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 S7, Crossing is doing research on secure and scalable blockchain technology.

Since the introduction of blockchain technology, cryptocurrencies have thrived. They enable people around the world to exchange money and value without having to rely on trusted authorities like central banks. One can think of blockchain systems as a distributed database that stores transactions.

Users can add transactions to the database, but there is no way to delete or hide any of these actions. However, public cryptocurrencies like Ethereum or Bitcoin have serious scalability problems. While traditional systems like Visa or MasterCard can process up to 50

,000 transactions per second, big cryptocurrencies can only process between 7 and 15. Furthermore, processing a transaction can take up to one hour and cost significant fees from 50 cents to 30 dollars. Unfortunately, this makes current cryptocurrencies infeasible for small transactions, known as microtransactions.

Why is that? Whenever a user issues a new transaction, it has to be propagated to every single node in the distributed system. They all have to form a consensus on the ordering of transactions that changes the state of the database.

Otherwise, one could spend money that does not belong to them or could spend the same money twice. Executing this complex process of agreement for every transaction, whether it's small or large, makes blockchain technologies very difficult to scale. That's why we in Project S7 aim to improve blockchain scalability.

Our first goal is to analyze and improve the consensus protocols which ensure a consistent view of the distributed database. We construct new provably secure protocols which improve existing solutions. In the second work package, we focus on second-layer off-chain protocols.

They can reduce the transaction load on the blockchain by performing computations off-chain and therefore make micropayments feasible. This is achieved via payment channel networks. Contrary to existing solutions, our protocol, Perun, eliminates the need for parties in the payment channel network to be online at all times.

Additionally, we collaborate with Projects S2 and P3 to reduce both costs and complexity of the channel networks by using trusted execution environments. We will also collaborate with other crossing projects in order to provide enhanced and scalable blockchain technologies that offer security, privacy, and usability.

To learn more about secure and scalable blockchain technology, please visit our website.