Systems for generating an identifying response pattern comprising a memory (120) used as a physically unclonable function configured for generating a response pattern dependent on physical, at least partially random characteristics of said memory may be vulnerable to freezing attacks and to aging. A memory-overwriting device (110) configured for overwriting at least a first portion of the plurality of memory locations to obscure the response pattern in the memory avoids freezing attacks. An anti-degradation device (160) configured to write to each respective location of a second portion of the plurality of memory locations an inverse of a response previously read from the memory reduces the effects of aging.