PKI

title	author	date
Public-Key Infrastructure (PKI) Lab	Xinyi Li	\today{}

Instruction: https://seedsecuritylabs.org/Labs_16.04/PDF/Crypto_PKI.pdf

Task 1

Copy the configuration file into current directory:

cp /usr/lib/ssl/openssl.cnf ./openssl.cnf

create new sub-directories and files according to what it specifies in its [ 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

Simply create an empty file for index.txt, put a single number in string format in serial:

mkdir ./demoCA
cd ./demoCA
mkdir certs
mkdir crl
mkdir newcerts
touch index.txt
echo "1000" > serial

Start to generate the self-signed certificate for the CA:

# return to the parent directory
# cd ..
openssl req -new -x509 -keyout ca.key -out ca.crt -config openssl.cnf

Notice that we apply policy_match in openssl.cnf, so we should keep some fields the same when creating certificates for CA and servers:

[ policy_match ]
countryName		= match
stateOrProvinceName	= match
organizationName	= match
organizationalUnitName	= optional
commonName		= supplied
emailAddress		= optional

When asked to type PEM pass phrase, remember the password you typed (e.g. I use 114514). It will then ask you to fill in some information, you can skip it by Enter, except for those required by policy_match.

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

As a root CA, we are ready to sign a digital certificate for SEEDPKILab2018.com.

Step 1: Generate public/private key pair

Generate an RSA key pair. Provide a pass phrase (e.g. I use soudayo) to encrypt the private key in server.key using AES-128 encryption algorithm.

openssl genrsa -aes128 -out server.key 1024

To see the actual content in server.key (pass phrase required):

openssl rsa -in server.key -text

Step 2: Generate a Certificate Signing Request (CSR)

Use SEEDPKILab2018.com as the common name of the certificate request

openssl req -new -key server.key -out server.csr -config openssl.cnf

Skip the unnecessary information as well, keep the necessary information (required by policy_match consistent with the CA.crt created in Task 1).

Now, the new Certificate Signing Request is saved in server.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)

Step 3: Generating Certificates

In this lab, we will use our own trusted CA to generate certificates.

Use ca.crt and ca.key to convert server.csr to server.crt:

openssl ca -in server.csr -out server.crt -cert ca.crt -keyfile ca.key \
-config openssl.cnf

Task 3

Step 1: Configuring DNS

Open and edit /etc/hosts:

sudo gedit /etc/hosts

Add one line:

127.0.0.1 SEEDPKILab2018.com

Step 2: Configuring the web server

Combine the secret key and certificate into one single file server.pem:

cp server.key server.pem
cat server.crt >> server.pem

Launch the web server using server.pem:

openssl s_server -cert server.pem -www

Now, the server is listening on port 4433. Browser https://seedpkilab2018.com:4433/

Step 3: Getting the browser to accept our CA certificate.

Search for "certificate" in Firefox's Preferences page, click on "View Certificates" and enter "certificate manager", click on "Authorities tab" and import CA.crt. Check "Trust this CA to identify web sites".

Reload https://seedpkilab2018.com:4433/.

Step 4. Testing our HTTPS website

Modify one byte in server.pem

It's up to which byte you modify. Most bytes make no differences after corrupted. But some will make the certificate invalid.

Use localhost

When browsing https://localhost:4433, it is reported unsafe HTTPS

Because the locolhost has no certificate, the website is using a certificate identified for seedpkilab2018.com.

Task 4

Open configuration file of Apache HTTPS server:

sudo gedit /etc/apache2/sites-available/default-ssl.conf

Add the entry and save:

<VirtualHost *:443>
        ServerName SEEDPKILab2018.com
        DocumentRoot /var/www/pki
        DirectoryIndex index.html

        SSLEngine On
        SSLCertificateFile /var/www/pki/server.crt
        SSLCertificateKeyFile /var/www/pki/server.pem
</VirtualHost>

Copy the server certificate and private key to the folder:

sudo mkdir /var/www/pki
sudo cp server.pem server.crt /var/www/pki

Test the Apache configuration file for errors:

sudo apachectl configtest

Enable the SSL module:

sudo a2enmod ssl

Enable the site we have just edited:

sudo a2ensite default-ssl

Restart Apache:

sudo service apache2 restart

Once Apache runs properly, open https://seedpkilab2018.com/

Task 5

Suppose we still use this VM (10.0.2.10) as the malicious server, start another VM (10.0.2.4) as the victim.

Generate a certificate for example.com

use a password (e.g. I use islander):

openssl genrsa -aes128 -out example.key 1024

Use example.com as the common name of the certificate request:

openssl req -new -key example.key -out example.csr -config openssl.cnf
openssl ca -in example.csr -out example.crt -cert ca.crt -keyfile ca.key \
-config openssl.cnf
cp example.key example.pem
cat example.crt >> example.pem

Copy the certificate and private key to the website root folder:

sudo mkdir /var/www/example
sudo cp example.crt example.pem /var/www/example

Config and start the server

On the server VM, open /etc/apache2/sites-available/default-ssl.conf and add the following entry:

<VirtualHost *:443>
        ServerName example.com
        DocumentRoot /var/www/example
        DirectoryIndex index.html

        SSLEngine On
        SSLCertificateFile /var/www/example/example.crt
        SSLCertificateKeyFile /var/www/example/example.pem
</VirtualHost>

Restart Apache:

sudo apachectl configtest
sudo service apache2 restart

Config on Victim VM

On the victim VM, modify /etc/hosts by:

sudo gedit /etc/hosts

add one line before the ending, which emulates a DNS cache positing attack:

10.0.2.10	example.com

To get the ca.crt, listen on a local port like:

nc -lvp 4444 > ca.crt

Then on the server VM, we send ca.crt by:

cat ca.crt | nc 10.0.2.4 4444

Once we receive the file on the victim VM, we install it on Firefox as above.

Now, when browsing https://example.com/, the user on this VM actually visit the fake website launched by the malicious server:

Task 6

Based on Task 5, we can assume if the attacker stole ca.key, which indicates that he/she can easily generate the CA certificate ca.crt by the compromised key:

openssl req -new -x509 -keyout ca.key -out ca.crt -config openssl.cnf

Then, ca.crt can be used to sign any server's certificate, including the forged ones. The process of such attacks can be described as what we did before, except that we don't even need to deploy the ca.crt on the victim machine because it has already installed the same ca.crt.