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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta name="generator" content="HTML Tidy, see www.w3.org" /><title>One-time Passwords</title><meta name="GENERATOR" content="Modular DocBook HTML Stylesheet Version 1.7" /><link rel="HOME" title="FreeBSD Handbook" href="index.html" /><link rel="UP" title="Security" href="security.html" /><link rel="PREVIOUS" title="DES, MD5, and Crypt" href="crypt.html" /><link rel="NEXT" title="TCP Wrappers" href="tcpwrappers.html" /><link rel="STYLESHEET" type="text/css" href="docbook.css" /></head><body class="SECT1" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#840084"alink="#0000FF"><div class="NAVHEADER"><table summary="Header navigation table" width="100%" border="0" cellpadding="0"cellspacing="0"><tr><th colspan="3" align="center">FreeBSD Handbook</th></tr><tr><td width="10%" align="left" valign="bottom"><a href="crypt.html"accesskey="P">Prev</a></td><td width="80%" align="center" valign="bottom">Chapter 14 Security</td><td width="10%" align="right" valign="bottom"><a href="tcpwrappers.html"accesskey="N">Next</a></td></tr></table><hr align="LEFT" width="100%" /></div><div class="SECT1"><h1 class="SECT1"><a id="ONE-TIME-PASSWORDS" name="ONE-TIME-PASSWORDS">14.5 One-timePasswords</a></h1><p>S/Key is a one-time password scheme based on a one-way hash function. FreeBSD uses theMD4 hash for compatibility but other systems have used MD5 and DES-MAC. S/Key has beenpart of the FreeBSD base system since version 1.1.5 and is also used on a growing numberof other operating systems. S/Key is a registered trademark of Bell CommunicationsResearch, Inc.</p><p>From version 5.0 of FreeBSD, S/Key has been replaced with the functionally equivalentOPIE (One-time Passwords In Everything). OPIE uses the MD5 hash by default.</p><p>There are three different sorts of passwords which we will discuss below. The first isyour usual <span class="TRADEMARK">UNIX</span>® style or Kerberos password; we willcall this a ``<span class="TRADEMARK">UNIX</span> password''. The second sort is theone-time password which is generated by the S/Key <tt class="COMMAND">key</tt> program orthe OPIE <a href="http://www.FreeBSD.org/cgi/man.cgi?query=opiekey&sektion=1"><spanclass="CITEREFENTRY"><span class="REFENTRYTITLE">opiekey</span>(1)</span></a> program andaccepted by the <tt class="COMMAND">keyinit</tt> or <ahref="http://www.FreeBSD.org/cgi/man.cgi?query=opiepasswd&sektion=1"><spanclass="CITEREFENTRY"><span class="REFENTRYTITLE">opiepasswd</span>(1)</span></a> programsand the login prompt; we will call this a ``one-time password''. The final sort ofpassword is the secret password which you give to the <tt class="COMMAND">key</tt>/<ttclass="COMMAND">opiekey</tt> programs (and sometimes the <ttclass="COMMAND">keyinit</tt>/<tt class="COMMAND">opiepasswd</tt> programs) which it usesto generate one-time passwords; we will call it a ``secret password'' or just unqualified``password''.</p><p>The secret password does not have anything to do with your <spanclass="TRADEMARK">UNIX</span> password; they can be the same but this is not recommended.S/Key and OPIE secret passwords are not limited to 8 characters like old <spanclass="TRADEMARK">UNIX</span> passwords<a id="AEN19199" name="AEN19199"href="#FTN.AEN19199"><span class="footnote">[1]</span></a>, they can be as long as youlike. Passwords of six or seven word long phrases are fairly common. For the most part,the S/Key or OPIE system operates completely independently of the <spanclass="TRADEMARK">UNIX</span> password system.</p><p>Besides the password, there are two other pieces of data that are important to S/Keyand OPIE. One is what is known as the ``seed'' or ``key'', consisting of two letters andfive digits. The other is what is called the ``iteration count'', a number between 1 and100. S/Key creates the one-time password by concatenating the seed and the secretpassword, then applying the MD4/MD5 hash as many times as specified by the iterationcount and turning the result into six short English words. These six English words areyour one-time password. The authentication system (primarily PAM) keeps track of the lastone-time password used, and the user is authenticated if the hash of the user-providedpassword is equal to the previous password. Because a one-way hash is used it isimpossible to generate future one-time passwords if a successfully used password iscaptured; the iteration count is decremented after each successful login to keep the userand the login program in sync. When the iteration count gets down to 1, S/Key and OPIEmust be reinitialized.</p><p>There are three programs involved in each system which we will discuss below. The <ttclass="COMMAND">key</tt> and <tt class="COMMAND">opiekey</tt> programs accept aniteration count, a seed, and a secret password, and generate a one-time password or aconsecutive list of one-time passwords. The <tt class="COMMAND">keyinit</tt> and <ttclass="COMMAND">opiepasswd</tt> programs are used to initialize S/Key and OPIErespectively, and to change passwords, iteration counts, or seeds; they take either asecret passphrase, or an iteration count, seed, and one-time password. The <ttclass="COMMAND">keyinfo</tt> and <tt class="COMMAND">opieinfo</tt> programs examine therelevant credentials files (<tt class="FILENAME">/etc/skeykeys</tt> or <ttclass="FILENAME">/etc/opiekeys</tt>) and print out the invoking user's current iterationcount and seed.