An Overview of Blockchain SecurityIn this presentation we will overview a number of important questions which underpin the security of blockchains. We study Chaumian and Nakamoto e-cash, see why bitcoin is quite slow, explain the role of digital signatures and mining in building so called "trustless systems", study the bitcoin network and 51% attacks, explain some issues with ECC cryptography. Then we study some techniques which allow to make bitcoin payments more secure (e.g. hardware wallets) and more private (stealth address, ring signatures).

Nicolas Courtois Nicolas Courtois is a cryptographer and senior lecturer in computer science at University College London. He was one of the co-authors of both the XSL attack against block ciphers such as the Advanced Encryption Standard and the XL system for solving systems of algebraic equations that was used in the attack. Other cryptographic results of Courtois include algebraic attacks on stream ciphers, attacks on the KeeLoq and Hitag 2 systems used for remote keyless automobile entry systems, and an analysis of cryptographic weaknesses in public transit smart cards including the London Underground Oyster card and the Dutch national analogue (OV-chipkaart). He holds more than a dozen patents, has more than a hundred publications and his blog is often cited in the press. More recently, he has been working on (and blogging about) cryptocurrencies and he’ll talk to us about security aspects of the innovative technology underlying them, blockchains!