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When "Security Through Obscurity" Isn't So Bad
Erik writes "In this article, Jay Beale (Bastille Linux Project, Mandrakesoft) explains why Security Through Obscurity is actually a really good idea if you do it right. A good read for sysadmins." Agreed... a lot of really interesting points well written and entertaining. For starters you can't rely just on obscurity to keep you safe. But it doesn't hurt to obscure things sometimes just to make it tougher for your attacker.
When does something stop being 'security through obscurity'? Depending on how you look at it, all forms of security, (or at least most of the ones employed over the internet) are based on picking access tokens that are really hard to guess.
Running a service with no authentication on a random port isn't great security, but in principle, it's the same kind of security as running on a well known port and requiring a unique access identifier and passcode. It's just harder to guess, but still fundamentally the same.
Real security would be achieved through schemes where all of the knowledge in the world won't gain you privileged access.
The answer is simple: ease of review. Obscurity is meant to put stumbling blocks in the path of those who desire to review the system, for whatever motive - be it academic curiosity, security assurance, or even to learn how to penetrate into it. The hidden web server trick described in the article, closed-source security software, and proprietary crypto are all examples of techniques that are meant to obscure and thus make review difficult.
The question of whether to obscure, then, reduces to whether you'd like the system you're building to be reviewed. There are several very bad reasons that could motivate you to hinder review of your system: attempting to hide security flaws you either know or suspect to be found therein is one of the bigger ones.
But the decision to impede review can be perfectly reasonable - depending on who the reviewers are likely to be. If you know, for instance, that your community of reviewers includes honest, skilled people who want to use your product and who will alert you to problems that they find, then that's a very big reason not to obscure anything. This is what motivates Linus, the Apache group, the GnuPG folks, and everyone else out there tirelessly trying to produce systems that function in the most security-hostile of environments. These folks have literally thousands to millions of users, almost all of whom are honest, and many of whom are skilled enough to discover flaws in the system.
Joe Sysadmin doesn't have that kind of community. His users are very likely incapable of discovering security flaws, or if they are, unlikely to share the information they find with Joe. The majority of people who might be interested in reviewing Joe's network are malicious and intent upon using any information they find to the detriment of Joe and his users.
In this case, the decision to put up walls of obscurity is as much of a no-brainer as the decision to use an open-source web server. Joe has assessed his community of potential reviewers and has determined that, on the whole, he'd rather not have that set of people learning things about his network. He will certainly use products that have proven themselves under strict review, but he is under no obligation to describe to anyone how he's configured his network. In his situation, doing so would only undermine his security.
(Not the part about the comparative ease of exploiting security holes in source code vs. binary code -- the part about OS advocates somehow "always" forgetting that fact.)
In my experience, advocates of open source are highly aware that it's easier to exploit security holes in source code.
After all, to do that, one must find them first, correct?
And unless most or all of the people looking for them also intend to exploit them in an offensive way, the result will be that said holes will be fixed in a defensive mode vs. offensive attack faster than for proprietary, binary code.
Remember, defense always has an advantage over offense, in terms of time and effort -- the "battle" is on the defender's own turf. Offense can make up for this inherent disadvantage to some extent by, for instance, having the element of surprise.
For most such offensive counter-measures, having the source code is not an advantage, in fact it's a disadvantage, if the defense also has the source code.
That's because the defense can deploy fixes to holes faster than the offense can attack them, so, assuming they both find out about them at the same time, the defense wins. (This is generalizing, by the way. Specifics always vary, of course.)
Now, ask yourself this question: when it comes to binary-only code, who is likely to know more about the internal operations of the code -- the defense, in this case, law-abiding users, or the offense, willing to obtain THE SOURCE CODE through illegal channels??
That's why Open Source has such an advantage here -- the defense, collectively, is encouraged to share, generously, insights about the software, while the offense must remain fairly isolated (a general rule about law-abiders versus law-breakers; while law-breakers sometimes pool their resources, they have an uphill battle with regard to such activities compared to law-abiders, who can do their pooling in the open and/or in hiding).
When it comes to proprietary software, law-abiders are increasingly discouraged from sharing insights, info, breakages, fixes, etc., while the opportunities for pooling resources on the law-breakers' side remains pretty much the same.
But there's a special prize law-abiders are denied that law-breakers have the opportunity to exploit should they gain access to it, when it comes to proprietary software: the source code.
Once they have that -- and they will, if the software "matters" at all -- the law-abiders will be on the losing end of things.
"If source code is outlawed, only outlaws will have source code."
Practice random senselessness and act kind of beautiful.
-- Stanislav Shalunov
This isn't about making your targets impossible to crack. It's about making harder to crack than the guy next to you.
The slowest animal in the herd principal.
Lets say me and you both run service A, when a remote exploit is discovered. Bob the happy script kiddy gets his scanner and starts looking for said service on it's default port. On your box he finds it fine, and cracks you. On mine he doesn't see it initially. So he skips me and moves on. Say bob _really_ wanted me, he would scan all my ports and find that service, but in the meantime I see a bunch of traffic searching my network in odd places.
