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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�13.�LanMan and NT Password Encryption</title><link rel="stylesheet" href="../samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="SAMBA Developers Guide"><link rel="up" href="pt03.html" title="Part�III.�Samba Subsystems"><link rel="prev" href="wins.html" title="Chapter�12.�Samba WINS Internals"><link rel="next" href="pt04.html" title="Part�IV.�Debugging and tracing"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�13.�LanMan and NT Password Encryption</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="wins.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Samba Subsystems</th><td width="20%" align="right">�<a accesskey="n" href="pt04.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="pwencrypt"></a>Chapter�13.�LanMan and NT Password Encryption</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="orgname">Samba Team</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><br>

<code class="email"><<a class="email" href="mailto:samba@samba.org">samba@samba.org</a>></code><br>

</p></div></div></div></div><div><p class="pubdate">19 Apr 1999</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="pwencrypt.html#id2560792">Introduction</a></span></dt><dt><span class="sect1"><a href="pwencrypt.html#id2560813">How does it work?</a></span></dt><dt><span class="sect1"><a href="pwencrypt.html#id2560896">The smbpasswd file</a></span></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2560792"></a>Introduction</h2></div></div></div><p>With the development of LanManager and Windows NT

compatible password encryption for Samba, it is now able

to validate user connections in exactly the same way as

a LanManager or Windows NT server.</p><p>This document describes how the SMB password encryption

algorithm works and what issues there are in choosing whether

you want to use it. You should read it carefully, especially

the part about security and the "PROS and CONS" section.</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2560813"></a>How does it work?</h2></div></div></div><p>LanManager encryption is somewhat similar to UNIX

password encryption. The server uses a file containing a

hashed value of a user's password. This is created by taking

the user's plaintext password, capitalising it, and either

truncating to 14 bytes or padding to 14 bytes with null bytes.

This 14 byte value is used as two 56 bit DES keys to encrypt

a 'magic' eight byte value, forming a 16 byte value which is

stored by the server and client. Let this value be known as

the "hashed password".</p><p>Windows NT encryption is a higher quality mechanism,

consisting of doing an MD4 hash on a Unicode version of the user's

password. This also produces a 16 byte hash value that is

non-reversible.</p><p>When a client (LanManager, Windows for WorkGroups, Windows

95 or Windows NT) wishes to mount a Samba drive (or use a Samba

resource), it first requests a connection and negotiates the

protocol that the client and server will use. In the reply to this

request the Samba server generates and appends an 8 byte, random

value - this is stored in the Samba server after the reply is sent

and is known as the "challenge". The challenge is different for

every client connection.</p><p>The client then uses the hashed password (16 byte values

described above), appended with 5 null bytes, as three 56 bit

DES keys, each of which is used to encrypt the challenge 8 byte

value, forming a 24 byte value known as the "response".</p><p>In the SMB call SMBsessionsetupX (when user level security

is selected) or the call SMBtconX (when share level security is

selected), the 24 byte response is returned by the client to the

Samba server. For Windows NT protocol levels the above calculation

is done on both hashes of the user's password and both responses are

returned in the SMB call, giving two 24 byte values.</p><p>The Samba server then reproduces the above calculation, using

its own stored value of the 16 byte hashed password (read from the

<code class="filename">smbpasswd</code> file - described later) and the challenge

value that it kept from the negotiate protocol reply. It then checks

to see if the 24 byte value it calculates matches the 24 byte value

returned to it from the client.</p><p>If these values match exactly, then the client knew the

correct password (or the 16 byte hashed value - see security note

below) and is thus allowed access. If not, then the client did not

know the correct password and is denied access.</p><p>Note that the Samba server never knows or stores the cleartext

of the user's password - just the 16 byte hashed values derived from

it. Also note that the cleartext password or 16 byte hashed values

are never transmitted over the network - thus increasing security.</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2560896"></a>The smbpasswd file</h2></div></div></div><a name="SMBPASSWDFILEFORMAT"></a><p>In order for Samba to participate in the above protocol

it must be able to look up the 16 byte hashed values given a user name.

