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| author | Gerald Carter <jerry@samba.org> | 2003-01-15 22:29:27 +0000 |
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| committer | Gerald Carter <jerry@samba.org> | 2003-01-15 22:29:27 +0000 |
| commit | 2a85f0cf33f303e091ce6f6bea7b7a072cd81c14 (patch) | |
| tree | 0ab129510034a715a9c31ff1433db404ee1c1e26 /docs/htmldocs/ENCRYPTION.html | |
| parent | 3a5a4159882635800b57fc766c7d4e2ec0297bb9 (diff) | |
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diff --git a/docs/htmldocs/ENCRYPTION.html b/docs/htmldocs/ENCRYPTION.html deleted file mode 100644 index e4d3ef5fed..0000000000 --- a/docs/htmldocs/ENCRYPTION.html +++ /dev/null @@ -1,656 +0,0 @@ -<HTML -><HEAD -><TITLE ->LanMan and NT Password Encryption in Samba 2.x</TITLE -><META -NAME="GENERATOR" -CONTENT="Modular DocBook HTML Stylesheet Version 1.57"></HEAD -><BODY -CLASS="ARTICLE" -BGCOLOR="#FFFFFF" -TEXT="#000000" -LINK="#0000FF" -VLINK="#840084" -ALINK="#0000FF" -><DIV -CLASS="ARTICLE" -><DIV -CLASS="TITLEPAGE" -><H1 -CLASS="TITLE" -><A -NAME="PWENCRYPT" ->LanMan and NT Password Encryption in Samba 2.x</A -></H1 -><HR></DIV -><DIV -CLASS="SECT1" -><H1 -CLASS="SECT1" -><A -NAME="AEN3" ->Introduction</A -></H1 -><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" -><HR><H1 -CLASS="SECT1" -><A -NAME="AEN7" ->How does it work?</A -></H1 -><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 - <TT -CLASS="FILENAME" ->smbpasswd</TT -> 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" -><HR><H1 -CLASS="SECT1" -><A -NAME="AEN18" ->Important Notes About Security</A -></H1 -><P ->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.</P -><P ->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). </P -><DIV -CLASS="WARNING" -><P -></P -><TABLE -CLASS="WARNING" -BORDER="1" -WIDTH="100%" -><TR -><TD -ALIGN="CENTER" -><B ->Warning</B -></TD -></TR -><TR -><TD -ALIGN="LEFT" -><P ->Note that Windows NT 4.0 Service pack 3 changed the - default for permissible authentication so that plaintext - passwords are <I -CLASS="EMPHASIS" ->never</I -> 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.</P -><P ->Other Microsoft operating systems which also exhibit - this behavior includes</P -><P -></P -><UL -><LI -><P ->MS DOS Network client 3.0 with - the basic network redirector installed</P -></LI -><LI -><P ->Windows 95 with the network redirector - update installed</P -></LI -><LI -><P ->Windows 98 [se]</P -></LI -><LI -><P ->Windows 2000</P -></LI -></UL -><P -><I -CLASS="EMPHASIS" ->Note :</I ->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.</P -></TD -></TR -></TABLE -></DIV -><DIV -CLASS="SECT2" -><HR><H2 -CLASS="SECT2" -><A -NAME="AEN37" ->Advantages of SMB Encryption</A -></H2 -><P -></P -><UL -><LI -><P ->plain text passwords are not passed across - the network. Someone using a network sniffer cannot just - record passwords going to the SMB server.</P -></LI -><LI -><P ->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. - </P -></LI -></UL -></DIV -><DIV -CLASS="SECT2" -><HR><H2 -CLASS="SECT2" -><A -NAME="AEN44" ->Advantages of non-encrypted passwords</A -></H2 -><P -></P -><UL -><LI -><P ->plain text passwords are not kept - on disk. </P -></LI -><LI -><P ->uses same password file as other unix - services such as login and ftp</P -></LI -><LI -><P ->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.</P -></LI -></UL -></DIV -></DIV -><DIV -CLASS="SECT1" -><HR><H1 -CLASS="SECT1" -><A -NAME="AEN53" -><A -NAME="SMBPASSWDFILEFORMAT" -></A ->The smbpasswd file</A -></H1 -><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 <TT -CLASS="FILENAME" -> /etc/passwd</TT -> and the <TT -CLASS="FILENAME" ->smbpasswd</TT -> file, - a utility, <B -CLASS="COMMAND" ->mksmbpasswd.sh</B ->, is provided to generate - a smbpasswd file from a UNIX <TT -CLASS="FILENAME" ->/etc/passwd</TT -> file. - </P -><P ->To generate the smbpasswd file from your <TT -CLASS="FILENAME" ->/etc/passwd - </TT -> file use the following command :</P -><P -><TT -CLASS="PROMPT" ->$ </TT -><TT -CLASS="USERINPUT" -><B ->cat /etc/passwd | mksmbpasswd.sh - > /usr/local/samba/private/smbpasswd</B -></TT -></P -><P ->If you are running on a system that uses NIS, use</P -><P -><TT -CLASS="PROMPT" ->$ </TT -><TT -CLASS="USERINPUT" -><B ->ypcat passwd | mksmbpasswd.sh - > /usr/local/samba/private/smbpasswd</B -></TT -></P -><P ->The <B -CLASS="COMMAND" ->mksmbpasswd.sh</B -> program is found in - the Samba source directory. By default, the smbpasswd file is - stored in :</P -><P -><TT -CLASS="FILENAME" ->/usr/local/samba/private/smbpasswd</TT -></P -><P ->The owner of the <TT -CLASS="FILENAME" ->/usr/local/samba/private/</TT -> - directory should be set to root, and the permissions on it should - be set to 0500 (<B -CLASS="COMMAND" ->chmod 500 /usr/local/samba/private</B ->). - </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 - (<B -CLASS="COMMAND" ->chmod 600 smbpasswd</B ->).