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ECEN 4133

Computer Security Fundamentals Project 3: Network Security
Project 3: Network Security

Introduction
This project will introduce you to common network protocols, the basics behind analyzing network
traces from both offensive and defensive perspectives, and several local network attacks.
Objectives
• Gain exposure to core network protocols and concepts.
• Understand offensive techniques used to attack local network traffic.
• Learn to apply manual and automated traffic analysis to detect security problems.
Part 1. Network Attacks

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ECEN 4133

Computer Security Fundamentals Project 3: Network Security
Project 3: Network Security

Introduction
This project will introduce you to common network protocols, the basics behind analyzing network
traces from both offensive and defensive perspectives, and several local network attacks.
Objectives
• Gain exposure to core network protocols and concepts.
• Understand offensive techniques used to attack local network traffic.
• Learn to apply manual and automated traffic analysis to detect security problems.
Part 1. Network Attacks
In this part of the project, you will experiment with network attacks by man-in-the-middling an
HTTP connection to a website we control, and replacing some of its content.
Setup
This part can optionally use a VM, if you need it. You are allowed to write a script and run it on
your own computer, but if you run into trouble installing scapy/pcap libraries, try the VM.
(optional) VM setup
1. Download VirtualBox from https://www.virtualbox.org/ and install it on your computer. VirtualBox runs on Windows, Linux, and Mac OS.
2. Get the VM file at https://file.ecen4133.org/4133-vm.ova. This file is 3 GB, so we recommend downloading it from campus.
3. Launch VirtualBox and select File B Import Appliance to add the VM.
4. Start the VM. There is a user named ubuntu with password ubuntu.
5. cd project3
6. Run ./getkey.py to see that it outputs a key.
7. In this project, you will edit ./attack.py to attack the output of ./getkey.py.
Attacking
You can download getkey.py and attack.py from here: https://ecen4133.org/static/proj3/getkey.py
https://ecen4133.org/static/proj3/attack.py
We have set up the website http://freeaeskey.xyz/, which is a website that provides “random” AES256 keys for free to anyone who visits. Professor Vuln has decided to use this website for encrypting his research. To do this, he has created a program that first fetches a fresh key from
freeaeskey.xyz, and uses it to encrypt the private data. Your goal is to get Professor Vuln to encrypt
the secret research under a key known to you.
To do this, you are able to get a program to run on Professor Vuln’s network. For the purposes of
this assignment, you will run your program as root on the same machine that Professor Vuln uses
to download his key (i.e. the provided VM). Your task is to edit the ./attack.py Python program
to watch for requests to freeaeskey.xyz, and replace the key provided with one known to you:
4d6167696320576f7264733a2053717565616d697368204f7373696672616765
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The rest of the web page should remain un-modified to avoid suspicion. When Professor Vuln runs
the ./getkey.py script, it should output this key every time. You are not allowed to modify the
getkey.py script.
Your script will run as root, and any other users on the same machine that visit freeaeskey.xyz
while it is running should receive this injected key. We will grade this project using the same VM
given to you.
You are welcome to use any of the following libraries. If you believe you need additional ones,
please ask on Piazza.
https://pypi.python.org/pypi/scapy
https://pypi.python.org/pypi/dpkt
https://pypi.python.org/pypi/dnet
Bonus: Attack HTTPS [Extra credit]
Professor Vuln has realized it is unwise to download keys over HTTP, and has switched to using
HTTPS to download his keys, from https://freeaeskey.xyz. Make a new script (attack_https.py
that caries out the same attack as before against HTTPS, this time fooling ./getkey-secure.py.
(Hint: what is secure about getkey-secure?)
What to submit Submit a Python script named attack.py that performs the attack when run as
root on the local machine. For the (optional) bonus, submit attack_https.py as well.
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Part 2. Anomaly Detection
In this part, you will programmatically analyze trace data to detect suspicious behavior. Specifically, you will be attempting to identify port scanning.
Port scanning is a technique used to find network hosts that have services listening on one or more
target ports. It can be used offensively to locate vulnerable systems in preparation for an attack, or
defensively for research or network administration. In one port scan technique, known as a SYN
scan, the scanner sends TCP SYN packets (the first packet in the TCP handshake) and watches for
hosts that respond with SYN+ACK packets (the second handshake step).
Since most hosts are not prepared to receive connections on any given port, typically, during a port
scan, a much smaller number of hosts will respond with SYN+ACK packets than originally received
SYN packets. By observing this effect in a packet trace, you can identify source addresses that may
be attempting a port scan.
Your task is to develop a Python program that analyzes a PCAP file in order to detect possible SYN
scans. You should use a library for packet manipulation and dissection, such as scapy. To learn
about scapy, visit https://scapy.readthedocs.io/en/latest/usage.html.
Your program will take one argument, the name of the PCAP file to be analyzed, e.g.:
python3 detector.py capture.pcap
The output should be the set of IP addresses (one per line) that sent more than 3 times as many
SYN packets as the number of SYN+ACK packets they received. Your program should silently ignore
packets that are malformed or that are not using Ethernet, IP, and TCP.
A sample PCAP file captured from a real network can be downloaded at https://file.ecen4133.org/
proj3.pcap. (You can examine the packets manually by opening this file in Wireshark.) For this
input, your program’s output should be these lines, in any order:
128.3.23.2
128.3.23.5
128.3.23.117
128.3.23.158
128.3.164.248
128.3.164.249
What to submit Submit a Python program that accomplishes the task specified above, as a file
named detector.py. You should assume that scapy 2.4 is available, and you may use standard
Python system libraries, but your program should otherwise be self-contained. We will grade your
detector using a variety of different PCAP files.
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Submission Checklist
Upload to Moodle a gzipped tarball (.tgz) named project3.identikey1.identikey2.tgz.
The tarball should contain only the files below:
Part 1: Network Attacks
attack.py A Python script that caries out the attack specified in Part 1.
attack_https.py* A Python script that does the HTTPS attack (extra credit)
Part 2: Anomaly Detection
detector.py Your Python program for SYN scan detection.
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