diff options
Diffstat (limited to 'share/doc/handbook/skey.sgml')
| -rw-r--r-- | share/doc/handbook/skey.sgml | 302 |
1 files changed, 0 insertions, 302 deletions
diff --git a/share/doc/handbook/skey.sgml b/share/doc/handbook/skey.sgml deleted file mode 100644 index ec80aed..0000000 --- a/share/doc/handbook/skey.sgml +++ /dev/null @@ -1,302 +0,0 @@ -<!-- $Id$ --> -<!-- The FreeBSD Documentation Project --> -<!-- -Copyright 1995 Massachusetts Institute of Technology - -Permission to use, copy, modify, and distribute this software and -its documentation for any purpose and without fee is hereby -granted, provided that both the above copyright notice and this -permission notice appear in all copies, that both the above -copyright notice and this permission notice appear in all -supporting documentation, and that the name of M.I.T. not be used -in advertising or publicity pertaining to distribution of the -software without specific, written prior permission. M.I.T. makes -no representations about the suitability of this software for any -purpose. It is provided "as is" without express or implied -warranty. - -THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS -ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE, -INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF -MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT -SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, -SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT -LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF -USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND -ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, -OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT -OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF -SUCH DAMAGE. ---> - -<sect><heading>S/Key<label id="skey"></heading> - -<p><em>Contributed by &a.wollman;<newline>25 September 1995.</em> - -<p>S/Key is a one-time password scheme based on a one-way hash function -(in our version, this is MD4 for compatibility; other versions have -used MD5 and DES-MAC). S/Key has been a standard part of all FreeBSD -distributions since version 1.1.5, and is also implemented on a large -and growing number of other systems. S/Key is a registered trademark -of Bell Communications Research, Inc. - -<!-- XXX - is there a better word to use than UNIX? --> -<p>There are three different sorts of passwords which we will talk about -in the discussion below. The first is your usual UNIX-style or Kerberos -password; we will call this a ``UNIX password''. The second sort is the -one-time password which is generated by the S/Key `<tt/key/' program and -accepted by the `<tt/keyinit/' program and the login prompt; we will call -this a ``one-time password''. The final sort of password is the -secret password which you give to the `<tt/key/' program (and sometimes the -`<tt/keyinit/' program) which it uses to generate one-time passwords; we will -call it a ``secret password'' or just unqualified ``password''. - -<p>The secret password does not necessarily have anything to do with your -UNIX password (while they can be the same, this is not recommended). -While UNIX passwords are limited to eight characters in length, your -S/Key secret password can be as long as you like; I use seven-word -phrases. In general, the S/Key system operates completely -independently of the UNIX password system. - -<p>There are in addition two other sorts of data involved in the S/Key -system; one is called the ``seed'' or (confusingly) ``key'', and -consists of two letters and five digits, and the other is the -``iteration count'' and is a number between 100 and 1. S/Key -constructs a one-time password from these components by concatenating -the seed and the secret password, then applying a one-way hash (the -RSA Data Security, Inc., MD4 secure hash function) iteration-count -times, and turning the result into six short English words. The -`<tt/login/' and `<tt/su/' programs keep track of the last one-time -password used, and the user is authenticated if the hash of the -user-provided password is equal to the previous password. Because a -one-way hash function is used, it is not possible to generate future -one-time passwords having overheard one which was successfully used; -the iteration count is decremented after each successful login to keep -the user and login program in sync. (When you get the iteration count -down to 1, it is time to reinitialize S/Key.) - -<p>There are four programs involved in the S/Key system which we will -discuss below. The `<tt/key/' program accepts an iteration count, a -seed, and a secret password, and generates a one-time password. The -`<tt/keyinit/' program is used to initialized S/Key, and to change -passwords, iteration