How can I use cryptography in telecommunications

SEMINAR WORK. Cryptography. Encryption and technology of mobile telecommunication systems using the example of terrestrial trunked radio


1 Abitur class 2012/14 SEMINAR WORK Cryptography, encryption and technology of mobile telecommunication systems using the example of Terrestrial Trunked Radio

2 Contents 1 Cellular networks, development and overview Terrestrial Trunked Radio (TETRA) Definition of the standard Classification and classification Significance and application Development of TETRA in Germany TETRA worldwide Technology trunked radio system, transmission Network architecture Digitization Operating functions and services Network operation (Trunked Mode Operation, TMO) Direct operation (Direct Mode Operation, DMO) Data services Communication security General Subscriber addressing Authentication Key formation and management TETRA in Germany Background to the introduction of digital radio for authorities and organizations with security tasks Disadvantages, criticism and resistance ... 14

3 3 Conclusion Appendix A: Sources and figures, abbreviations, CD-ROM ... A A.1 Bibliography ... A A.2 Internet sources ... A A.3 List of figures ... C A.4 List of tables ... C A.5 List of Abbreviations ... C A.6 CD-ROM ... E

4 1 Cellular networks, development and overview 1 1 Cellular networks, development and overview As Horace around the year 23 BC When he wrote his hymn of praise 1 on the Roman messenger of the gods Mercurius (Greek: Hermes), he probably did not expect that his work as a messenger between gods and humans would long ago be overtaken by modern telecommunications systems, because today the ancient gods would probably be rather pick up the convenient mobile phone. Telegraphy was used as the first telecommunications system since 1793 [12], then landline telephony since 1860 [13] and, since 1896, radiotelephony in the form of Morse, operating the first public cellular network with which one could communicate over long distances without being tied to a location. nte. The network operated by the Bundespost under the name of "publicly mobile land radio service (öbl)" formed the counterpart sign [14]. It was not until 1958 that the so-called A-Netz began in Germany for the "Non-public mobile land radio (NömL)", which was primarily intended for authorities or transport companies and was a national system that was transmitted in analog form and was based on a largely nationwide system [4] . The A network, like the successors B and C networks, belonged to the first generation of mobile radio systems. Since it was technically out of date and also overloaded, it was switched off in 1977 [8]. The main advantage of the B-network, which has been in operation since 1972, was the automated ated connection establishment. It was also possible to make calls to compatible networks, for example in Austria, the Netherlands or Great Britain. On the other hand, the B network also had disadvantages, for example it was not possible to continue the call when the radio cell 2 was changed (so-called handover). Furthermore, the area in which the called subscriber was located had to be known [4]. Most of these problems were resolved with the next, also analog, first-generation standard, the so-called C-Netz, which was operated by DeTeMobil from 1985 to 2000 under the name "C-Tel" [8]. It was now possible "to save the whereabouts of a mobile subscriber in the network and with each radio communication. Figure 1 Temporal overview of the development of public mobile radio in Germany 1 Q. Horatii Flacci: carmina, carmen 1,10: Hymn to Mercurius, liber primus 2 Geographical area in which radio communication takes place [4, p. 382]

