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!

AoC 2016 Day 21: Scrambler

2016-12-21

Source: Scrambled Letters and Hash

Part 1: Another virtual machine, of sorts. Start with the string abcdefgh and apply a sequence of the following commands to it:

swap position X with position Y = swap two positions
swap letter X with letter Y = swap to letters, no matter where they are
rotate (left|right) X steps = rotate forward or backward
rotate based on position of letter X = find X, rotate right based on its position; if the original position was >= 4, rotate one more¹
reverse positions X through Y = reverse a subset of the string
move position X to position Y = take a character at a position out of the string and put it somewhere else specific

AoC 2016 Day 20: Filter Table

2016-12-20

Source: Firewall Rules

Part 1: Given a list of integer ranges (a la 5-8), what is the first value not in any given range?

AoC 2016 Day 19: Blist Table

2016-12-19

Source: An Elephant Named Joseph

Part 1: Create a circular list of the numbers 1 through n. Going around the list, each currently remaining number removes the number after it. What is the last remaining number?

AoC 2016 Day 18: Its A Trap

2016-12-18

Source: Like a Rogue

Part 1: Starting with a sequence of . and ^, generate additional rows using the rules based on the three characters above the new position.

^^. -> ^
.^^ -> ^
^.. -> ^
..^ -> ^
Otherwise -> .

How many safe tiles (.) are there after 40 generations?

AoC 2016 Day 17: Md5 Maze

2016-12-17

Source: Two Steps Forward

Part 1: Create a 4x4 grid of rooms with doors Up, Down, Left, and Right from each location. To determine if a door is currently open:

Calculate MD5(salt + sequence) where sequence is a string containing any combination of UDLR depending on how you got to this room
The first four hex values represent the doors Up, Down, Left, and Right respectively: bcdef means open; anything else is closed

Find the shortest path from (0, 0) to (3, 3).

AoC 2016 Day 16: Dragon Data

2016-12-16

Source: Dragon Checksum

Part 1: Generate noise using a modified dragon curve:

Start with data a
Create a copy of the data b, reverse and invert it (0 <-> 1)
Create the string a0b

Repeat until you have enough data, truncate at the end if needed.

From this string calculate a checksum as follows:

xor each pair of bits, concatenate the results
If the resulting string has an even length, repeat; if it’s odd, stop

Calculate the checksum of a given initial state expanded to 272 bits.

AoC 2016 Day 15: Capsule Dropper

2016-12-15

Source: Timing is Everything

Part 1: Given a series of openings one second apart, each with n positions that advance one position per second, what is the first time you can start the simulation so that you pass each in position 0.

AoC 2016 Day 14: Bad One Time Pads

2016-12-14

Source: One-Time Pad

Part 1: Calculate a series of MD5 hashes (the same as Day 5). A hash is considered valid if it contains a triple (three characters in a row) and somewhere in the next 1000 hashes there is a quintuple of that same character.

What index produces the 64th key?

AoC 2016 Day 13: Noisy Puzzle

2016-12-13

Source: A Maze of Twisty Little Cubicles¹

Part 1: Generate a procedurally generated maze using the following equation:

x^2 + 3x + 2xy + y + y^2 + c

x and y are the coordinates of a point and c is a constant.

Count the number of bits for each point. Even is open spaces, odd is walls.

What is the shortest route from (0, 0) to (31, 39)?

AoC 2016 Day 12: Assembunny

2016-12-12

Source: Leonardo’s Monorail

Part 1: Create a virtual machine that has four registers (a, b, c, and d) and can process the following instructions:

cpy x y - copies x into y (x can be an integer or a register)
inc x - increases register x by one
dec x - decreases register x by one
jnz x y - jumps over y instructions if x is not zero (x can be an integer or a register)

What is the final value in register a?

Source: Scrambled Letters and Hash

Source: Firewall Rules

Source: An Elephant Named Joseph

Source: Like a Rogue

Source: Two Steps Forward

Source: Dragon Checksum

Source: Timing is Everything

Source: One-Time Pad

Source: A Maze of Twisty Little Cubicles1

Source: Leonardo’s Monorail

Source: A Maze of Twisty Little Cubicles¹