Search This Blog

Friday, November 30, 2007

Exercise for the Reader

Okay, here's one you can apply to your real, daily lives (well, some of you, anyway). When does throwing a stronger punch/kick (something along those lines) require using less strength/energy than throwing a weaker one?

No, there's no esoteric Zen metaphysics at work, here. Nothing but classical European physics.

Edit: Also, English is a bit ambiguous for the question. I'm asking when is it necessary to punch weaker in order to punch stronger?

Thursday, November 29, 2007


The basic steps used in the link to find the distance between P3 and P are:
1. Calculate the distance between P1 and P
2. Calculate the exact location of P
3. Calculate the distance between P and P3

Now, a little common sense suggests there are two too many steps here. But we can't compute the distance between P and P3 directly, because at this point the location of P is unknown.

Yet there's a very simple solution: we rotate P2 90 degrees around P1 to create P2'. By definition the distance between P1 and P' is the same as the distance between P3 and P. This has exactly the same form as the version in the link, but it is able to find the distance between P1 and P' in the first step, instead of the distance between P1 and P. Thus we've eliminated steps 2 and 3 entirely, and use exactly the same math as before:
u' = ( (x3 - x1)(x2' - x1) + (y3 - y1)(y2' - y1) ) / ( ||p2' - p1||^2 )

A visual proof:

While understanding the way the distance is calculated using the dot product requires knowledge of calculus/linear algebra, deriving this improved equation from the original in the link is just trivial high school geometry. That's why it's neat.

Sucky Test Teacher Strikes Again

So, just got back the graded midterms in networking class (theoretical stuff), taught by the same teacher. Not surprisingly, it was disappointing. As before, this guy could teach a class on how not to write (and grade) tests. Among smaller gripes were two main things:

1. One question (in particular) was taken straight out of the book, and was fairly simple. What could go wrong? Well, giving the same answer to the problem as in the book got you a wrong answer on the test (and no, it wasn't an essay question where theoretically he could expect more detail).

2. Throughout the semester (there's one week left), whenever math was used, it was exclusively high-school-level math (basic algebra and such; there was one area under the curve problem, but as the "curve" was a line, it could be calculated with basic algebra). Neither the book, the lectures, nor any homework has gone beyond that. So, what does he do? He puts a calculus question on the test, and makes it worth 25% of the test (note that calculus is not a prerequisite for this class; I wonder if he could get in trouble with the dean for this).

Ultimately, Q got (like always, although it's always hard to believe in classes with this teacher) an A on the test. I don't know what the exact ranges for grades are, but I talked to one person who got an A- for 58%, and rumor has it that one person got a C for 18%.

Which brings me back to what I said in the previous post about this guy: CURVING THE SCORE DOES NOT MAKE UP FOR A HORRIBLE TEST.

Wednesday, November 28, 2007

Exercise for the Reader

Oh no, not another one of Q's easy but slightly tricky quiz questions. Today it's regarding finding the shortest distance between a point and a line. This explains the theory behind it, and how to calculate it.

But if you are only interested in the distance between P and P3 itself, and you don't care what P is, this math is moderately wasteful, as you have to first find P, then calculate the distance between P and P3. Surely there must be a way to calculate the distance without ever calculating P. And in fact, there is.

Find it, without cheating (looking up the answer online of through friends. It's actually pretty easy and simple. I just thought it was kind of neat.

Monday, November 05, 2007

& Insanity

*evil, maniacal laughter*

No, that's not me starting to panic about E Terra and deadlines (although I am starting to panic about E Terra and deadlines, as indicated by my physical stress symptoms that are starting to appear). Let's just say that I'm very pleased with my class schedule and related things, and gloating without being able to say exactly why.

Happy, happy months ahead (and at least one very stressful month)!

