A method for generating a pseudonym using an ID token for a user, the ID token being assigned to the user, and the ID token including a protected memory area for storing at least one private key of a first asymmetric cryptographic key pair assigned to the ID token, and the pseudonym of the user being assigned to a service computer system from a set of service computer systems (150, 150', 150",...), comprising the following steps: - opening a website of one of the service computer systems selected by the user, using a web browser of a user computer system via a network; - generating a request, by the selected service computer system, for the pseudonym of the user; - transmitting the request from the service computer system to an ID provider computer system via the network; - authenticating the user with respect to the ID token; - authenticating the ID provider computer system with respect to the ID token via the network using a certificate, which includes a public key of a second asymmetric cryptographic key pair assigned to the ID provider computer and in which a read authorization of the ID provider computer system for a read access for reading an ID token pseudonym from the ID token is defined; - generating the ID token pseudonym, by the ID token, by cryptographic derivation of the ID token pseudonym from the private key and the public key; - temporarily storing the ID token pseudonym in the ID token; - after successful authentication of the user and of the ID provider computer system with respect to the ID token, providing read access for the ID provider computer system to the ID token pseudonym stored in the ID token via the network; - transmitting the ID token pseudonym from the ID token to the ID provider computer system, using end-to-end encryption, via the network based on the read access; - checking the validity of the ID token pseudonym, by the ID provider computer system; - deriving, by the ID provider computer system, the pseudonym of the user assigned to the selected service computer system from the ID token pseudonym of the user, using a cryptographic function specific to the selected service computer system; - signing the derived pseudonym, by the ID provider computer system; - transmitting the signed pseudonym from the ID provider computer system to the selected service computer system via the network, a one-way function being assigned to each of the service computer systems so that the ID provider computer system, for the derivation of the pseudonym, accesses the one-way function assigned to the selected service computer so as to derive the pseudonym from the ID token pseudonym using this one-way function, wherein the pseudonym is derived by the calculation of a hash-based message authentication code (HMAC), the ID token pseudonym is used as a secret key for generating the HMAC of an identifier of the selected service computer system, and the identifier is the URL of the website opened by the user. - opening a website of one of the service computer systems selected by the user, using a web browser of a user computer system via a network; - generating a request, by the selected service computer system, for the pseudonym of the user; - transmitting the request from the service computer system to an ID provider computer system via the network; - authenticating the user with respect to the ID token; - authenticating the ID provider computer system with respect to the ID token via the network using a certificate, which includes a public key of a second asymmetric cryptographic key pair assigned to the ID provider computer and in which a read authorization of the ID provider computer system for a read access for reading an ID token pseudonym from the ID token is defined; - generating the ID token pseudonym, by the ID token, by cryptographic derivation of the ID token pseudonym from the private key and the public key; - temporarily storing the ID token pseudonym in the ID token; - after successful authentication of the user and of the ID provider computer system with respect to the ID token, providing read access for the ID provider computer system to the ID token pseudonym stored in the ID token via the network; - transmitting the ID token pseudonym from the ID token to the ID provider computer system, using end-to-end encryption, via the network based on the read access; - checking the validity of the ID token pseudonym, by the ID provider computer system; - deriving, by the ID provider computer system, the pseudonym of the user assigned to the selected service computer system from the ID token pseudonym of the user, using a cryptographic function specific to the selected service computer system; - signing the derived pseudonym, by the ID provider computer system; - transmitting the signed pseudonym from the ID provider computer system to the selected service computer system via the network, a one-way function being assigned to each of the service computer systems so that the ID provider computer system, for the derivation of the pseudonym, accesses the one-way function assigned to the selected service computer so as to derive the pseudonym from the ID token pseudonym using this one-way function,