Almost Everything You Ever Wanted To Know About Security*                       *(but were afraid to ask!)This document is meant to answer some of the questions which regularlyappear in the Usenet newsgroups "comp.security.misc" and "alt.security",and is meant to provide some background to the subject for newcomers tothat newsgroup.This FAQ is maintained by Alec Muffett (aem@aber.ac.uk, uknet!aber!aem),with contributions from numerous others [perhaps].  The views expressedin the document are the personal views of the author(s), and it shouldnot be inferred that they are necessarily shared by anyone with whom theauthor(s) are now, or ever may be, associated.Many thanks go to (in no particular order): Steve Bellovin, Matt Bishop,Mark Brader, Ed DeHart, Dave Hayes, Jeffrey Hutzelman, William LeFebvre,Wes Morgan, Rob Quinn, Chip Rosenthal, Wietse Venema, Gene Spafford,John Wack and Randall Atkinson.Disclaimer: Every attempt is made to ensure that the informationcontained in this FAQ is up to date and accurate, but no responsibilitywill be accepted for actions resulting from information gained herein.Questions which this document addresses:Q.1 What are alt.security and comp.security.misc for?Q.2 Whats the difference between a hacker and a cracker?Q.3 What is "security through obscurity"Q.4 What makes a system insecure?Q.5 What tools are there to aid security?Q.6 Isn't it dangerous to give cracking tools to everyone?Q.7 Where can I get these tools?Q.8 Why and how do systems get broken into?Q.9 Who can I contact if I get broken into?Q.10 What is a firewall?Q.11 Why shouldn't I use setuid shell scripts?Q.12 Why shouldn't I leave "root" permanently logged on the console?Q.13 Why shouldn't I create Unix accounts with null passwords?Q.14 What security holes are associated with X-windows (and other WMs)?Q.15 What security holes are associated with NFS?Q.16 How can I generate safe passwords?Q.17 Why are passwords so important?Q.18 How many possible passwords are there?Q.19 Where can I get more information?Q.20 How silly can people get?---------------------------------------------------------------------------Q.1 What are alt.security and comp.security.misc for?Comp.security.misc is a forum for the discussion of computer security,especially those relating to Unix (and Unix like) operating systems.Alt.security used to be the main newsgroup covering this topic, as wellas other issues such as car locks and alarm systems, but with thecreation of comp.security.misc, this may change.This FAQ will concentrate wholly upon computer related security issues.The discussions posted range from the likes of "What's such-and-suchsystem like?" and "What is the best software I can use to do so-and-so"to "How shall we fix this particular bug?", although there is often alow signal to noise ratio in the newsgroup (a problem which this FAQhopes to address).The most common flamewars start when an apparent security novice posts amessage saying "Can someone explain how the such-and-such security holeworks?" and s/he is immediately leapt upon by a group of self appointedpeople who crucify the person for asking such an "unsound" question in apublic place, and flame him/her for "obviously" being a cr/hacker.Please remember that grilling someone over a high flame on the groundsthat they are "a possible cr/hacker" does nothing more than generate alot of bad feeling.  If computer security issues are to be dealt with inan effective manner, the campaigns must be brought (to a large extent)into the open.Implementing computer security can turn ordinary people into rampagingparanoiacs, unable to act reasonably when faced with a new situation.Such people take an adversarial attitude to the rest of the human race,and if someone like this is in charge of a system, users will rapidlyfind their machine becoming more restrictive and less friendly (fun?) touse.This can lead to embarrasing situations, eg: (in one university) banninga head of department from the college mainframe for using a networkutility that he wasn't expected to.  This apparently required a lot ofexplaining to an unsympathetic committee to get sorted out.A more sensible approach is to secure a system according to its needs,and if its needs are great enough, isolate it completely.  Please, don'tlose your sanity to the cause of computer security; it's not worth it.Q.2 What's the difference between a hacker and a cracker?Lets get this question out of the way right now:On USENET, calling someone a "cracker" is an unambiguous statement thatsome person persistently gets his/her kicks from breaking from intoother peoples computer systems, for a variety of reasons.  S/He may posesome weak justification for doing this, usually along the lines of"because it's possible", but most probably does it for the "buzz" ofdoing something which is illicit/illegal, and to gain status amongst apeer group.Particularly antisocial crackers have a vandalistic streak, and deletefilestores, crash machines, and trash running processes in pursuit oftheir "kicks".The term is also widely used to describe a person who breaks copyprotection software in microcomputer applications software in order tokeep or distribute free copies.On USENET, calling someone a "hacker" is usually a statement that saidperson holds a great deal of knowledge and expertise in the field ofcomputing, and is someone who is capable of exercising this expertisewith great finesse.  For a more detailed definition, readers arereferred to the Jargon File [Raymond].In the "real world", various media people have taken the word "hacker"and coerced it into meaning the same as "cracker" - this usageoccasionally appears on USENET, with disastrous and confusing results.Posters to the security newsgroups should note that they currently riska great deal of flamage if they use the word "hacker" in place of"cracker" in their articles.NB: nowhere in the above do I say that crackers cannot be true hackers.It's just that I don't say that they are...Q.3 What is "security through obscurity"Security Through Obscurity (STO) is the belief that a system of any sortcan be secure so long as nobody outside of its implementation group isallowed to find out anything about its internal mechanisms.  