Friday, November 02, 2007

World Without Windows

Okay, so that title is a bit misleading. Anyway, this post hopes to provide some meaningful answers to the question: what would the world be like if the overwhelmingly dominant operating system was secure in ways that Windows is not. For the purposes of this discussion, I'm defining "secure" by several criteria:
1. All users run as limited users - they can't do administrative tasks or screw with the OS without explicitly logging on as admin or running a program as administrator (e.g. Windows run as or Unix sudo)
2. The system is fully isolating with respect to users - one user may not access another user's data without explicit permission
3. There are no privilege escalation exploits in the OS - tricks that limited users could use to gain administrator privilege without having to enter the administrator password
4. There are no remote exploits in the OS itself - in the kernel, standard drivers, basic services, etc.

So, we have this idealized, nonexistent operating system; let's call it Qunix. How exactly, then, would the world look if Qunix had 95% market share? Would this be, as the average Slashdotter seems to believe, a secure and malware-free utopia, where nobody knows what viruses, worms, spyware, or security breaches are, because they don't exist?

The answer, actually, is somewhat depressing: the world would look pretty similar to how it looks right now. Malware and security breaches would still be prominent, the security industry (anti-malware products) would still be big business, and the black hat industry would have similar job security. Granted, the nature of malware would be different, but that would not make it any less prolific or dangerous.

Ultimately, those four criteria I specified have one intended goal: to put everything the user does in a sandbox, where it can't harm the OS or other users (this was how Windows NT was originally envisioned, but time has proved that hope misplaced). Let's assume, for the moment, that these measures achieve that goal (we'll come back to why they don't, later). With this assumption, it becomes impossible for a piece of malware (or a hacker exploiting a buffer overflow, or some such) to invade the kernel, either to destroy the system or to merely hide its existence from the user and malware scanners (a rootkit, in other words).

Unfortunately, while there's no denying that this would make the lives of evil-doers harder, this is anything but the doom of malware/security breaches. Even without the ability to harm the OS itself, a piece of malware could still damage that user's data, and data is often more valuable than the computer it resides on.

Furthermore, the ability to invade the kernel is no requirement for a virile piece of malware. While hiding is more difficult, creating a virus/worm/etc. that runs entirely in user mode is completely viable. Macro viruses, worms that spread through chat programs, and old-fashioned viruses that spread from a disk/e-mail to the computer and back would still be viable and common (although, amusingly, Windows is more resistant to this last type of virus than Linux). There would still inevitably be security holes in third party applications allowing an attacker to get a foothold in the computer and execute code under the user's privileges, and the user could still get (their data) owned, without the attacker ever invading the kernel.

Thus, the necessity of anti-malware products would remain. Now, it would be reasonable to assume that anti-malware products would run with administrative privileges. However, this advantage of privilege would only make life more difficult for malware authors. While it would make it impossible to completely hide from a scanner running at higher privilege, there are many ways of obfuscating, evolving, and encrypting a piece of malware such that it is not readily recognizable by a malware scanner.

Clearly this could be overcome by the malware scanner being updated to respond to a new threat... but that's exactly how the world works right now: anti-malware programs must be kept up to date, or they will not be able to protect against everything that has been analyzed (not to mention the time between when a piece of malware is released into the wild and protection is added to anti-malware products). Consequently, malware analysis labs would still be working frantically, and companies would still have support contracts with anti-malware companies to keep their computers perpetually updated with the latest malware protection.

Now, let's make one final invalid assumption, for the sake of argument: through a combination of various methods, such as security cookies, data execution prevention, and other manner of code hardening, that it's impossible for an attacker to penetrate an application running on the computer (e.g. code injection into a web server, an office application executing code in a document, etc.). That leaves one final mode of attack, one which has been used for decades with incredible success, and one which all of the aforementioned measures combined can't stop: PEBKAC; that is, user naivety.

