Modelling and characterization of physically unclonable functions

Physically Unclonable Functions, or PUFs, are innovative technologies devoted to solve some security and identification issues. Similarly to a human fingerprint, PUFs allows to identify uniquely electronic devices as they produce an instance-specific signature. Applications as authentication or key generation can take advantage of this embedded function. The main property that we try to obtain from a PUF is the generation of a unique response that varies randomly from one physical device to another without allowing its prediction. Another important property of these PUF is to always reproduce the same response for the same input challenge even in a changing environment. Moreover, the PUF system should be secure against attacks that could reveal its response. In this thesis, we are interested in silicon PUF which take advantage of inherent process variations during the manufacturing of CMOS integrated circuits. We present several PUF constructions, discuss their properties and the implementation techniques to use them in security applications. We first present two novel PUF structures. The first one, called “Loop PUF” is a delay based PUF which relies on the comparison of delay measurements of identical serial delay chains. The major contribution brought by the use of this structure is its implementation simplicity on both ASIC and FPGA platforms, and its flexibility as it can be used for reliable authentication or key generation. The second proposed structure is a ring-oscillator based PUF cells “TERO PUF”. It exploits the oscillatory metastability of cross-coupled elements, and can also be used as True Random Number Generator (TRNG). More precisely, the PUF response takes advantage from the introduced oscillatory metastability of an SR flip-flop when the S and R inputs are connected to the same input signal. Experimental results show the high performance of these two proposed PUF structures. Second, in order to fairly compare the quality of different delay based PUFs, we propose a specific characterization method. It is based on statistical measurements on basic delay elements. The main benefit of this method is that it allows the designer to be sure that the PUF will meet the expected performances before its implementation and fabrication. Finally, Based on the unclonability and unpredictability properties of the PUFs, we present new techniques to perform “loop PUF” authentication and cryptographic key generation. Theoretical and experimental results show the efficiency of the introduced techniques in terms of complexity and reliability