</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 -><P -><PRE -CLASS="PROGRAMLISTING" ->username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX: - [Account type]:LCT-<last-change-time>:Long name - </PRE -></P -><P ->Although only the <TT -CLASS="REPLACEABLE" -><I ->username</I -></TT ->, - <TT -CLASS="REPLACEABLE" -><I ->uid</I -></TT ->, <TT -CLASS="REPLACEABLE" -><I -> XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</I -></TT ->, - [<TT -CLASS="REPLACEABLE" -><I ->Account type</I -></TT ->] and <TT -CLASS="REPLACEABLE" -><I -> last-change-time</I -></TT -> sections are significant - and are looked at in the Samba code.</P -><P ->It is <I -CLASS="EMPHASIS" ->VITALLY</I -> 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 - <TT -CLASS="CONSTANT" ->"NO PASSWORD"</TT -> (minus the quotes).</P -><P ->For example, to clear the password for user bob, his smbpasswd file - entry would look like :</P -><P -><PRE -CLASS="PROGRAMLISTING" -> bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:[U ]:LCT-00000000:Bob's full name:/bobhome:/bobshell - </PRE -></P -><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 - <B -CLASS="COMMAND" ->smbpasswd</B -> program must be able to connect to the - <B -CLASS="COMMAND" ->smbd</B -> daemon as that user with no password. Enable this - by adding the line :</P -><P -><B -CLASS="COMMAND" ->null passwords = yes</B -></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 - to enable this on your server.</P -><P -><I -CLASS="EMPHASIS" ->Note : </I ->This file should be protected very - carefully. Anyone with access to this file can (with enough knowledge of - the protocols) gain access to your SMB server. The file is thus more - sensitive than a normal unix <TT -CLASS="FILENAME" ->/etc/passwd</TT -> file.</P -></DIV -><DIV -CLASS="SECT1" -><HR><H1 -CLASS="SECT1" -><A -NAME="AEN105" ->The smbpasswd Command</A -></H1 -><P ->The smbpasswd command maintains the two 32 byte password fields - in the smbpasswd file. If you wish to make it similar to the unix - <B -CLASS="COMMAND" ->passwd</B -> or <B -CLASS="COMMAND" ->yppasswd</B -> programs, - install it in <TT -CLASS="FILENAME" ->/usr/local/samba/bin/</TT -> (or your - main Samba binary directory).</P -><P ->Note that as of Samba 1.9.18p4 this program <I -CLASS="EMPHASIS" ->MUST NOT - BE INSTALLED</I -> setuid root (the new <B -CLASS="COMMAND" ->smbpasswd</B -> - code enforces this restriction so it cannot be run this way by - accident).</P -><P -><B -CLASS="COMMAND" ->smbpasswd</B -> 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.</P -><P -></P -><UL -><LI -><P ->smbpasswd no longer has to be setuid root - - an enormous range of potential security problems is - eliminated.</P -></LI -><LI -><P -><B -CLASS="COMMAND" ->smbpasswd</B -> 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).</P -></LI -></UL -><P ->To run smbpasswd as a normal user just type :</P -><P -><TT -CLASS="PROMPT" ->$ </TT -><TT -CLASS="USERINPUT" -><B ->smbpasswd</B -></TT -></P -><P -><TT -CLASS="PROMPT" ->Old SMB password: </TT -><TT -CLASS="USERINPUT" -><B -><type old value here - - or hit return if there was no old password></B -></TT -></P -><P -><TT -CLASS="PROMPT" ->New SMB Password: </TT -><TT -CLASS="USERINPUT" -><B -><type new value> - </B -></TT -></P -><P -><TT -CLASS="PROMPT" ->Repeat New SMB Password: </TT -><TT -CLASS="USERINPUT" -><B -><re-type new value - </B -></TT -></P -><P ->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.</P -><P ->If invoked by an ordinary user it will only allow the user - to change his or her own Samba password.</P -><P ->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.</P -><P -><B -CLASS="COMMAND" ->smbpasswd</B -> is designed to work in the same way - and be familiar to UNIX users who use the <B -CLASS="COMMAND" ->passwd</B -> or - <B -CLASS="COMMAND" ->yppasswd</B -> commands.</P -><P ->For more details on using <B -CLASS="COMMAND" ->smbpasswd</B -> refer - to the man page which will always be the definitive reference.</P -></DIV -><DIV -CLASS="SECT1" -><HR><H1 -CLASS="SECT1" -><A -NAME="AEN144" ->Setting up Samba to support LanManager Encryption</A -></H1 -><P ->This is a very brief description on how to setup samba to - support password encryption. </P -><P -></P -><OL -TYPE="1" -><LI -><P ->compile and install samba as usual</P -></LI -><LI -><P ->enable encrypted passwords in <TT -CLASS="FILENAME" -> smb.conf</TT -> by adding the line <B -CLASS="COMMAND" ->encrypt - passwords = yes</B -> in the [global] section</P -></LI -><LI -><P ->create the initial <TT -CLASS="FILENAME" ->smbpasswd</TT -> - password file in the place you specified in the Makefile - (--prefix=<dir>). See the notes under the <A -HREF="#SMBPASSWDFILEFORMAT" ->The smbpasswd File</A -> - section earlier in the document for details.</P -></LI -></OL -><P ->Note that you can test things using smbclient.</P -></DIV -></DIV -></BODY -></HTML ->
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