Homework 06

Name: ____________________________________________________ Alpha: ________________________

[10pts] Fill in the blank in the code so that the output is correct. Note: do not use any string operation, any loop, or any if statement. Use bit operations.


#===========================================================================
# fill in the blank: Write a function get_at
# input 
#  - n: an 8-bit integer
#  - i: an integer between 0 and 7 (inclusive)
# output 
#    the i-th bit of n (as an integer) 
# WARNING:
#  - You are only allowed to use the following operations:
#      bitwise-and, bitwise-or, bitwise-xor, shift-left, 
#      shift-right, parenthesis, addition, subtraction.
#    All the other operations (e.g., multiplication, string, list, etc.) 
#       are prohibited. 
#
#  - The function should work correctly for any 8-bit integer n. 
def get_at(n, i):

   return _________________________________________________

Here are sample runs. Carefully inspect the sample run to see how the indexing of i works


>>> for i in range(8):
...   print( get_at(0b11101100, i) )
... 
1
1
1 
0
1
1 
0 
0


>>> print( get_at(0b00110011, 0) )
0
>>> print( get_at(0b00110011, 1) )
0
>>> print( get_at(0b00110011, 2) )
1
>>> print( get_at(0b00110011, 6) )
1 
>>> print( get_at(0b00110011, 7) )
1

[5pt] List the Five Eyes countries.
[6pts] The descriptions below are from "Security Engineering, 3rd ed". Choose the word from the box that best fits each description.
```
Tempora      Prism        Muscular      Bullrun       Stuxnet
Xkeyscore    Longhorn     Edgehill      Quantum       Duqu 
```
- It is a federated system, which one query scan all sites. It also lets analysts build a fingerprint of any target's online activity so that they can be followed automatically around the world. Al-Qaida's Sheikh Atiyatallah blew his cover by googling himself, his various aliases, and the name of his book, etc.
- It is an internal NSA codename for an access channel that had been provided to the FBI to conduct warranted wiretaps. This program allegedly had started at Microsoft in 2007. Yahoo, Google, Facebook, and Apple followed the suit by 2012.
- It is an NSA codename for tampering with supplies and suppliers at all level of the stack. For example, the NSA covertly bought Crypto AG, a Swiss firm that was the main supplier of cryptographic equipment to non-aligned countries during the Cold War.

[20pts] Let's write a simple TCP netcat client tcp_cli.py. Your program should work with nc program running as a server. See the sample run below:

Client

~$ python3 tcp_cli.py 127.0.0.1 9000
from server
from client
bye
quit

Server

~$ nc -l 9000
from server
from client
bye

Complete the code. Make sure that your code works correctly as shown in the sample run above.

# tcp_cli.py
import sys
import socket
import select

ip_addr = sys.argv[1]
port = int(sys.argv[2])
sock = socket.socket()

# add code below


while True:
  socklist = [_____________, _____________]   # fill in the blanks
  (r_sockets, w_sockets, e_sockets) = select.select(socklist, [], [])

  if ___________ in ____________:             # fill in the blanks
     # add code below


     print(data)

  if sys.stdin in _____________: 
     s = input()
     # add code below


sock.close()