Advanced Network Security
Attempt all questions. This is an individual assignment, and it is expected students answer the questions themselves. Discussion of approaches to solving questions is allowed (and encouraged), however each student should develop and write-up their own answers. See CQUniversity resources on Referencing and Plagiarism. Guidelines for this assignment include:
• Do not exchange files (reports, captures, diagrams) with other students.
• Complete tasks with virtnet yourself – do not use results from another student.
• Draw your own diagrams. Do not use diagrams from other sources (Internet, textbooks) or from other students.
• Write your own explanations. In some cases, students may arrive at the same numerical answer, however their explanation of the answer should always be their own.
• Do not copy text from websites or textbooks. During research you should read and understand what others have written, and then write in your own words.
• Perform the tasks using the correct values listed in the question and using the correct file names.
Discuss, Explain, Design Style Questions
A number of questions in this assignment require short, specific answers. These will normally be marked on correctness. That is, if the answer given is correct, then full marks, otherwise 0 marks. In some cases, partial marks may be given.
Other questions require more elaborate answers. They typically include words such as discuss, explain, design, compare or propose. For such questions, to achieve full marks your answer should not only be correct, but also clear and detailed. While your answers don’t necessarily have to be long (many paragraphs), the level of detail should be similar to that covered in lectures. Some hints on writing your answers to these style of questions include:
• Use terminology that has been used throughout the lectures. Using non-standard terminology, or terminology that significantly differs from that in this topic, is an example of unclear writing.
• Be specific, referring to files, algorithms, keys or other relevant data elements.
• When relevant, use examples to assist your explanation (although don’t use just examples; give a general explanation as well).
• Including wrong or irrelevant information in your answer will result in low marks. An answer with multiple wrong/irrelevant statements as well as a correct statement, may receive 0 marks.
• Don’t rely heavily on images (unless they are asked for). If you do include images, then draw them yourself – don’t take images from the Internet, textbook or lecture notes.
For this question you must use virtnet (as used in the tutorials) to perform an interception attack. This assumes you have already setup and are familiar with virtnet. See Moodle and tutorial instructions for information on setting up and using virtnet. The tasks and sub-questions are grouped into multiple phases. You must complete all phases, in order.
Phase 1: Setup
1. Create topology 5 in virtnet. node1 will be referred to as the client, node2 the router, and node3 the server.
2. The attacker has access to the router, and will run tcpdump to capture packets.
3. Users on the client and server will use applications to communicate. For this task, netcat and scp will be used to generate the application traffic.
4. Server port numbers must be assigned based on the last three (3) digits of your student ID, xyz, as defined below. Examples are given for a student ID of 12345678.
• For netcat server use port 8xyz. Example port: 8678
Phase 2: Create Test Data
For netcat and scp, a file will be transferred from client (node1) to server (node3). Create the file on the client using a text editor such as nano. Name the file [StudentID]-data.txt and add the following four (4) lines:
Be sure to replace [StudentID] and [StudentName] with your actual ID and your full name. Phase 3: Intercept Netcat Application Traffic
The attacker should capture traffic on the router (node2) for the following Netcat (nc) application traffic. When performing the capture, make sure there are no other applications or traffic in the background (e.g. from your own SSH connections). The resulting capture file must only contain packets relevant to the following steps.
1. Start the netcat TCP server using the assigned port on the server (node3), and redirecting received output to the file [StudentID]-netcat.txt. For example:
nc -l 8678 > 12345678-netcat.txt
2. Start the netcat TCP client on the client (node1), redirecting the file [StudentID]-data.txt as input. For example:
nc 192.168.2.21 8678 < 12345678-data.txt
3. On the server, check the contents of the received data in [StudentID]-netcat.txt match those on client.
The use of redirection (< and >) means the data from the file [StudentID]-data.txt is read at the client and sent via a TCP connection to the server, where the data is saved in
The attacker should then stop the capture, and save the file as:[StudentID]-netcat.pcap.
Phase 4: Intercept scp Application Traffic
The attacker should capture traffic on the router (node2) for the following scp application traffic. When performing the capture, make sure there are no other applications or traffic in the background (e.g. from your own SSH connections). The resulting capture file must only contain packets relevant to the following steps.
1. Use scp on the client (node1) to copy the file [StudentID]-data.txt to the server (node3), saving it as [StudentID]-scp.txt. For example:
scp 12345678-data.txt 192.168.2.21:/home/network/12345678-scp.txt
2. On the server, check the contents of the received data in [StudentID]-scp.txt match those on client.
The attacker should then stop the capture, and save the file as:[StudentID]-scp.pcap.
