Wireless Network Security

SNOW 3G is a synchronous, word-oriented stream cipher used by the 3GPP standards as a confidentiality and integrity algorithms. It is used as first set in long term evolution (LTE) and as a second set in universal mobile telecommunications system (UMTS) networks. The cipher uses 128-bit key and 128 bit IV to produce 32-bit ciphertext. The paper presents two techniques for performance enhancement. The first technique uses novel CLA architecture to minimize the propagation delay of the 2 32 modulo adders. The second technique uses novel architecture for S-box to minimize the chip area. The presented work uses VHDL language for coding. The same is implemented on the FPGA device Virtex xc5vfx100e manufactured by Xilinx. The presented architecture achieved a maximum frequency of 254.9 MHz and throughput of 7.2235 Gbps. Keywords: Cryptography FPGA SNOW 3G Stream cipher VHDL Wireless network security This is an open access article under the CC BY-SA license. 1. INTRODUCTION Security of the records is important in the systems where personal and financial matters are involved. Hiding of information from unauthorized users becomes essential in such systems and services. Cryptography is one of the widely used techniques for securing information from eavesdroppers. Considering the need to secure information many researchers are working in the area of information security. To maintain advanced network security, the concern network architecture must change from traditional security to advanced security. The same may be achieved by sinking holes in the security wall. Cryptography algorithms and their associated key are more secure when it is implemented on a hardware platform [1]. Side-channel attacks and fault attacks may exist. However, developed algorithms must be fast enough to support autonomous protocols. These protocols use different encryption algorithms for a different session. Many recent autonomous protocols like secure sockets layer (SSL) and internet protocol security (IPsec) use different ciphers for different sessions. Hardware implementation of the cryptographic algorithm on FPGA devices is attractive solutions because FPGAs are reconfigurable [2-8]. This property provides flexibility for dynamic system development and capable of implementing a wide range of functions/architectures/algorithms. It seems to be significant to emphasize FPGA based implementations of cryptographic algorithms, especially high throughput architectures [9]. SNOW 3G algorithm is the core of the 3rd generation partnership project (3GPP) algorithms UEA2 and UIA2. The 3GPP is a joint attempt between telecommunication associations (TG) to make globally applicable specifications for long term evolution (LTE) mobile phone systems [10, 11].

In this research a survey is conducted that looks into the architecture of VANETs and their areas of application. The architecture is broadly discussed in the introductory part, which also outlines the key role players. The paper also keenly focuses on the various security and privacy concerns that are experienced in the implementation of VANETs. Privacy and security issues found to affect VANET are based on integrity, confidentiality, availability, and reliability of data and information exchanged in VANETs. Attacks are major security concerns that are thoroughly surveyed in this work. Some of the means that attackers use in VANET include DoS attack, masquerade, eavesdropping, jamming, and others. Some of the popular means through which these attacks can be controlled include cryptographic means such as encryption. Other security measures that can be practiced to control the attacks include authentication and others that are broadly discussed in the paper. There is more to be done in the future to increase capabilities, security, and privacy of VANETs.

As in today's date fuel consumption is important in everything from scooters to oil tankers, power consumption is a key parameter in most electronics applications. The most obvious applications for which power consumption is critical are battery-powered applications, such as home thermostats and security systems, in which the battery must last for years. Low power also leads to smaller power supplies, less expensive batteries, and enables products to be powered by signal lines (such as fire alarm wires) lowering the cost of the end-product. As a result, low power consumption has become a key parameter of microcontroller designs. The purpose of this paper is to summarize, mainly by way of examples,what in our experience are the most trustful approaches to lowpower design. In other words, our contribution should not be intended as an exhaustive survey of the existing literature on low-power esign; rather, we would like to provide insights a designer can rely upon when power consumption is a critical constraint.We will focus on the reduction of power consumption on different technologies for different values of oicapacitance and also compare power saving in technologies.

