A method of manufacturing a secure device having a physical unclonable function includes embedding a phase change memory in the secure device, where the phase change memory includes a plurality of cells, and setting the phase change memory in a manner that results in a phase variation over the plurality of cells, wherein the phase variation is the physical unclonable function. A method for retrieving a cryptographic key from an integrated circuit, wherein the cryptographic key is stored in the integrated circuit, includes measuring a property of a phase change memory embedded in the integrated circuit, wherein the phase change memory includes a plurality of cells and the property is a function of a phase variation over the plurality of cells, deriving a signature from the property, and deriving the cryptographic key from the signature.