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<title>8.4 crypt -- Function to check Unix passwords</title>
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<H1><A NAME="SECTION0010400000000000000000">
8.4 <tt class="module">crypt</tt> --
Function to check <span class="Unix">Unix</span> passwords</A>
</H1>
<P>
<A NAME="module-crypt"></A>
<p class="availability">Availability: <span
class="platform">Unix</span>.</p>
<P>
This module implements an interface to the
<span class="manpage"><i>crypt</i>(3)</span><a id='l2h-2984' xml:id='l2h-2984'></a> routine, which is a one-way hash
function based upon a modified DES<a id='l2h-2982' xml:id='l2h-2982'></a> algorithm; see
the <span class="Unix">Unix</span> man page for further details. Possible uses include
allowing Python scripts to accept typed passwords from the user, or
attempting to crack <span class="Unix">Unix</span> passwords with a dictionary.
<P>
Notice that the behavior of this module depends on the actual implementation
of the <span class="manpage"><i>crypt</i>(3)</span><a id='l2h-2985' xml:id='l2h-2985'></a> routine in the running system.
Therefore, any extensions available on the current implementation will also
be available on this module.
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-2983' xml:id='l2h-2983' class="function">crypt</tt></b>(</nobr></td>
<td><var>word, salt</var>)</td></tr></table></dt>
<dd>
<var>word</var> will usually be a user's password as typed at a prompt or
in a graphical interface. <var>salt</var> is usually a random
two-character string which will be used to perturb the DES algorithm
in one of 4096 ways. The characters in <var>salt</var> must be in the
set <tt class="regexp">[./a-zA-Z0-9]</tt>. Returns the hashed password as a
string, which will be composed of characters from the same alphabet
as the salt (the first two characters represent the salt itself).
<P>
Since a few <span class="manpage"><i>crypt</i>(3)</span><a id='l2h-2986' xml:id='l2h-2986'></a> extensions allow different
values, with different sizes in the <var>salt</var>, it is recommended to use
the full crypted password as salt when checking for a password.
</dl>
<P>
A simple example illustrating typical use:
<P>
<div class="verbatim"><pre>
import crypt, getpass, pwd
def login():
username = raw_input('Python login:')
cryptedpasswd = pwd.getpwnam(username)[1]
if cryptedpasswd:
if cryptedpasswd == 'x' or cryptedpasswd == '*':
raise "Sorry, currently no support for shadow passwords"
cleartext = getpass.getpass()
return crypt.crypt(cleartext, cryptedpasswd) == cryptedpasswd
else:
return 1
</pre></div>
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