5 1 Mobile networks, development and overview 2 to update cell change "[4, p. 434]. The handover function was also invented and made it possible to change the radio cell during a call - The difference between mobile phones and radio masts was the use of a chip card, a kind of forerunner of today's SIM card [2], [1] In addition, in contrast to the A and B networks, C-Tel with the so-called concealment function 3 was the first Almost secure transmission of private calls enables [8] Due to a technical overhaul, C-Tel was taken off the network in 2000. In other countries there are systems such as Nordic Mobile Telephone (NMT, especially Scandinavia), Advanced Mobile Phone System (AMPS, especially USA) and Japanese representatives of the first generation [4], which, however, will not be discussed in more detail at this point, rather only the development in Deut considered schland. CEPT 4 and later ETSI 5 reached a major milestone in the history of public mobile communications around 1991 with the development of the Global System for Mobile Communications (GSM) [9], [1]. With this first-ever digital mobile communications standard of the so-called second generation, the foundation for most of the successors was primarily a faster transmission not only of voice, but also of text and data packets that were later laid on the systems for the invention of SMS. The digital transmission (Short Message Service) led. Furthermore, it was now possible to use much better encryption techniques [8]. In Germany, representatives of GSM are the GSM900 systems under the names D1 and D2 and the DCS known as E-Netz [1]. With the aim of achieving new inventions such as higher transmission speeds, GSM was later transferred to the 3GPP. GSM is still being developed further, so that faster systems such as GPRS 8 emerged [2] The competitive pressure on the cell phone market led to the fact that 10 cell phones were using massively declining 1 GPRS EDGE UMTS (with LTE prices, again with HSPA + for the economy ) beneficial effects that became affordable for the general public. The analog signal is transmitted strongly distorted, only the authorized recipient receives an intelligible voice signal. 4 Conférence Européenne des Administrations des Postes et des Télécommunications, German: European Conference of Administrations for Post and Telecommunications. Organization for cooperation between regulatory authorities (e.g. Federal Network Agency). 5 European Telecommunications Standards Institute, German: European Institute for Standardization in Telecommunications. 6 In principle, it is the same standard, but GSM900 uses the 900 MHz frequency range, while DCS1800 is located at 1800 MHz. 7 3rd Generation Partnership Project, cooperation project between standardization organizations. Members: ARIB, TTC (Japan), ETSI (Europe), ATIS (USA), TTA (Korea). 8 General Packet Radio System, GSM packet data service kbit / s Figure 2 Transmission speeds of different mobile radio standards. Logarithmic representation. Data from [11]

6 1 Cellular Networks, Development and Overview 3, the Global System for Mobile Communications was the most widely used cellular system with 1.7 billion customers worldwide [43]. GSM is still in use today. EDGE, Enhanced Data for Global Evolution, should be mentioned in particular as the transition from the second to the third generation. This is an extension of GSM, which above all offers higher transmission speeds and a more effective frequency economy, i.e. can use smaller frequency ranges more efficiently, since these are considered to be a scarce resource [15]. Since around 2003, UMTS (Universal Mobile Telecommunications System) represents the third generation of public mobile communications standards in Germany. In addition to improved security features, UMTS offers several extensions such as the so-called HSPA + (High Speed ​​Packet Access Plus) above all significantly higher transmission rates (Fig. 2), which enable mobile Internet, for example. As a result, so-called smartphones with Internet applications have been and are being developed that offer the user a wide variety of services. At the end of 2008, the development of LTE (Long Term Evolution) was completed, a cellular and network standard which is based on the same basic scheme as UMTS and which is now part of the fourth generation. For mobile phones it offers an even higher transmission rate, which is playing a major role, especially because of the increasing importance of the mobile Internet [16]. The LTE-Advanced protocol extension enables higher data transmission rates with bandwidths of up to 1000 megabits per second and is to be implemented in Germany from 2014 [17]. The systems described above are intended for the public. At the same time, due to other requirements of the users, the non-public mobile radio, also known as a private network, which is only accessible to an internal group of participants, such as employees of a company or authorities [1], developed. In mobile communications, a distinction is made between analog and digital transmission methods: While in an analog network "signals are transmitted continuously in terms of time and value" [1, p. or "Power off" and can thus transmit data with almost no distortion, largely independent of analog factors [1]. Cellular networks are also differentiated according to network architecture, of which the cellular structure is found most frequently.9. In addition to these categories, radio networks are further divided according to the transmission medium, e.g. Radio paging systems, satellite systems, cable-connected systems, directional radio or mobile radio [1], although we will not go into more detail at this point on these individual media, but specifically on non-public mobile radio. In the following, the focus will be on the non-public trunked radio system TETRA (Terrestrial Trunked Radio), which in Germany is also known as the "digital radio of the authorities and organizations with security tasks (BOS)". 9 See below for explanations.

