Advanced Network Security : Cryptographic Operations with OpenSSL…
Question 1. Cryptographic Operations with OpenSSL [8 marks]
Your task is to 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.
Perform the following steps:
(a) For all the following steps, record the command(s) you used in a file called
commands.bash. This file should be a Bash shell script, containing only commands that
can be executed and optionally comments (starting with # character).
(b) Generate your own RSA 2048-bit key pair. Use the public exponent of 65537. Save
your key pair as keypair.pem.
(c) Extract your public key and save it as pubkey.pem.
(d) Create a text file called message.txt and include your student ID and full name inside
the file. This file is referred to as the message or plaintext.
(e) Sign your message file using SHA256, saving the signature as signature.bin.
(f) Generate a 128 bit random value using OpenSSL. This value will be used as a secret
key. Store the key as a 32 hex digit string in a file key.txt.
(g) Encrypt your message file using AES-128-CBC and the key generated in step (f). Use
an IV of all 0’s (that is, 32 hex 0’s). Save the ciphertext as ciphertext.bin.
(h) Encrypt your key.txt file using RSA so that only the Unit Coordinator can view the
contents. Save the encrypted key as secretkey.bin.
Multiple files are output from the above steps. You must all the files listed above. The file
names must be exactly as listed above. Use lowercase for all files and double-check the
extensions (be careful that Windows doesn’t change the extension).
Examples of the OpenSSL operations needed to complete this task are on Moodle.
Marking Scheme
Once files are submitted, they will be decrypted/verified using the reverse operations of what
you were expected to do.
• If your files successfully decrypt/verify, and the commands (commands.bash)
submitted are correct, then you will receive 8 marks.
• If your files successfully decrypt/verify, but the commands contain errors, then you will
receive between 5 and 7 marks, depending on the severity of the errors (e.g. small typo
vs wrong command).
• If your files do NOT successfully decrypt/verify, then your commands will be reviewed
to determine what mistakes you made. You will receive between 0 and 6 marks,
depending on the severity of the errors.
Up to 5 marks may be deducted for incorrect submissions (e.g. not all files submitted,
additional files submitted, wrong files submitted, wrong filenames).
COIT20262 Assignment 2 Term 1, 2018
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Question 2. HTTPS and Certificates [15 marks]
For this question you must use virtnet (as used in the workshops) to study HTTPS and
certificates. This assumes you have already setup and are familiar with virtnet. See Moodle
and workshop instructions for information on setting up and using virtnet, deploying the
website, and testing the website.
Your task is to:
1. Create topology 5 in virtnet
2. Deploy the MyUni demo website on the nodes
3. Setup the webserver to support HTTPS, including obtaining a certificate certmyuni-YourID.pem.
4. Capture traffic from the web browser on node1 to the web server that includes a
HTTPS session. Save the file as https.pcap.
5. Test and analyse the HTTPS connection.
Step 3, involves obtaining a certificate from a Certificate Authority. Another student from
COIT20262 must act as the Certificate Authority for you, and similarly, you can act as the
Certificate Authority for them (that is, do this phase in pairs). You must do that in the following
way:
1. Use your RSA key pair from Question 1 to generate a certificate signing request, saved
as cert-myuni-YourID.csr (where YourID is replaced with your student ID).
2. Send the certificate signing request to another student in COIT20262.
3. That other student will act as the Certificate Authority and generate your certificate as
cert-myuni-YourID.pem. They will send your certificate, as well as the CA’s
certificate as cert-ca-TheirID.pem (where TheirID is the student ID of your partner),
back to you.
In the same way that your partner will act as your CA, you will act as your partners CA. You
will need to setup a CA, using your RSA key pair from Question 1 to generate a self-signed
certificate cert-ca-YourID.pem, and then you receive their certificate signing request that you
sign.
Answer the following sub-questions based on above test and analysis.
(a) Submit the following files on Moodle. Each will be analysed to ensure they include
correct information (e.g. values specific to you).
