This example shows collisions in the 4th and 7th bits. This information is used to identify tags faster and decrease the number of collisions in an identification round.Figure 2.Example of Manchester coding.2.3. Collision Tree (CT)The collision tree (CT) protocol [16,17] is a QT based protocol that implements bit-tracking. CT uses Manchester coding to seek the first collided bit so as to split the tags into two subsets. For a query q1q2��qL of length L, where qi ? 0,1, tags matching the reader query respond their remaining ID bits p1p2��pc��pT, of length T, where pi ? 0,1 and pc is the first collided bit. The reader then, assembles two new queries q1��qL p1��pc-1��0��, which will match the first subset of tags and q1��qL p1��pc-1��1��, which will match the other subset.
The CT protocol decreases the number of collisions compared to the QT and removes idle slots. All new queries are generated according to a collided bit, assuring that both new queries are going to be responded by at least two tags. Figure 3 shows an example of the identification of five tags using CT. The protocol eliminates idle slots and, extending the prefixes dynamically, outperforms QT with less slots and collisions.Figure 3.Example of CT protocol.3.?Window MethodologyAloha-based protocols are probabilistic and rely on more sophisticated tags than tree-based ones, which are deterministic [6]. However, the tags of the tree-based protocols usually need to transmit a higher number of bits to be identi
Recent improvements in semi-conductor technology have enabled the computing environment to become mobile, and accelerated the change to a ubiquitous era.
The use of small mobile devices is growing explosively, and the importance of security is increasing daily. One of the essential ingredients of smart device security is a block cipher, and lightweight energy-efficient implementation techniques are required for small mobile devices.Techniques for securing resource-constrained devices such as RFID (Radio-frequency Identification) tags have been proposed. In 2005, Lim and Korkishko [1] presented a lightweight block cipher called mCrypton that encrypts plaintext into ciphertext by using 4 by 4 nibble (4-bit) matrix-based simple operations such as substitution (S-Box), permutation, transposition, and key addition (XOR). The following year, Hong et al.
[2] proposed a lightweight block cipher called HIGHT, which has a Feistel structure and operates with simple calculations such as XOR, addition, subtraction, Anacetrapib and rotation. In 2007, Bogdanov et al. [3] introduced PRESENT, which is comprised of substitution, permutation, and XOR. In 2009, KATAN and KTANTAN were proposed by Cammoere et al. [4] KATAN divides plaintext into two parts and stores them into two registers, and the outputs from non-linear functions are stored in the least significant bit (LSB) of each other’s register.