 From a privacy perspective a better solution would be the use of attribute-based authentication (Goyal et al. 2006) which allows access of online services based on the attributes of users, for example their friends, nationality, age etc. Depending on the attributes used, they might still be traced back to specific individuals, but this is no longer crucial. In addition, users can no longer be tracked to different services because they can use different attributes to access different services which makes it difficult to trace online identities over multiple transactions, thus providing unlinkability for the user. Recently (Allen 2016, Other Internet Resources), the concept of self-sovereign identity has emerged, which aims for users to have complete ownership and control about their own digital identities. Blockchain technology is used to make it possible for users to control a digital identity without the use of a traditional trusted third party (Baars 2016).