Some embodiments are directed to an electronic cryptographic device configured to determine a cryptographic key. The cryptographic device has a physically unclonable function, a debiasing unit, and a key reconstruction unit. The PUF is configured to produce a first noisy bit string during an enrollment phase and a second noisy bit string during a reconstruction phase. The debiasing unit (120) is configured to determine debiasing data from the first noisy bit string during the enrollment phase. The debiasing data marks bits in the first noisy bit string as retained or discarded. The key reconstruction unit is configured to determine the cryptographic key from bits in the second noisy bit string marked as retained by the debiasing data, the cryptographic key being independent from bits in the second noisy bit string marked as discarded by the debiasing data.