Attacks 51%: ZenCash (ZEN) added to the list of victims

In recent weeks there has been a veritable epidemic of attacks by 51% on cryptocurrencies. After Bitcoin Gold (BTG) and Verge (XVG) , it is ZenCash to suffer this attack, which consists in taking control of more than 51% of the mining power of a cryptocurrency, to be able to corrupt the blocks of its blockchain.

We had recently made an article on the site Crypto51 , which lists the costs of an attack of 51% for a list of different cryptocurrencies: we can see that lead such an attack on ZenCash is estimated at just under 8,000 $ per hour of attack .

It is on the ZenCash blog that we learn that the cryptocurrency has suffered a 51% attack this Sunday morning , around 4:43 French time .

The purpose of the attack was to allow "double spend" , double spending, which allows to use a certain amount of the attacked crypto for the first time (for example by sending it on an exchange to obtain the BTC ), and use that same amount to get it on another wallet, which the attackers control.

But the ZenCash team was very responsive , we can also see the details of their counterattack reaction on their blog:

• After receiving a warning about the potential attack of one of our pool operators;
• An investigation was immediately initiated and the distribution of the mining power evaluated;
• In parallel, exchange platforms have been contacted to increase confirmation times;
• The investigation showed that suspicious transactions were double expenses;
• Post-attack research is conducted in a joint investigation with the affected exchange platform.

As explained, the best mitigation strategy for the attack was to recommend to all exchanges to increase the number of minimum confirmations required to at least 100 confirmations.

The first double expense recorded was 6600 ZenCash , and the second observed double expenditure was 13 000 ZEN.

The ZEN price was about $ 30 at the time of the attack, which would amount to a steal of just under $ 600,000 .

The attacks of the 51% are a plague for young / small cryptocurrency, who do not have a total power of total mining enough to make sufficiently complex (and especially sufficiently expensive) this type of attack. However, note here that a good and quick reaction of the ZenCash team has certainly managed to limit the breakage.