Add some text I originally wrote for work describing how to use
S/Key.
This commit is contained in:
Garrett Wollman
parent
e508a00419
commit
82af4efbfc
@ -1,4 +1,4 @@
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# $Id: Makefile,v 1.1 1995/09/08 19:34:26 jfieber Exp $
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# $Id: Makefile,v 1.2 1995/09/25 04:53:26 jfieber Exp $
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SRCS= authors.sgml basics.sgml bibliography.sgml boothelp.sgml
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SRCS+= booting.sgml contrib.sgml crypt.sgml ctm.sgml current.sgml dialup.sgml
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@ -6,7 +6,7 @@ SRCS+= diskless.sgml dma.sgml eresources.sgml esdi.sgml glossary.sgml
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SRCS+= handbook.sgml history.sgml hw.sgml install.sgml kerberos.sgml
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SRCS+= kerneldebug.sgml memoryuse.sgml mirrors.sgml nfs.sgml nutshell.sgml
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SRCS+= porting.sgml ports.sgml ppp.sgml relnotes.sgml scsi.sgml sections.sgml
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SRCS+= slipc.sgml slips.sgml submitters.sgml sup.sgml
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SRCS+= skey.sgml slipc.sgml slips.sgml submitters.sgml sup.sgml
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SRCS+= troubleshooting.sgml userppp.sgml
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.include <bsd.sgml.mk>
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@ -1,4 +1,4 @@
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<!-- $Id: handbook.sgml,v 1.27 1995/09/03 21:12:27 jfieber Exp $ -->
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<!-- $Id: handbook.sgml,v 1.28 1995/09/25 04:53:31 jfieber Exp $ -->
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<!-- The FreeBSD Documentation Project -->
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<!DOCTYPE linuxdoc PUBLIC "-//FreeBSD//DTD linuxdoc//EN" [
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@ -76,7 +76,7 @@ Web server">.
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<chapt><heading>Users, groups and security</heading>
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&crypt;
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<sect><heading>* S/Key</heading>
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&skey;
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&kerberos;
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<sect><heading>* Firewalls</heading>
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@ -1,4 +1,4 @@
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<!-- $Id: sections.sgml,v 1.1 1995/09/03 21:12:29 jfieber Exp $ -->
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<!-- $Id: sections.sgml,v 1.2 1995/09/25 04:53:33 jfieber Exp $ -->
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<!-- The FreeBSD Documentation Project -->
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<!-- Entities containing all the pieces of the handbook are -->
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@ -32,6 +32,7 @@
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<!ENTITY ppp SYSTEM "ppp.sgml">
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<!ENTITY relnotes SYSTEM "relnotes.sgml">
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<!ENTITY scsi SYSTEM "scsi.sgml">
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<!ENTITY skey SYSTEM "skey.sgml">
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<!ENTITY slipc SYSTEM "slipc.sgml">
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<!ENTITY slips SYSTEM "slips.sgml">
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<!ENTITY submitters SYSTEM "submitters.sgml">
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302
share/doc/handbook/skey.sgml
Normal file
302
share/doc/handbook/skey.sgml
Normal file
@ -0,0 +1,302 @@
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<!-- $Id$ -->
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<!-- The FreeBSD Documentation Project -->
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<!--
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Copyright 1995 Massachusetts Institute of Technology
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Permission to use, copy, modify, and distribute this software and
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its documentation for any purpose and without fee is hereby
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granted, provided that both the above copyright notice and this
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permission notice appear in all copies, that both the above
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copyright notice and this permission notice appear in all
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supporting documentation, and that the name of M.I.T. not be used
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in advertising or publicity pertaining to distribution of the
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software without specific, written prior permission. M.I.T. makes
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no representations about the suitability of this software for any
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purpose. It is provided "as is" without express or implied
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warranty.
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THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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SUCH DAMAGE.
