Information Security

CSC-201
Term Project (CLO Mapping -> CLO 4)
Objective:

Public key cryptography is the foundation of today’s secure communication, but it is subject to man-
in-the middle attacks when one side of communication sends its public key to the other side. The
fundamental problem is that there is no easy way to verify the ownership of a public key, i.e., given
a public key and its claimed owner information, how do we ensure that the public key is indeed
owned by the claimed owner? The Public Key Infrastructure (PKI) is a practical solution to this
problem.
The learning objective of this lab is for students to gain the first-hand experience on PKI. SEED labs
have a series of labs focusing on the public-key cryptography, and this one focuses on PKI. By doing
the tasks in this lab, students should be able to gain a better understanding of how PKI works, how
PKI is used to protect the Web, and how Man-in-the-middle attacks can be defeated by PKI.
Moreover, students will be able to understand the root of the trust in the public-key infrastructure,
and what problems will arise if the root trust is broken.
This lab covers the following topics:
• Public-key encryption
• Public-Key Infrastructure (PKI)
• Certificate Authority (CA) and root CA
• X.509 certificate and self-signed certificate
• Apache, HTTP, and HTTPS
• Man-in-the-middle attacks

Readings and related topics. Detailed coverage of PKI can be found in Chapter 18 of the SEED
book, Computer Security: A Hands-on Approach, by Wenliang Du. A topic related to this lab is the
Transport Layer Security (TLS), which is based on PKI. How TLS works and how to write secure
programs using TLS are covered in details in Chapter 19 of the SEED book. We also have a separate
lab, RSA Public-Key Encryption and Signature Lab, for students who are interested in learning how
the underlying public-key algorithm works.

Lab Tasks
Task 1: Becoming a Certificate Authority (CA)
A Certificate Authority (CA) is a trusted entity that issues digital certificates. The digital certificate certi-
fies the ownership of a public key by the named subject of the certificate. A number of commercial CAs
are treated as root CAs; VeriSign is the largest CA at the time of writing. Users who want to get digital
certificates issued by the commercial CAs need to pay those CAs.
In this lab, we need to create digital certificates, but we are not going to pay any commercial CA. We will
become a root CA ourselves, and then use this CA to issue certificate for others (e.g. servers). In this
task, we will make ourselves a root CA, and generate a certificate for this CA. Unlike other certificates,
which are usually signed by another CA, the root CA’s certificates are self-signed. Root CA’s certificates
are usually pre-loaded into most operating systems, web browsers, and other software that rely on PKI.
Root CA’s certificates are unconditionally trusted.

The Configuration File openssl.conf. In order to use OpenSSL to create certificates, you have to
have a configuration file. The configuration file usually has an extension .cnf. It is used by three
OpenSSL commands: ca, req and x509. The manual page of openssl.conf can be found using
Google search. You can also get a copy of the configuration file from
/usr/lib/ssl/openssl.cnf. After copying this file into your current directory, you need to create
several sub-directories as specified in the configuration file (look at the [CA default] section):
dir = ./demoCA # Where everything is kept
certs = $dir/certs # Where the issued certs are kept
crl_dir = $dir/crl # Where the issued crl are kept
new_certs_dir = $dir/newcerts # default place for new
certs. database = $dir/index.txt # database index file.
serial = $dir/serial # The current serial number

For the index.txt file, simply create an empty file. For the serial file, put a single number in
string format (e.g. 1000) in the file. Once you have set up the configuration file openssl.cnf, you can
create and issue certificates.

Certificate Authority (CA). As we described before, we need to generate a self-signed certificate for
our CA. This means that this CA is totally trusted, and its certificate will serve as the root certificate. You
can run the following command to generate the self-signed certificate for the CA:
$ openssl req -new -x509 -keyout ca.key -out ca.crt -config openssl.cnf

You will be prompted for information and a password. Do not lose this password, because you will have
to type the passphrase each time you want to use this CA to sign certificates for others. You will also be
asked to fill in some information, such as the Country Name, Common Name, etc. The output of the
command are stored in two files: ca.key and ca.crt. The file ca.key contains the CA’s private
key, while ca.crt contains the public-key certificate.

Task 2: Creating a Certificate for SEEDPKILab2018.com

Now, we become a root CA, we are ready to sign digital certificates for our customers. Our first customer
is a company called SEEDPKILab2018.com. For this company to get a digital certificate from a CA, it
needs to go through three steps.
Step 1: Generate public/private key pair. The company needs to first create its own public/private key
pair. We can run the following command to generate an RSA key pair (both private and public keys).
You will also be required to provide a password to encrypt the private key (using the AES-128 encryption
algorithm, as is specified in the command option). The keys will be stored in the file server.key:
$ openssl genrsa -aes128 -out server.key 1024

The server.key is an encoded text file (also encrypted), so you will not be able to see the actual
content, such as the modulus, private exponents, etc. To see those, you can run the following command:
$ openssl rsa -in server.key -text

Step 2: Generate a Certificate Signing Request (CSR). Once the company has the key file, it should
generates a Certificate Signing Request (CSR), which basically includes the company’s public key. The
CSR will be sent to the CA, who will generate a certificate for the key (usually after ensuring that identity
information in the CSR matches with the server’s true identity). Please use SEEDPKILab2018.com as
the common name of the certificate request.
$ openssl req -new -key server.key -out server.csr -config openssl.cnf

It should be noted that the above command is quite similar to the one we used in creating the self-signed
certificate for the CA. The only difference is the -x509 option. Without it, the command generates a
request; with it, the command generates a self-signed certificate.

