There is provided an entity authentication method for a network including a first entity and a second entity, the method including: selecting, at the first entity, one or more pieces of data processed by the first entity to be used for authenticating the second entity; tagging, at the first entity, each of the one or more pieces of data selected with a respective tag generated based on a first secret key of the first entity; sending, from the first entity, a set of authentication data comprising the one or more pieces of data and the respective tags to the second entity; and authenticating, by the first entity, the second entity using a challenge-response authentication technique based on the set of authentication data and the first secret key. There is also provided a corresponding system with entity authentication for a network, and an entity in a network with entity authentication.