Because it is open source and will be audited by anyone who wants to audit it. Also because the people making it are not going to backdoor it (and if you don't believe me read the source code!) . They could always download something from themselves, because they know the strings it is indexed by, and then they can match the ciphertext they obtained to the ciphertext on their server. Pretty much this. EKS servers have plausible deniability kind of how Freenet nodes do. They cannot decrypt arbitrary files looking for illegal content. However if they also store plaintext stuff at all it would be a different story. Also since all nodes have all files, they could easily be told by police that a certain ciphertext is illegal etc. It would be better if the content of the database is hidden as well, I just don't know how to do this with EKS and have not read of any such systems, only for PIR. The EKS servers have no concept of a thread, only individual posts. The threading is done client side.