Hidingaccount passwords in binary files or scripts with the presumption that"nobody will ever find it" is a prime case of STO.STO is a philosophy favoured by many bureaucratic agencies (military,governmental, and industrial), and it used to be a major method ofproviding "pseudosecurity" in computing systems.Its usefulness has declined in the computing world with the rise of opensystems, networking, greater understanding of programming techniques, aswell as the increase in computing power available to the average person.The basis of STO has always been to run your system on a "need to know"basis.  If a person doesn't know how to do something which could impactsystem security, then s/he isn't dangerous.Admittedly, this is sound in theory, but it can tie you into trusting asmall group of people for as long as they live.  If your employees getan offer of better pay from somewhere else, the knowledge goes withthem, whether the knowledge is replaceable or not.  Once the secret getsout, that is the end of your security.Nowadays there is also a greater need for the ordinary user to knowdetails of how your system works than ever before, and STO falls down aas a result.  Many users today have advanced knowledge of how theiroperating system works, and because of their experience will be able toguess at the bits of knowledge that they didn't "need to know".  Thisbypasses the whole basis of STO, and makes your security useless.Hence there is now a need is to to create systems which attempt to bealgorithmically secure (Kerberos, Secure RPC), rather than justphilosophically secure.  So long as your starting criteria can be met,your system is LOGICALLY secure."Shadow Passwords" (below) are sometimes dismissed as STO, but this isincorrect, since (strictly) STO depends on restricting access to analgorithm or technique, whereas shadow passwords provide security byrestricting access to vital data.Q.4 What makes a system insecure?Switching it on.  The adage usually quoted runs along these lines: "The only system which is truly secure is one which is switched off and unplugged, locked in a titanium lined safe, buried in a concrete bunker, and is surrounded by nerve gas and very highly paid armed guards.  Even then, I wouldn't stake my life on it."(the original version of this is attributed to Gene Spafford)A system is only as secure as the people who can get at it.  It can be"totally" secure without any protection at all, so long as its continuedgood operation is important to everyone who can get at it, assuming allthose people are responsible, and regular backups are made in case ofhardware problems.  Many laboratory PC's quite merrily tick away thehours like this.The problems arise when a need (such as confidentiality) has to befulfilled.  Once you start putting the locks on a system, it is fairlylikely that you will never stop.Security holes manifest themselves in (broadly) four ways:1) Physical Security Holes.- Where the potential problem is caused by giving unauthorised personsphysical access to the machine, where this might allow them to performthings that they shouldn't be able to do.A good example of this would be a public workstation room where it wouldbe trivial for a user to reboot a machine into single-user mode and muckaround with the workstation filestore, if precautions are not taken.Another example of this is the need to restrict access to confidentialbackup tapes, which may (otherwise) be read by any user with access tothe tapes and a tape drive, whether they are meant to have permission ornot.2) Software Security Holes- Where the problem is caused by badly written items of "privledged"software (daemons, cronjobs) which can be compromised into doing thingswhich they shouldn't oughta.The most famous example of this is the "sendmail debug" hole (seebibliography) which would enable a cracker to bootstrap a "root" shell.This could be used to delete your filestore, create a new account, copyyour password file, anything.(Contrary to popular opinion, crack attacks via sendmail were not justrestricted to the infamous "Internet Worm" - any cracker could do thisby using "telnet" to port 25 on the target machine.  The story behind asimilar hole (this time in EMACS) is described in [Stoll].)New holes like this appear all the time, and your best hopes are to:  a: try to structure your system so that as little software as possible  runs with root/daemon/bin privileges, and that which does is known to  be robust.  b: subscribe to a mailing list which can get details of problems  and/or fixes out to you as quickly as possible, and then ACT when you  receive information.3) Incompatible Usage Security Holes- Where, through lack of experience, or no fault of his/her own, theSystem Manager assembles a combination of hardware and software whichwhen used as a system is seriously flawed from a security point of view.It is the incompatibility of trying to do two unconnected but usefulthings which creates the security hole.Problems like this are a pain to find once a system is set up andrunning, so it is better to build your system with them in mind.  It'snever too late to have a rethink, though.Some examples are detailed below; let's not go into them here, it wouldonly spoil the surprise.4) Choosing a suitable security philosophy and maintaining it.>From: Gene Spafford <spaf@cs.purdue.edu>>The fourth kind of security problem is one of perception and>understanding.  Perfect software, protected hardware, and compatible>components don't work unless you have selected an appropriate security>policy and turned on the parts of your system that enforce it.  