Blockchain Consensus and Bitcoin’s SPV

First an announcement: On 14-16 of November the next Decentralized conference will take place in Athens. The first Decentralized conference in Cyprus was very successful and this one is expected to be even better. You will find more information at

They were kind enough to offer us free tickets for the members of the meetup. During the break we will make a draw and two lucky members will be able to attend the conference for free.

The agenda for the meetup is:

19.00 – 19.45 Consensus Algorithms — Thomas Sermpinis
19.45 – 20.15 Break
20.15 – 21.00 Simplified Payment Verification in Bitcoin — George Vlahavas
21.00 – 21.30 Discussion / networking / end


– Consensus Algorithms
Bitcoin and especially blockchain technologies presented a new era of decentralization, and the need for methods to reach consensus became imperative. Because of that, several consensus algorithms were developed and used by blockchains and cryptocurrencies, in order to secure these networks, but none of them is perfect and each of them has its strengths. In this presentation we will discuss several consensus algorithms, which are widely used by decentralized technologies.

– Simplified Payment Verification in Bitcoin
Description of how SPV wallets work in Bitcoin and the reasons why SPV is needed for lightweight clients. Transaction verification with SPV clients. Security and privacy issues. Bloom filters and their use in SPV clients.

Short Biographies of presenters:

– Thomas Sermpinis is a security and blockchain engineer with a Masters Degree in Informatics and Management. He has worked as an instructor in the field of cyber security, covering a wide variety of topics. Also, he is deeply involved in the cyber security community, with a strong social media presence (security blog and popular YouTube channel). For the last year he is dedicated to blockchain technology and currently works as a blockchain research engineer in Aristotle University.

– George Vlahavas is a PhD candidate and researcher in the Department of Informatics, Aristotle University of Thessaloniki. He has extensive experience developing open source software and has been actively involved in the Linux community, both at a local and global level. He is the founder and project lead of Salix (, a GNU/Linux distribution based on Slackware that is simple, fast and easy to use, with stability being the primary goal. His current research interests are focused on blockchain technologies.

The environment is casual and there will be plenty of opportunities to learn and more importantly get to know each other. After the event everyone is welcome to one of the nearby cafeterias to get to know each other.

Hope to see you there!