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-<chapter id="securitylevels">
-<chapterinfo>
- &author.tridge;
- &author.jelmer;
-</chapterinfo>
-<title>Samba as Stand-Alone Server</title>
-
-<para>
-In this section the function and purpose of Samba's <emphasis>security</emphasis>
-modes are described.
-</para>
-
-<sect1>
-<title>User and Share security level</title>
-
-<para>
-A SMB server tells the client at startup what "security level" it is
-running. There are two options "share level" and "user level". Which
-of these two the client receives affects the way the client then tries
-to authenticate itself. It does not directly affect (to any great
-extent) the way the Samba server does security. I know this is
-strange, but it fits in with the client/server approach of SMB. In SMB
-everything is initiated and controlled by the client, and the server
-can only tell the client what is available and whether an action is
-allowed.
-</para>
-
-<sect2>
-<title>User Level Security</title>
-
-<para>
-I'll describe user level security first, as its simpler. In user level
-security the client will send a "session setup" command directly after
-the protocol negotiation. This contains a username and password. The
-server can either accept or reject that username/password
-combination. Note that at this stage the server has no idea what
-share the client will eventually try to connect to, so it can't base
-the "accept/reject" on anything other than:
-</para>
-
-<orderedlist>
-<listitem><para>the username/password</para></listitem>
-<listitem><para>the machine that the client is coming from</para></listitem>
-</orderedlist>
-
-<para>
-If the server accepts the username/password then the client expects to
-be able to mount any share (using a "tree connection") without
-specifying a password. It expects that all access rights will be as
-the username/password specified in the "session setup".
-</para>
-
-<para>
-It is also possible for a client to send multiple "session setup"
-requests. When the server responds it gives the client a "uid" to use
-as an authentication tag for that username/password. The client can
-maintain multiple authentication contexts in this way (WinDD is an
-example of an application that does this)
-</para>
-
-</sect2>
-
-<sect2>
-<title>Share Level Security</title>
-
-<para>
-Ok, now for share level security. In share level security the client
-authenticates itself separately for each share. It will send a
-password along with each "tree connection" (share mount). It does not
-explicitly send a username with this operation. The client is
-expecting a password to be associated with each share, independent of
-the user. This means that samba has to work out what username the
-client probably wants to use. It is never explicitly sent the
-username. Some commercial SMB servers such as NT actually associate
-passwords directly with shares in share level security, but samba
-always uses the unix authentication scheme where it is a
-username/password that is authenticated, not a "share/password".
-</para>
-
-<para>
-Many clients send a "session setup" even if the server is in share
-level security. They normally send a valid username but no
-password. Samba records this username in a list of "possible
-usernames". When the client then does a "tree connection" it also adds
-to this list the name of the share they try to connect to (useful for
-home directories) and any users listed in the <command>user =</command> &smb.conf;
-line. The password is then checked in turn against these "possible
-usernames". If a match is found then the client is authenticated as
-that user.
-</para>
-
-</sect2>
-
-<sect2>
-<title>Server Level Security</title>
-
-<para>
-Finally "server level" security. In server level security the samba
-server reports to the client that it is in user level security. The
-client then does a "session setup" as described earlier. The samba
-server takes the username/password that the client sends and attempts
-to login to the "password server" by sending exactly the same
-username/password that it got from the client. If that server is in
-user level security and accepts the password then samba accepts the
-clients connection. This allows the samba server to use another SMB
-server as the "password server".
-</para>
-
-<para>
-You should also note that at the very start of all this, where the
-server tells the client what security level it is in, it also tells
-the client if it supports encryption. If it does then it supplies the
-client with a random "cryptkey". The client will then send all
-passwords in encrypted form. You have to compile samba with encryption
-enabled to support this feature, and you have to maintain a separate
-smbpasswd file with SMB style encrypted passwords. It is
-cryptographically impossible to translate from unix style encryption
-to SMB style encryption, although there are some fairly simple management
-schemes by which the two could be kept in sync.
-</para>
-
-<para>
-"security = server" means that Samba reports to clients that
-it is running in "user mode" but actually passes off all authentication
-requests to another "user mode" server. This requires an additional
-parameter "password server =" that points to the real authentication server.
-That real authentication server can be another Samba server or can be a
-Windows NT server, the later natively capable of encrypted password support.
-</para>
-
-<note><para>
-<emphasis>Server</emphasis> level security is incompatible with what is known
-as <emphasis>schannel</emphasis> or "sign and seal" protocols. This means that
-if you want to use <emphasis>server</emphasis> level security you must disable
-the use of "sign and seal" on all machines on your network.
-</para></note>
-
-<sect3>
-<title>Configuring Samba for Seemless Windows Network Integration</title>
-
-<para>
-MS Windows clients may use encrypted passwords as part of a challenege/response
-authentication model (a.k.a. NTLMv1) or alone, or clear text strings for simple
-password based authentication. It should be realized that with the SMB protocol
-the password is passed over the network either in plain text or encrypted, but
-not both in the same authentication request.
-</para>
-
-<para>
-When encrypted passwords are used a password that has been entered by the user
-is encrypted in two ways:
-</para>
-
-<itemizedlist>
- <listitem><para>An MD4 hash of the UNICODE of the password
- string. This is known as the NT hash.
- </para></listitem>
-
- <listitem><para>The password is converted to upper case,
- and then padded or trucated to 14 bytes. This string is
- then appended with 5 bytes of NULL characters and split to
- form two 56 bit DES keys to encrypt a "magic" 8 byte value.
- The resulting 16 bytes for the LanMan hash.