Having>the best password mechanism in the world is worthless if your users>think that their login name backwards is a good password! Security is>relative to a policy (or set of policies) and the operation of a system>in conformance with that policy.Q.5 What tools are there to aid security?1) "COPS"Managed by Dan Farmer, this is a long established suite of shell scriptswhich forms an extensive security testing system; There is a rudimentarypassword cracker, and routines to check the filestore for suspiciouschanges in setuid programs, others to check permissions of essentialsystem and user files, and still more to see whether any system softwarebehaves in a way which could cause problems.The software comes in two versions - one written in Perl and one(largely equivalent) written in shell scripts.  The latest version isvery up-to-date on Unix Security holes.2) "Crack" (+ "UFC").Written by Alec Muffett, this is a program written with one purpose inmind: to break insecure passwords.  It is probably the most efficent andfriendly password cracker that is publically available, with the abilityto let the user to specify precisely how to form the words to use asguesses at users passwords.It also has an inbuilt networking capability, allowing the load ofcracking to be spread over as many machines as are available on anetwork, and it is supplied with an optimised version of the Unix crypt()algorithm.An even faster version of the crypt() algorithm, "UFC" by Michael Glad,is freely available on the network, and the latest versions of UFC andCrack are compatible and can be easily hooked together.3) NPasswd (Clyde Hoover) & Passwd+ (Matt Bishop)These programs are written to redress the balance in the passwordcracking war.  They provide replacements for the standard "passwd"command, but prevent a user from selecting passwords which are easilycompromised by programs like Crack.Several versions of these programs are available on the network, hackedabout to varying degrees in order to provide compatibility for System Vbased systems, NIS/YP, shadow password schemes, etc.  The usual term forthis type of program is a 'fascist' password program.4) "Shadow" - a Shadow Password SuiteThis program suite (by John F Haugh II) is a set of program and functionreplacements (compatible with most Unixes) which implements shadowpasswords, ie: a system where the plaintext of the password file ishidden from all users except root, hopefully stopping all passwordcracking attempts at source.  In combination with a fascist passwdfrontend, it should provide a good degree of password file robustness.>From: jfh@rpp386.lonestar.org (John F. Haugh II)>Shadow does much more than hide passwords.  It also provides for>terminal access control, user and group administration, and a few>other things which I've forgotten.  There are a dozen or more>commands in the suite, plus a whole slew of library functions.5) TCP Wrappers (Wietse Venema)These are programs which provide a front-end filter to many of thenetwork services which Unix provides by default.  If installed, they cancurb otherwise unrestricted access to potential dangers like incomingFTP/TFTP, Telnet, etc, and can provide extra logging information, whichmay be of use if it appears that someone is trying to break in.6) SecureLib>From: phil@pex.eecs.nwu.edu (William LeFebvre)>You may want to add a mention of securelib, a security enhancer>available for SunOS version 4.1 and higher.>Securelib contains replacement routines for three kernel calls:>accept(), recvfrom(), recvmsg().  These replacements are compatible with>the originals, with the additional functionality that they check the>Internet address of the machine initiating the connection to make sure>that it is "allowed" to connect.  A configuration file defines what>hosts are allowed for a given program.  Once these replacement routines>are compiled, they can be used when building a new shared libc library.>The resulting libc.so can then be put in a special place.  Any program>that should be protected can then be started with an alternate>LD_LIBRARY_PATH.7) SPI>From: Gene Spafford <spaf@cs.purdue.edu>>Sites connected with the Department of Energy and some military>organizations may also have access to the SPI package.  Interested (and>qualified) users should contact the CIAC at LLNL for details.>SPI is a screen-based administrator's tool that checks configuration>options, includes a file-change (integrity) checker to monitor for>backdoors and viruses, and various other security checks.  Future>versions will probably integrate COPS into the package.  It is not>available to the general public, but it is available to US Dept of>Energy contractors and sites and to some US military sites.  A version>does or will exist for VMS, too.  Further information on availabilty can>be had from the folks at the DoE CIAC.Q.6 Isn't it dangerous to give cracking tools to everyone?That depends on your point of view.  Some people have complained thatgiving unrestricted public access to programs like COPS and Crack isirresponsible because the "baddies" can get at them easily.Alternatively, you may believe that the really bad "baddies" have hadprograms like this for years, and that it's really a stupendously goodidea to give these programs to the good guys too, so that they may checkthe integrity of their system before the baddies get to them.So, who wins more from having these programs freely available? The goodguys or the bad ? You decide, but remember that less honest tools thanCOPS and Crack tools were already out there, and most of the good guysdidn't have anything to help.Q.7 Where can I get these tools?COPS:  V1.04, available for FTP from cert.sei.cmu.edu in pub/cops and  archive.cis.ohio-state.edu in pub/cops.Crack/UFC:  Crack v4.1f and UFC Patchlevel 1.  Available from any major USENET  archive (eg: ftp.uu.net) in volume 28 of comp.sources.misc.NPasswd:  Currently suffering from being hacked about by many different people.  