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diff --git a/docs/textdocs/ENCRYPTION.txt b/docs/textdocs/ENCRYPTION.txt index 046b473e9a1..010446915ad 100644 --- a/docs/textdocs/ENCRYPTION.txt +++ b/docs/textdocs/ENCRYPTION.txt @@ -1,9 +1,16 @@ - LanManager / Samba Password Encryption. - --------------------------------------- +!== +!== ENCRYPTION.txt for Samba release 2.0.0-alpha6 19 Sep 1998 +!== +Contributor: Jeremy Allison <samba-bugs@samba.anu.edu.au> +Updated: March 19, 1998 +Note: Please refer to WinNT.txt also -With the development of LanManager 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. +Subject: LanManager / Samba Password Encryption. +============================================================================ + +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. This document describes how the SMB password encryption algorithm works and what issues there are in choosing whether you want to use @@ -13,15 +20,19 @@ and the "PROS and CONS" section. How does it work ? ------------------ - LanManager encryption is somewhat similar to UNIX password +LanManager encryption is somewhat similar to UNIX password encryption. The server uses a file containing a hashed value of a -users password. This is created by taking the users paintext +users password. This is created by taking the users 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*. +Windows NT encryption is a higher quality mechanism, consisting +of doing an MD4 hash on a Unicode version of the users password. This +also produces a 16 byte hash value that is non-reversible. + 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 @@ -31,7 +42,7 @@ Samba server after the reply is sent and is known as the *challenge*. The challenge is different for every client connection. -The client then uses the hashed password (16 byte value described +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*. @@ -39,6 +50,9 @@ value known as the *response*. 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 users password and both responses are returned +in the SMB call, giving two 24 byte values. The Samba server then reproduces the above calculation, using it's own stored value of the 16 byte hashed password (read from the smbpasswd @@ -52,8 +66,8 @@ is this allowed access. If not then the client did not know the correct password and is denied access. Note that the Samba server never knows or stores the cleartext of the -users password - just the 16 byte hashed function derived from it. Also -note that the cleartext password or 16 byte hashed value are never +users 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. IMPORTANT NOTE ABOUT SECURITY @@ -63,10 +77,10 @@ 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 nextwork 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 value -on disk. This is also bad. Why? Because the 16 byte hashed value is a -"password equivalent". You cannot derive the users password from it, -but it could potentially be used in a modified client to gain access +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 users 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 @@ -108,17 +122,18 @@ ftp ftp) which send plain text passwords over the net, so not sending them for SMB isn't such a big deal. -- the SMB encryption code in Samba is new and has only had limited -testing. We have tried hard to make it secure but in any new -implementation of a password scheme there is the possability of an -error. - +Note that Windows NT 4.0 Service pack 3 changed the default for +permissible authentication so that plaintext passwords are *never* +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. The smbpasswd file. ------------------- - In order for Samba to participate in the above protocol it must -be able to look up the 16 byte hashed value given a user name. +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 users password given the UNIX hash of it) then a separate password file @@ -162,14 +177,16 @@ chmod 600 smbpasswd. The format of the smbpasswd file is -username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:Long name:user home dir:user shell +username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:Long name:user home dir:user shell Although only the username, uid, and XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX sections are significant and are looked at in the Samba code. It is *VITALLY* important that there by 32 'X' characters between the -two ':' characters - the smbpasswd and Samba code will fail to validate -any entries that do not have 32 characters between ':' characters. +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. When the password file is created all users have password entries consisting of 32 'X' characters. By default this disallows any access @@ -185,12 +202,21 @@ NO PASSWORD Eg. To clear the password for user bob, his smbpasswd file entry would look like : -bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:Bob's full name:/bobhome:/bobshell +bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:Bob's full name:/bobhome:/bobshell 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). +password (not recommended). In order for you to allow this the +smbpasswd program must be able to connect to the smbd daemon as +that user with no password. Enable this by adding the line : + +null passwords = true + +to the [global] section of the smb.conf file (this is why the +above scenario is not recommended). Preferebly, allocate your +users a default password to begin with, so you do not have +to enable this on your server. Note : This file should be protected very carefully. Anyone with access to this file can (with enough knowledge of the protocols) gain @@ -200,25 +226,31 @@ normal unix /etc/passwd file. The smbpasswd Command. ---------------------- - The smbpasswd command maintains the 32 byte password field in +The smbpasswd command maintains the two 32 byte password fields in the smbpasswd file. If you wish to make it similar to the unix passwd or yppasswd programs, install it in /usr/local/samba/bin (or your main -Samba binary directory) and make it setuid root. +Samba binary directory). -Note that if you do not do this then the root user will have to set all -users passwords. +Note that as of Samba 1.9.18p4 this program MUST NOT BE INSTALLED +setuid root (the new smbpasswd code enforces this restriction so +it cannot be run this way by accident). -To set up smbpasswd as setuid root, change to the Samba binary install -directory and then type (as root) : +smbpasswd now works in a client-server mode where it contacts +the local smbd to change the users password on its behalf. This +has enormous benefits - as follows. -chown root smbpasswd -chmod 4555 smbpasswd +1). smbpasswd no longer has to be setuid root - an enourmous +range of potential security problems is eliminated. -If smbpasswd is installed as setuid root then you would use it as -follows. +2). smbpasswd 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 users password). + +To run smbpasswd as a normal user just type : smbpasswd -Old SMB password: <type old alue here - just hit return if there is NO PASSWORD> +Old SMB password: <type old value here - or hit return if there was no old password > New SMB Password: < type new value > Repeat New SMB Password: < re-type new value > @@ -238,15 +270,8 @@ forgotten their passwords. smbpasswd is designed to work in the same way and be familiar to UNIX users who use the passwd or yppasswd commands. -NOTE. As smbpasswd is designed to be installed as setuid root I would -appreciate it if everyone examined the source code to look for -potential security flaws. A setuid program, if not written properly can -be an open door to a system cracker. Please help make this program -secure by reporting all problems to me (the author, Jeremy Allison). - -My email address is :- - -jra@vantive.com +For more details on using smbpasswd refer to the man page which +will always be the definitive reference. Setting up Samba to support LanManager Encryption. -------------------------------------------------- @@ -255,27 +280,15 @@ This is a very brief description on how to setup samba to support password encryption. More complete instructions will probably be added later. -1) get and compile the libdes libraries. the source is available from -nimbus.anu.edu.au in pub/tridge/libdes/libdes.tar.92-10-13.gz - -2) enable the encryption stuff in the Samba makefile, making sure you -point it to the libdes library and include file (it needs des.h) -The entries you need to uncomment are the four lines after the comment :- - -# This is for SMB encrypted (lanman) passwords. +1) compile and install samba as usual -Note that you may have to change the variable DES_BASE to -point at the place where you installed the DES library. - -3) compile and install samba as usual - -4) f your system can't compile the module getsmbpass.c then remove the +2) if your system can't compile the module getsmbpass.c then remove the -DSMBGETPASS define from the Makefile. -5) enable encrypted passwords in smb.conf by adding the line +3) enable encrypted passwords in smb.conf by adding the line "encrypt passwords = yes" in the [global] section -6) create the initial smbpasswd password file in the place you +4) create the initial smbpasswd password file in the place you specified in the Makefile. A simple way to do this based on your existing Makefile (assuming it is in a reasonably standard format) is like this: @@ -300,34 +313,18 @@ If this fails then you will find that you will need entries that look like this: # SMB password file. -tridge:148:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:Andrew Tridgell:/home/tridge:/bin/tcsh +tridge:148:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:Andrew Tridgell:/home/tridge:/bin/tcsh note that the uid and username fields must be right. Also, you must get the number of X's right (there should be 32). -If you wish, install the smbpasswd program as suid root. - -chown root /usr/local/samba/bin/smbpasswd -chmod 4555 /usr/local/samba/bin/smbpasswd - -7) set the passwords for users using the smbpasswd command. For +5) set the passwords for users using the smbpasswd command. For example, as root you could do "smbpasswd tridge" -8) try it out! +6) try it out! Note that you can test things using smbclient, as it also now supports encryption. -NOTE TO USA Sites that Mirror Samba ------------------------------------ - -The DES library is considered a munition in the USA. Under US Law it is -illegal to export this software, or to put it in a freely available ftp -site. - -Please do not mirror the DES directory from the site on nimbus.anu.edu.au - -Thank you, - -Jeremy Allison. - +============================================================================== +Footnote: Please refer to WinNT.txt also |