Tag-reader secure communication protocol in RFID application system
1 Introduction to RFID technology
Radio frequency identification technology (radio frequency idenTIficaTIon, RFID) or electronic tag technology is a non-contact automatic identification technology that emerged from the 1960s and 1970s. It uses radio frequency for non-contact two-way communication to achieve the purpose of automatically identifying the target object and obtaining relevant data. It has many advantages such as high accuracy, strong adaptability to the environment, strong anti-interference, and fast operation. The most basic RFID system is mainly composed of the following 3 parts:
(1) Tag: It is also called electronic tag, smart card, identification card or identification card, and is composed of embedded microprocessor and its software, transmitting and receiving antennas in the card, and transceiver circuit. The label is an information carrier and contains a built-in antenna for communication with the RF antenna.
(2) Reader (reader): a device that reads / writes tag information.
(3) Backend database (backend): used to store relevant data corresponding to the label identification.
In general, the communication between the reader and the back-end database can be regarded as safe and reliable, and this article treats the two as equivalent.
2 Security issues facing RFID
Although the application of radio frequency identification technology is very extensive, but there is a hidden danger that cannot be ignored-security mechanism. Without reliable security mechanisms, the data information in RFID tags cannot be effectively protected. At present, the security of RFID has become an important factor restricting the widespread application of RFID. The main security attacks against RFID can be simply divided into two types: active attacks and passive attacks. Active attacks mainly include: (1) From the obtained RFID tag entity, through reverse engineering means, a complex attack on the reconstruction of the target RFID tag; (2) Through software, using the general-purpose communication connection of the microprocessor 13, by scanning the RFID tag And respond to readers' inquiries, seek security protocols, encryption algorithms, and their weaknesses, and then delete RFID tag content or tamper with attacks that can rewrite RFID tag content; (3) generate anomalies by interfering with broadcasting, blocking channels, or other means Application environment, causing legitimate processors to malfunction, denial of service attacks, etc.
Passive attacks mainly include: through the use of eavesdropping or illegal scanning and other technologies, to obtain communication data between RFID tags and readers or other RFID communication devices, tracking the dynamics of goods circulation, etc.
The attacker will actively or passively attack the tag in the RFID system, the data stored in the tag, and the communication between the tag and the reader, which will expose the RFID system to a huge security risk.
The main security risk in RFID systems is "data confidentiality". Obviously, RFID tags without a security mechanism will leak the contents of the tags and some sensitive information to nearby readers. Due to the lack of support for point-to-point encryption and PKI key exchange, in the application of RFID systems, attackers have many opportunities to obtain data on RFID tags. Another security risk in RFID systems is "location confidentiality". Just as the trademarks of personally carried items may reveal personal identities, RFID tags of personally carried items may also reveal personal identities, and individuals who carry a series of unsafe RFID tags can be tracked through the reader. In addition, attackers can also use fake labels to replace actual items to deceive the consignor and make them mistakenly believe that the items are still on the shelf. An attacker may also obtain illegal benefits by tampering with the data on the RFID tag and replacing the high-priced item tag with a low-priced item tag.
3 Secure communication protocol based on Hash function
In order to solve the security problems of the RFID system and minimize the security risks it faces, a reliable security mechanism must be constructed for the RFID system for mutual authentication and data transmission between the tag and reader. All security mechanisms need to be based on an encryption algorithm [2]. However, due to the large number and wide range of RFID tags used, their cost must be controlled at a relatively low level, which makes RFID tags usually only have about 5,000 to 10,000 logic gates, and these logic gates are mainly used to implement Some of the most basic label functions, only a few can be used to implement security functions. But the realization of AES (advanced encrypTIon standard) algorithm requires about 20,000 ~ 30,000 logic gates [3], and the realization of RSA, elliptic curve cryptography and other public key cryptographic algorithms requires more logic gates. Therefore, most RFID tags simply cannot provide enough resources to implement some more mature and advanced encryption algorithms, but can only use some "PIN code" or "password" mechanism to protect secret data.
According to the existing technology and chip manufacturing level, the realization of mature hash algorithms such as SHA-1 in tag tag chips requires about 3,000 to 4,000 logic gates. Therefore, this paper proposes a secure communication protocol based on hash functions. In order to ensure the security of data transmission between the tag and the reader, and at the same time prevent the leakage of personal information and location information carried by the tag during transmission.
3.1 Hash function in the protocol
In this protocol, two Hash functions are needed: H and G. The implementation of these two Hash functions can be made public without confidentiality. Moreover, H and G can be the same algorithm in theory, but considering that H is only used to calculate the hash value of a tag identification string, a simpler algorithm can be used, and G is used to calculate the mutual authentication and transmission session between tag and backend The Hash value at the time of the key, therefore, the Hash algorithm with greater security strength should be used. Obviously, as a Hash function, both H and G should satisfy [4]:
(1) For a message M of any length, H and G return a fixed length m function value h = H (M) or G (M);
(2) Given M, it is easy to calculate h, even under the condition of limited computing resources on the RFID chip;
(3) Given h, it is difficult to restore M, even if the algorithm of H and G is known;
(4) For a particular M, it is difficult to find another M ', so that H (M) = H (M'), even if the algorithms of H and G are known.
3.2 Initialization of the protocol
The protocol requires that the backend database and the tags used by the system be initialized before use.
(1) Tag end: The initial value written in the tag is composed of 3 parts: 1) Private information S0, such as EPC bar code and other tags that can be used to identify the tag; 2) Counter initial value C0; 3) Session key R0
(2) Backend: a form of all tags is stored in the database. The form records the current value of S0, session key R0, S0 corresponding to each tag Si (equal to S0) and the counter value of the backend (equal to CibC0 ).
3.3 Algorithm steps of the protocol
(1) The backend sends an R / W request to the tag.
(5) Protection of communication content. Because the protocol first authenticates the tag and backend mutually, both parties passing the authentication pass the session key at step (4) of the protocol, and this key will be used to encrypt the data transmission during this session, so the attack Even if the person can eavesdrop on the communication data between the tag and the reader, they cannot get the real content.
5 Conclusion
At present, there are many protocols and schemes on the security issues of RFID systems published, but most of them are only for certain aspects of security issues, and there is no mature and complete solution. On the other hand, due to the limitations of passive tag chip performance and computing power, some more mature and advanced encryption algorithms such as AES, RSA, and elliptic curve ciphers cannot be applied to RFID tag encryption in the near future.
The RFID security communication protocol proposed in this paper is based on the traditional challenge-response framework, and its Hash function requires lower computing power of the tag chip, which is more suitable for the current actual situation and cost control goals. At the same time, the framework of the protocol has the characteristics of backward compatibility with public key cryptosystems. When the performance of the tag chip can support some public key cryptographic algorithms today, it is convenient to change the Hash function part to the public key cryptographic algorithm. To perform the steps, only a few changes are required.
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