Blockchain für Privacy im großen Stil ungeeignet

Von Ralf Keuper

Eines der noch weitgehend ungelösten Probleme (öffentlicher) Blockchains, ist, dass es sich dabei im Grunde um ein offenes, digitales (Haupt-)Buch handelt, aus dem sich, wenngleich mit einigem Aufwand, rückverfolgen lässt, welche Person was für Transaktionen mit wem durchgeführt hat. Die Blockchain, ebenso wie ihre prominenteste Anwendung Bitcoin, ist nicht anonym, sondern lediglich pseudoanonym. Das ist auch der Grund weshalb der GNU-Guru Richard Stallmann Bitcoin durch sein Bezahlsystem Taler ablösen will. In dem Beitrag Richard Stallmann verschmäht Bitcoins und will neues Bezahlsystem wird Stallmann mit den Worten zitiert:

“Was ich mir wirklich wünsche, ist anonym in verschiedenen Geschäften einzukaufen, leider wäre dies für mich mit Bitcoin nicht möglich”. Die Verwendung einer Krypto-Börse würde letztlich der Regierung ermöglichen, ihn zu identifizieren

Ein weiterer Pionier, der erhebliche Zweifel an der Anonymität der Blockchain äußert, ist David Chaum. Chaum ist der Erfinder von Digital Cash und des Blinding Algorithm. In dem Interview Elixxir CEO David Chaum: “Blockchains Lack the Ability for Privacy at Scale” erläutert Chaum das Funktionsprinzip des Blinding Algorithm.

Die Ausgangsfrage, das Ausgangsproblem: 

“you see, back in the early 80s, the only way the consumer payment systems could work was using massive computers and banks, POS devices, and this kind of infrastructure. I wanted to find a way to allow for people to hold their own money in such a way that it couldn’t be taken from them and to be able to pay with it in such a way that they could not be linked to those payments.

Die Lösung:

So I invented this notion of a blind signature. Think of it like an ATM where you as a consumer would be able to get money out of the machine but only you would know the serial number of the notes.

This worked by a cryptographic blinding of the serial number, where the bank would have a signed version of your own serial number but they wouldn’t know what serial number you had chosen. Only you could remove the blinding. Then you could decide when you wanted to spend it and they wouldn’t know that is was the money you had withdrawn.”

Dass private Zahlungssysteme kriminellen Handlungen Vorschub leisten würden und damit eine Gefahr für die Gesellschaft sind, ist für Chaum absurd:

The idea that privacy of some payments could be hugely detrimental to society or that consumer privacy is at odds with the interest of society is really a farce. There are so many ways that large amounts of money are illicitly transferred through ownership schemes, foundations, offshore entities, uncut diamonds flying around the world, it’s ludicrous to say that my mother’s personal payments on a day to day basis could eventually impact national security. It’s silliness.”

Die Blockchain sei, so Chaum, aufgrund fundamentaler Defizite für die Sicherung der Anonymität ungeeignet:

Blockchain not only technically lacked the ability to scale but it also lacked the concept of aspects that would be needed for widespread consumer adoption, for meaningful privacy and scaling–for privacy at scale.

There are some blockchain-based technologies that provide some level of privacy but they’re the ones that seem to be the least scalable and, you know, they have some bad associations, and that’s a different thing. But if you want a consumer product, you can’t transparently and immutably put peoples’ payments online.

Alternativen:

You need privacy at scale and a level of security that would be acceptable to countries because they do not want other countries messing with their payment system or tracing their macroeconomics and their citizens and possibly being able to disrupt or disable their economies, and so on.

You need a different level of security and moreover, all this has to work in a way that’s as fast as consumers expect on the smartphone platform without burning up a load of data plan and battery and also while insulating them from any knowledge about the underlying platform.”

Trotz alledem: Ein Vorzug der Blockchain bleibt:

“The single most important thing that blockchain can bring to the world is a decentralized global secure playing field for all kinds of financial transactions and communication and new creative uses of computing.”

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