Phase 5: Analysis
Answer the following sub-questions regarding the previous phases.
(a) Add [StudentID]-data.txt to [StudentID]-files.zip.
(b) Add [StudentID]-netcat.pcap to [StudentID]-files.zip.
(c) Add [StudentID]-scp.pcap to [StudentID]-files.zip.
(d) Draw a message sequence diagram that illustrates all the TCP packets generated by
using nc in phase 3. Do not draw any packets generated by other applications or protocols, such as ARP, DNS or SSH, and do not draw the UDP packets. Only draw TCP packets. A message sequence diagram uses vertical lines to represent events that happen at a computer over time (time is increasing as the line goes down). Addresses of the computers/software are given at the top of the vertical lines. Horizontal or sloped arrows are used to show messages (packets) being sent between computers. Each arrow should be labelled with the protocol, packet type and important information of the message. Examples of message sequence diagrams are given in tutorials. Note that you do not need to show the packet times, and the diagram does not have to be to scale. You must draw your own diagram; you cannot use the diagram generated by Wireshark.
(e) As the attacker you can learn information from intercepting the packets. Based on the packet capture file from phase 3 (nc) only, answer the following questions.
i. What port number did the client application use?
ii. What was the duration of the TCP connection? Give your answer in microseconds.
iii. What is the absolute sequence number of the first TCP segment containing data?
iv. What is the length of the data (payload) in the first TCP segment containing data?
v. An attacker can sometimes learn useful information from knowing when a TCP connection occurs, relative to other TCP connections. TCP senders optionally include timestamps in all packets. For the first TCP segment sent by the client in the connection, what is the hexadecimal value of the timestamp?
vi. Attackers often create fake IP packets, e.g. with fake source addresses. To do so, the checksum must be calculated. What is the hexadecimal value of the IP checksum in the first TCP segment containing data?
vii. If an attacker had to write code to automatically detect TCP segments that contain data based on the binary value of the flags field, what binary value would they search for?
Now consider the information captured from intercepting scp traffic in phase 4. scp uses SSH as the underlying protocol. Hint: you can use the ssh filter keyword in Wireshark to show only the scp/SSH packets.
(f) As the attacker you can learn information from intercepting the packets. Based on the packet capture file from phase 4 (scp) and any research you do about scp/SSH, answer the following questions.
i. What port number did the server application use?
ii. OpenSSH is one implementation of SSH. What version of OpenSSH did the server advertise?
iii. SSH clients and servers inform each other of the algorithms they support in order of preference (that is, listing their first preference first), and then the client selects algorithms to use by identifying the client’s highest preference algorithm that is also supported by the server. What is the name (as referred to by SSH) of the key exchange algorithm selected and used by the client?
iv. After the client and server agree upon algorithms, a key exchange is performed using a public key exchange protocol. What is the name of that key exchange protocol (also referred to as a key agreement scheme)? (Hint: the answer is NOT the same as the above).
v. In the key exchange protocol, the client sends a public key to the server. What are the last 4 hex digits of that public key?
vi. The data transfer between client and server should be encrypted. How many encrypted packets are sent by the client to the server?
vii. For the first encrypted packet sent by client to server, what are the last 4 hex digits of the message authentication code?
Answer the following questions based on your captures and understanding of the protocols and algorithms.
(g) In phase 3 and 4 you transferred the exact same data file from client to server. Compare the two approaches to data transfer with respect to: authentication, confidentiality, performance (specifically, number of packets).
(h) Consider the SSH encryption algorithm chacha20-poly1305. A widely used encryption cipher is AES. Discuss why chacha20 may be used instead of AES.
Question 2. Cryptography
For this question you must use openssl to perform a set of cryptographic operations. When performing cryptographic operations you must be very careful, as a small mistake (such as a typo) may mean the result is an insecure system. Read the instructions carefully, understand the examples, and where possible, test your approach (e.g. if you encrypt a file, test it by decrypting it and comparing the original to the decrypted). It is recommended you use virtnet to perform the operations.
The tasks and sub-questions are grouped into multiple phases. You must complete all phases. Phase 1: Download
Normally in public key cryptography you generate your own public/private key pair. However in this assignment to simplify the tasks, the Unit Coordinator has generated a key pair for you. Your key pair will be available to you on Moodle to download, with filename:
In addition to your key pair, a number of files will be available to all students on Moodle to download. Each file starting with [StudentID] must be downloaded by you. You may also need to download files with other student’s IDs (see the next phase).
The download URL will be published on Moodle.