Version 2.0 is in the offing, but many versions exist in many  different configurations. Will chase this up with authors - AEMPasswd+:  "alpha version, update 3" - beta version due soon.  Available from  dartmouth.edu as pub/passwd+.tar.ZShadow:  This is available from the comp.sources.misc directory at any major  USENET archive (see entry for Crack)TCP Wrappers:  Available for anonymous FTP:    cert.sei.cmu.edu: pub/network_tools/tcp_wrapper.shar    ftp.win.tue.nl: pub/security/log_tcp.shar.ZSecurelib:  The latest version of securelib is available via anonymous FTP from the  host "eecs.nwu.edu".  It is stored in the file "pub/securelib.tar".Q.8 Why and how do systems get broken into?This is hard to answer definitively.  Many systems which crackers breakinto are only used as a means of entry into yet more systems; by hoppingbetween many machines before breaking into a new one, the cracker hopesto confuse any possible pursuers and put them off the scent.  There isan advantage to be gained in breaking into as many different sites aspossible, in order to "launder" your connections.Another reason may be psychological: some people love to play withcomputers and stretch them to the limits of their capabilities.Some crackers might think that it's "really neat" to hop over 6 Internetmachines, 2 gateways and an X.25 network just to knock on the doors ofsome really famous company or institution (eg: NASA, CERN, AT+T, UCB).Think of it as inter-network sightseeing.This view is certainly appealing to some crackers, and certainly leadsto both the addiction and self-perpetuation of cracking.As to the "How" of the question, this is again a very sketchy area.  Inuniversities, it is extremely common for computer account to be passedback and forth between undergraduates:  "Mary gives her account password to her boyfriend Bert at another  site, who has a friend Joe who "plays around on the networks".  Joe  finds other crackable accounts at Marys site, and passes them around  amongst his friends..." pretty soon, a whole society of crackers is  playing around on the machines that Mary uses.This sort of thing happens all the time, and not just in universities.One solution is in education.  Do not let your users develop attitudeslike this one:       "It doesn't matter what password I use on _MY_ account,            after all, I only use it for laserprinting..."                                - an Aberystwyth Law student, 1991Teach them that use of the computer is a group responsibility.  Makesure that they understand that a chain is only as strong as it's weaklink.Finally, when you're certain that they understand your problems as asystems manager and that they totally sympathise with you, configureyour system in such a way that they can't possibly get it wrong.Believe in user education, but don't trust to it alone.Q.9 Who can I contact if I get broken into?If you're connected to the Internet, you should certainly get in touchwith CERT, the Computer Emergency Response Team.        To quote the official blurb:>From: Ed DeHart> The Computer Emergency Response Team (CERT) was formed by the Defense> Advanced Research Projects Agency (DARPA) in 1988 to serve as a focal> point for the computer security concerns of Internet users.  The> Coordination Center for the CERT is located at the Software Engineering> Institute, Carnegie Mellon University, Pittsburgh, PA.> Internet E-mail: cert@cert.sei.cmu.edu> Telephone: 412-268-7090 24-hour hotline:>     CERT/CC personnel answer 7:30a.m. to 6:00p.m. EST(GMT-5)/EDT(GMT-4),>     and are on call for emergencies during other hours....and also, the umbrella group "FIRST", which mediates between theincident handling teams themselves...>From: John Wack <wack@csrc.ncsl.nist.gov>>[...] FIRST is actually a very viable and growing>organization, of which CERT is a member.  It's not actually true that,>if you're connected to the Internet, you should call CERT only - that>doesn't do justice to the many other response teams out there and in the>process of forming.>NIST is currently the FIRST secretariat; we maintain an anonymous ftp>server with a directory of FIRST information (csrc.ncsl.nist.gov:>~/pub/first).  This directory contains a contact file that lists the>current members and their constituencies and contact information>(filename "first-contacts").>While CERT is a great organization, other response teams who do handle>incidents on their parts of the Internet merit some mention as well ->perhaps mentioning the existence of this file would help to do that in a>limited space.The file mentioned is a comprehensive listing of contact points pernetwork for security incidents.  It is too large to reproduce here, Isuggest that the reader obtains a copy for his/her self by the meansgiven.Q.10 What is a firewall?A (Internet) firewall is a machine which is attached (usually) betweenyour site and a wide area network.  It provides controllable filteringof network traffic, allowing restricted access to certain internet portnumbers (ie: services that your machine would otherwise provide to thenetwork as a whole) and blocks access to pretty well everything else.Similar machines are available for other network types, too.Firewalls are an effective "all-or-nothing" approach to dealing withexternal access security, and they are becoming very popular, with therise in Internet connectivity.For more information on these sort of topics, see the Gateway paper by[Cheswick], below.Q.11 Why shouldn't I use setuid shell scripts?You shouldn't use them for a variety of reasons, mostly involving bugsin the Unix kernel.  Here are a few of the more well known problems,some of which are fixed on more recent operating systems.1) If the script begins "#!/bin/sh" and a link (symbolic or otherwise)can be made to it with the name "-i", a setuid shell can be immediatelyobtained because the script will be invoked: "#!