7 2 Terrestrial Trunked Radio (TETRA) - Definition 4 2 Terrestrial Trunked Radio (TETRA) In the following, the trunked radio system TETRA (Terrestrial Trunked Radio, German: terrestrial trunked radio) will first be defined and then examined in more detail according to technical and safety-related aspects. The current status of non-public digital trunked radio in Germany will then be discussed as an example. 2.1 Definition Terrestrial Trunked Radio (TETRA) is the most widespread European standard of the second generation for digital trunked radio 10. This standard, also known as digital radio, is used in mobile commercial radio and as secure communication technology for authorities and organizations with security tasks [3 ]. Figure 3 Logo of TETRA [29] The standard The system technology used in Germany was developed according to the TETRA 25 standard in the 1990s by ETSI [19] and is intended for "professional mobile radio users such as the military, authorities, security services, transport companies and energy supply" [5, p. 13] can be used. The aim was to develop a Europe-wide standard that can also interact with PMR systems 11. Above all, TETRA offers improved voice quality and better security features than analog systems, more efficient frequency economy, and has different options for data transmission. In addition to voice, text and image messages can also be sent and received, for example [5], [20] Classification and classification TETRA is a non-public system that is mainly used by authorities and industrial users. Furthermore, it is a digital network that, in contrast to analog radio, offers improved voice quality and the possibility of encryption. The end devices are mostly mobile. In addition, data is transmitted using the trunked radio principle, while the network architecture, similar to that of GSM, corresponds to that of a cellular system 12 [4]. 10 see section 2.3.1: technology, trunked radio system and transmission 11 private mobile radio, "Jedermann-Funk" in the MHz frequency range 12 see section 2.3: technology

8 2 Terrestrial Trunked Radio (TETRA) - Significance and application Significance and application TETRA is currently being introduced in Germany under the name of digital radio for authorities and organizations with security tasks (BOS) 13. Nationwide, users are to be connected to the new, tap-proof network, which would make it the largest of its kind in the world. [5] Development of TETRA in Germany In 1990, the Schengen states committed themselves to setting up a transnational communication system. As a result of several resolutions by the federal state interior ministers' conference, project groups were set up to deal with the development of a digital, nationwide uniform voice and data radio system. A two-year pilot test was carried out in Aachen in mid-2001. The federal and state governments then agreed on a minimum standard and set the goal of introducing the nationwide digital radio system by the end of 2010. In April 2007, the newly founded Federal Agency for Digital Radio for Authorities and Organizations with Security Tasks (BDBOS) began its work. This agency performs tasks such as setting up, managing and monitoring the security of digital radio. The financing of the radio network and the participation of the individual countries were then regulated. In June 2007 the digital radio network was put into operation in six German cities [5] TETRA worldwide 121 countries worldwide used TETRA systems at the end of 2010, for example numerous Asian countries and almost all European countries [21]. Mainly authorities, industry and transport companies use this standard. There are several providers on the market because TETRA is an open standard. Figure 4 Use of TETRA TRA worldwide. There are plans to introduce the system in the US and other countries as well. Data from [21] 13 E.g. police, fire brigade, ambulance service

9 2 Terrestrial Trunked Radio (TETRA) - Technology Technology Although TETRA took over some elements of the GSM, an enormous technological leap was made. With the replacement of analog by digital radio, several new developments of recent years have been integrated at the same time, such as new transmission methods, improved device technology and the digitization of voice and data trunked radio system, transmission The analog radio used by many companies so far has many disadvantages: The Radio channels are overloaded, reception interference results in poor voice quality [4] and messages can also be heard without significant effort. The old, analog system is increasingly being heard by digital systems. Therefore replaced. Second-generation digital trunked radio systems, including TETRA, are ideal for this. The best-known representative of the analog first generation is "Chekker", a system used in commercial radio [1]. The "idea of ​​trunked radio [...] is that different user groups are grouped together on common frequencies and that these are better exploited through the bundling effect" [4, p. 455]. The result of this effect is an increased frequency economy, the available radio frequencies are better used because they are considered a scarce resource. In contrast to analog radio, radio channels are used evenly and are not overloaded, and there is no loss of quality when broadcasting on channels that are close to one another [5]. TETRA is based on a multiplex process, "a process that" [assigns] several signals to a transmission channel for simultaneous transmission "[5, p. 26]. Many independent signals are binary-coded within a time window, transmitted sters (a so-called time slot) and then again in channels on additional channels by the receivers [22]. The multiplex method results (in network operation 14) the channel bandwidth is probably the same: Several logical channels are assigned to a physical channel [1]. This means that several participants can send data at the same time on each TETRA frequency. "The assignment of the data to the participants and the synchronization of the time slots is done by the central network control" [5, p. 28]. Similar to analog radio, TETRA uses frequencies in the lower band ("Uplink", MHz) and upper band ("Downlink", MHz). The mobile device transmits in the sub-band to the base station. In the upper band, the message to the other call participants is broadcast more intensely (see also Fig. 5). Figure 5 Network architecture of the analog BOS 14 see: Network operation (Trunked Mode Operation, TMO) Network architecture of the analog BOS radio. A radio subscriber, e.g. a vehicle, sends a voice message in the sub-band to the nearest relay station. This amplifies the analog signal and broadcasts it in the upper band to all subscribers in the radio communication circuit who have set the same channel.