• cert-myuni-YourID.csr (your certificate signing request) [0.5 mark]
• cert-myuni-YourID.pem (your certificate) [1 mark]
• cert-ca-TheirID.pem (partner’s CA certificate) [1 mark]
• default-ssl.conf (a copy of the Apache configuration file from your web
server) [0.5 mark]
• https.pcap (the capture of HTTPS session) [2 marks]
COIT20262 Assignment 2 Term 1, 2018
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(b) Draw a message sequence diagram that illustrates the TLS/SSL packets belonging to
the first HTTPS session in the file. Refer to the instructions in assignment 1 for drawing
a message sequence diagram, as well as these additional requirements:
• Only draw the TLS/SSL packets; do not draw the 3-way handshake, TCP ACKs
or connection close. Hint: identify which packets belong to the first TCP
connection and then filter with “ssl” in Wireshark. Depending on your
Wireshark version, the protocol may show as “TLSv1.2”.
• A single TCP packet may contain one or more SSL messages (in Wireshark
look inside the packet for each “Record Layer” entry to find the SSL message
names). Make sure you draw each SSL message. If a TCP packet contains
multiple SSL messages, then draw multiple arrows, one for each SSL message,
and clearly label each with SSL message name.
• Clearly mark which packets/messages are encrypted. [3 marks]
(c) Based on your certificate and the capture, write answers to the following questions in
the table. When giving algorithms, you may use the abbreviation but must accurately
identify the variant. For example, AES128 is different from AES256, and SHA256 is
different from SHA512. [4 marks, 0.5 mark each]
How many bytes is the hash value in the certificate
signature?
What hash algorithm is used to generate the certificate
signature?
What encryption algorithm is used to generate the
certificate signature?
How many bytes is the public key modulus in the
certificate?
In the TLS cipher suite used between client and server,
what algorithm is used for:
– Encrypting session data?
– Hashing for the MAC?
– Key exchange?
How many bytes of random data are sent from the client to
server at the start of the handshake?
(d) In practice, some Certificate Authorities use self-signed certificates, while others have
their certificate signed by another CA. Explain why self-signed certificates are needed
by CAs, as well as the benefits of one CA signing another CA’s certificate. [2 marks]
(e) In practice, Certificate Authorities must keep their private keys very secure, usually
storing them offline in special hardware devices. Explain an attack a malicious user
could be perform if they could compromise the CA private key. Use your MyUni
website as an example. [1 mark]
COIT20262 Assignment 2 Term 1, 2018
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Question 3. Access Control [10 marks]
For this question you must use virtnet (as used in the workshops) to study Linux access
control and passwords. This assumes you have already setup and are familiar with virtnet.
See Moodle and workshop instructions for information on setting up and using virtnet, and
using Linux access control commands.
Your task is to:
1. Create topology 1 in virtnet (or any topology that has a node; you could use nodes
from previous questions).
2. Create five new users named student1, student2, teacher3, teacher4 and other5.
Set the passwords to be different except for two users (that is, two users have the same
password, the other users have different passwords), however do not use passwords that
you use on other systems.
3. View the password information stored for the new users in /etc/passwd and
/etc/shadow. Understand the information stored.
4. Create two new groups named student and teacher. Allocate the users to groups as
follows:
o User 1, student1: primary group student
o User 2, student2: primary group student
o User 3, teacher3: primary group teacher
o User 4, teacher4: primary group teacher
o User 5, other5: primary group is their own (i.e. not in student or teacher).
Even though there are only five users created, in the following you should assume there
may be more users (e.g. more users in the student group, more users in the teacher
group, and more users not in either of the groups).
5. Create the following files and directories for each user. Unless specified, the
files/directories can be any name and can contain any content:
o Both students (User 1 and 2) have directories personal and shared in their
home directory. All teachers have read-only access to each students shared
directory (and files within). Only the user can access their personal directory.
o The first teacher (User 3) has directory security, which has two subdirectories: lectures and exam. lectures is read-only by all teachers. exam is
only accessible by the user.
o The second teacher (User 4) has directories network and personal. network
is editable by everyone, while personal is only accessible by the user.
o Each directory mentioned above should have at least 1 file in it (the name and
contents of the file doesn’t matter).
o Every user (including User 5) has a file in their home directory called
schedule.txt. This file is readable and writable by everyone.
6. In addition to the access control rules mentioned above, assume:
o Every user has read, write permissions on their own files, and full permissions
on their own directories.
o No other user can access the files/directories of other users.
o If permissions are not covered by the above, then assume the defaults.
COIT20262 Assignment 2 Term 1, 2018
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o If there are conflicts in the above, then assume the most restrictive permission.
o Use only the basic Linux permissions (see example commands below). Do NOT
use advanced permissions such as with setfacl or getfacl.