Today’s wireless networks are vulnerable in many ways (eavesdropping, illegal use, unauthorized access, denial of service attacks, so called warchalking etc). These problems and concerns are one of main obstacles for wider usage of wireless networks.  People are worried to unknowingly “expose” their computers to illegally access through air from undefined location. On wired networks intruder can access by wire, but in wireless he has possibility to access to your computer from anywhere in neighborhood.

In this paper solution to overcome this obstacle is presented. Here is proposed WIDS (Wireless Intrusion Detection System) based on client based IDS agents, their cooperation and capabilities such as: self learning, autonomy and decision, self-decision and self defense including alerting. This is multidimensional system in development which is intended to cover most of wireless networks specific vulnerabilities on intrusion. It should work in real-time and defend user i.e. his computer or system against majority of intrusions nevertheless of fact if they are already known or new kind of attacks. System is integrated in clients and performs local data collection and filtering, works as local detection engine cooperating with neighboring IDS agents (cooperative detection engine). It provides local response and/or global response against intrusion.

This system can be coupled together with authentication systems and air encryption systems proposed by 802.11i (including AES encryption) and 802.1x (EAP and its implementations) for better security.

At present time there are IDS but mostly wired networks based and rules/signs based. These systems can’t answer on demanding environments and every day practice where we can see new and new types of attacks uncovered by current “signs” present in IDS, so its efficiency is dependent on frequency of signs / rules discovering and  updates.

WIDS system, as described here, will require existence of next components WIDS Agent, Sensor, Server and Management & Reporting Tool and these components are object of analyze.

Wireless Sensor Network (WSN) is an emerging technology that shows great promise for various futuristic applications both for mass public and military. The sensing technology combined with processing power and wireless communication makes it lucrative for being exploited in abundance in future. The inclusion of wireless communication technology also incurs various types of security threats. The intent of this paper is to investigate the security related issues and challenges in wireless sensor networks. We identify the security threats, review proposed security mechanisms for wireless sensor networks. We also discuss the holistic view of security for ensuring layered and robust security in wireless sensor networks.

— Any algorithm is evaluated based on its confusion and diffusion property determining its strength to withstand the intruding attacks. AES (Advanced Encryption Standard), using 128-bit key size has the number of rounds processed over plaintext to obtain unbreakable ciphertext. The key factor that determines the security of the algorithm is the processing of four different stages in each round during encryption and decryption. The algorithm has confusion property implemented in the form of S-Box (Substitution Box) which works in a static manner in each round. This may prove to be the loophole where an attacker may analyze the static S-Box processing and may get successful in determining plaintext by implementing reverse S-Box during the transmission of encrypted data. In this paper, authors propose a solution to strengthen the S-BOX implemented in the stage of "SubBytes" by implementing novel approach of "SMX (Sum Modulus XOR) Algorithm" with a gain of added complexity with reduced processing time.

Wireless (Wi-Fi) networks based on IEEE 802.11 1 family of standards have been spreading its coverage last years and this trend is expected to grow. Every day more and more people use this type of networks to access Internet, company or other types of networks. Today's wireless networks are vulnerable in many ways (rogue access points, hijacking sessions, eavesdropping, illegal use, unauthorized access, denial of service attacks, floods, stealing data and other types of misuse and attacks etc). People are worried about unknowingly exposing their computers to illegal access through the air, from an undefined location. On wired networks the intruder can access by wire, but in wireless environments the intruder can access the network from anywhere in the neighborhood. At the present time there are IDS's but mostly deployed on wired networks, and based on rules and signatures of already known and analyzed intrusions. These systems can't answer the demand in environments where new intrusions are occurring every day due their legacy IDS's limitations. Intrusion detection agent presented in this paper is part of WIDSwireless intrusion detection system. WIDS Agent is software installed on mobile computer device. It detects intrusions and attacks by analyzing traffic and making conclusions and denies it. It works as standalone module or coupled (in contribution) with WIDS Sensor and Server that are also part of this system. Position of application is on personal computer (PC), including Pocket PC (PPC), other PDA devices and similar computerized and mobile devices. This system has capabilities such as: self learning, autonomy and decision, self-decision and self defense including alerting. This is multidimensional system in development which is intended to cover most of wireless networks specific vulnerabilities and intrusion. It should work in real-time and defend user i.e. his computer or system against majority of intrusions nevertheless of fact if they are already known or new kind of attacks. System is integrated in clients and performs local data collection and filtering, works as local detection engine cooperating with neighboring WIDS agents (cooperative detection engine). It provides local response and/or global response against intrusion. Also, this system works in the closest relationship with firewall software and devices, antivirus software, network management and other security tools.

