samba-mirror/docs/docbook/projdoc/ENCRYPTION.sgml

<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>