iQuHack2022

spiNYpizza

A quantum secure chat among N users

Just some nice dudes and a lady, 4 italians spread around the world and one NY guy

So we are:

Lisa Bombieri
Andrea Maiani
Leonardo Placidi
Ciro Gus Salcedo
Alessandro Summer

Authentication scheme

Network topology

Nodes of the network

S: Messaging server
I: Interface (authentication server)
U1, U2, U3, ... : Users

## Authentication protocol The point of the authentication protocol is to establish a series of *secure links* between the server (S) and each user (U_i). For each user, the messaging server (S) plays the role of Alice and the user (U_i) plays the role of Bob. They interact with direct messages to the interface server (I). In this way, the basis are shared _only_ between Alice, Bob and the Interface. The authentication algorithm is as follows: FOR EACH USER U_i: 1. S sends MESSAGE_i to I 2. S sends A_BASIS_i to I 3. U_i sends B_BASIS_i to I 4. I execute BB84 5. I sends RESULTS_i to U_i 6. U_i sends B_BASIS_i to S 7. S sends A_BASIS_i to U_i 8. U_i eliminates bits with wrong basis from RESULTS_i : U_i has key K_i 9. U_i sends index of bits to be eliminated to S 10. S eliminates the bits : S has key K_i

Implementation

a main server used to communicate between different users classically
the ‘quantum servers’ are used to communicate only with the Intermediate interface
The intermediate interface communicate with the Quantum Computer assembling a circuit that implements Ekert91 or BB84 depending on the input received by a couple of users
The basis used for the qkd protocol are then shared between the users passing through the main server (S)

The actual example

Two users communicate with a main server classically
When one of the two write the command ‘/BASIS’
- A protocol between the E91 and BB84 is chose
- Alice generates automatically her basis and the bitstring (in the case the BB84 is selected)
- Bob generates automatically his basis
- Both the txt files are sent to the private servers that communicates them to the intermediate interface
- The intermediate interface assemble the circuit and run it on the QuTech computer
- Two output are created and sent back to the two users
- Comparing the basis using the main server the quantum-key is selected
The communication between the two users is now quantic secure using the quantum-key to encrypt and decrypt the files privately

Team Experiences

We chose to work on the Quantum Key Distribution challenge. We split up into two groups: one working on the classical end and another on the quantum. On the classical end, we had a task brand new to all of us, network programming. We decided to implement our system as a chatroom where the two users could talk to each other classically and each user had a personal server for sending quantum information to the quantum computer. We underestimated the complexity of this task as the network code was difficult to produce in the first place, given our experience. The challenge ended around when we were working on integrating the classical and quantum system. On the quantum end, we replicated the BB84 and E91 algorithm and developed a format from sending classical instructions from the users to the quantum interface.

Gruntrexpewrus / 2022_qutech_challenge