Abstract: A cryptographic system for reproducibly establishing a reliable data string, such as a cryptographic key, from a noisy physically unclonable function (PUF, 110) is provided. The system comprises a hard decision decoder (150) to decode a first multiple of error correctable data words to obtain a second multiple of corrected and decoded data words and a reliability information extractor (180) to determine reliability information, e.g. soft decision information, that is indicative of a reliability of corrected and decoded data words. The system further comprises a soft decision decoder (160) configured to use the reliability information to decode at least one further correctable data word. Error correcting a PUF using reliability information decreases the false rejection rate.