A method is provided for securely activating or deactivating functionality in a data processing system. The method includes determining to activate or deactivate a selected functional block of a plurality of functional blocks in the data processing system. An authentication key and a unique identifier are provided to a key derivation function of a function control circuit to produce a derived key value. The key derivation function is iteratively input with a sequence of function set identifiers, where each function set identifier is for identifying one or more of the functional blocks. Each function set identifier is paired with a previously derived key value from a previous iteration. A final iteration of the key derivation function provides a verification key for verifying the authenticity of the derived key value corresponding to the selected functional block to be activated or deactivated.