The earliest memory I have of ‘programming’ is in the early/mid 90s when my father brought home a computer from work. We could play games on it … so of course I took the spreadsheet program he used (LOTUS 123, did I date myself with that?) and tried to modify it to print out a helpful message for him. It … halfway worked? At least I could undo it so he could get back to work…

After that, I picked up programming for real in QBASIC (I still have a few of those programs lying around), got my own (junky) Linux desktop from my cousin, tried to learn VBasic (without a Windows machine), and eventually made it to high school… In college, I studied computer science and mathematics, mostly programming in Java/.NET, although with a bit of everything in the mix. A few of my oldest programming posts on this blog are from that time.

After that, on to grad school! Originally, I was going to study computational linguistics, but that fell through. Then programming languages (the school’s specialty). And finally I ended up studying censorship and computer security… before taking a hard turn into the private sector to follow my PhD advisor.

Since then, I’ve worked in the computer security space at a couple of different companies. Some don’t exist any more, some you’ve probably heard of. I still program for fun too, and not just in security.

But really, I still have a habit of doing a little bit of everything. Whatever seems interesting at the time!

Extending Racket's DNS capabilities

2013-09-25

As I mentioned on Monday, I wrote my DNS-based censorship around the world–and to do that, I need a fair bit of control over the DNS packets that I’m sending back and over parsing the ones that I get back.

Extending Racket structs to bitfields

2013-09-23

Keen eyed observers may have noticed that last Friday when I posted about converting my various Racket libraries to Planet 2 packages, that there was a new package there I haven’t otherwise talked about: bit-struct. Today seems like a good time to talk about that. Theoretically, I’ll also have another post or two this week showing exactly what I’m doing with it (spoilers: it involves sending on the order of billions of DNS requests¹).

Deploy Racket libraries to Planet 2

2013-09-20

Over the last few years, I’ve managed to write a fair bit of Racket code. It’s a lovely language and an even better ecosystem for writing quick/clean code (batteries included! ). Several times throughout that, I’ve written code that I thought could be useful to others, including several libraries that I used to write my Racket Roguelike and code that I’ve used working with the C211 class at Indiana University. I’ve always said that I should turn these into packages that others can use and… I’ve finally figured it out.

Smallest consecutive four-factor composites

2013-09-19

Another post from Programming Praxis, from this past Tuesday:

The smallest pair of consecutive natural numbers that each have two distinct prime factors are 14 = 2 * 7 and 15 = 3 * 5. The smallest triplet of consecutive natural numbers that each have three distinct prime factors are 644 = 2^2 * 7 * 23, 645 = 3 * 5 * 43 and 646 = 2 * 17 * 19. What is the smallest set of four consecutive natural numbers that each have four distinct prime factors?

Diffie-Hellman Key Exchange

2013-09-14

Today we’re going to be talking about cryptography, specifically Diffie-Hellman key exchange¹. The basic idea isn’t necessarily to communicate in secret, but rather to establish the information that makes doing so much easier.

Visualizing the Monkey Grid

2013-08-30

I’m a bit behind the times, but this post from Programming Praxis intrigued me enough that I kept it in my todo list for rather a while. So let’s get around to it.

I’ll just copy the description straight from the Programming Praxis website (although there are at least two previous version:[1][2]):

There is a monkey which can walk around on a planar grid. The monkey can move one space at a time left, right, up or down. That is, from (x, y) the monkey can go to (x+1, y), (x-1, y), (x, y+1), and (x, y-1). Points where the sum of the digits of the absolute value of the x coordinate plus the sum of the digits of the absolute value of the y coordinate are lesser than or equal to 19 are accessible to the monkey. For example, the point (59, 79) is inaccessible because 5 + 9 + 7 + 9 = 30, which is greater than 19. Another example: the point (-5, -7) is accessible because abs(-5) + abs(-7) = 5 + 7 = 12, which is less than 19. How many points can the monkey access if it starts at (0, 0), including (0, 0) itself?

Wombat IDE - New semester / bug fixes

2013-08-26

We’re about to start up the Fall semester, so it seems like a good time to be updating Wombat for the new semester. With that, a whole slew of bugs have been squashed:

'Tiny' Turing completeness without MMOV

2013-08-22

Something was bugging me about my proof from yesterday. If we take another tack on proving Turing completeness, all we would have to prove is that we can simulate SUBLEQ. Since SUBLEQ is Turing complete, that’s all we need–just convert each SUBLEQ into a SUB, JZ, and a JLS. So that means that Tiny as written should be Turing complete.

So how does that work?

A 'Tiny' virtual machine in Racket

2013-08-21

Today’s challenge at /r/dailyprogrammer asks to implement an assembler for a small virtual machine. It has only 16 mnemonics which in unique opcodes (each instruction can have multiple forms for if they’re accessing memory or literals), so it’s a simple virtual machine indeed. As a challenge, you’re supposed to write an interesting program (I actually wrote a virtual machine as well to test them). As an even better challenge, we’re supposed to prove that Tiny is Turing complete. Well, let’s get to it!

Adventures in Racket: gzip

2013-08-06

In my research, I work with a lot of rather large text files–on the order of gigabytes if not terabytes per file. Since they’re plain text, they’re generally rather compressible though, so it makes sense to gzip them while they’re on disk. The drawback though comes when you’re working with them. There are a few options though.