/bin/sh -i", ie: aninteractive shell.2) Many kernels suffer from a race condition which can allow you toexchange the shellscript for another executable of your choice betweenthe times that the newly exec()ed process goes setuid, and when thecommand interpreter gets started up.  If you are persistent enough, intheory you could get the kernel to run any program you want.3) The IFS bug: the IFS shell variable contains a list of characters tobe treated like whitespace by a shell when parsing command names.  Bychanging the IFS variable to contain the "/" character, the command"/bin/true" becomes "bin true".All you need do is export the modified IFS variable, install a commandcalled "bin" in your path, and run a setuid script which calls"/bin/true".  Then "bin" will be executed whilst setuid.If you really must write scripts to be setuid, either  a) Put a setuid wrapper in "C" around the script, being very careful  to reset IFS and PATH to something sensible before exec()ing the  script.  If your system has runtime linked libraries, consider the  values of the LD_LIBRARY_PATH also.  b) Use a scripting language like Perl which has a safe setuid  facility, and is proactively rabid about security.- but really, it's safest not to use setuid scripts at all.Q.12 Why shouldn't I leave "root" permanently logged on the console?Using a 'smart' terminal as console and leaving "/dev/console" worldwritable whilst "root" is logged in is a potential hole.  The terminalmay be vulnerable to remote control via escape sequences, and can beused to 'type' things into the root shell.  The terminal type canusually be obtained via the "ps" command.Various solutions to this can be devised, usually by giving the consoleowner and group-write access only , and then using the setgid mechanismon any program which has need to output to the console (eg: "write").Q.13 Why shouldn't I create Unix accounts with null passwords?Creating an unpassworded account to serve any purpose is potentiallydangerous, not for any direct reason, but because it can give a crackera toehold.For example, on many systems you will find a unpassworded user "sync",which allows the sysman to sync the disks without being logged in.  Thisappears to be both safe and innocuous.The problem with this arises if your system is one of the many whichdoesn't do checks on a user before authorising them for (say) FTP.  Acracker might be able to connect to your machine for one of a variety ofFTP methods, pretending to be user "sync" with no password, and thencopy your password file off for remote cracking.Although there are mechanisms to prevent this sort of thing happening inmost modern vesions of Unix, to be totally secure requires an in-depthknowledge of every package on your system, and how it deals with theverification of users.  If you can't be sure, it's probably better notto leave holes like this around.Another hole that having null-password accounts opens up is thepossibility (on systems with runtime linked libraries) of spoofingsystem software into running your programs as the "sync" user, bychanging the LD_LIBRARY_PATH variable to a library of your own devising,and running "login -p" or "su" to turn into that user.Q.14 What security holes are associated with X-windows (and other WMs)?Lots, some which affect use of X only, and some which impact thesecurity of the entire host system.I would prefer not to go into too much detail here, and would refer anyreader reader looking for detailed information to the other FAQ's inrelevant newsgroups.  (comp.windows.*)One point I will make is that X is one of those packages which oftengenerates "Incompatible Usage" security problems, for instance theability for crackers to run xsessions on hosts under accounts with nopassword (eg: sync), if it is improperly set up.  Read the questionabout unpassworded accounts in this FAQ.Q.15 What security holes are associated with NFS?Lots, mostly to do with who you export your disks to, and how.  Thesecurity of NFS relies heavily upon who is allowed to mount the filesthat a server exports, and whether they are exported read only or not.The exact format for specifying which hosts can mount an exporteddirectory varies between Unix implementations, but generally theinformation is contained within the file "/etc/exports".This file contains a list of directories and for each one, it has aseries of either specific "hosts" or "netgroups" which are allowed toNFS mount that directory.  This list is called the "access list".The "hosts" are individual machines, whilst "netgroups" are combinationsof hosts and usernames specified in "/etc/netgroup".  These are meant toprovide a method of finetuning access.  Read the relevant manual pagefor more information about netgroups.The exports file also contains information about whether the directoryis to be exported as read-only, read-write, and whether super-useraccess is to be allowed from clients which mount that directory.The important point to remember is that if the access list for aparticular directory in /etc/exports contains:1) <nothing>Your directory can be mounted by anyone, anywhere.2) <a specific hostname>Your directory can be mounted by anyone permitted to run the mountcommand at hostname.  This might not be a trustworthy person; forinstance, if the machine is a PC running NFS, it could be anyone.3) <a netgroup name>If the netgroup:a) is empty, anyone can mount your directory, from anywhere.b) contains "(,,)", anyone can mount your directory, from anywhere.c) contains the name of a netgroup which is empty or contains "(,,)",   anyone can mount your directory, from anywhere.d) contains "(hostname,,)", anyone on the named host who is permissioned   to mount files can mount your directory.e) contains "(,username,)", the named user can mount your directory,   from anywhere.4) <a word which is neither a hostname or a netgroup>If you meant to export the directory to the host "athena" but actuallytype "ahtena", the word "ahtena" is taken as a netgroup name, is foundto be an empty netgroup, and thus the directory can be mounted byanyone, anywhere.So, if you aren't careful about what you put into /etc/exports and/etc/netgroup you could find that a user with a PC could  a) mount your mainframe filestore as a network disk  b) edit your /etc/passwd or .rhosts or /etc/hosts.equiv ...  