Step 3: Generating Certificates. The CSR file needs to have the CA’s signature to form a certificate.
In the real world, the CSR files are usually sent to a trusted CA for their signature. In this lab, we will
use our own trusted CA to generate certificates. The following command turns the certificate signing re-
quest (server.csr) into an X509 certificate (server.crt), using the CA’s ca.crt and ca.key:
$ openssl ca -in server.csr -out server.crt -cert ca.crt -keyfile ca.key \
-config openssl.cnf

If OpenSSL refuses to generate certificates, it is very likely that the names in your requests do not match
with those of CA. The matching rules are specified in the configuration file (look at the [policy
match] section). You can change the names of your requests to comply with the policy, or you can
change the policy. The configuration file also includes another policy (called policy anything),
which is less restrictive. You can choose that policy by changing the following line:
"policy = policy_match" change to "policy = policy_anything".

Task 3: Deploying Certificate in an HTTPS Web Server

In this lab, we will explore how public-key certificates are used by websites to secure web browsing. We
will set up an HTTPS website using openssl’s built-in web server.

Step 1: Configuring DNS. We choose SEEDPKILab2018.com as the name of our website. To get
our computers recognize this name, let us add the following entry to /etc/hosts; this entry basically
maps the hostname SEEDPKILab2018.com to our localhost (i.e., 127.0.0.1):
127.0.0.1 SEEDPKILab2018.com
Step 2: Configuring the web server. Let us launch a simple web server with the certificate generated
in the previous task. OpenSSL allows us to start a simple web server using the s server command:
# Combine the secret key and certificate into one file

% cp server.key server.pem

% cat server.crt >> server.pem

By default, the server will listen on port 4433. You can alter that using the -accept option. Now, you
can access the server using the following URL: https://SEEDPKILab2018.com:4433/. Most
likely, you will get an error message from the browser. In Firefox, you will see a message like the
following: “seedpkilab2018.com:4433 uses an invalid security certificate. The certificate is not trusted
because the issuer certificate is unknown”.

Step 3: Getting the browser to accept our CA certificate. Had our certificate been assigned by
VeriSign, we will not have such an error message, because VeriSign’s certificate is very likely preloaded
into Firefox’s certificate repository already. Unfortunately, the certificate of SEEDPKILab2018.com
is signed by our own CA (i.e., using ca.crt), and this CA is not recognized by Firefox. There are two
ways to get Firefox to accept our CA’s self-signed certificate.

• We can request Mozilla to include our CA’s certificate in its Firefox software, so everybody using
Firefox can recognize our CA. This is how the real CAs, such as VeriSign, get their certificates into
Firefox. Unfortunately, our own CA does not have a large enough market for Mozilla to include
our certificate, so we will not pursue this direction.

• Load ca.crt into Firefox: We can manually add our CA’s certificate to the Firefox browser by
clicking the following menu sequence:
Edit -> Preference -> Privacy & Security -> View Certificates.

You will see a list of certificates that are already accepted by Firefox. From here, we can “import” our
own certificate. Please import ca.crt, and select the following option: “Trust this CA to identify web
sites”. You will see that our CA’s certificate is now in Firefox’s list of the accepted certificates.

Step 4. Testing our HTTPS website. Now, point the browser to

https://SEEDPKILab2018.com: 4433. Please describe and explain your observations. Please
also do the following tasks:

1. Modify a single byte of server.pem, and restart the server, and reload the URL. What do you
observe? Make sure you restore the original server.pem afterward. Note: the server may not be
able to restart if certain places of server.pem is corrupted; in that case, choose another place to
modify.

2. Since SEEDPKILab2018.com points to the localhost, if we use

https://localhost:4433 instead, we will be connecting to the same web server. Please do
so, describe and explain your observations.
Task 4: Deploying Certificate in an Apache-Based HTTPS Website
The HTTPS server setup using openssl’s s server command is primarily for debugging and
demon- stration purposes. In this lab, we set up a real HTTPS web server based on Apache. The Apache
server, which is already installed in our VM, supports the HTTPS protocol. To create an HTTPS website,
we just need to configure the Apache server, so it knows where to get the private key and certificates. We
give an example in the following to show how to enable HTTPS for a website www.example.com.
You task is to do the same for SEEDPKILab2018.com using the certificate generated from previous
tasks.
An Apache server can simultaneously host multiple websites. It needs to know the directory where a
website’s files are stored. This is done via its VirtualHost file, located in the /etc/apache2/
sites-available directory. To add an HTTP website, we add a VirtualHost entry to the file
000-default.conf. See the following example.
<VirtualHost *:80>

ServerName one.example.com
DocumentRoot /var/www/Example_One
DirectoryIndex index.html

