In a method for generating a cryptographic key in a system-on-a-chip having a hardware-programmable logic unit, a circuit region of the hardware-programmable logic unit is configured in such a way that a first physical unclonable function is executed in the circuit region in order to generate a first cryptographic key, and the circuit region is reconfigured in such a way that (i) a further physical unclonable function is executed in order to generate a further cryptographic key or (ii) another functionality that does not encompass a physical unclonable function is executed.