Since the liberalization of the telecommunication sector in Uganda in 1998, the key services have been voice, data and low rate Internet. The backbone link to the rest of the world has been via satellite which is characterized by low bandwidth limiting broadband usage in Uganda. With the arrival of undersea cables at the East African coast, Uganda is now linked to the rest of the world via optic fiber which offers high bandwidth rendering access to broadband services. Internally, wired, Optic fiber and wireless technologies such as 3G mobile and WiMAX infrastructure have brought broadband services within reach of the urban population. These improvements have revolutionized telecommunication by making broadband access more affordable and enabling converged voice, data and video/entertainment services to the urban population.  Rural areas with low level or absent grid power and telecommunication infrastructure to deliver such services are still in a broadband blackout. In this paper, we discuss the challenges to rural broadband deployment in Uganda and propose possible technical solutions to address these challenges.

In Network Security and Cryptography, hash functions play a very important role. To check the Integrity, Authenticity of information or data transmitting between the Seder and receiver party hash algorithms are used. Digital signature also uses the hash algorithm. Hash function used for key generation in Symmetric and Asymmetric Key Cryptosystems. Different algorithms provide different level of security depending on how difficult is to break them. The most well-known hash algorithms are SHA-1, SHA-2, SHA-3, MD4, MD5 and Whirlpool etc. This paper discusses importance of hash functions, description about various well known hash functions, and comparative analysis of various hash algorithms.

With rapid progress in the field of radio technology, Wireless networks have grown to have many beneficial features, the main one is MOBILITY. The downside of these networks is susceptibility to attacks, which has persisted since the very beginning. Therefore, it is a major concern to secure these networks! This paper focuses on securing WiFi networks both domestic & Industrial.

This paper presents a brief overview of the different cryptographic methods used in mobile networks. The focus here is on the mobile communication standards-1G to 4G. The purpose of this paper is to appreciate the evolution of security measures in mobile networks from 1G to 4G, and examine the cryptosystems in each of the standards. This will be useful to offer a perspective on the development of 5G security.

Wireless sensor networks (WSNs) have attracted a lot of interest over the last decade in wireless and mobile computing research community.  Applications of WSNs are numerous and growing, which range from indoor deployment scenarios in the home and office to outdoor deployment in adversary’s territory in a tactical battleground. However, due to distributed nature and their deployment in remote areas, these networks are vulnerable to numerous security threats that can adversely affect their performance. This problem is more critical if the network is deployed for some mission-critical applications such as in a tactical battlefield. Random failure of nodes is also very likely in real-life deployment scenarios. Due to resource constraints in the sensor nodes, traditional security mechanisms with large overhead of computation and communication are infeasible in WSNs. Design and implementation of secure WSNs is, therefore, a particularly challenging task. This chapter provides a comprehensive discussion on the state of the art in security technologies for WSNs. It identifies various possible attacks at different layers of the communication protocol stack in a typical WSN and presents their possible countermeasures. A brief discussion on the future direction of research in WSN security is also included.

Modbus is the de facto standard communication protocol for the industrial world. It was initially designed to be used in serial communications (Modbus RTU/ASCII). However, not long ago, it was adapted to TCP due to the increasing popularity of the TCP/IP stack. Since it was originally designed for controlled serial lines, Modbus does not have any security features. In this paper, we wrote several benchmarks to evaluate the performance of networking devices that run Modbus TCP. Parameters reported by our benchmarks include: (1) response time for Modbus requests, (2) maximum number of requests successfully handled by Modbus devices in a specific amount of time, and (3) monitoring of Modbus devices when suffering a Distributed Denial of Service attack. Due to the growing adoption of IoT technologies, we also selected two widely known and inexpensive development boards (ESP8266 and Raspberry Pi 3 B+/OpenPLC) to realize a performance evaluation of Modbus TCP.