Even if you could stop all remote and automated methods of invading a system, it will always be trivial to trick the user into running something that is actually malware. This fact nullifies every one of the defense measures proposed previously. Even if a user cannot be attacked other ways, an executed program could wipe all their data. Even if a user only runs as an administrator to install new programs/drivers and perform administrative tasks, an executed "installer" could wipe the data of all other users, and an installed "driver" could install a rootkit for future or immediate use. Similarly, even an air-gapped computer (one which has no network connection at all) still remains susceptible to infection (remember, viruses were rampant on air-gapped computers long before networks or the internet entered the average home/business).

To give you an idea how easily malware can spread relying only on tricking users into manually running it, you only need to take a brief look at the Storm worm. While this worm has been revised and updated extensively over its life, it began as a humble executable that was e-mailed to people; when run, it infected the computer. This worm is now considered to compose the largest botnet in history.

Thursday, November 01, 2007

It's That Time Again

Time to register for spring classes.

So, what's on the plate this semester? After talking to the adviser, it looks like I have exactly 8 classes (3 units each) needed to graduate (I've already finished my biology major, including GE courses, so all 8 are in computer science - third year and fourth year courses). Some of these courses are mandatory, either because they're directly required by the major, or they're required as prerequisites for courses I absolutely want to take. The ones I need specifically, along with their description from the school catalog:

Programming Languages and Translation
Introduce both basic concepts of programming languages and principles of translation. The topics include the history of programming languages and various programming paradigms, language design issues and criteria, developing practical translator for modern programming languages.

Software Engineering
Basic concepts, principles, methods, techniques and practices of software engineering. All aspects of software engineering fields will be covered briefly. Software engineering tools are recommended to use.

Artificial Intelligence
Use of computers to simulate human intelligence. Topics include production systems, pattern recognition, problem solving, searching game trees, knowledge representation, and logical reasoning. Programming in AI environments.

Principles of Computer Graphics
Examination and analysis of computer graphics; software structures, display processor organization, graphical input/output devices, display files. Algorithmic techniques for clipping, windowing, character generation and viewpoint transformation.

Advanced Game Programming
Intermediate and advanced game programming techniques including 3D game development, realtime rendering, physic simulation, etc.

Game Development Project [thesisish thingy]
Individual or team develops realistic games based on the theories and techniques, present and demonstrate their work regularly.

I definitely need to take advanced game programming and computer graphics this semester. The other two slots are open. I'm thinking of taking AI, since that would be useful for E Terra. Unfortunately, that and compilers are at the same time (so are mutually exclusive), and they would both be used for E Terra AI :P I'm hoping to be able to use E Terra for the game project, but I won't be able to take that until the fall.

Besides those, I have a couple decisions to make. I have to take one other programming language than C++ - either Visual Basic, Java, or C#. VB is definitely out of the running, but I'm not sure whether Java or C# would be better. I'm learning some C# this semester because we use it in the game programming class (with XNA), but other than that I'm not sure which is better.

Finally, if my petition to drop one class (not mentioned), which the teacher says is unnecessary, is accepted, I'll need one more upper-division class for the units. Not too sure about which to take for that one. Here are the most appealing prospects, although none of them are something I'd be inclined to take if I didn't have to:

UNIX and Open Source Systems
Introduces the UNIX operating systems, various open source applications and systems, open source programming languages, and open source software development techniques.

Data Security and Encryption Techniques
System security and encryption. Current issues in security, encryption and privacy of computer based systems.

Advanced Operating Systems
The course covers internal structures of a modern operating system. The specific topics include processing, process communication, file systems, networking, and the I/O system. There are several programming assignments which include system calls, and other low level interfaces.

Web Programming and Data Management
Various techniques for developing Web-based database applications using software engineering methodology. Introduce concept and architecture of Web servers, Web database design techniques, client/server side programming, and Web application tools and techniques.

Or, I suppose there's always...
Independent Study
Special topic in Computer Science selected in consultation with and completed under the supervision of instructor.

Internship in Computer Science
Practical experience and service learning relevant to computer science in industry or organizations. Written and oral reports are required.

Hmmmm. Are you thinking what I'm thinking, Pinky?