An electronic system (100) having a memory (1 12, 1 14, 1 16) with multiple memory locations, each specific memory location of the multiple memory locations being arranged to produce a respective value, the respective value depending on a physical, at least partially random, configuration of components constructing the specific memory location, the electronic system comprises a key extraction means (130) arranged to retrieve multiple values in a first order from the multiple memory locations and for determining a reproducible cryptographic key in dependency on the multiple values, characterized in that the electronic system further comprises a re-ordering (120) means in between the memory and the key extraction means for providing the multiple values to the key extraction means in a second order, different from the first order, prior to determining the cryptographic key.