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-->
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<sect><heading>S/Key<label id="skey"></heading>
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<p><em>Contributed by &a.wollman;<newline>25 September 1995.</em>
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<p>S/Key is a one-time password scheme based on a one-way hash function
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(in our version, this is MD4 for compatibility; other versions have
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used MD5 and DES-MAC). S/Key has been a standard part of all FreeBSD
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distributions since version 1.1.5, and is also implemented on a large
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and growing number of other systems. S/Key is a registered trademark
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of Bell Communications Research, Inc.
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<!-- XXX - is there a better word to use than UNIX? -->
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<p>There are three different sorts of passwords which we will talk about
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in the discussion below. The first is your usual UNIX-style or Kerberos
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password; we'll call this a ``UNIX password''. The second sort is the
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one-time password which is generated by the S/Key `<tt/key/' program and
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accepted by the `<tt/keyinit/' program and the login prompt; we'll call
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this a ``one-time password''. The final sort of password is the
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secret password which you give to the `<tt/key/' program (and sometimes the
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`<tt/keyinit/' program) which it uses to generate one-time passwords; we'll
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call it a ``secret password'' or just unqualified ``password''.
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<p>The secret password does not necessarily have anything to do with your
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UNIX password (while they can be the same, this is not recommended).
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While UNIX passwords are limited to eight characters in length, your
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S/Key secret password can be as long as you like; I use seven-word
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phrases. In general, the S/Key system operates completely
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independently of the UNIX password system.
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<p>There are in addition two other sorts of data involved in the S/Key
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system; one is called the ``seed'' or (confusingly) ``key'', and
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consists of two letters and five digits, and the other is the
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``iteration count'' and is a number between 100 and 1. S/Key
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constructs a one-time password from these components by concatenating
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the seed and the secret password, then applying a one-way hash (the
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RSA Data Security, Inc., MD4 secure hash function) iteration-count
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times, and turning the result into six short English words. The
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`<tt/login/' and `<tt/su/' programs keep track of the last one-time
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password used, and the user is authenticated if the hash of the
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user-provided password is equal to the previous password. Because a
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one-way hash function is used, it is not possible to generate future
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one-time passwords having overheard one which was successfully used;
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the iteration count is decremented after each successful login to keep
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the user and login program in sync. (When you get the iteration count
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down to 1, it's time to reinitialize S/Key.)
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<p>There are four programs involved in the S/Key system which we will
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discuss below. The `<tt/key/' program accepts an iteration count, a
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seed, and a secret password, and generates a one-time password. The
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`<tt/keyinit/' program is used to initialized S/Key, and to change
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passwords, iteration counts, or seeds; it takes either a secret
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password, or an iteration count, seed, and one-time password. The
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`<tt/keyinfo/' program examines the <tt>/etc/skeykeys</tt> file and
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prints out the invoking user's current iteration count and seed.
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Finally, the `<tt/login/' and `<tt/su/' programs contain the necessary
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logic to accept S/Key one-time passwords for authentication. The
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`<tt/login/' program is also capable of disallowing the use of UNIX
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passwords on connections coming from specified addresses.
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<p>There are four different sorts of operations we will cover. The first
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is using the `<tt/keyinit/' program over a secure connection to set up
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S/Key for the first time, or to change your password or seed. The
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second operation is using the `<tt/keyinit/' program over an insecure
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connection, in conjunction with the `<tt/key/' program over a secure
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connection, to do the same. The third is using the `<tt/key/' program to
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log in over an insecure connection. The fourth is using the `<tt/key/'
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program to generate a number of keys which can be written down or
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printed out to carry with you when going to some location without
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secure connections to anywhere (like at a conference).
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<sect1><heading>Secure connection initialization</heading>
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<p>To initialize S/Key, change your password, or change your seed while
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logged in over a secure connection (e.g., on the console of a machine),
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use the `<tt/keyinit/' command without any parameters while logged in as
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yourself:
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<tscreen><verb>
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$ keyinit
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Updating wollman: ) these will not appear if you
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Old key: ha73895 ) have not used S/Key before
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Reminder - Only use this method if you are directly connected.
