CROSSING is a joint effort of scientists from quantum physics, cryptography, system security and software engineering, who collaborate in three interconnected project areas. In Project S4, CROSSING is doing research on strongly secure connection establishment.

Today's communication relies on the internet. Global connections transport sensitive data between private users, businesses and cloud storage. It is essential that connections are secure and provide confidentiality for the data exchanged. Therefore, cryptographic procedures, called protocols, are run to establish a shared secret

key which is then used to protect the exchanged data. Common cryptographic channel protocols, like TLS, are used billions of times every day. Our aim is to advance the field of secure connections by investigating the security of

channel protocols and by looking at new means to build long-term secure solutions via hardware tokens and quantum technology. To capture the security of deployed channel protocols as precisely as possible, we develop mathematical models. Our goal is to evaluate the security of today's internet connections and to establish

mathematical guarantees for the provided security level. Another research topic is the complex interplay of different protocols, particularly between key exchange and data transport. We study intersections between different sub-protocols to establish conditions which allow us to

compose secure components. In collaboration with Project E1, we assist developers in choosing the protocols to combine in their implementations. Beyond classical attacks, we predict that the security of connections will soon be

threatened by rapidly evolving quantum computing power. While a scalable quantum computer hasn't been built yet, we can predict that this type of computer would be able to solve several hard mathematical problems that are the foundation of most secure channels in use today.

A promising defense against quantum computers is to build connections whose security relies on information-theoretic assumptions, which are unbreakable no matter how much time and computation power are applied. One way to achieve information-theoretic security is to employ hardware tokens.

A key piece of our project is to construct key exchange protocols based on these hardware tokens, which allow shared secret keys to be created in a quantum-secure way. Our research enables strongly secure connection establishment for the next-generation Internet.

To learn more about strongly secure connection establishment, please visit our website.