1. A computer implemented method for storing data of a first user in a database, the first user having a private key, the method comprising: directly receiving the first user's private key or generating the first user's private key, wherein generating the first user's private key comprises receiving an input value and applying a cryptographic one-way function to the input value for generation of the first user's private key, wherein the cryptographic one-way function is an injective function; calculating, in a computer, a set of public keys, wherein the first user's private key and each public key of the set of public keys form an asymmetric cryptographic key pair, generating a digital signature for the data using the first user's private key; storing, in the computer, the data pseudonymously in the database with the data being assigned to an identifier, wherein the identifier comprises one of the public keys or wherein the identifier is a pseudonym of the first user or wherein the identifier is an access key to the data in the database, wherein the digital signature is stored into the database with the data.