A cryptographic system for reproducibly establishing a reliable data string from a noisy physically unclonable function in a use phase after an enrollment phase (PUF, 110), the system comprising - the physically unclonable function being configured for establishing in the use phase an initial data string depending at least in part upon partially random physical characteristics of the physically unclonable function, - a normalizer configured for determining in the use phase a first multiple of error correctable data words on the basis of the initial data string, - a hard decision decoder configured to decode in the use phase the first multiple of error correctable data words to obtain a second multiple of corrected and decoded data words , - a reliability information extractor configured to determine in the use phase reliability information , that is indicative of a reliability of said decoding of the first multiple of error correctable data words, - a data arranger configured to arrange in the use phase the second multiple of corrected and decoded data words to obtain at least one further correctable data word, and - a soft decision decoder configured to decode in the use phase the at least one further correctable data word using the reliability information to obtain at least one further corrected and decoded data word, the reliable data string being obtained from the at least one further corrected and decoded data word, wherein the reliability information comprises a reliability value that is indicative of the reliability of the decoding of a particular error correctable data word of the first multiple of error correctable data words into a particular corrected and decoded data word of the second multiple of corrected and decoded data words. - the physically unclonable function being configured for establishing in the use phase an initial data string depending at least in part upon partially random physical characteristics of the physically unclonable function, - a normalizer configured for determining in the use phase a first multiple of error correctable data words on the basis of the initial data string, - a hard decision decoder configured to decode in the use phase the first multiple of error correctable data words to obtain a second multiple of corrected and decoded data words , - a reliability information extractor configured to determine in the use phase reliability information , that is indicative of a reliability of said decoding of the first multiple of error correctable data words, - a data arranger configured to arrange in the use phase the second multiple of corrected and decoded data words to obtain at least one further correctable data word, and - a soft decision decoder configured to decode in the use phase the at least one further correctable data word using the reliability information to obtain at least one further corrected and decoded data word, the reliable data string being obtained from the at least one further corrected and decoded data word, wherein the reliability information comprises a reliability value that is indicative of the reliability of the decoding of a particular error correctable data word of the first multiple of error correctable data words into a particular corrected and decoded data word of the second multiple of corrected and decoded data words. <EOS>