c) log into your mainframe as another user, possibly "root"Disclaimer: The above information may not be true for all platformswhich provide an NFS serving capability, but is true for all of the onesin my experience (AEM).  It should be noted that the SAFE way to createan "empty" netgroup entry is:                           ngname (-,-,-)Which is a netgroup which matches no-one on no-host on no-NIS-domain.[ I am STILL working on PC NFS packages / ethics at the moment - AEM ]Q.16 How can I generate safe passwords?You can't.  The key word here is GENERATE.  Once an algorithm forcreating passwords is specified using upon some systematic method, itmerely becomes a matter of analysing your algorithm in order to findevery password on your system.Unless the algorithm is very subtle, it will probably suffer from a verylow period (ie: it will soon start to repeat itself) so that either:  a) a cracker can try out every possible output of the password  generator on every user of the system, or  b) the cracker can analyse the output of the password program,  determine the algorithm being used, and apply the algorithm to other  users to determine their passwords.A beautiful example of this (where it was disastrously assumed that arandom number generator could generate an infinite number of randompasswords) is detailed in [Morris & Thompson].The only way to get a reasonable amount of variety in your passwords(I'm afraid) is to make them up.  Work out some flexible method of yourown which is NOT based upon:  1) modifying any part of your name or name+initials  2) modifying a dictionary word  3) acronyms  4) any systematic, well-adhered-to algorithm whatsoeverFor instance, NEVER use passwords like:alec7           - it's based on the users name (& it's too short anyway)tteffum         - based on the users name againgillian         - girlfiends name (in a dictionary)naillig         - ditto, backwardsPORSCHE911      - it's in a dictionary12345678        - it's in a dictionary (& people can watch you type it easily)qwertyui        - ...ditto...abcxyz          - ...ditto...0ooooooo        - ...ditto...Computer        - just because it's capitalised doesn't make it safewombat6         - ditto for appending some random character6wombat         - ditto for prepending some random charactermerde3          - even for french words...mr.spock        - it's in a sci-fi dictionaryzeolite         - it's in a geological dictionaryze0lite         - corrupted version of a word in a geological dictionaryze0l1te         - ...ditto...Z30L1T3         - ...ditto...I hope that these examples emphasise that ANY password derived from ANYdictionary word (or personal information), modified in ANY way,constitutes a potentially guessable password.For more detailed information in the same vein, you should read theAPPENDIX files which accompany Crack [Muffett].Q.17 Why are passwords so important?Because they are the first line of defence against interactive attackson your system.  It can be stated simply: if a cracker cannot interactwith your system(s), and he has no access to read or write theinformation contained in the password file, then he has almost noavenues of attack left open to break your system.This is also why, if a cracker can at least read your password file (andif you are on a vanilla modern Unix, you should assume this) it is soimportant that he is not able to break any of the passwords containedtherein.  If he can, then it is also fair to assume that he can (a) logon to your system and can then (b) break into "root" via an operatingsystem hole.Q.18 How many possible passwords are there?Most people ask this at one time or another, worried that programs likeCrack will eventually grow in power until they can do a completelyexhaustive search of all possible passwords, to break into a specificusers' account - usually root.If (to simplify the maths) we make the assumptions that:  1) Valid passwords are created from a set of 62 chars [A-Za-z0-9]  2) Valid passwords are to be between 5 and 8 chars longThen the size of the set of all valid passwords is: (in base 62)                                   100000 +                                  1000000 +                                 10000000 +                                100000000 =                                ---------                                111100000       (base 62)A figure which is far too large to usefully undertake an exhaustivesearch with current technologies.  Don't forget, however, that passwordsCAN be made up with even more characters then this; you can use <space>,all the punctuation characters, and symbols (~<>|\#$%^&*) too.  If youcan use some of all the 95 non-control characters in passwords, thisincreases the search space for a cracker to cover even further. However, it's still MUCH more efficient for a cracker to get a copy of"Crack", break into ANY account on the system (you only need one), logonto the machine, and spoof his way up to root priviledges via operatingsystems holes. Take comfort from these figures.  If you can slam the door in the faceof a potential crackers with a robust password file, you have sealedmost of the major avenues of attack immediately.Q.19 Where can I get more information?Books:[Kochan & Wood]Unix System SecurityA little dated for modern matters, but still a very good book on thebasics of Unix security.[Spafford & Garfinkel]Practical Unix SecurityThis wonderful book is a worthy successor to the above, and covers awide variety of the topics which the Unix (and some non Unix) systemmanager of the 90's will come across.