DEF CON CTF Qualifier 2014: add ‘zombies’ write-up

Closes ctfs#72.

def-con-ctf-qualifier-2014/zombies/README.md

@@ -10,7 +10,183 @@
 
 ## Write-up
 
-(TODO)
+TODO: Add detailed challenge description
+
+Here is a working example:
+
+```python
+import socket
+import math
+import numpy
+import time
+
+def parse_level(text):
+  level = 0
+  for line in text.split('\n'):
+    if line.strip().startswith("Level"):
+      levelline = line.strip().split()
+      level = int(levelline[1])
+
+  if level < 10:
+    x,y = parse_level1(text)
+  else:
+    x,y = parse_level2(text)
+
+  return x, y
+
+def parse_level1(text):
+  x = 0
+  y = 0
+  level = 0
+  for line in text.split('\n'):
+    if line.startswith("The zombie is stalking"):
+      line = line.split()
+      x = int(line[6].replace('m', ''))
+      y = int(line[11].replace('m', ''))
+      print "Zombie is at: "
+      print "x: ", x
+      print "y: ", y
+  return x,y
+
+def parse_level2(text):
+  x = 0
+  y = 0
+  level = 0
+  for line in text.split('\n'):
+    if line.startswith("The zombie is stalking"):
+      splitline = line.split()
+      zx = int(splitline[14].replace('m', ''))
+      zy = int(splitline[19].replace('m', ''))
+      px = int(splitline[28].replace('m', ''))
+      py = int(splitline[33].replace('m', ''))
+
+      print "Zombie is at: "
+      print "x: ", zx
+      print "y: ", zy
+      print "Puppy is at: "
+      print "x: ", px
+      print "y: ", py
+
+    if line.find("eats the puppy") != -1:
+      eta = int(line.split(' ')[2])
+      print "ETA dead puppy:", eta
+
+    if line.find("gone by") != -1:
+      # Consider +1 because of the wait
+      my_time = int(line.split(' ')[0]) + 1
+      print "Elapsed time:", my_time + 1
+
+  new_x, new_y = calculate_position(zx, zy, px, py, eta, my_time)
+  dummy = s.recv(1024)
+  print dummy
+  return new_x,new_y
+
+def calculate_angle(velocity, x, y):
+
+  angle1 = None
+  angle2 = None
+
+  g = 9.80665
+  root = math.sqrt( (velocity**4) - g*( (g * (x**2)) + (2 * y * (velocity**2)) ))
+  print "G", x
+  angle1 = numpy.arctan((velocity**2 + root) / (g*x))
+  angle2 = numpy.arctan((velocity**2 - root) / (g*x))
+
+  angle1 = 180 * angle1 / math.pi
+  angle2 = 180 * angle2 / math.pi
+
+  print "Calculated angles:"
+  print "Angle1:", angle1
+  print "Angle2:", angle2
+
+  return angle1, angle2
+
+def calculate_position(zx, zy, px, py, eta, mytime):
+
+  distx = px - zx
+  disty = py - zy
+
+  ratio = float(mytime) / float(eta)
+
+  new_x = (distx * ratio) + zx
+  new_y = (disty * ratio) + zy
+
+  print "new coords:", new_x, new_y
+
+  return new_x, new_y
+
+def shoot(angle, x, y, gun="r"):
+
+  dump = ""
+  if gun == 'r':
+    dump += "r, "
+    # I'm sorry...
+    global rcpt
+    rcpt += 1
+    print "Riffle count: " ,rcpt
+  else:
+    dump += "p, "
+    # I'm sorry...
+    global pcpt
+    pcpt += 1
+    print "pistol count: ", pcpt
+  angle = str(angle)
+  dump += angle + ', '
+  dump += str(x) +", "
+  dump += str(y) + "\n"
+
+  print "Sending:"
+  print dump
+
+  s.send(dump)
+  data = s.recv(1024)
+  print data
+  return data
+
+
+HOST = "zombies_8977dda19ee030d0ea35e97ad2439319.2014.shallweplayaga.me"
+PORT = 20689
+
+RIFFLE = "2\n"
+PISTOL = "3\n"
+
+riffle_velocity = 975
+pistol_velocity = 375
+
+rcpt = 0
+pcpt = 0
+
+s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+s.connect((HOST,PORT))
+
+# intro
+data = s.recv(1024)
+
+# pick guns
+s.send(RIFFLE)
+data = s.recv(1024)
+s.send(PISTOL)
+data = s.recv(1024)
+print data
+
+#Game Start
+while(True):
+  # Need to sleep otherwise misses on gun changes
+  # This needs to be accounted for in the zombie's position
+  time.sleep(2)
+  x, y = parse_level(data)
+  # Hint said 50ish... not enough pistolling at 50ish
+  if x < 55 and pcpt < 43:
+    a1, a2 = calculate_angle(pistol_velocity, x, y)
+    data = shoot(a2, x, y, gun='p')
+  else:
+    a1, a2 = calculate_angle(riffle_velocity, x, y)
+    data = shoot(a2, x, y, gun='r')
+  if data.lower().find("flag") != -1:
+    break
+
+s.close()
+```
 
 ## Other write-ups