diff options
Diffstat (limited to 'docs/docbook/devdoc/encryption.xml')
| -rw-r--r-- | docs/docbook/devdoc/encryption.xml | 197 |
1 files changed, 0 insertions, 197 deletions
diff --git a/docs/docbook/devdoc/encryption.xml b/docs/docbook/devdoc/encryption.xml deleted file mode 100644 index 56a1d10c9c..0000000000 --- a/docs/docbook/devdoc/encryption.xml +++ /dev/null @@ -1,197 +0,0 @@ -<chapter id="pwencrypt"> - - -<chapterinfo> - <author> - <firstname>Jeremy</firstname><surname>Allison</surname> - <affiliation> - <orgname>Samba Team</orgname> - <address> - <email>samba@samba.org</email> - </address> - </affiliation> - </author> - - <pubdate>19 Apr 1999</pubdate> -</chapterinfo> - -<title>LanMan and NT Password Encryption</title> - -<sect1> - <title>Introduction</title> - - <para>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.</para> - - <para>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.</para> - -</sect1> - -<sect1> - <title>How does it work?</title> - - <para>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".</para> - - <para>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.</para> - - <para>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.</para> - - <para>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".</para> - - <para>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.</para> - - <para>The Samba server then reproduces the above calculation, using - its own stored value of the 16 byte hashed password (read from the - <filename>smbpasswd</filename> 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.</para> - - <para>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.</para> - - <para>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.</para> -</sect1> - -<sect1> - <title>The smbpasswd file</title> - <anchor id="SMBPASSWDFILEFORMAT"/> - <para>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 <filename> - /etc/passwd</filename> and the <filename>smbpasswd</filename> file, - a utility, <command>mksmbpasswd.sh</command>, is provided to generate - a smbpasswd file from a UNIX <filename>/etc/passwd</filename> file. - </para> - - - <para>To generate the smbpasswd file from your <filename>/etc/passwd - </filename> file use the following command:</para> - - <para><prompt>$ </prompt><userinput>cat /etc/passwd | mksmbpasswd.sh - > /usr/local/samba/private/smbpasswd</userinput></para> - - <para>If you are running on a system that uses NIS, use</para> - - <para><prompt>$ </prompt><userinput>ypcat passwd | mksmbpasswd.sh - > /usr/local/samba/private/smbpasswd</userinput></para> - - <para>The <command>mksmbpasswd.sh</command> program is found in - the Samba source directory. By default, the smbpasswd file is - stored in :</para> - - <para><filename>/usr/local/samba/private/smbpasswd</filename></para> - - <para>The owner of the <filename>/usr/local/samba/private/</filename> - directory should be set to root, and the permissions on it should - be set to 0500 (<command>chmod 500 /usr/local/samba/private</command>). - </para> - - <para>Likewise, the smbpasswd file inside the private directory should - be owned by root and the permissions on is should be set to 0600 - (<command>chmod 600 smbpasswd</command>).</para> - - - <para>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.)</para> - - <para><programlisting> -username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX: - [Account type]:LCT-<last-change-time>:Long name - </programlisting></para> - - <para>Although only the <replaceable>username</replaceable>, - <replaceable>uid</replaceable>, <replaceable> - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX</replaceable>, - [<replaceable>Account type</replaceable>] and <replaceable> - last-change-time</replaceable> sections are significant - and are looked at in the Samba code.</para> - - <para>It is <emphasis>VITALLY</emphasis> 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.</para> - - <para>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.</para> - - <para>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 - <constant>"NO PASSWORD"</constant> (minus the quotes).</para> - - <para>For example, to clear the password for user bob, his smbpasswd file - entry would look like :</para> - - <para><programlisting> -bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX: - [U ]:LCT-00000000:Bob's full name:/bobhome:/bobshell - </programlisting></para> - - <para>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 - <command>smbpasswd</command> program must be able to connect to the - <command>smbd</command> daemon as that user with no password. Enable this - by adding the line :</para> - - <para><command>null passwords = yes</command></para> - - <para>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.</para> - - <para><emphasis>Note : </emphasis>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 <filename>/etc/passwd</filename> file.</para> -</sect1> - -</chapter> |