Unfortunately, as the UNIX password value is also a one way hash

function (ie. it is impossible to retrieve the cleartext of the user's

password given the UNIX hash of it), a separate password file

containing this 16 byte value must be kept. To minimise problems with

these two password files, getting out of sync, the UNIX <code class="filename">

/etc/passwd</code> and the <code class="filename">smbpasswd</code> file,

a utility, <code class="literal">mksmbpasswd.sh</code>, is provided to generate

a smbpasswd file from a UNIX <code class="filename">/etc/passwd</code> file.

</p><p>To generate the smbpasswd file from your <code class="filename">/etc/passwd

</code> file use the following command:</p><p><code class="prompt">$ </code><strong class="userinput"><code>cat /etc/passwd | mksmbpasswd.sh

> /usr/local/samba/private/smbpasswd</code></strong></p><p>If you are running on a system that uses NIS, use</p><p><code class="prompt">$ </code><strong class="userinput"><code>ypcat passwd | mksmbpasswd.sh

> /usr/local/samba/private/smbpasswd</code></strong></p><p>The <code class="literal">mksmbpasswd.sh</code> program is found in

the Samba source directory. By default, the smbpasswd file is

stored in :</p><p><code class="filename">/usr/local/samba/private/smbpasswd</code></p><p>The owner of the <code class="filename">/usr/local/samba/private/</code>

directory should be set to root, and the permissions on it should

be set to 0500 (<code class="literal">chmod 500 /usr/local/samba/private</code>).

</p><p>Likewise, the smbpasswd file inside the private directory should

be owned by root and the permissions on is should be set to 0600

(<code class="literal">chmod 600 smbpasswd</code>).</p><p>The format of the smbpasswd file is (The line has been

wrapped here. It should appear as one entry per line in

your smbpasswd file.)</p><pre class="programlisting">

username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:

[Account type]:LCT-<last-change-time>:Long name

</pre><p>Although only the <em class="replaceable"><code>username</code></em>,

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</code></em>,

[<em class="replaceable"><code>Account type</code></em>] and <em class="replaceable"><code>

last-change-time</code></em> sections are significant

and are looked at in the Samba code.</p><p>It is <span class="emphasis"><em>VITALLY</em></span> important that there by 32

'X' characters between the two ':' characters in the XXX sections -

the smbpasswd and Samba code will fail to validate any entries that

do not have 32 characters between ':' characters. The first XXX

section is for the Lanman password hash, the second is for the

Windows NT version.</p><p>When the password file is created all users have password entries

consisting of 32 'X' characters. By default this disallows any access

as this user. When a user has a password set, the 'X' characters change

to 32 ascii hexadecimal digits (0-9, A-F). These are an ascii

representation of the 16 byte hashed value of a user's password.</p><p>To set a user to have no password (not recommended), edit the file

using vi, and replace the first 11 characters with the ascii text

<code class="constant">"NO PASSWORD"</code> (minus the quotes).</p><p>For example, to clear the password for user bob, his smbpasswd file

entry would look like :</p><pre class="programlisting">

bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:

[U ]:LCT-00000000:Bob's full name:/bobhome:/bobshell

</pre><p>If you are allowing users to use the smbpasswd command to set

their own passwords, you may want to give users NO PASSWORD initially

so they do not have to enter a previous password when changing to their

new password (not recommended). In order for you to allow this the

<code class="literal">smbpasswd</code> program must be able to connect to the

<code class="literal">smbd</code> daemon as that user with no password. Enable this

by adding the line :</p><p><code class="literal">null passwords = yes</code></p><p>to the [global] section of the smb.conf file (this is why

the above scenario is not recommended). Preferably, allocate your

users a default password to begin with, so you do not have

100

to enable this on your server.</p><p><span class="emphasis"><em>Note : </em></span>This file should be protected very

101

carefully. Anyone with access to this file can (with enough knowledge of

102

the protocols) gain access to your SMB server. The file is thus more

103

sensitive than a normal unix <code class="filename">/etc/passwd</code> file.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="wins.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="pt03.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="pt04.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter�12.�Samba WINS Internals�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�Part�IV.�Debugging and tracing</td></tr></table></div></body></html>