challenges

Crypto I

Assignment details

This assignment has two parts. It is due by 4/5/18 at 11:59PM. To submit your work, please post either a public note or a link to your publicly available writeup on Piazza.

There will be a late penalty of 5% per day late!

Part 1

You have successfully infiltrated one of the servers at Briong, and have extracted an /etc/shadow file! Use what you've learned so far to answer the following questions:

1. What is the hashing algorithm(s) used to secure these passwords?
2. What salt is used for these passwords, if any?
3. When were the passwords changed, if at all?
4. What are the restrictions each user has on changing their password, if any?
5. Have any passwords expired? If so, whose?
6. Use one of the tools discussed in class (hashcat, JohnTheRipper) to try and recover each password and show how you used the tool.

Part 2

You have also found various hashes laying around on the server. From the notes you have gathered during your penetration testing, you think that they are passwords picked from this password list. You also found out that these passwords are salted with a single lowercase letter (a, b, c, ..., z) prepended to each password before being hashed with the SHA512 algorithm, though you don't know if the same salt is used for each password. Your task is to try and manually break these hashes with a sort of custom rainbow table and recover the passwords and the salts. Use your Python-fu to crack these hashes, providing both the salt and the password for each hash. Stub code is provided in part2.py.

Part 3

You stumbled upon a hidden service not discovered by your port scans. It seems like one of Briong's interns desperately needs a calculator for his Algebra homework. He's fairly good at mental math, but not good enough -- try and write a script to do his homework faster than he can, and he might give you a flag for your help. nc irc.csec.umiacs.umd.edu 4444 (Stub code is in part3.py) Submit the flag you get in return.

Important notes

Make sure to submit all of the code you write, even if based on the stub code! You will need to submit your code for both Part 2 and Part 3.

Scoring

• Part 1 is worth 30 points
• Part 2 is worth 35 points
• Part 3 is worth 35 points

Tips

Remember to document your thought process for maximum credit!

Review the slides for help with using any of the tools or libraries discussed in class, as well as consult the man pages for any of the tools discussed and for the shadow file format and the hash format (shadow(5) and crypt(3))

Look back at your Homework 2 code if you need a refresher on working with sockets for Part 3.

Pro tip: along with the online Python references, you can also open up an interactive Python session (by typing python in your shell) and import the module of choice (e.g. import sys) and call help() on that module (e.g. help(sys)) to get a manpage-like reference to how to use that module!

• Python 2 - hashlib
• Python 2 - socket
• Python 3 - hashlib
• Python 3 - socket