This repository contains the final project of Applied Cryptography course (Master's Degree in Cybersecurity at University of Pisa). The project has been developed for educational purposes and represents a multithread client-server chat application in which every communication between peers is encrypted using OpenSSL APIs.

When a client correctly connects to the server, the server will show a list of online users to this client, then the client can request a chat session with other clients. This client will wait for the peer response. As for now there are 3 users registered to the server. If you want to create your own client, you should generate a pair of 2048-bit RSA keys and the private key must be protected by password. The server has a public certificate that is granted to be safe by the CA SimpleAuthority.

The programs needs the installation of OpenSSL, a TLS/SSL and crypto library, and SimpleAuthority, a trusted CA.

First of all, install build dependencies, then clone OpenSSL and configure it.

sudo apt-get -y install build-essential checkinstall git zlib1g-dev
git clone --depth 1 --branch OpenSSL_1_1_1g https://github.com/openssl/openssl.git
cd openssl
./config zlib '-Wl,-rpath,$(LIBRPATH)'

After you have built and tested, install OpenSSL and configure the shared libs.

make
make test
sudo make install
sudo ldconfig -v

Finally, check the OpenSSL version to make sure you have successfully completed all the steps.

openssl version

To generate a certificate, install SimpleAuthority at the following link: SimpleAuthority

Before running the program , the user should generate a pair of 2048-bit RSA keys using OpenSSL command-line tools.

• RSA private key: the following command generate a .pem file, protected by a user-chosen password, containing a 2048-bit key.

openssl genrsa -aes128 -out private_key.pem 2048

• RSA public key: a private key in OpenSSL is represented with a strcuture that contains also the public key, so the following command extract the public key from the private key.

openssl rsa -pubout -aes128 -in private_key.pem -out public_key.pem

Before running the programs, you have first to compile them with -lcrypto flag, in order to include crypto features of OpenSSL, and -lpthread flag.

cd server/src
g++ main_server.cpp -lcrypto -lpthread -o server.out
./server.out

cd client/src
g++ client_test.cpp -lcrypto -lpthread -o client_test.out
./client_test.out

• Francesco Carli
• Gianluca Boschi
• Paola Petri