Differential uncloneable variability-based cryptography techniques are provided. The differential cryptography includes a hardware based public physically uncloneable function (PPUF) to perform the cryptography. The PPUF includes a first physically uncloneable function (PUF) and a second physically uncloneable function. An arbiter determines the output of the circuit using the outputs of the first and second PUFs. Cryptography can be performed by simulating the PPUF with selected input. The output of the simulation, along with timing information about a set of inputs from where the corresponding input is randomly selected for simulation, is used by the communicating party that has the integrated circuit with the PPUF to search for an input that produces the output. The input can be configured to be the secret key or a part of the secret key.