This assignment has three parts, with three different due dates. Please be mindful of that. Everything you submit through Google Forms will be ASCII-encoded and look at least somewhat like English, so don’t click the submit button if you can’t read it. Also, sha512 sums will be provided, so if you want a guaranteed 100% of the points, work to match the sha512 sum before submitting.
First, you must fill out this Google form so that I have an MD5 digest for you, then wait until I’ve added you in the gradebok and added your tarball. If you get this done before 11:59pm on Thursday, September 23rd I’ll get your tar ball uploaded by Friday, September 24th. Otherwise, it’ll just happen when I get around to it.
You will download a tarball by taking this URL and replacing “NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN” with your MD5 digest:
https://207.246.62.10/filesforstudents/NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN.tgz
The SHA-256 sum for the certificate on that web server is “7E:F1:12:D4:A5:4F:92:30:AA:DC:D1:F5:14:3C:D8:D0:A5:FE:DB:52:9E:FC:A6:D2:22:4F:D1:D7:7A:BA:71:8C”, please confirm it manually and then make an exception for your web browser to go to the site.
The tar balls are unique to each student. Do not share your tarball with others.
There is also a common tarball, with source code and other things you will find helpful, here.
For all of the code provided to run properly, you’ll need to set up your environment. If you’re using the same version of MX Linux as me, this should be as simple as:
sudo apt install python3-pip
pip3 install --upgrade setuptools
pip3 install pyshark
sudo apt install python3-cryptoThere are two different ways to install libraries for Python 3 as shown above. One is to apt install the package, which usually looks like python3-* for the package name, and the other is to use pip3. They each have their advantages, for this assignment if you try one and it doesn’t work, try the other way.
This is an individual assignment. DO NOT share your solution with others or use solutions from others. You may discuss the assignment at a high level with your classmates and others, e.g., exploring potential solutions without giving the answer. You may use, and share with your classmates, any code that existed before this assignment was assigned and is not related to any similar assignment for any pat offering of CSE 365 at ASU. You may not share any code with future students of CSE 365 at ASU. If you’re not sure about if any particular activity will be considered cheating or not, ask.
About grading, make sure your answer matches the sha512 sum before submitting, and you’ll get full points. Don’t open the file in Windows or do anything else that could modify it before submitting, I recommend submitting directly from your Linux virtual machine. Be careful about the exact formatting and how the file should end, to achieve the correct sha512 sum. If the answer you submit does not match the sha512 sum, I’ll attempt to give you extra credit but I reserve the right to give you a zero on that part of the assignment. I.e., you’re at the mercy of my grading script if the sha 512 sum doesn’t match.
For all Google Forms submissions, you must use your @asu.edu Google account.
Due date: 1 October 2021 at 11:59pm MST
20 out of 100 points, 10 each cipher
In your tarball in the withkey directory, you’ll find five files:
ciphertext.txt - A ciphertext encrypted with a Caesar cipher.caesarkey.txt - The key used for the Caesar cipher.juliaplaintext.txt.gz.enc - A ciphertext encrypted as described below.juliakey.txt - The key used for Julia’s cipher.sha512sums.txt - sha51sums of the correct answers.For each of the two ciphers, Ceasar’s and Julia’s, you’ll need to write some code so you can plug in the key and decrypt (and then also decompress if necessary). You’ll submit two different plaintexts, one for each cipher, for part 1. In the src/ directory cse365encrypt.py is the code that was used for encrypting both ciphertexts.
For the Caesar cipher, the alphabet for the plaintext and ciphertext is the capital letters [A-Z], and the key is a number between 0 and 25.
For Julia’s cipher, the crypto algorithm is:
enc_char = bit_rotate(plain_char, N) xor key_bytewhere N is a fixed integer, and key_byte is a byte of the key. If the key is shorter than the length of the file, the key will be used again for xor from the beginning. Julia’s cipher works on binary files, so basically raw bytes.
You will submit exactly two text files: plaintext.txt (for the Caesar cipher) and juliaplaintext.txt (for Julia’s cipher). They should both be ASCII-encoded English text. In some cases there may be some extra steps after decryption before you get to English text.
After completing this part you should be confident with dealing with files and basic calculations in Python, and familiar with the two cryptosystems (that you’ll be using in the next part, as well).
Submit both the plaintext.txt and juliaplaintext.txt files for Homework 1.2 using this Google form.
Due date: 15 October 2021 at 11:59pm MST
30 out of 100 points, 15 each cipher
In your tarball in the withoutkey directory, you’ll find three files:
ciphertext.txt - A ciphertext encrypted with a Caesar cipher.secretfile.txt.gz.enc - A ciphertext encrypted with Julia’s cipher, as described in Homework 1.2.sha512sums.txt - sha51sums of the correct answers.This time you are not provided with any keys. Use the techniques discussed in class to mount ciphertext-only attacks on both of these ciphertexts. Note that Julia’s cipher is not the same as a Vigenere cipher. You’ll need to use the basic insights you learned, but the specifics from the slides won’t be exactly what you’re doing.