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If you are using telnet or rlogin exit with no password and use keyinit -s.
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Enter secret password: ) I typed my pass phrase here
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Again secret password: ) I typed it again
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ID wollman s/key is 99 ha73896 ) discussed below
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SAG HAS FONT GOUT FATE BOOM )
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</verb></tscreen>
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<p>There is a lot of information here. At the `Enter secret password:'
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prompt, you should enter some password or phrase (I use phrases of
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minimum seven words) which will be needed to generate login keys. The
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line starting `ID' gives the parameters of your particular S/Key
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instance: your login name, the iteration count, and seed. When
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logging in with S/Key, the system will remember these parameters and
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present them back to you so you don't have to remember them. The last
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line gives the particular one-time password which corresponds to those
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parameters and your secret password; if you were to re-login
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immediately, this one-time password is the one you would use.
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<sect1><heading>Insecure connection initialization</heading>
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<p>To initialize S/Key or change your password or seed over an insecure
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connection, you will need to already have a secure connection to some
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place where you can run the `<tt/key/' program; this might be in the form
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of a desk accessory on a Macintosh, or a shell prompt on a machine you
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trust (we'll show the latter). You will also need to make up an
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iteration count (100 is probably a good value), and you may make up
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your own seed or use a randomly-generated one. Over on the insecure
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connection (to the machine you are initializing), use the `<tt/keyinit -s/'
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command:
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<tscreen><verb>
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$ keyinit -s
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Updating wollman:
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Old key: kh94741
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Reminder you need the 6 english words from the skey command.
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Enter sequence count from 1 to 9999: 100 ) I typed this
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Enter new key [default kh94742]:
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s/key 100 kh94742
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</verb></tscreen>
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To accept the default seed (which the `keyinit' program confusingly
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calls a `key'), press return. Then move over to your secure
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connection or S/Key desk accessory, and give it the same parameters:
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<tscreen><verb>
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$ key 100 kh94742
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Reminder - Do not use this program while logged in via telnet or rlogin.
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Enter secret password: ) I typed my secret password
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HULL NAY YANG TREE TOUT VETO
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</verb></tscreen>
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Now switch back over to the insecure connection, and copy the one-time
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password generated by `<tt/key/' over to the `<tt/keyinit/' program:
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<tscreen><verb>
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s/key access password: HULL NAY YANG TREE TOUT VETO
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ID wollman s/key is 100 kh94742
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HULL NAY YANG TREE TOUT VETO
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</verb></tscreen>
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The rest of the description from the previous section applies here as
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well.
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<sect1><heading>Diversion: a login prompt</heading>
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<p>Before explaining how to generate one-time passwords, we should go
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over an S/Key login prompt:
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<tscreen><verb>
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$ telnet himalia
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Trying 18.26.0.186...
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Connected to himalia.lcs.mit.edu.
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Escape character is '^]'.
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s/key 92 hi52030
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Password:
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</verb></tscreen>
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>Note that, before prompting for a password, the login program
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prints out the iteration number and seed which you will need in order
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to generate the appropriate key. You will also find a useful feature
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(not shown here): if you press return at the password prompt, the
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login program will turn echo on, so you can see what you are typing.
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This can be extremely useful if you are attempting to type in an S/Key
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by hand, such as from a printout.
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<p>If this machine were configured to disallow UNIX passwords over a
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connection from my machine, the prompt would have also included the
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annotation `<tt>(s/key required)</tt>', indicating that only S/Key one-time
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passwords will be accepted.