</p><p>There are four different sorts of operations we will cover. The first is using <ttclass="COMMAND">keyinit</tt> or <tt class="COMMAND">opiepasswd</tt> over a secureconnection to set up one-time-passwords for the first time, or to change your password orseed. The second operation is using <tt class="COMMAND">keyinit</tt> or <ttclass="COMMAND">opiepasswd</tt> over an insecure connection, in conjunction with <ttclass="COMMAND">key</tt> or <tt class="COMMAND">opiekey</tt> over a secure connection, todo the same. The third is using <tt class="COMMAND">key</tt>/<ttclass="COMMAND">opiekey</tt> to log in over an insecure connection. The fourth is using<tt class="COMMAND">key</tt> or <tt class="COMMAND">opiekey</tt> to generate a number ofkeys which can be written down or printed out to carry with you when going to somelocation without secure connections to anywhere.</p><div class="SECT2"><h2 class="SECT2"><a id="AEN19226" name="AEN19226">14.5.1 Secure ConnectionInitialization</a></h2><p>To initialize S/Key for the first time, change your password, or change your seedwhile logged in over a secure connection (e.g., on the console of a machine or via <bclass="APPLICATION">ssh</b>), use the <tt class="COMMAND">keyinit</tt> command withoutany parameters while logged in as yourself:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">keyinit</kbd>Adding unfurl: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: Again secret password: ID unfurl s/key is 99 to17757DEFY CLUB PRO NASH LACE SOFT</pre><p>For OPIE, <tt class="COMMAND">opiepasswd</tt> is used instead:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">opiepasswd -c</kbd>[grimreaper] ~ $ opiepasswd -f -cAdding unfurl:Only use this method from the console; NEVER from remote. If you are usingtelnet, xterm, or a dial-in, type ^C now or exit with no password.Then run opiepasswd without the -c parameter.Using MD5 to compute responses.Enter new secret pass phrase:Again new secret pass phrase:ID unfurl OTP key is 499 to4268MOS MALL GOAT ARM AVID COED</pre><p>At the <samp class="PROMPT">Enter new secret pass phrase:</samp> or <sampclass="PROMPT">Enter secret password:</samp> prompts, you should enter a password orphrase. Remember, this is not the password that you will use to login with, this is usedto generate your one-time login keys. The ``ID'' line gives the parameters of yourparticular instance: your login name, the iteration count, and seed. When logging in thesystem will remember these parameters and present them back to you so you do not have toremember them. The last line gives the particular one-time password which corresponds tothose parameters and your secret password; if you were to re-login immediately, thisone-time password is the one you would use.</p></div><div class="SECT2"><h2 class="SECT2"><a id="AEN19243" name="AEN19243">14.5.2 Insecure ConnectionInitialization</a></h2><p>To initialize or change your secret password over an insecure connection, you willneed to already have a secure connection to some place where you can run <ttclass="COMMAND">key</tt> or <tt class="COMMAND">opiekey</tt>; this might be in the formof a desk accessory on a <span class="TRADEMARK">Macintosh</span>®, or a shell prompton a machine you trust. You will also need to make up an iteration count (100 is probablya good value), and you may make up your own seed or use a randomly-generated one. Over onthe insecure connection (to the machine you are initializing), use the <ttclass="COMMAND">keyinit -s</tt> command:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">keyinit -s</kbd>Updating unfurl:Old key: to17758Reminder you need the 6 English words from the key command.Enter sequence count from 1 to 9999: <kbd class="USERINPUT">100</kbd>Enter new key [default to17759]: s/key 100 to 17759s/key access password:s/key access password:<kbd class="USERINPUT">CURE MIKE BANE HIM RACY GORE</kbd></pre><p>For OPIE, you need to use <tt class="COMMAND">opiepasswd</tt>:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">opiepasswd</kbd>Updating unfurl:You need the response from an OTP generator.Old secret pass phrase: otp-md5 498 to4268 ext Response: GAME GAG WELT OUT DOWN CHATNew secret pass phrase: otp-md5 499 to4269 Response: LINE PAP MILK NELL BUOY TROYID mark OTP key is 499 gr4269LINE PAP MILK NELL BUOY TROY</pre><p>To accept the default seed (which the <tt class="COMMAND">keyinit</tt> programconfusingly calls a <var class="LITERAL">key</var>), press <b class="KEYCAP">Return</b>.Then before entering an access password, move over to your secure connection or S/Keydesk accessory, and give it the same parameters:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">key 100 to17759</kbd>Reminder - Do not use this program while logged in via telnet or rlogin.Enter secret password: <kbd class="USERINPUT"><secret password></kbd>CURE MIKE BANE HIM RACY GORE</pre><p>Or for OPIE:</p><pre class="SCREEN"><samp class="PROMPT">%</samp> <kbd class="USERINPUT">opiekey 498 to4268</kbd>Using the MD5 algorithm to compute response.Reminder: Don't use opiekey from telnet or dial-in sessions.Enter secret pass phrase:GAME GAG WELT OUT DOWN CHAT</pre><p>Now switch back over to the insecure connection, and copy the one-time passwordgenerated over to the relevant program.</p></div><div class="SECT2"><h2 class="SECT2"><a id="AEN19273" name="AEN19273">14.5.3 Generating a Single One-timePassword</a></h2><p>Once you have initialized S/Key or OPIE, when you login you will be presented with a⌨️ 快捷键说明
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