Jean-Paul Delahaye is Professor Emeritus at the University of Lille, a specialist in theoretical computer science and algorithmic complexity. he just wrote Beyond Bitcoin. In the world of blockchain and cryptocurrencies (Dunod, 270 pages, €19.90), an educational but also engaging book on the strengths and weaknesses of cryptocurrencies, as well as their future.
Why is a mathematician like you interested in cryptocurrencies?
In 2008, Satoshi Nakamoto, whose name is still unknown, proposed a protocol, Bitcoin, which creates a currency independent of any central authority, whose operation is based on collective control, everything being robust and secure. The key idea is that of the blockchain, a kind of account book that records transactions without the possibility of deleting pages, which is shared throughout the network. It is a brilliant invention. Before him, others had tried to develop electronic currencies, but without success. What is new and revolutionary is the development of a protocol that combines functions that are already known, but in an unexpected way, and that no one had imagined.
This protocol has also benefited from several advances for its launch in 2009. The encryption, essential for its operation, was quite mature, as evidenced by the success of banking transactions on the Internet. Similarly, peer-to-peer or distributed networks had been running smoothly for several years. Finally, since the system is based on sharing a large file of around 500 GB, the computers had to have enough memory and computing capacity.
However, he foresees the failure of Bitcoin, which he describes as a “diplodocus”, “Minitel of cryptocurrencies”, to be “stored in a computer museum”. Why ?
The main problem of the protocol lies in the way in which the validators of the new transaction pages to be registered in the block chain are designated. With Bitcoin, the chosen validator is the one who wins a calculation contest equivalent to proposing a kind of increasingly valid Sudoku grid, or rolling out a sextuple six with six dice… In practice, the calculation is linked to a difficult cryptographic problem . The consequence is that there is competition, increasingly tougher and more expensive in energy. Initially, the energy cost was low, then it multiplied by ten approximately every year to represent, according to estimates, the equivalent of the annual consumption of Switzerland or Sweden, of the order of 100 terawatt hours! But it is a useless expense, because we can do without this type of method. That’s why I’m talking about a bug, a Bitcoin bug, that could have been better designed from the start.
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