International Journal of Microwave Engineering (JMICRO) is a peer-reviewed, open access journal which invites high quality manuscripts that focuses on Engineering and theory associated with microwave / millimeter-wave technology, guided wave structures, electromagnetic theory and implementation. Authors are invited to submit original research works that stimulate the development of latest technology in industry and academia. Good quality review papers and short communications are also acceptable. Research areas suitable for publication include, but are not limited to the following fields:

International Journal of Computer Networks & Communications (IJCNC)

(Scopus, ERA Listed)


ISSN 0974 - 9322 (Online); 0975 - 2293 (Print)


http://airccse.org/journal/ijcnc.html

New Issue: January 2020, Volume 12, Number 1 --- Table of Contents

http://airccse.org/journal/ijc2020.html

Physical Unclonable Functions (PUFs) are promising security primitives for resource-constrained network nodes. The XOR Arbiter PUF (XOR PUF or XPUF) is an intensively studied PUF invented to improve the security of the Arbiter PUF, probably the most lightweight delay-based PUF. Recently, highly powerful machine learning attack methods were discovered and were able to easily break large-sized XPUFs, which were highly secure against earlier machine learning attack methods. Component-differentially-challenged XPUFs (CDC-XPUFs) are XPUFs with different component PUFs receiving different challenges. Studies showed they were much more secure against machine learning attacks than the conventional XPUFs, whose component PUFs receive the same challenge. But these studies were all based on earlier machine learning attack methods, and hence it is not clear if CDC-XPUFs can remain secure under the recently discovered powerful attack methods. In this paper, the two current most powerful two machine learning methods for attacking XPUFs are adapted by fine-tuning the parameters of the two methods for CDCXPUFs. Attack experiments using both simulated PUF data and silicon data generated from PUFs implemented on field-programmable gate array (FPGA) were carried out, and the experimental results showed that some previously secure CDC-XPUFs of certain circuit parameter values are no longer secure under the adapted new attack methods, while many more CDC-XPUFs of other circuit parameter values remain secure. Thus, our experimental attack study has re-defined the boundary between the secure region and the insecure region of the PUF circuit parameter space, providing PUF manufacturers and IoT security application developers with valuable information in choosing PUFs with secure parameter values.

In this contemporary world, network computing has become one of the major requirements in
today’s world. It can be seen in various places such as in home, universities, hospitals, airports,
hotels, retail shops, banks, government sectors, etc. With all of these growths, the network
computing has continuously expanded in several aspects and areas such as in term of the
infrastructure’s size, complexity as well as the number of users that can accommodate.
(Malgaonkar, Patil, Rai, & Singh, 2017)Therefore, network computing can be categorized into
two types which are wired network and wireless network. Both of them work and operate
differently as well as they have different setup and architecture.
In the simplest sense, wireless technology enables and allows devices to start communicating
without the need of physical connections such as network cabling, whereas wired network
requires the users to communicate physically through a connection cable between the user’s
device and the network device. The wireless technology uses radio frequency transmissions to
transmit the generated data by the connected devices. Besides that, wireless networks can also
be classified into several groups based on their coverage. These classifications can be like
Wireless Wide Area Network “WWAN,” Wireless Personal Area Network “WPAN” and
WLANs. WWAN is typically responsible for transmitting the data for mobile communication
which includes 2G cellular, Global System for mobile communication “GSM” and more (AbuTair & Bhatti, 2017).
For WLAN technology, it can be divided into different technologies which are wireless LANs
and Ad Hoc Networks. For wireless LANs, it allows greater portability and flexibility than the
traditional wired local area network “LAN” since it allows the users to connect remotely using
wireless card device which is usually built-in devices in laptops. For Ad hoc networks, they
are considered as a network designed to dynamically connect remote devices like cell phones
and laptop through Bluetooth technologies. This type of technology is considered as shifting
network topologies and maintain random network configuration whereas the WLANs use a
fixed network infrastructure (Lutui, Tete'Imoana, & Maeakafa, 2017).
Based on that, the wireless network provides and offers several benefits such as user mobility,
rapid installation, flexibility, and scalability. Because of these primary benefits, WLANs are
still gaining high popularity nowadays, and it becomes a compelling alternative to traditional
wired technology since it makes it easier for users to conduct their daily operations. Therefore,
wireless LAN technology offers a type of authentication services to verify the identity of the
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communicating clients that provides an access control mechanism to the network and deny any
client that cannot complete the authentication stage properly. The main aim of this research is
to study and discuss the main wireless security and IEEE 802.11 standards based on their
performance which includes throughput and delay, confidentially, integrity and availability.

