According to an example aspect of the present invention, there is provided a cryptoprocessor comprising physical unclonable function circuitry comprising at least one physical unclonable function, and at least one processing core configured to process a challenge received from outside the cryptoprocessor by at least deriving a response to the challenge by providing the challenge as input to the physical unclonable function circuitry, using the response as an encryption key to encrypt a second encryption key, and by causing the encrypted second encryption key to be provided to a party which issued the challenge.