The invention performs anonymous read/write accesses of a set of user devices to a server. Write accesses of the user devices of the set comprise generating an encrypted file by an anonymous encryption scheme; computing a pseudorandom tag; indexing the encrypted file with the tag as user set index of the user set and writing the encrypted file and the associated tag to the a storage system of the server. Read accesses of the user devices of the set comprise downloading tag data corresponding to a plurality of tags from the server, the tag data enabling the user devices of a respective set to recognize so-called “own” tags computed by one of the user devices of the respective set of user devices; determining the own tags among the plurality of tags; reading one or more encrypted files associated to the own tags; and decrypting the encrypted files.