International Journal of Wireless & Mobile Networks (IJWMN) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Wireless & Mobile Networks. The journal focuses on all technical and practical aspects of Wireless & Mobile Networks. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced wireless & mobile networking concepts and establishing new collaborations in these areas.

Wireless communications, nowadays, becomes a vital element of people's daily life. Providing global connectivity in future communication systems via the heterogeneous network opens up many research topics to investigate potentialities, enabling technologies, and challenges from the perspective of the integrated wireless systems. This paper aims to drive a comprehensive and comparative study on terrestrial-aerial platforms-satellite wireless communications systems, includes their characteristics and unravelling challenges. The comparison focuses on issues that reportedly can evaluate any wireless systems for temporary events. These issues are altitude and coverage, Radio Frequency (RF) propagation, interference, handover, power supply constraints, deployment and maintenance challenges, reliability on special events or disaster relief, cost-effectiveness and environmental impact. Last, Quality of service (QoS) performance is analysed for the four wireless communication systems from the temporary events perspective using the OPNET Modeller simulation tool. Results infer that space-based wireless systems outperform terrestrial ones.

In recent years, AdHoc networks have been attracting much interest in both academic and industrial communities. International Journal on AdHoc Networking Systems is an open access peer-reviewed journal that serves as a forum to discuss on ongoing research and new contributions. The journal addresses both practical and theoretical research in the areas of ad hoc networks, sensor networks, mesh networks and vehicular networks. Its main focus is on all issues from link layer up to the application layer. The journal solicits original technical papers that were not previously published and are not currently under review for publication elsewhere.

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications .The journal focuses on all technical and practical aspects of Computer Networks & data Communications. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced networking concepts and establishing new collaborations in these areas.

In an enterprise network, it is normal to use multiple dynamic routing protocols for forwarding packets. Therefore, the route redistribution is an important issue in an enterprise network that has been configured by multiple different routing protocols in its routers. In this study, we analyse the performance of the combination of three routing protocols in each scenario and make a comparison among our scenarios. We have used the OPNET 17.5 simulator to create the three scenarios in this paper by selecting three different routing protocols from the distance vector and link state routing protocols in each scenario. In the first scenario, the network routers are configured from EIGRP, IGRP, and IS-IS that is named EIGRP_IGRP_ISIS in our simulation. The OSPF_IGRP_ISIS scenario is a mixed from EIGRP, IGRP, and IS-IS protocols that is the second scenario. The third scenario is OSPF_IGRP_EIGRP that is the route redistribution among OSPF, IGRP, and IS-IS protocols. The simulation results showed that the performance of the EIGRP_IGRP_ISIS scenario is better than the other scenarios in terms of network convergence time, throughput, video packet delay variation, and FTP download response time. In contrast, the OSPF_IGRP_ISIS has less voice packet delay variation, video conferencing and voice packet end to end delays, and queuing delay as compared with the two other scenarios. On the other hand, the performance of the OSPF_IGRP_EIGRP scenario has better FTP upload response time, and voice jitter.