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<sect1><heading>Generating a single one-time password</heading>
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<p>Now, to generate the one-time password needed to answer this login
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prompt, we use a trusted machine and the `<tt/key/' program. (There are
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versions of the `<tt/key/' program from DOS and Windows machines, and there
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is an S/Key desk accessory for Macintosh computers as well.) The
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command-line `<tt/key/' program takes as its parameters the iteration count
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and seed; you can cut-and-paste right from the login prompt starting
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at ``<tt/key/'' to the end of the line. Thus:
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<tscreen><verb>
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$ key 92 hi52030 ) pasted from previous section
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Reminder - Do not use this program while logged in via telnet or rlogin.
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Enter secret password: ) I typed my secret password
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ADEN BED WOLF HAW HOT STUN
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</verb></tscreen>
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And in the other window:
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<tscreen><verb>
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s/key 92 hi52030 ) from previous section
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Password:
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(turning echo on)
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Password:ADEN BED WOLF HAW HOT STUN
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Last login: Wed Jun 28 15:31:00 from halloran-eldar.l
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[etc.]
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</verb></tscreen>
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This is the easiest mechanism <em/if/ you have a trusted machine.
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<sect1><heading>Generating multiple one-time passwords</heading>
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<p>Sometimes we have to go places where no trusted machines or
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connections are available. In this case, it is possible to use the
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`<tt/key/' command to generate a number of one-time passwords in the same
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command; these can then be printed out. For example:
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<tscreen><verb>
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$ key -n 25 57 zz99999
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Reminder - Do not use this program while logged in via telnet or rlogin.
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Enter secret password:
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33: WALT THY MALI DARN NIT HEAD
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34: ASK RICE BEAU GINA DOUR STAG
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[...]
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56: AMOS BOWL LUG FAT CAIN INCH
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57: GROW HAYS TUN DISH CAR BALM
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</verb></tscreen>
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The `<tt/-n 25/' requests twenty-five keys in sequence; the `<tt/57/' indicates
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the <em/ending/ iteration number; and the rest is as before. Note that
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these are printed out in <em/ending/ order of eventual use. If you're
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really paranoid, you might want to write the results down by hand;
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otherwise you can cut-and-paste into `<tt/lpr/'. Note that each line shows
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both the iteration count and the one-time password; you may still find
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it handy to scratch off passwords as you use them.
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<sect1><heading>Restricting use of UNIX passwords</heading>
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<p>The configuration file <tt>/etc/skey.access</tt> can be used to
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configure restrictions on the use of UNIX passwords based on the host
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name, user name, terminal port, or IP address of a login session. The
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complete format of the file is documented in the <em/skey.access/(5)
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manual page; there are also some security cautions there which should
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be read before depending on this file for security.
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<p>If there is no <tt>/etc/skey.access</tt> file (which is the default
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state as FreeBSD is shipped), then all users will be allowed to use
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UNIX passwords. If the file exists, however, then all users will be
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required to use S/Key unless explicitly permitted to do otherwise by
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configuration statements in the <tt/skey.access/ file. In all cases,
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UNIX passwords are permitted on the console.
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<p>Here is a sample configuration file which illustrates the three most
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common sorts of configuration statements:
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<tscreen><verb>
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permit internet 18.26.0.0 255.255.0.0
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permit user jrl
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permit port ttyd0
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</verb></tscreen>
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The first line (`<tt/permit internet/') allows users whose IP source
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address (which is vulnerable to spoofing) matches the specified value
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and mask, to use UNIX passwords. This should not be considered a
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security mechanism, but rather, a means to remind authorized users
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that they are using an insecure network and need to use S/Key for
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authentication.
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<p>The second line (`<tt/permit user/') allows the specified user to
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use UNIX passwords at any time. Generally speaking, this should only
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be used for people who are either unable to use the `<tt/key/'
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program, like those with dumb terminls, or those who are uneducable.
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<p>The third line (`<tt/permit port/') allows all users logging in on
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the specified terminal line to use UNIX passwords; this would be used
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for dial-ups.
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Loading…
Reference in New Issue
Block a user