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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.10 $ -->
<refentry xml:id="function.mcrypt-generic" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>mcrypt_generic</refname>
<refpurpose>This function encrypts data</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>string</type><methodname>mcrypt_generic</methodname>
<methodparam><type>resource</type><parameter>td</parameter></methodparam>
<methodparam><type>string</type><parameter>data</parameter></methodparam>
</methodsynopsis>
<para>
This function encrypts data. The data is padded with "<literal>\0</literal>"
to make sure the length of the data is n * blocksize. This
function returns the encrypted data. Note that the length
of the returned string can in fact be longer then the input,
due to the padding of the data.
</para>
<para>
If you want to store the encrypted data in a database make sure to store
the entire string as returned by mcrypt_generic, or the string will not
entirely decrypt properly. If your original string is 10 characters long
and the block size is 8 (use
<function>mcrypt_enc_get_block_size</function> to determine the
blocksize), you would need at least 16 characters in your database field.
Note the string returned by <function>mdecrypt_generic</function> will be
16 characters as well...use rtrim($str, "\0") to remove the padding.
</para>
<para>
If you are for example storing the data in a MySQL database remember that
varchar fields automatically have trailing spaces removed during
insertion. As encrypted data can end in a space (ASCII 32), the data will
be damaged by this removal. Store data in a tinyblob/tinytext (or
larger) field instead.
</para>
<para>
The encryption handle should always be initialized with
<function>mcrypt_generic_init</function> with a key and an IV before
calling this function. Where the encryption is done, you should free the
encryption buffers by calling <function>mcrypt_generic_deinit</function>.
See <function>mcrypt_module_open</function> for an example.
</para>
<para>
See also <function>mdecrypt_generic</function>,
<function>mcrypt_generic_init</function>, and
<function>mcrypt_generic_deinit</function>.
</para>
</refsect1>
</refentry>
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