Cryptocurrencies and blockchains - How to create trust

Mathematical cryptography has matured remarkably since World War II. At the same time, advances in the design and physical implementation of computer networks have led to the development of networks that operate without a central control center: peer-to-peer networks. These two elements, combined with the computing and storage power available to every machine today, have made it possible to design new means of payment that are unlike any other and are likely to revolutionize the economy and finance, and even many other sectors of activity.

On October 31, 2008, the enigmatic Satoshi Nakamoto – —a pseudonym, and we still don't know who is behind it – —published a text online describing how it is possible to set up a system for exchanging monetary units (which he calls bitcoins) that does not require any centralized control to function, unlike all conventional currencies issued by central banks and all online payment systems. On January 3, 2009, the programs needed to launch this first "cryptocurrency" were ready, and it was created. After a quiet start, with only a few cryptology experts aware of its existence and interested in it, it began to flourish. Its value, which was negligible in 2009 (it was not even worth one hundredth of a dollar at the time), took off, giving it concrete reality, despite volatility that led to it losing 80% of its value several times in a few months (for example, in early 2018).

At the beginning of 2015, one bitcoin is worth approximately $300.

At the beginning of 2020, one bitcoin is worth approximately $7,000.

At the beginning of 2025, one bitcoin is worth approximately $93,000.

Contrary to what had been predicted by some analysts hostile to this strange and often misunderstood digital object, Bitcoin is holding up fairly well, albeit with unpredictable fluctuations that make it unsuitable for many commercial uses, with the result that it is mainly used as a speculative investment tool. Today, the total capitalization of the 19.9 million bitcoins issued exceeds two trillion dollars (as of September 16, 2025). The total capitalization of crypto-assets has reached four trillion dollars, which is more than France's debt, more than the market capitalization of Apple or Microsoft, and almost as much as that of Nvidia ($4.3 trillion).

Starting from scratch, mathematical cryptology and network technology have created digital currencies that can be exchanged for hard cash, enabling, for example, a Norwegian student – Kristoffer Koch – who bought €25 worth of bitcoins in 2009 to sell some of them to buy an apartment in central Oslo. Several thousand crypto-assets, more or less copying Bitcoin, have been introduced, but Bitcoin remains very dominant:...