Abstract: A method for authenticating a radio key for a vehicle involving determining a distance between the radio key and the vehicle and authenticating the radio key. A character string generated by the radio key is transmitted to the vehicle to determine the distance. The character string is generated independently of an item of information transmitted by the vehicle, and the authentication is based on the character string.

Abstract: A method is described for revoking a group of certificates, each of which includes a key, for an authenticated communication between one first subscriber and at least one second subscriber, one first key and one revocation value, with the aid of which the keys of the group of certificates may be calculated from the first key, being transmitted for the purpose of revocation to the at least one second subscriber.