Blockchain technologies have rapidly acquired popularity and promise to become one of the pillars of the digital society. They, however, are not immune from open challenges in terms of security, privacy and scalability. First, the complexity of blockchain applications makes their security analysis prohibitive, which may lead to coin losses by honest users. Second, the fundamental requirement of including every single transaction in the blockchain for transparency is at odds with the privacy of transactions and users. Last, but not least, storing all data in the blockchain creates severe scalability issues: currently, blockchain technologies typically support a dozen transactions per second, which is far from the throughput of other payment systems available today.

In this talk, I will present my research on security, privacy and scalability in blockchain technologies. In particular, I will focus our findings on the security and privacy issues with currently deployed scalability solutions such as the Lightning Network that affected to all its users in practice. Moreover, I will overview the cryptographic protocols that we have designed to mitigate the aforementioned issues. They have been implemented and tested for the Lightning Network and other currently deployed solutions. I will finish this talk with an overview of some of the open problems with current blockchain technologies.