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authorJohn Terpstra <jht@samba.org>2003-04-04 05:19:59 +0000
committerJohn Terpstra <jht@samba.org>2003-04-04 05:19:59 +0000
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-<chapter id="pwencrypt">
-
-
-<chapterinfo>
- <author>
- <firstname>Jeremy</firstname><surname>Allison</surname>
- <affiliation>
- <orgname>Samba Team</orgname>
- <address>
- <email>jra@samba.org</email>
- </address>
- </affiliation>
- </author>
-
- <author>
- <firstname>Jelmer</firstname><surname>Vernooij</surname>
- <affiliation>
- <orgname>Samba Team</orgname>
- <address>
- <email>jelmer@samba.org</email>
- </address>
- </affiliation>
- </author>
-
- <pubdate>4 November 2002</pubdate>
-</chapterinfo>
-
-<title>LanMan and NT Password Encryption in Samba</title>
-
-
-<sect1>
- <title>Introduction</title>
-
- <para>Newer windows clients send encrypted passwords over
- the wire, instead of plain text passwords. The newest clients
- will only send encrypted passwords and refuse to send plain text
- passwords, unless their registry is tweaked.</para>
-
- <para>These passwords can't be converted to unix style encrypted
- passwords. Because of that you can't use the standard unix
- user database, and you have to store the Lanman and NT hashes
- somewhere else. For more information, see the documentation
- about the <command>passdb backend = </command> parameter.
- </para>
-
-</sect1>
-
-<sect1>
- <title>Important Notes About Security</title>
-
- <para>The unix and SMB password encryption techniques seem similar
- on the surface. This similarity is, however, only skin deep. The unix
- scheme typically sends clear text passwords over the network when
- logging in. This is bad. The SMB encryption scheme never sends the
- cleartext password over the network but it does store the 16 byte
- hashed values on disk. This is also bad. Why? Because the 16 byte hashed
- values are a "password equivalent". You cannot derive the user's
- password from them, but they could potentially be used in a modified
- client to gain access to a server. This would require considerable
- technical knowledge on behalf of the attacker but is perfectly possible.
- You should thus treat the smbpasswd file as though it contained the
- cleartext passwords of all your users. Its contents must be kept
- secret, and the file should be protected accordingly.</para>
-
- <para>Ideally we would like a password scheme which neither requires
- plain text passwords on the net or on disk. Unfortunately this
- is not available as Samba is stuck with being compatible with
- other SMB systems (WinNT, WfWg, Win95 etc). </para>
-
- <warning>
- <para>Note that Windows NT 4.0 Service pack 3 changed the
- default for permissible authentication so that plaintext
- passwords are <emphasis>never</emphasis> sent over the wire.
- The solution to this is either to switch to encrypted passwords
- with Samba or edit the Windows NT registry to re-enable plaintext
- passwords. See the document WinNT.txt for details on how to do
- this.</para>
-
- <para>Other Microsoft operating systems which also exhibit
- this behavior includes</para>
-
- <itemizedlist>
- <listitem><para>MS DOS Network client 3.0 with
- the basic network redirector installed</para></listitem>
-
- <listitem><para>Windows 95 with the network redirector
- update installed</para></listitem>
-
- <listitem><para>Windows 98 [se]</para></listitem>
-
- <listitem><para>Windows 2000</para></listitem>
- </itemizedlist>
-
- <para><emphasis>Note :</emphasis>All current release of
- Microsoft SMB/CIFS clients support authentication via the
- SMB Challenge/Response mechanism described here. Enabling
- clear text authentication does not disable the ability
- of the client to participate in encrypted authentication.</para>
- </warning>
-
- <sect2>
- <title>Advantages of SMB Encryption</title>
-
- <itemizedlist>
- <listitem><para>plain text passwords are not passed across
- the network. Someone using a network sniffer cannot just
- record passwords going to the SMB server.</para>
- </listitem>
-
- <listitem><para>WinNT doesn't like talking to a server
- that isn't using SMB encrypted passwords. It will refuse
- to browse the server if the server is also in user level
- security mode. It will insist on prompting the user for the
- password on each connection, which is very annoying. The
- only things you can do to stop this is to use SMB encryption.
- </para></listitem>
- </itemizedlist>
- </sect2>
-
-
- <sect2>
- <title>Advantages of non-encrypted passwords</title>
-
- <itemizedlist>
- <listitem><para>plain text passwords are not kept
- on disk. </para></listitem>
-
- <listitem><para>uses same password file as other unix
- services such as login and ftp</para></listitem>
-
- <listitem><para>you are probably already using other
- services (such as telnet and ftp) which send plain text
- passwords over the net, so sending them for SMB isn't
- such a big deal.</para></listitem>
- </itemizedlist>
- </sect2>
-</sect1>
-
-
-<sect1>
- <title>The smbpasswd Command</title>
-
- <para>The smbpasswd command maintains the two 32 byte password fields
- in the smbpasswd file. If you wish to make it similar to the unix
- <command>passwd</command> or <command>yppasswd</command> programs,
- install it in <filename>/usr/local/samba/bin/</filename> (or your
- main Samba binary directory).</para>
-
- <para><command>smbpasswd</command> now works in a client-server mode
- where it contacts the local smbd to change the user's password on its
- behalf. This has enormous benefits - as follows.</para>
-
- <para><command>smbpasswd</command> now has the capability
- to change passwords on Windows NT servers (this only works when
- the request is sent to the NT Primary Domain Controller if you
- are changing an NT Domain user's password).</para>
-
- <para>To run smbpasswd as a normal user just type :</para>
-
- <para><prompt>$ </prompt><userinput>smbpasswd</userinput></para>
- <para><prompt>Old SMB password: </prompt><userinput>&lt;type old value here -
- or hit return if there was no old password&gt;</userinput></para>
- <para><prompt>New SMB Password: </prompt><userinput>&lt;type new value&gt;
- </userinput></para>
- <para><prompt>Repeat New SMB Password: </prompt><userinput>&lt;re-type new value
- </userinput></para>
-
- <para>If the old value does not match the current value stored for
- that user, or the two new values do not match each other, then the
- password will not be changed.</para>
-
- <para>If invoked by an ordinary user it will only allow the user
- to change his or her own Samba password.</para>
-
- <para>If run by the root user smbpasswd may take an optional
- argument, specifying the user name whose SMB password you wish to
- change. Note that when run as root smbpasswd does not prompt for
- or check the old password value, thus allowing root to set passwords
- for users who have forgotten their passwords.</para>
-
- <para><command>smbpasswd</command> is designed to work in the same way
- and be familiar to UNIX users who use the <command>passwd</command> or
- <command>yppasswd</command> commands.</para>
-
- <para>For more details on using <command>smbpasswd</command> refer
- to the man page which will always be the definitive reference.</para>
-</sect1>
-
-</chapter>