
     <constant>MCRYPT_DEV_URANDOM</constant> 
     (<type>int</type>)
    </term>
    <listitem>
     <simpara>
      
     </simpara>
    </listitem>
   </varlistentry>
   <varlistentry xml:id="constant.mcrypt-rand">
    <term>
     <constant>MCRYPT_RAND</constant> 
     (<type>int</type>)
    </term>
    <listitem>
     <simpara>
      
     </simpara>
    </listitem>
   </varlistentry>
  </variablelist>
 </para>
</appendix>

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