The paper presents a Riverbed simulator implementation with both routing and medium access control (MAC) protocols for mobile ad-hoc network wireless networks with multi-beam smart antennas (MBSAs). As one of the latest promising antenna techniques, MBSAs can achieve concurrent transmissions / receptions in multiple directions/beams. Thus it can significantly improve the network throughput. However, so far there is still no accurate network simulator that can measure the MBSA-based routing/MAC protocol performance. In this paper, we describe the simulation models with the implementation of MBSA antenna model in physical layer, MAC layer, and routing layer protocols, all in Riverbed Modeler. We will compare two routing scenarios, i.e., multi-hop diamond routing scenario and multi-path pipe routing. We will analyze the network performance for those two scenarios and illustrate the advantages of using MBSAs in wireless networks. INDEX TERMS Multi-beam Smart Antennas (MBSAs), Medium Access Control (MAC), Multi-path routing, Riverbed Modeler.

The International Journal of Network Security & Its Applications (IJNSA) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of the computer Network Security & its applications. The journal focuses on all technical and practical aspects of security and its applications for wired and wireless networks. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on understanding Modern security threats and countermeasures, and establishing new collaborations in these areas.

Wireless technology provides us many benefits like portability and flexibility, increased productivity, and lower installation costs. Wi-Fi networks can be accessed with laptops, mobile phones, cameras, game consoles, and an increasing number of other consumer electronic devices. Wireless technologies have become increasingly popular everyday in business as well as in personal lives. Wireless Networking changed completely the way people communicate and share information by eliminating the boundaries of distance and location

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications. The journal focuses on all technical and practical aspects of Computer Networks & data Communications. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced networking concepts and establishing new collaborations in these areas.

In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight approximate moment generating function (MGF) of end-to-end signalto-noise ratio of 2-hop multi-relay system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-andforward (CAF) relay system. This is accomplished by employing a very tight approximate moment applicable to myriad of fading environments including mixed and composite fading channels. Three distinct adaptive source transmission policies were considered in our analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading environments (especially for the analysis of the mixed fading case)and provides significant advantage to model wireless system for mixed and composite fading channel. In addition to simplifying computation complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.

Wireless communication is the most effective communication to convey audio or video information among the population. It enables the masses to connect throughout the world. Wireless technologies improve the lifestyle of individuals in rural and poor communication areas. In this view, the quality of a reliable signal can be enhanced by minimizing carrier interference. In this paper bit error rate of an image, signal is transmitted over fading channel is analyzed using orthogonal frequency multiplexing and channel estimation technique. An Orthogonal Frequency Multiplexing (OFDM) provides prominent bandwidth effectiveness and improved immunity to the fading environments. In OFDM, the data is modulated using multiple numbers of subcarriers that are orthogonal to each other. A cyclic prefix is infixed between OFDM symbols to annihilate the inter symbol interference (ISI) and inter-carrier interference (ICI). The least square channel estimation method is used to minimize the effect of multipath fading. An image, signal is modulated using BPSK, QPSK, 16QAM and 64QAM digital modulation schemes with OFDM and channel estimation and transmitted over AWGN and fading channel. The objective of this work is to improve the signal to noise ratio by reducing interference. The bit error rate vs. signal to noise ratio for BPSK, QPSK, 16QAM and 64QAM without channel estimation at 5dB is 0.4948, 0.4987, 0.4965 and 0.4983 and with channel estimation is 0.099, 0.2600, 0.3900 and 0.4300 respectively. The bit error rate obtained with BPSK, QPSK, 16QAM and 64QAM without channel estimation at SNR of 10dB is 0.4964, 0.4985, 0.4957 and 0.4982 and with channel estimation is 0.033, 0.19, 0.34 and 0.38 respectively. The bit error rate obtained with BPSK, QPSK, 16QAM and 64QAM without channel estimation at SNR of 15dB is 0.4938, 0.4985, 0.4953 and 0.4979 and with channel estimation is 0.0072, 0.1900, 0.3241 and 0.3762 respectively. The error rate is minimized with channel estimation. The error rate increases with the order of modulation and it is noticed that the error rate is minimum with the BPSK modulator and is maximum with 64QAM.