>From: Gene Spafford <spaf@cs.purdue.edu>>Mention appendix E in "Practical Unix Security."Okay: Appendix E contains an extensive bibliography with even morepointers to security books than this FAQ contains.[Stoll]The Cuckoo's EggA real life 1980's thriller detailing the tracing of a cracker fromBerkeley across the USA and over the Atlantic to Germany.  An excellentview from all points: a good read, informative about security, funny,and a good illustration of the cracker psyche.  Contains an excellentrecipie for chocolate chip cookies.A videotape of the "NOVA" (PBS's Science Program on TV) episode thatexplained/reenacted this story is available from PBS Home Video.  Theyhave a toll-free 800 number within North America.I believe that this program was aired on the BBC's "HORIZON" program,and thus will be available from BBC Enterprises, but I haven't checkedthis out yet - AEM[Raymond] (Ed.)The New Hackers Dictionary/Online Jargon FileA mish-mash of history and dictionary definitions which explains why itis so wonderful to be a hacker, and why those crackers who aren'thackers want to be called "hackers".  The Jargon File version isavailable online - check an archie database for retails.  Latestrevision: 2.99.[Gasser]Building a Secure Computer System.By Morrie Gasser, and van Nostrand Reinhold; explains what is requiredto build a secure computer system.[Rainbow Series] (Especially the "Orange Book")>From: epstein@trwacs.fp.trw.com (Jeremy Epstein)>The "Rainbow Series" consists of about 25 volumes.  Some of the>more interesting ones are:>>       The "Orange Book", or Trusted Computer Systems Evaluation>               Criteria, which describes functional and assurance>               requirements for computer systems>>       Trusted Database Interpretation, which talks both about>               trusted databases and building systems out of trusted>               components>>       Trusted Network Interpretation, which (obviously) talks>               about networked systems>>A (possibly) complete list is:>       -- Department of Defense Trusted Computer System Evaluation Criteria>          (TCSEC), aka the "Orange Book">       -- Computer Security Subsystem Interpretation of the TCSEC>       -- Trusted Data Base Management System Interpretation of the TCSEC>       -- Trusted Network Interpretation of the TCSEC>       -- Trusted Network Interpretation Environments Guideline -- Guidance>          for Applying the Trusted Network Interpretation>       -- Trusted Unix Working Group (TRUSIX) Rationale for Selecting>          Access Control List Features for the Unix System>       -- Trusted Product Evaulations -- A Guide for Vendors>       -- Computer Security Requirements -- Guidance for Applying the DoD>          TCSEC in Specific Environments>       -- Technical Rationale Behind CSC-STD-003-85: Computer Security>          Requirements>       -- Trusted Product Evaluation Questionnaire>       -- Rating Maintenance Phase -- Program Document>       -- Guidelines for Formal Verification Systems>       -- A Guide to Understanding Audit in Trusted Systems>       -- A Guide to Understanding Trusted Facility Management>       -- A Guide to Understanding Discretionary Access Control in Trusted>          Systems>       -- A Guide to Understanding Configuration Management in TrustedSystems>       -- A Guide to Understanding Design Documentation in Trusted Systems>       -- A Guide to Understanding Trusted Distribution in Trusted Systems>       -- A Guide to Understanding Data Remanence in Automated Information>          Systems>       -- Department of Defense Password Management Guideline>       -- Glossary of Computer Security Terms>       -- Integrity in Automated Information Systems>>You can get your own copy (free) of any or all of the books by>writing or calling:>>       INFOSEC Awareness Office>       National Computer Security Centre>       9800 Savage Road>       Fort George G. Meade, MD  20755-6000>       Tel +1 301 766-8729>>If you ask to be put on the mailing list, you'll get a copy of each new>book as it comes out (typically a couple a year).>From: kleine@fzi.de (Karl Kleine)>I was told that this offer is only valid for US citizens ("We only send>this stuff to a US postal address").  Non-US people have to PAY to get>hold of these documents.  They can be ordered from NTIS, the National>Technical Information Service:>       NTIS,>       5285 Port Royal Rd,>       Springfield VA 22151,>       USA>       order dept phone: +1-703-487-4650, fax +1-703-321-8547>From: Ulf Kieber <kieber@de.tu-dresden.inf.freia>>just today I got my set of the Rainbow Series.>>There are three new books:> -- A Guide to Understanding Trusted Recovery in Trusted Systems> -- A Guide to Understanding Identification and Authentication in Trusted>    Systems> -- A Guide to Writing the Security Features User's Guide for Trusted Systems>>They also shipped> -- Advisory Memorandum on Office Automation Security Guideline>issued by NTISS.  Most of the books (except three or four) can also be>purchased from>>       U.S. Government Printing Office>       Superintendent of Documents>       Washington, DC 20402            phone: (202) 783-3238>>>-- Integrity in Automated Information Systems>THIS book was NOT shipped to me--I'm not sure if it is still in>the distribution.>From: epstein@trwacs.fp.trw.com (Jeremy Epstein)>...>The ITSEC (Information Technology Security Evaluation Criteria) is a>harmonized document developed by the British, German, French, and>Netherlands governments.  It separates functional and assurance>requirements, and has many other differences from the TCSEC.>>You can get your copy (again, free/gratis) by writing:>>       Commission of the European Communities>       Directorate XIII/F>       SOG-IS Secretariat>       Rue de la Loi 200>       B-1049 BRUSSELS>       BelgiumAlso note that NCSC periodically publish an "Evaluated Products List"which is the definitive statement of which products have been approvedat what TCSEC level under which TCSEC interpretations.  