counts, or seeds; it takes either a secret -password, or an iteration count, seed, and one-time password. The -`<tt/keyinfo/' program examines the <tt>/etc/skeykeys</tt> file and -prints out the invoking user's current iteration count and seed. -Finally, the `<tt/login/' and `<tt/su/' programs contain the necessary -logic to accept S/Key one-time passwords for authentication. The -`<tt/login/' program is also capable of disallowing the use of UNIX -passwords on connections coming from specified addresses. - -<p>There are four different sorts of operations we will cover. The first -is using the `<tt/keyinit/' program over a secure connection to set up -S/Key for the first time, or to change your password or seed. The -second operation is using the `<tt/keyinit/' program over an insecure -connection, in conjunction with the `<tt/key/' program over a secure -connection, to do the same. The third is using the `<tt/key/' program to -log in over an insecure connection. The fourth is using the `<tt/key/' -program to generate a number of keys which can be written down or -printed out to carry with you when going to some location without -secure connections to anywhere (like at a conference). - -<sect1><heading>Secure connection initialization</heading> - -<p>To initialize S/Key, change your password, or change your seed while -logged in over a secure connection (e.g., on the console of a machine), -use the `<tt/keyinit/' command without any parameters while logged in as -yourself: - -<tscreen><verb> -$ keyinit -Updating wollman: ) these will not appear if you -Old key: ha73895 ) have not used S/Key before -Reminder - Only use this method if you are directly connected. -If you are using telnet or rlogin exit with no password and use keyinit -s. -Enter secret password: ) I typed my pass phrase here -Again secret password: ) I typed it again - -ID wollman s/key is 99 ha73896 ) discussed below -SAG HAS FONT GOUT FATE BOOM ) -</verb></tscreen> - -<p>There is a lot of information here. At the `Enter secret password:' -prompt, you should enter some password or phrase (I use phrases of -minimum seven words) which will be needed to generate login keys. The -line starting `ID' gives the parameters of your particular S/Key -instance: your login name, the iteration count, and seed. When -logging in with S/Key, the system will remember these parameters and -present them back to you so you do not have to remember them. The last -line gives the particular one-time password which corresponds to those -parameters and your secret password; if you were to re-login -immediately, this one-time password is the one you would use. - -<sect1><heading>Insecure connection initialization</heading> - -<p>To initialize S/Key or change your password or seed over an insecure -connection, you will need to already have a secure connection to some -place where you can run the `<tt/key/' program; this might be in the form -of a desk accessory on a Macintosh, or a shell prompt on a machine you -trust (we will show the latter). You will also need to make up an -iteration count (100 is probably a good value), and you may make up -your own seed or use a randomly-generated one. Over on the insecure -connection (to the machine you are initializing), use the `<tt/keyinit -s/' -command: - -<tscreen><verb> -$ keyinit -s -Updating wollman: -Old key: kh94741 -Reminder you need the 6 English words from the skey command. -Enter sequence count from 1 to 9999: 100 ) I typed this -Enter new key [default kh94742]: -s/key 100 kh94742 -</verb></tscreen> - -To accept the default seed (which the `keyinit' program confusingly -calls a `key'), press return. Then move over to your secure -connection or S/Key desk accessory, and give it the same parameters: - -<tscreen><verb> -$ key 100 kh94742 -Reminder - Do not use this program while logged in via telnet or rlogin. -Enter secret password: ) I typed my secret password -HULL NAY YANG TREE TOUT VETO -</verb></tscreen> - -Now switch back over to the insecure connection, and copy the one-time -password generated by `<tt/key/' over to the `<tt/keyinit/' program: - -<tscreen><verb> -s/key access password: HULL NAY YANG TREE TOUT VETO - -ID wollman s/key is 100 kh94742 -HULL NAY YANG TREE TOUT VETO -</verb></tscreen> - -The rest of the description from the previous section applies here as -well. - -<sect1><heading>Diversion: a login prompt</heading> - -<p>Before explaining how to generate one-time passwords, we should go -over an S/Key login prompt: - -<tscreen><verb> -$ telnet himalia -Trying 18.26.0.186... -Connected to himalia.lcs.mit.edu. -Escape character is '^]'. -s/key 92 hi52030 -Password: -</verb></tscreen> - -Note that, before prompting for a password, the login program -prints out the iteration number and seed which you will need in order -to generate the appropriate key. You will also find a useful feature -(not shown here): if you press return at the password prompt, the -login program will turn echo on, so you can see what you are typing. -This can be extremely useful if you are attempting to type in an S/Key -by hand, such as from a printout. - -<p>If this machine were configured to disallow UNIX passwords over a -connection from my machine, the prompt would have also included the -annotation `<tt>(s/key required)</tt>', indicating that only S/Key one-time -passwords will be accepted. - -<sect1><heading>Generating a single one-time password</heading> - -<p>Now, to generate the one-time password needed to answer this login -prompt, we use a trusted machine and the `<tt/key/' program. (There are -versions of the `<tt/key/' program from DOS and Windows machines, and there -is an S/Key desk accessory for Macintosh computers as well.) The -command-line `<tt/key/' program takes as its parameters the iteration count -and seed; you can cut-and-paste right from the login prompt starting -at ``<tt/key/'' to the end of the line. Thus: - -<tscreen><verb> -$ key 92 hi52030 ) pasted from previous section -Reminder - Do not use this program while logged in via telnet or rlogin. -Enter secret password: ) I typed my secret password -ADEN BED WOLF HAW HOT STUN -</verb></tscreen> - -And in the other window: - -<tscreen><verb> -s/key 92 hi52030 ) from previous section -Password: - (turning echo on) -Password:ADEN BED WOLF HAW HOT STUN -Last login: Wed Jun 28 15:31:00 from halloran-eldar.l -[etc.] -</verb></tscreen> - -This is the easiest mechanism <em/if/ you have a trusted machine. - -<sect1><heading>Generating multiple one-time passwords</heading> - -<p>Sometimes we have to go places where no trusted machines or -connections are available. In this case, it is possible to use the -`<tt/key/' command to generate a number of one-time passwords in the same -command; these can then be printed out. For example: - -<tscreen><verb> -$ key -n 25 57 zz99999 -Reminder - Do not use this program while logged in via telnet or rlogin. -Enter secret password: -33: WALT THY MALI DARN NIT HEAD -34: ASK RICE BEAU GINA DOUR STAG -[...] -56: AMOS BOWL LUG FAT CAIN INCH -57: GROW HAYS TUN DISH CAR BALM -</verb></tscreen> - -The `<tt/-n 25/' requests twenty-five keys in sequence; the `<tt/57/' indicates -the <em/ending/ iteration number; and the rest is as before. Note that -these are printed out in <em/reverse/ order of eventual use. If you are -really paranoid, you might want to write the results down by hand; -otherwise you can cut-and-paste into `<tt/lpr/'. Note that each line shows -both the iteration count and the one-time password; you may still find -it handy to scratch off passwords as you use them. - -<sect1><heading>Restricting use of UNIX passwords</heading> - -<p>The configuration file <tt>/etc/skey.access</tt> can be used to -configure restrictions on the use of UNIX passwords based on the host -name, user name, terminal port, or IP address of a login session. The -complete format of the file is documented in the <em/skey.access/(5) -manual page; there are also some security cautions there which should -be read before depending on this file for security. - -<p>If there is no <tt>/etc/skey.access</tt> file (which is the default -state as FreeBSD is shipped), then all users will be allowed to use -UNIX passwords. If the file exists, however, then all users will be -required to use S/Key unless explicitly permitted to do otherwise by -configuration statements in the <tt/skey.access/ file. In all cases, -UNIX passwords are permitted on the console. - -<p>Here is a sample configuration file which illustrates the three most -common sorts of configuration statements: - -<tscreen><verb> -permit internet 18.26.0.0 255.255.0.0 -permit user jrl -permit port ttyd0 -</verb></tscreen> - -The first line (`<tt/permit internet/') allows users whose IP source -address (which is vulnerable to spoofing) matches the specified value -and mask, to use UNIX passwords. This should not be considered a -security mechanism, but rather, a means to remind authorized users -that they are using an insecure network and need to use S/Key for -authentication. - -<p>The second line (`<tt/permit user/') allows the specified user to -use UNIX passwords at any time. Generally speaking, this should only -be used for people who are either unable to use the `<tt/key/' -program, like those with dumb terminals, or those who are uneducable. - -<p>The third line (`<tt/permit port/') allows all users logging in on -the specified terminal line to use UNIX passwords; this would be used -for dial-ups. - |