To add an HTTPS website, we need to add a VirtualHost entry to the default-ssl.conf file
in the same folder.
<VirtualHost *:443>
ServerName two.example.com

DocumentRoot /var/www/Example_Two
DirectoryIndex index.html
SSLEngine On
SSLCertificateFile /etc/apache2/ssl/example_cert.pem À
SSLCertificateKeyFile /etc/apache2/ssl/example_key.pem ➁

</VirtualHost>
The ServerName entry specifies the name of the website, while the DocumentRoot entry specifies
where the files for the website are stored. The above example sets up the HTTPS site https://two.
example.com (port 443 is the default HTTPS port). In the setup, we need to tell Apache where the
server certificate (Line À) and private key (Line ➁) are stored.
After the default-ssl.conf file is modified, we need to run a series of commands to enable SSL.
Apache will ask us to type the password used for encrypting the private key. Once everything is set up
properly, we can browse the web site, and all the traffic between the browser and the server will be
encrypted.
// Test the Apache configuration file for errors

$ sudo apachectl configtest

// Enable the SSL module

$ sudo a2enmod ssl

// Enable the site we have just edited

Please use the above example as guidance to set up an HTTPS server for SEEDPKILab2018.com.
Please describe the steps that you have taken, the contents that you add to Apache’s configuration file,
and the screenshots of the final outcome showing that you can successfully browse the HTTPS site.

Task 5: Launching a Man-In-The-Middle Attack

In this task, we will show how PKI can defeat Man-In-The-Middle (MITM) attacks. Figure 1 depicts how
MITM attacks work. Assume Alice wants to visit example.com via the HTTPS protocol. She needs to
get the public key from the example.com server; Alice will generate a secret, and encrypt the secret
using the server’s public key, and send it to the server. If an attacker can intercept the communication
between Alice and the server, the attacker can replace the server’s public key with its own public key.
Therefore, Alice’s secret is actually encrypted with the attacker’s public key, so the attacker will be able
to read the secret. The attacker can forward the secret to the server using the server’s public key. The
secret is used to encrypt the communication between Alice and server, so the attacker can decrypt the
encrypted communication.

Mallory’s public key Server’s public key

[ secret] [ secret]
User (Alice) Mallory example.com

Figure 1: A Man-In-The-Middle (MITM) attack

The goal of this task is to help students understand how PKI can defeat such MITM attacks. In the task,
we will emulate an MITM attack, and see how exactly PKI can defeat it. We will select a target website
first. In this document, we use example.com as the target website, but in the task, to make it more
meaningful, students should pick a popular website, such as a banking site and social network site.

Step 1: Setting up the malicious website. In Task 4, we have already set up an HTTPS website for
SEEDPKILab2018.com. We will use the same Apache server to impersonate example.com (or the
site chosen by students). To achieve that, we will follow the instruction in Task 4 to add a
VirtualHost entry to Apache’s SSL configuration file: the ServerName should be
example.com, but the rest of the configuration can be the same as that used in Task 4. Our goal is the
following: when a user tries to visit example.com, we are going to get the user to land in our server,
which hosts a fake website for example.com. If this were a social network website, The fake site can
display a login page similar to the one in the target website. If users cannot tell the difference, they may
type their account credentials in the fake webpage, essentially disclosing the credentials to the attacker.

Step 2: Becoming the man in the middle There are several ways to get the user’s HTTPS request to
land in our web server. One way is to attack the routing, so the user’s HTTPS request is routed to our web
server. Another way is to attack DNS, so when the victim’s machine tries to find out the IP address of the
target web server, it gets the IP address of our web server. In this task, we use “attack” DNS. Instead of
launching an actual DNS cache poisoning attack, we simply modify the victim’s machine’s /etc/hosts
file to emulate the result of a DNS cache positing attack (the IP Address in the following should be
replaced by the actual IP address of the malicious server).
<IP_Address> example.com

Step 3: Browse the target website. With everything set up, now visit the target real website, and
see what your browser would say. Please explain what you have observed.

Task 6: Launching a Man-In-The-Middle Attack with a Compromised CA

Unfortunately, the root CA that we created in Task 1 is compromised by an attacker, and its private
key is stolen. Therefore, the attacker can generate any arbitrary certificate using this CA’s private
key. In this task, we will see the consequence of such a compromise.
Please design an experiment to show that the attacker can successfully launch MITM attacks on any
HTTPS website. You can use the same setting created in Task 5, but this time, you need to
demonstrate that the MITM attack is successful, i.e., the browser will not raise any suspicion when
the victim tries to visit a website but land in the MITM attacker’s fake website.

Submission Instructions:

1. Assignments will be evaluated on Friday from 12-2pm, i.e. 9 May, 2025.

2. You need to submit a detailed lab report to describe what you have done and what
you have observed; you also need to provide explanation to the observations that are
interesting or surprising. In your report, you need to answer all the questions listed in
assigned tasks.
3. All the required files are attached.
4. Understanding of each question will be evaluated in viva.
5. Assignment will be evaluated only in executable form.
6. This assignment is individual.
7. For any query you may ask any time.

Deadline:
9 May, 2025.