From calculations made by the University of Twente, Holland, it appears that an attack on Bitcoin is easier to carry out than what has generally been accepted. If a group of Bitcoin users, who collectively have over 20 percent of the computing power, unite, then this group can carry out an attack over a few days and force other users to accept a new standard for Bitcoin. Th researchers published their results recently at a scientific conference organised by NASA in the United States.
The Bitcoin network uses blockchain technology. The blockchain links individual transactions (blocks) together into a chain that any user can view. Within the Bitcoin network there are agreements as to how the transactions are joined together.
The Bitcoin world is currently divided into several camps. One camp want to continue with the current standard, while other camps advocate for changes that, for example, ensure that more transactions can be processed in a shorter time. With the current protocol, because of a hard upper limit, at most seven transactions per second world-wide can be processed. This makes the network, in the opinion of many, much too slow. Certainly when compared to the number of transactions that the credit card companies can handle in a second.
Changes to the Bitcoin protocol can really only be implemented when they are accepted by the majority of the users. From calculations made by the University of Twente it has been shown that a limited group (if these have 20 percent of the 'mining power' at their disposal) - with the aid of a so-called Andresen attack – are able to introduce a new protocol in a few days and force all other users to adopt it. Ansgar Fehnker, one of the researchers involved, compares this to a situation in which 20 percent of the shareholders in a company can impose their will on the great majority. Through the attack, all the transactions that were carried out in the previous hours will be retrospectively cancelled, which will greatly undermine the trust in the present standard.