This is usefulfor separating the output of marketdroids from the truth.Papers:[Morris & Thompson]Password Security, A Case HistoryA wonderful paper, first published in CACM in 1974, which is now oftento found in the Unix Programmer Docs supplied with many systems.[Curry]Improving the Security of your Unix System.A marvellous paper detailing the basic security considerations everyUnix systems manager should know.  Available as "security-doc.tar.Z"from FTP sites (check an Archie database for your nearest site.)[Klein]Foiling the Cracker: A Survey of, and Improvements to, Password Security.A thorough and reasoned analysis of password cracking trends, and thereasoning behind techniques of password cracking.  Your nearest copyshould be easily found via Archie, searching for the keyword "Foiling".[Cheswick]The Design of a Secure Internet Gateway.Great stuff.  It's research.att.com:/dist/Secure_Internet_Gateway.ps[Cheswick]An Evening With Berferd: in which a Cracker is Lured, Endured and Studied.Funny and very readable, somewhat in the style of [Stoll] but morecondensed.  research.att.com:/dist/berferd.ps[Bellovin89]Security Problems in the TCP/TP Protocol Suite.A description of security problems in many of the protocols widely usedin the Internet.  Not all of the discussed protocols are officialInternet Protocols (i.e.  blessed by the IAB), but all are widely used.The paper originally appeared in ACM Computer Communications Review,Vol 19, No 2, April 1989.  research.att.com:/dist/ipext.ps.Z[Bellovin91]Limitations of the Kerberos Authentication SystemA discussion of the limitations and weaknesses of the KerberosAuthentication System.  Specific problems and solutions are presented.Very worthwhile reading.  Available on research.att.com via anonymousftp, originally appeared in ACM Computer Communications Review but therevised version (identical to the online version, I think) appeared inthe Winter 1991 USENIX Conference Proceedings.[Muffett]Crack documentation.The information which accompanies Crack contains a whimsical explanationof password cracking techniques and the optimisation thereof, as well asan incredibly long and silly diatribe on how to not choose a crackablepassword.  A good read for anyone who needs convincing that passwordcracking is _really easy_.[Farmer]COPSRead the documentation provided with COPS.  Lots of hints andphilosophy.  The where, why and how behind the piece of securitysoftware that started it all.[CERT]maillists/advisories/clippingsCERT maintains archives of useful bits of information that it gets fromUSENET and other sources.  Also archives of all the security"advisories" that it has posted (ie: little messages warning people thatthere is a hole in their operating system, and where to get a fix)[OpenSystemsSecurity]A notorious (but apparently quite good) document, which has been doggedby being in a weird postscript format.>From: amesml@monu1.cc.monash.edu.au (Mark L. Ames)>I've received many replies to my posting about Arlo Karila's paper,>including the news (that I and many others have missed) that a>manageable postscript file and text file are available via anonymous ftp>from ajk.tele.fi (131.177.5.20) in the directory PublicDocuments.These are all available for FTP browsing from "cert.sei.cmu.edu".[RFC-1244]Site Security HandbookRFC-1244 : JP Holbrook & JK Reynolds (Eds.) "The Site Security Handbook"covering incident handling and prevention.  July 1991; 101 pages(Format: TXT=259129 bytes), also called "FYI 8"[USENET]comp.virus: for discussions of virii and other nasties, with a PC bent.comp.unix.admin: for general administration issuescomp.unix.<platform>: for the hardware/software that YOU use.comp.protocols.tcp-ip: good for problems with NFS, etc.Q.20 How silly can people get?This section (which I hope to expand) is a forum for learning byexample; if people have a chance to read about real life (preferablysilly) security incidents, it will hopefully instill in readers some ofthe zen of computer security without the pain of experiencing it.If you have an experience that you wish to share, please send it to theeditors.  It'll boost your karma no end.---------------------------------------------------------------------------aem@aber.ac.uk: The best story I have is of a student friend of mine(call him Bob) who spent his industrial year at a major computermanufacturing company.  In his holidays, Bob would come back to collegeand play AberMUD on my system.Part of Bob's job at the company involved systems management, and thecompany was very hot on security, so all the passwords were randomstrings of letters, with no sensible order.  It was imperative that thepasswords were secure (this involved writing the random passwords downand locking them in big, heavy duty safes).One day, on a whim, I fed the MUD persona file passwords into Crack as adictionary (the passwords were stored plaintext) and then ran Crack onour systems password file.  A few student accounts came up, but nothingspecial.  I told the students concerned to change their passwords - thatwas the end of it.Being the lazy guy I am, I forgot to remove the passwords from the Crackdictionary, and when I posted the next version to USENET, the words wenttoo.  It went to the comp.sources.misc moderator, came back over USENET,and eventually wound up at Bob's company.  Round trip: ~10,000 miles.Being a cool kinda student sysadmin dude, Bob ran the new version ofCrack when it arrived.  When it immediately churned out the rootpassword on his machine, he damn near fainted...The moral of this story is: never use the same password in two differentplaces, and especially on untrusted systems (like MUDs).-- aem@aber.ac.uk aem@uk.ac.aber aem%aber@ukacrl.bitnet mcsun!uknet!aber!aem   - send (cryptographic) comp.sources.misc material to: aem@aber.ac.uk -