1. A method of using a physically unclonable function (PUF) as a key-encrypting key, comprising: encrypting data using a session key; generating, from a PUF, a set of PUF values with a plurality of input challenges to the PUF, wherein the generating includes generating one or more PUF values of the set of PUF values under environmental conditions that are different from the environmental conditions under which one or more others of the set of PUF values are generated; encrypting the session key and a correctness indicator into a plurality of session key pairs using a plurality of PUF values of the set of PUF values as an encryption key, respectively; and adding the plurality of session key pairs to the encrypted data.