In response to: “Cryptocurrencies and Blockchains” (Vol. 2, No. 4).


To the editors:

To thank Jean-Paul Delahaye for his excellent article, as well as for his monthly columns in Pour la science, which are always exciting and varied, I wanted to send him 2 mBTC (2 millibitcoins) so that he might drink a coffee to my health.

Google, our GPS for the internet, listed a multitude of sites that would allow me to create a bitcoin wallet and to change euros into bitcoins. I began with Electrum, and created an account without difficulty. To change euros into mBTC, I chose Paymium, a site on which I created another account.

In order to transfer ten euros to this last account (a bitcoin was worth, depending on the day, between 850 and 900 euros when I performed the operation), I had to ask my bank to authorize an online money transfer to Belgium. I sent my transfer order on Saturday, January 21, and Paymium informed me on the 25th around noon that my account had indeed been credited with 10 euros. Curiously, no fees were deducted. A small miracle! I thus instantly obtained 11.7 mBTC, but without being able to determine precisely the commission. The price of the BTC is so variable from hour to hour (as of February 14, it is 955 euros), that verification is, in fact, impossible.

I first tried to use the option offered by Paymium for sending mBTC by email, and so, it would seem, without going through the blockchain. But Delahaye does not have a Paymium account, and did not wish to open one. I canceled my transfer order, and managed, by consulting the blog “Benji1000” for guidance, to understand how I could transfer millibitcoins from my Paymium account to my e-wallet. I transferred 10 mBTC on February 2nd, and on the 3rd, my wallet was credited with this sum, as confirmed by Electrum.

All that remained was to send my 2 mBTC to Delahaye by Electrum. The transfer, in principle, offers the possibility of adding whatever amount one might wish to designate as a fee, in other words, as a bakshish for those who do mining. I tried to offer a minuscule fee, but Electrum refused the transaction. Electrum instead imposed the maximum, 0.226 mBTC—more than 10%! I may have made a mistake here somewhere.

Delahaye explained to me that the fee is not proportional to the amount transferred, but to the space used in the blockchain. It is, in fact, impractical to transfer very small amounts, as I did, for a test.

All this took me a while. If I have not forgotten all the passwords and other shortcuts, it will be a quicker process next time.

My conclusion:

The bitcoin system seems to me to have a ludic interest, for show, and for the personal satisfaction derived from coping with a technological—but, above all, speculative—novelty. That said, I do regret not having bought 100 BTC, or more, when the value of bitcoins was less than a euro.

Bitcoin also allows illegal cash transfers and ransoming, although feeding an account by changing euros must certainly leave traces. Similarly, converting bitcoins into cold hard cash is not necessarily discreet. This may depend on the country involved. Finally, the blockchain being public, police and customs officials must be able to inspect it.

Bitcoin allows one to preserve one’s money in a time of economic crisis such as galloping inflation. Of course, it does not depend on a central bank, as is the case for ordinary currency, but this level of security seems limited to me. We depend on centralized bodies in many ways, in particular, for electricity, or an internet connection. So what? A little more, or a little less, how does it matter? In the case of a major economic crisis that involves the banks, I do not see how bitcoin would be immune from problems. The blockchain would probably be preserved, but one would no longer be able to convert bitcoins into euros or dollars. I am not going to place large sums of money in bitcoins, although I would like to avoid the capital gains taxes imposed on life insurance contracts. In another very technical article, Delahaye analyzes the risks involved, which are mainly technical, but also political.1

Moreover, the mining system is a waste of considerable computing and electrical resources. It would amuse me to know if advocates of this system are also activists for energy conservation. It is not impossible!

Bruno Courcelle


Jean-Paul Delahaye replies:

Many thanks to Bruno Courcelle for his letter, which describes the practical difficulties involved in using bitcoin for someone who has just discovered it. I agree with him about the speculative and fraudulent uses to which bitcoin is put, but not with the idea that it is employed just for show, as those who use it, in general, do so discreetly.

I have already explained that bitcoin has weaknesses that may eventually lead to its collapse, or to it requiring complete secrecy. One of the problems that I consider particularly serious is that it might be used for ransomware.2

There is contradiction of sorts in the legislation of a country like France, which prohibits cash transactions for sums over a thousand euros, but at the same time authorizes unlimited transactions in bitcoins… which are simply digital cash.


Bruno Courcelle is Emeritus Professor of Computer Science at the Université de Bordeaux.

Jean-Paul Delahaye is a mathematician and professor emeritus in computer science at the University of Lille.

Translated from the French by the editors.

  1. Jean-Paul Delahaye, “Une épée de Damoclès sur le Bitcoin,” Pour La Science Blogs, August 27, 2016. 
  2. Wikipedia, “Ransomware.”