7. Test that the access control works by logging in as each user and checking they can(not)
access the specified files/directories.
Answer the following questions after completing the task.
(a) Submit the following files on Moodle:
a. /etc/passwd named as passwd.txt when you submit [0.5 mark]
b. /etc/shadow as shadow.txt [0.5 mark]
c. /etc/group as group.txt [0.5 mark]
d. The output of the following command as files.txt:
sudo sh -c ‘ls -lR /home > /home/network/files.txt’
The listing in files.txt will be used to determine if you have set the correct
permissions. [4.5 marks]
(b) Explain where and how password information is stored in Linux. You should mention
the files, formats of storing passwords (e.g. what is stored, how is the information
created) and any specific algorithms used. [1 mark]
(c) In the above task on Linux you used a form of discretionary access control. Two other
forms of access control are role-based access control (RBAC) and mandatory access
control (MAC). Give a description of both RBAC and MAC, and using the
student/teacher scenario, give an example of each that demonstrates the key
characteristics of these forms of access control. [3 marks]
COIT20262 Assignment 2 Term 1, 2018
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Question 4. Firewalls [9 marks]
An educational institute has a single router, referred to as the gateway router, connecting its
internal network to the Internet. The institute has the public address range 138.53.0.0/16 and
the gateway router has address 138.53.178.1 on its external interface (referred to as interface
ifext). The internal network consists of four subnets:
• A DMZ, which is attached to interface ifdmz of the gateway router and uses address
range 138.53.179.0/24.
• A small network, referred to as shared, with interface ifint of the gateway router
connected to three other routers, referred to as staff_router, student_router, and
research_router. This network has no hosts attached (only four routers) and uses
network address 10.4.0.0/16.
• A staff subnet, which is for use by staff members only, that is attached to the
staff_router router and uses network address 10.4.1.0/24.
• A student subnet, which is for use by students only, that is attached to the
student_router router and uses network address 10.4.2.0/24.
• A research subnet, which is for use by research staff, that is attached to the
research_router router and uses network address 10.4.3.0/24.
In summary, there are four routers in the network: the gateway router, and routers for each of
the staff, student and research subnets. There are five subnets: DMZ, shared, staff, student, and
research.
There are two servers in the DMZ that all can accept requests from the Internet: a web server
supporting HTTP and HTTPS, and a SMTP email server. Members of the staff, student and
research subnets can access the web server; members of the staff subnet only can access the
email server but using IMAP.
The gateway router also runs a stateful packet filtering firewall and performs port address
translation. In addition to the DMZ setup as described above, security requirements for the
educational institute are:
• External Internet users cannot access any internal computers (except in DMZ and as
stated in other requirements).
• Staff, students and researchers can access websites in the Internet.
• The researchers (on the research subnet) run a server for sharing data with selected
research partners external to the educational institute. That server provides SSH access
and a specialised file transfer protocol using TCP and port 6789 to the partners. The
server has internal address 10.4.3.31 and NAT is setup on the gateway router to map
the public address 138.53.179.44 to the internal address. Currently there are two partner
organisations that can access the server, and they have network addresses:
31.13.75.0/24 and 104.55.9.0/24.
• The professor that leads the research staff also wants access to the data sharing server
while they are at home. At home that professor uses a commercial ISP that dynamically
allocates IP addresses in the range 23.63.0.0/16.
Considering the above information, answer the following questions:
COIT20262 Assignment 2 Term 1, 2018
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(a) Draw a diagram illustrating the network. Although there may be many computers in the
staff, student and research subnets, for simplicity you only have to draw three
computers in the staff subnet, three computers in the student subnet and three computers
in the research subnet (one of those in the research subnet should be the data sharing
server). Label all computers and router interfaces with IP addresses. [3 marks]
(b) Specify the firewall rules using the format as in the table below. You may add/remove
rows as needed. After the table, add an explanation of the rules (why you design the
firewall rules the way you did). [5 marks]
Rule
No.
Transport Source
IP
Source
Port
Dest.
IP
Dest.
Port
Action
1
2
3
4
…
(c) Consider the rule(s) that allows the professor to access from home. Discuss the
limitations, and suggest possible solutions. [1 mark]
Attachments:
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