- </para></listitem>
-</itemizedlist>
-
-<para>
-MS Windows 95 pre-service pack 1, MS Windows NT versions 3.x and version 4.0
-pre-service pack 3 will use either mode of password authentication. All
-versions of MS Windows that follow these versions no longer support plain
-text passwords by default.
-</para>
-
-<para>
-MS Windows clients have a habit of dropping network mappings that have been idle
-for 10 minutes or longer. When the user attempts to use the mapped drive
-connection that has been dropped, the client re-establishes the connection using
-a cached copy of the password.
-</para>
-
-<para>
-When Microsoft changed the default password mode, support was dropped for caching
-of the plain text password. This means that when the registry parameter is changed
-to re-enable use of plain text passwords it appears to work, but when a dropped
-service connection mapping attempts to revalidate it will fail if the remote
-authentication server does not support encrypted passwords. This means that it
-is definitely not a good idea to re-enable plain text password support in such clients.
-</para>
-
-<para>
-The following parameters can be used to work around the issue of Windows 9x client
-upper casing usernames and password before transmitting them to the SMB server
-when using clear text authentication.
-</para>
-
-<para><programlisting>
- <ulink url="smb.conf.5.html#PASSWORDLEVEL">passsword level</ulink> = <replaceable>integer</replaceable>
- <ulink url="smb.conf.5.html#USERNAMELEVEL">username level</ulink> = <replaceable>integer</replaceable>
-</programlisting></para>
-
-<para>
-By default Samba will lower case the username before attempting to lookup the user
-in the database of local system accounts. Because UNIX usernames conventionally
-only contain lower case character, the <parameter>username level</parameter> parameter
-is rarely needed.
-</para>
-
-<para>
-However, passwords on UNIX systems often make use of mixed case characters.
-This means that in order for a user on a Windows 9x client to connect to a Samba
-server using clear text authentication, the <parameter>password level</parameter>
-must be set to the maximum number of upper case letter which <emphasis>could</emphasis>
-appear is a password. Note that the server OS uses the traditional DES version
-of crypt(), a <parameter>password level</parameter> of 8 will result in case
-insensitive passwords as seen from Windows users. This will also result in longer
-login times as Samba has to compute the permutations of the password string and
-try them one by one until a match is located (or all combinations fail).
-</para>
-
-<para>
-The best option to adopt is to enable support for encrypted passwords
-where ever Samba is used. There are three configuration possibilities
-for support of encrypted passwords:
-</para>
-
-</sect3>
-<sect3>
-<title>Use MS Windows NT as an authentication server</title>
-
-<para>
-This method involves the additions of the following parameters in the &smb.conf; file:
-</para>
-
-<para><programlisting>
- encrypt passwords = Yes
- security = server
- password server = "NetBIOS_name_of_PDC"
-</programlisting></para>
-
-
-<para>
-There are two ways of identifying whether or not a username and
-password pair was valid or not. One uses the reply information provided
-as part of the authentication messaging process, the other uses
-just an error code.
-</para>
-
-<para>
-The down-side of this mode of configuration is the fact that
-for security reasons Samba will send the password server a bogus
-username and a bogus password and if the remote server fails to
-reject the username and password pair then an alternative mode
-of identification of validation is used. Where a site uses password
-lock out after a certain number of failed authentication attempts
-this will result in user lockouts.
-</para>
-
-<para>
-Use of this mode of authentication does require there to be
-a standard Unix account for the user, this account can be blocked
-to prevent logons by other than MS Windows clients.
-</para>
-
-</sect3>
-</sect2>
-
-<sect2>
-<title>Domain Level Security</title>
-
-<para>
-When samba is operating in <emphasis>security = domain</emphasis> mode this means that
-the Samba server has a domain security trust account (a machine account) and will cause
-all authentication requests to be passed through to the domain controllers.
-</para>
-
-<sect3>
-<title>Samba as a member of an MS Windows NT security domain</title>
-
-<para>
-This method involves addition of the following parameters in the &smb.conf; file:
-</para>
-
-<para><programlisting>
- encrypt passwords = Yes
- security = domain
- workgroup = "name of NT domain"
- password server = *
-</programlisting></para>
-
-<para>
-The use of the "*" argument to <command>password server</command> will cause samba to locate the
-domain controller in a way analogous to the way this is done within MS Windows NT.
-This is the default behaviour.
-</para>
-
-<para>
-In order for this method to work the Samba server needs to join the
-MS Windows NT security domain. This is done as follows:
-</para>
-
-<itemizedlist>
- <listitem><para>On the MS Windows NT domain controller using
- the Server Manager add a machine account for the Samba server.
- </para></listitem>
-
- <listitem><para>Next, on the Linux system execute:
- <command>smbpasswd -r PDC_NAME -j DOMAIN_NAME</command> (samba 2.x)
-
- <command>net join -U administrator%password</command> (samba-3)
- </para></listitem>
-</itemizedlist>
-
-<para>
-Use of this mode of authentication does require there to be a standard Unix account
-for the user in order to assign a uid once the account has been authenticated by
-the remote Windows DC. This account can be blocked to prevent logons by clients other than
-MS Windows through things such as setting an invalid shell in the
-<filename>/etc/passwd</filename> entry.
-</para>
-
-<para>
-An alternative to assigning UIDs to Windows users on a Samba member server is
-presented in the <link linkend="winbind">Winbind Overview</link> chapter
-in this HOWTO collection.
-</para>
-
-</sect3>
-</sect2>
-
-<sect2>
-<title>ADS Level Security</title>
-
-<para>
-For information about the configuration option please refer to the entire section entitled
-<emphasis>Samba as an ADS Domain Member.</emphasis>
-</para>
-
-</sect2>
-</sect1>
-</chapter>