1 Chapter 1 Security Terminology Ming Li Shandong University, China & State Grid Corporation, China ABSTRACT The widespread use of RFID technology gives rise to security concerns. Cryptographic technology provides various valuable tools to enhance the security of RFID systems. In the literature, many cryptographic protocols have been proposed and designed for safeguarding RFID systems. In this chapter, the author describes some fundamental terminologies in information security and cryptology. More information on cryptography can be found in (Mao, 2003; Koblitz, 1994; Stinson, 2005; Stallings, 2006). 1.1 BACKGROUND the cashier of pharmacies to read the prices of different drugs. RFID has also been used for more RFID (Radio-Frequency IDentification) systems complex applications, such as passport verifica- are made up of readers and tags. The readers read tion, employee cards and payment for bus tickets. the tags with non-contact communication. In order As with other new technology (such as com- to complete this function, each tag comprises at puter networks), in the beginning, RFID systems least two parts. One is a microchip for storing and designers were mainly focused on creating an processing data, which is similar to that in a smart available system without adequate consideration card or USB key, while the other is an antenna for of security and privacy. Without access control, receiving and transmitting radio waves. Because RFID tags could leak information and erode us of its convenience and low cost, RFID technology of privacy. For example, an attacker could read has been widely used in industry to improve the the identifier in tags easily and track which items efficiency of tracking and managing goods and that an individual is using. If a RFID tags stores production. For example, we are using RFID at the Electronic Product Code (EPC) of an item, DOI: 10.4018/978-1-4666-3685-9.ch001 Copyright © 2013, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Security Terminology we could identify the item by checking it on Ob- algorithms are either based on symmetric key ject Name Service (ONS), which is provided by cryptography or asymmetric key (public key) EPCglobal (Fabian et al. 2005). cryptography. In symmetric key cryptography, the Cryptography is the study of hiding information encryption methods require that the sender and and protecting communications. In order to keep receiver share the same key. The encryption key privacy in a RFID system, many cryptographic and the decryption key are different in asymmetric protocols have been designed to protect the sensi- cryptosystems. Whatever cryptographic algorithm tive information in tags, such as basic hash protocol Alice is using, she needs to share the right key or and hash chain protocol. Cryptographic protocols key pairs with Bob. We describe how to achieve hide tag ID by using cryptographic algorithms with key sharing in the next section. After that, some secret keys. We give a simple example to show fundamental concepts of security requirements are which aspects of security we need to consider explained. Lastly, we introduce the quantities that transmitting a message protected by cryptography. measure the security of an algorithm. Imagine that Alice is to send Bob a message “I am going to meet you at 19:00 tomorrow night.” We list what services we will need to keep this 1.2 KEY SHARING information secure. That is to say, which aspects we should consider to implement a secure com- Before two parties start an encrypted communica- munication. tion, they have to share the right cryptographic keys. In symmetric cryptography, two parties must • Confidentiality: This message must be se- share the same key that is secret to all others. But cret to others. in asymmetric key cryptography, the encryption • Authentication: Alice knows for sure that key and the decryption key are different. Each she is communicating with Bob, and so user possesses a pair of keys, namely the public does Bob. key and the private key. The public key (or a • Integrity: The receiver, Bob, can verify if certificate) can be accessed by anyone, and may this message has been modified, such as if be stored, for example, in public servers managed “tomorrow” has been changed to “today.” by the so-called Certificate Authority (CA). Thus • Non-repudiation: Alice cannot deny that anyone else can send a ciphertext that is encrypted she has sent the message if she did send it, using the public key, but only the user who owns and Bob cannot deny receiving of the mes- the private key can decrypt it. The foundation sage if he does receive it. of public key (or asymmetric key) cryptography • Availability: This message must be deliv- was a revolutionary change for key distribution. ered in time, which means the communica- We have asymmetric key exchange protocols that tion channel have to always be in working can establish a secure communication channel in order if needed. open networks. For symmetric cryptography, it is more difficult The security requirements above can all be to establish a shared cryptographic key. Two or satisfied by cryptographic methods. If Alice wants more communication parties have to establish the to send the message secretly, she encrypts this shared key by some other means. A direct method message into a ciphertext using a cryptographic is to establish the key using secure communica- key. Then she sends the ciphertext of the message tion, such as mail, email or face-to-face. to Bob. Bob decrypts the cipher, firstly using a One key establishment technique is key decryption algorithm with the right key, and reads distribution, which requires a trusted dealer to the message. In general, encryption/decryption delivers a key to two or more parties who want 2 Security Terminology to build a secure communication channel. The response. The reader verifies the ID of a tag when disadvantages of this method are the bottleneck its hash value is found in the database. The key of the Trusted Third Party (TTP) and the inef- distribution here is similar to the first scenario ficiency of the system for a large group of many above. The hash function is a one-way function communication parties. that maps a message to a random string of bits. Many more key establishment techniques are For example, Secure Hash Algorithm (SHA-1) implemented using public key techniques. The (FIPS 2004), which is published by NIST as a Diffie-Hellman key exchange is a cryptographic Federal Information Processing Standard, pro- protocol that enables two parties to establish duces a 160-bit digit from a message that is 64 a secret key through an insecure communica- shorter than 2− 1 bits. tion channel. A practical secure mechanism is a In the third scenario, we make use of a trusted digital envelope technique combining symmetric third party to help us distribute the keys. KDC cryptography and public key cryptography, which (Stallings, 2006) is a trusted server that is respon- encrypts a secret symmetric key using a public key. sible for managing all the keys in a system, and verifies the identity of every user. The KDC shares 1.2.1 Symmetric Key different keys, called user keys, with each user. When Alice and Bob want to establish a secret In symmetric key cryptography, the encryption key to start a secure session, the KDC assigns a methods require that the sender and receiver share session key and sends it to Alice and Bob using the same key. Here are three possible means to their user keys separately. In general, a session achieve key distribution for symmetric key encryp- key expires quickly, and a new session key can be tion between two parties, Alice and Bob. created with the help of KDC before the expira- tion of the previous one. For reducing the burden 1. Alice selects a key and physically deliver it of the KDC server, the new session key can also to Bob. be established by the second method above. The 2. If Alice and Bob have already shared a Kerberos protocol is a successful commercial key, they can establish a new key under the authentication protocol based on symmetric protection of the old key. key cryptography. It realizes secure information 3. If Alice and Bob are sharing different keys exchange using a KDC. More information on with a Key Distribution Center (KDC) sepa- Kerberos protocol can be found in (Miller et al., rately, the KDC can deliver a key to Alice 1988) and (Kohl & Neuman, 1993). and Bob though secure channels. 1.2.2 Asymmetric Key In basic hash protocol (Weis et al., 2004), which is one of the first cryptographic protocol In a symmetric key cryptosystem, users who want proposed for protecting RFID privacy, the keys to build a protected communication channel must of each tag are distributed physically before the have the same secret key prior to starting this use of these tags. Every tag has a secret key that channel. Before the appearance of asymmetric is shared with the reader. When a tag is queried, key cryptography, distribution or exchange of it generates a random number n and sends keys was extremely troublesome, because we (,n H(,k n)) to the reader as a response, where needed a trusted channel to do the key exchange. In H(, k n) is a hash function. The reader maintains general, such a channel often had to be a physical a database that stores the keys of all tags. When channel. Thanks to the proposition of asymmetric the reader receives(,n H(,k n)), it tries all keys key (or public key) cryptography, we can now to hash n and checks which one matches the exchange keys over an insecure communication 3 Security Terminology Table 1.