Phase 2: Read the Messages
The files for download have been created by another student, denoted as the sender:
1. Sender student created a message to you [StudentID]-message[N].txt, where [N] is an integer, e.g. 1, 2, 3, …
2. The sender signed the message to produce [StudentID]-message[N].sgn.
3. The sender wrote their student ID into a text file [StudentID]-sender[N].txt.
4. The sender signed the sender file to produce [StudentID]-sender[N].sgn.
5. The sender used openssl to generate a random 256-bit secret key, in Hex, and saved it in [StudentID]-key[N].txt.
6. The sender generated a random Initialisation Value (IV), in Hex, and saved it in
7. The sender encrypted the message using symmetric key encryption, the random secret key, and the random IV, producing [StudentID]-message[N].enc.
8. The sender encrypted the random secret key file using public key encryption, producing [StudentID]-key[N].enc.
9. The sender encrypted the IV file using public key encryption, producing
The sender then sends to you the necessary files from above.
Note that the files were actually created by the Unit Coordinator, but in this assignment you can assume they were created by a student. The “sending” of files to you is performed by the sender (Unit Coordinator) uploading them to Moodle, and you downloading them from Moodle.
Your task is, for every message, decrypt and verify the files. Be careful: there may have been attacks on some messages!
The algorithms used in this question are:
• Public key: RSA, 2048 bit
• Symmetric key: AES-256-CBC
• Hash: SHA256
Phase 3: Report Your Results
After downloading, decrypting and verifying all messages, you need to create a summary of the results for each message. The summary must be in a text file called [StudentID]-summary[N].txt. The summary must contain exactly two lines, of the format:
where ResultType is one of the following strings:
• Success – means all files successfully decrypted and successfully verified.
• FailDecryptKey – means the decryption of secret key was unsuccessful.
• FailDecryptMessage – means the decryption of message was unsuccessful.
• FailVerifySender – means the verification of sender file was unsuccessful.
• FailVerifyMessage – means the verification of message was unsuccessful.
If ResultType is Success, then include the contents of the message on the next line. If ResultType is another value, then include “NoMessage” on the next line. Examples of possible summary files are:
You must sign each summary file, producing [StudentID]-summary[N].sgn.
Phase 4: Analysis
(a) Add all summary text files, e.g. [StudentID]-summary1.txt, [StudentID]-summary2.txt, [StudentID]-summary3.txt, ... to [StudentID]-files.zip.
(b) Add all summary signature files, e.g. [StudentID]-summary1.sgn, [StudentID]-summary2.sgn, [StudentID]-summary3.sgn, … to [StudentID]-files.zip.
(c) Consider the information that was encrypted and sent to the receiver in phase 2. Different encryption algorithms were used to encrypt different types of information. Explain why different algorithms are typically used for different information.
(d) Assume that MD5 was used instead of SHA256. Explain a successful attack that takes advantage of the fact MD5 is used. The attack description should be at a level of detail similar to the steps in phase 2, referring to files. In your description, refer to the entities involved as “sender”, “receiver”, “attacker” or similar. Assume the keys you downloaded from Moodle are trustworthy (i.e. not compromised).
In this question the Unit Coordinator created your public/private key pair. For the following sub-questions, assume you create your own key pair on your own computer.
Consider the following scheme. You create your own key pair on your computer, extract the public key .pem file, and then encrypt that file with AES and a secret key known by the entire class (including the Unit Coordinator). You then send the encrypted public key to the Unit Coordinator.
(e) Explain how a masquerade attack could be performed on the above scheme, including how/why that attack would be successful.
(f) Design a scheme for which a masquerade attack would not be successful.
(g) Explain why your above designed scheme defeats the masquerade attack.
Assume a university has been infected by ransomware, affecting primarily their grading system (such as Moodle). You must write a short report to university staff addressing the following:
• What is ransomware? Give a short introduction/overview so that management can understand.
• What are the possible ways in which an organisation can be infected? Again, aim this at university management.
• What is the role of cryptography in ransomware? This should be explained for a technical audience, that is, the IT staff in the university. Refer to types of algorithms used and how they are used.
• If the university decides not to pay the ransom, what are the options?
• If the university is considering paying the ransom, what are the advantages and disadvantages? How is payment normally made (and why)?
• Recommend methods the university should take in the future to avoid becoming infected.
Your report must have six (6) sections, each section addressing a point above. While there is no page limit, each section should be less than half a page, and a good answer could be given in 1 to 3 paragraphs. Do NOT include pictures or tables in the report. Use text only. While you may use numbered lists and dot points, the report cannot entirely be lists. References are not necessary (although the normal rules of academic integrity are expected).
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