The slowest animal in the heard is already down, but in the few seconds I gained I realize some clever escape, and viola, I'm free. Obscurity doesn't make you uncrackable, but it gives you an edge.
Security through unpopularity. Let's face it, if you run a web server under BeOS, the likelyhood of getting hacked compared to running IIS, is roughly the same as the ratio between BeOS users and Windows users. Cheap ass security advice: find the most unpopular system you can (put those Commodore 64s to use!), lock it down to the best of your sysadmin abilities, and start praying!
Well, your fingers weave quick minarets; Speak in secret alphabets;
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A feeling of having made the same mistake before: Deja Foobar
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Jonathan Swift
So a big apache expliot comes out, and a half hour later there's a patch (thanks to open source) and you apply it/ recompile. Then you look at the apache log files and don't see any unusual activity. So you're safe, right? wrong. Your system was compromised and a rootkit was installed. It cleaned up all the logs. It added a backdoor to getty. It modified your MD5 checksum verification. It modified your rpm so that it points to the hackers server, no matter what you say. It modified gcc to include a backdoor into any program that requires authenitcation and insert this code into any gcc recompiles.
Do I really need to prove that it's easier to change:
if (checkPassword(password)) {goCrazy();}
to
if (checkPassword(password) || !strcmp(password, "k00ldud3") {goCrazy();}
than it is to use a disassembler on an executable with no symbols to figure out what the hell is going on and insert a back door? Not only does this require a much higher level of expertise, it also requires significantly more time for the person who can do it.
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Furthermore, running services on non-standard ports provides no real obscurity but it makes administration substanitally harder. In this way, it is in no way good policy.
Good obscurity tactics involve hiding internal systems from your external DNS servers, trying to avoid letting people see what OS you are using, etc. Forcing people to do guesswork is good, but it should not inconvenience your users (that should be left for the more fundamental security measures.
Attackers should be forced to make their attack based on limited information. By limiting the information they have, you can limit the effectiveness of the attacks and maximize their effort. But it should not be used as a standalone strategy.
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LedgerSMB: Open source Accounting/ERP
There are two kinds of "Security through obscurity", and it confused some people. (Insert funny joke about clueless managers and Microsoft-heads here)
First there is the bad kind: you're a software vendor and you hope that nobody will notice that your "secure" software uses ROT-13 instead of RSA. You are protected by the DMCA anyway (remember: crack ROT-13, go to jail).
Then there is the second, good kind: if I'm an admin, there is not reason I shouldn't strip outgoing email of any headers that my reveal the structure of my internat network (some people ARE arguing that you shouldn't do that.)
I don't really like this "security through obscurity" thingie. Let's make the difference between full specs release and not telling anyone more than they should know. This is the way to built a really secure network.
Nobox: Only simple products.
This was written in 1853 by Charles Tomlinson, and is only an excerpt of the the treatise, but it shows that people recognized that 'security' trough obscurity was not really security at all, way before the digital age.
...The unscrupulous have the command of much of this kind of knowledge without our aid; and there is moral and commercial justice in placing on their guard those who might possibly suffer therefrom. We employ these stray expressions concerning adulteration, debasement, roguery, and so forth, simply as a mode of illustrating a principle -- the advantage of publicity. In respect to lock-making, there can scarcely be such a thing as dishonesty of intention: the inventor produces a lock which he honestly thinks will posess such and such qualities; and he declares his belief to the world. If others differ from him in opinion concerning those qualities, it is open to them to say so; and the discussion, truthfully conducted, must lead to public advantage: the discussion stimulates curiosity, and curiosity stimulates invention. Nothing but a partial and limited view of the question could lead to the opinion that harm can result: if there be harm, it will be much more than counterbalanced by good.
A commercial, and in some respects a social, doubt has been started within the last year or two, whether or not it is right to discuss so openly the security or insecurity of locks. Many well-meaning persons suppose that the discussion respecting the means for baffling the supposed safety of locks offers a premium for dishonesty, by showing others how to be dishonest. This is a fallacy. Rogues are very keen in their profession, and already know much more than we can teach them respecting their several kinds of roguery. Rogues knew a good deal about lockpicking long before locksmiths discussed it among themselves, as they have lately done. If a lock -- let it have been made in whatever country, or by whatever maker -- is not so inviolable as it has hitherto been deemed to be, surely it is in the interest of honest persons to know this fact, because the dishonest are tolerably certain to be the first to apply the knowledge practically; and the spread of knowledge is necessary to give fair play to those who might suffer by ignorance. It cannot be too earnestly urged, that an acquintance with real facts will, in the end, be better for all parties.
Some time ago, when the reading public was alarmed at being told how London milk is adulterated, timid persons deprecated the exposure, on the plea that it would give instructions in the art of adulterating milk; a vain fear -- milkmen knew all about it before, whether they practiced it or not; and the exposure only taught purchasers the necessity of a little scrutiny and caution, leaving them to obey this necessity or not, as they pleased.