You will submit exactly two text files: plaintext.txt (Caesar cipher) and secretfile.txt (Julia’s cipher). They should both be ASCII-encoded English text.
After completing this part you should have some understanding of how simple codes can leave statistical clues in the ciphertext that lead to plaintext-only or known plaintext attacks.
Submit both the plaintext.txt and secretfile.txt files for Homework 1.3 using this Google form.
Due date: 29 October 2021 at 11:59pm MST
10 out of 100 points
This part will be a significant effort and you shouldn’t underestimate the amount of time it will take compared to the first two parts, or based on the number of points. The attack itself is based on a real attack on QQ Browser that is described at https://arxiv.org/abs/1802.03367. We’ll go over it in class, and the majority of your effort will be in reading Python code and understanding the attack, the amount of Python you’ll actually need to write is minimal. Some more info about the attack is available in rsaattack.pdf in the common tar ball. You are also given buildkey-givetostudents.py and streamy.py. streamy.py parses the pcap file and dumps the stream to stdout, and buildkey-givetostudents.py launches the attack. Between streamy.py and buildkey-givetostudents.py, you only need to write two lines of code for this part. However, you’ll need to understand the attack source code to know which two lines to write.
In the rsa directory of your tar ball you’ll find a packet capture (or pcap) of an attack that was carried out to recover an AES session key, and thereby decrypt a message. The server expects to receive an AES session key RSA encrypted with its public key, followed by a message encrypted with that AES session key. The attacker mounted a side channel attack against the server, using an encrypted communication that they eavesdropped when a victim client communicated with the server in the past. As the attacker carried out their attack, they left hints embedded in the TCP protocol to make it easier to know what phase of the attack each TCP session corresponds to. You’ll be provided with all source code used by the server, client, and attacker, as well as the server’s public key (which you probably don’t need). You’ll also be provided with a Python script to extract the attacker hints from the packet capture and print them as two integers per line that can be piped into your own source code for reconstructing the AES session key and decrypting the message to get the plaintext. Again, submit the whole plaintext as an ASCII text file.
You will submit exactly one text file: plaintext.txt. It should be ASCII-encoded English text. The sha512 sum is available in your tarball.
After completing this part you should have a solid understanding of the difference between symmetric and asymmetric crypto, knowledge of the AES and RSA algorithms specifically, and a general idea of how a chosen ciphertext attack on a modern cipher is structured.
Submit the plaintext.txt file for Homework 1.4 using this Google form.
Due date: 31 October 2021 at 11:59pm MST
Note that not turning this one in won’t count against your grade, it is extra credit
Number of points of extra credit TBD
A 3-round implementation of AES is available in the common tar ball linked to above. Develop a chosen plaintext attack against it. When you have a working attack (please don’t request ciphertext before your attack is actually working in your own tests because the file transfers will be large and logistics non-trivial), make arrangements with Prof. Crandall to receive ciphertext corresponding to plaintext you provide. Prof. Crandall will use the same key he used for encrypting part4ciphertext.bin, so you can then turn in the plaintext that corresponds with it along with your source code. Note that if you choose to attempt the extra credit you’ll be largely on your own when it comes to figuring out the details of mounting a chosen plaintext attack. We can provide resources and general directions but cannot invest too much time in helping with specifics because of the large number of students who will likely need help on the main part of the assignment.
You will submit this one over email to Prof. Crandall. Submit a tarball with the plaintext and your source code.
The new deadline for homeworks 1.2, 1.3, and 1.4 is October 31st, 2021. You can now resubmit as many times as you like, I’ll always grade the latest one. You can check your grades (which I’ll post periodically between now and the deadline) and update your submission. You can submit and get full credit even if you didn’t submit anything by the original deadline. I want to get this right and make sure you all do well on homework 1. I’ll try to fix all the logistical issues with how homeworks are submitted for homework 2.
You can check your grades on 1.2 and 1.3 by taking this URL and replacing “NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN” with your MD5 digest:
https://207.246.62.10/gradestoreturn/NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN.txt
Send me an email from your @asu.edu email address and give me your MD5 and ID number.
No, no need to resubmit.
Make sure that you turned in the right file in the right place, everything you turned in was a text file with something at least resembling English in it, and that you matched the sha512sum. If you still don’t know what the problem was, post a private message to me in Piazza and include your ASUrite ID.
I plan on doing one last round of tar balls soon. You should have started on the homework a long time ago, you’re benefiting from the extension that was due to logistical errors but you really need to start keeping up with the course. Homework 2 will be assigned very soon and overlap with homework 1, so the sooner you get homework 1 done the better.
You’ll need to resubmit 1.2 or 1.3 through the Google form. I received too many such emails to manually grade them all. I haven’t yet graded the extra credit for 1.1, but will.