# A Novel RFID Authentication Protocol Based on Reconfigurable RRAM PUF
## 2 Research on RFID Security Mechanism Based on PUF  
Similar to the uniqueness of finger prints or irises, PUFs uniquely identify targets by amplifying the subtle physical differences that occur during chip fabrication. In 2002, [PERSON] [14] first designed and implemented optical PUF. Later, with the demand for light weight encryption and decryption authentication algorithms, more PUF implementation methods have emerged [15; 16; 17; 18; 19; 20; 21]. Through the analysis and summary of PUF, we can draw some basic security attributes about PUF. Here are some of them:  
(1) Non-clonality, even for any two PUF modules F having the same internal structure, given an input x, the difference between their outputs \(F\)(x) and \(F^{\prime}\)(x) is greater than a determinable distance. The distance between \(F\)(x) and \(F^{\prime}\)(x) is called the inter-chip Hamming Distance (inter-HD);  
(2) Unpredictability, in the case where a plurality of challenge response pairs (CRPs) of the PUF module are known to be (x\({}_{i}\), \(F\)(x\({}_{i}\))) (i = 1, 2, \(\ldots\), q). It is difficult to predict \(F\)(x) for any x (x\({}_{1}\), x\({}_{2}\), \(\ldots\), x\({}_{q}\));  
(3) Robustness, for any PUF module, the \(F\)(x) and \(F^{\prime}\)(x) obtained within a certain error range are always equal after the same excitation x is input twice. The difference between \(F\)(x) and \(F^{\prime}\)(x) is called intra-chip Hamming distance (Intra-HD). The size of intra-HD and its fluctuation with the working environment are important criteria to measure the reliability of a PUF. Although PUF has many security attributes, most of the RFID systems based on PUF are still affected by security threats such as replay attack, asynchronous attack and tracking attack. On this basis, domestic and foreign scholars have proposed many RFID authentication schemes based on PUF. We have studied and analyzed some of them. [PERSON] [3] firstly utilized PUF in RFID systems, where each response of the PUF tag is stored in the backend database, and the responses will be extracted from the database during authentication. If the generated response of the tag is consistent with that in the database, the authentication is successful. Note that this protocol has realized one-way authentication of the tag. In 2016, [PERSON] et al. [22] presented a novel PUF based LMAP+ protocol. It is an effective solution to resist the heuristic attack strategy in [23]. The protocol is also immune to tracing attack and asynchronous attack. In [24], a double PUF based bidirectional RFID identity authentication protocol is proposed, aimed at providing authentication for IC, such as a low-cost RFID system. In 2019, [PERSON] et al. [25] proposes a lightweight RFID authentication protocol based on PUF, which uses the machine learning algorithm and string-matching algorithm, and presents a new mechanism of PUF challenge generation. A PUF-based anonymous RFID system ownership transfer protocol is presented in [26], using the anonymous RFID system and some encryption schemes to protect the location privacy of tags and the problem of information privacy during transfer. In [27], a lightweight RFID security authentication protocol based on a cloud server is studied. Using physical unclonable function (PUF), permutation, string matching and other lightweight encryption algorithms to reduce hardware resource consumption. However, among the many proposals currently proposed, there are heavy computations in complex updating algorithm and many data interactions between tag, reader and backend database as well. Although security is improved, it causes large hardware overhead. Besides, many protocols cannot resist multiple attacks and have high cost. Based on this, this paper proposes an RFID authentication protocol based on the RRAM PUF. The protocol uses a special RRAM PUF model and a multi-level response computer system to complete the authentication information encryption between the reader and the tag.