10 2 Terrestrial Trunked Radio (TETRA) - Technology Network architecture In analog radio, there is a locally limited infrastructure that is made up of several interconnected relay points (Fig. 5). Each organization uses its own infrastructure with a specially assigned radio channel (e.g. channels for the police, fire brigade, rescue service, etc.) [5].TETRA, on the other hand, has network components similar to the GSM system [4], for example, the cellular structure is used here (Fig. 6), in that each of the cells is supplied by a base station and the respective neighboring cells use different frequencies to communicate with each other To prevent interference. This makes it possible to use the same frequencies several times if they have a sufficient distance [5]. If a call participant leaves a Figure 6 cell structure in the TETRA system. With hexagonal cells, so-called clusters (cell bundles) are formed from seven neighboring cells. Cells labeled with the same number use identical frequencies. The coverage area of ​​a cell (R) is determined by geographical and technical conditions [5]. Cell, the connection still remains (handover: an existing connection is automatically tracked when the radio zone changes [2]). However, there are some differences to the GSM network architecture. TETRA has the subsystems Mobile Station (MS), TETRA Base Station (TBS) and switching centers (DXT: Digital Exchange for TETRA), which are connected to one another via several interfaces [5]. The subscriber's equipment (e.g. radio) with the associated interface with which the user accesses the services (e.g. data transmission) is referred to as the mobile station [3]. The TETRA base station has the task of "transferring radio communication into the fixed network infrastructure Figure 7 The TETRA architecture [23]" [5, p. 36], thus contains a transmitting and receiving unit and thus represents an interface to the fixed network infrastructure DXT is a logical database that stores subscriber profiles. The connection broker, often referred to as Switching & Management Infrastructure (SwMI), also regulates the authentication of the participants [3], [5]. The control center (in the figure "dispatcher", German: dispatcher) is responsible for the documentation of the radio traffic, the subscriber administration, short data services (e.g. status reports) and the alerting. The two most important, standardized radio interfaces are the Air Interface (AI), which represents the "basis for communication between mobile stations and the fixed network infrastructure" [4, p. 456], and the AI ​​Direct Mode Operation

11 2 Terrestrial Trunked Radio (TETRA) - Technology 8 (AI DMO), which forms the "radio interface for direct communication between mobile stations" [4, p. 456] Digitization In analog radio, signals are continuously transmitted and are through a certain physical Size marked and measurable. Modern mobile radio systems, on the other hand, transmit signals exclusively digitally. This results in some advantages, for example the transmission is less error-prone, can be stored digitally and offers the possibility of using encryption. An analog-to-digital converter (ADC) is used to convert the acoustic signal of human speech into a digital signal Integrated network operation. However, you reserve the right to e.g. to switch to a direct mode in the event of malfunctions [5] Network operation (Trunked Mode Operation, TMO) In order to be able to work in network operation (English: Trunked Mode Operation, TMO), the radio device must authenticate itself, ie the closest base station is contacted and switched on exchanged the key information with the exchange (DXT). Only then can the device be reached in the entire network. TMO provides several operating functions: Emergency call: All radio devices have an emergency call button, which has either the control center or a previously defined group as its destination. The emergency call is given priority, i.e. other connections are interrupted if necessary. Telephone call: Calls can be made in intercom mode 15. Connections to other radio and telephone networks are also possible. Group call: In the digital radio network, static (stored in the device) or dynamic (via the network management / air interface) groups can be formed. This means that the groups are independent of physical frequencies, i.e. when a group is selected, all devices defined in it are contacted. Individual call: In contrast to a telephone call, the participants take turns talking to each other (intercom) after the network management has approved the connection [5]. 15 The call participants can talk to each other at the same time and do not have to wait until the other person releases the talk button.

12 2 Terrestrial Trunked Radio (TETRA) technology Direct mode operation (DMO) If no connection is available or should not be used, direct mode operation (DMO) can be selected on the radio. The terminals then function without a physical network, i.e. within a radius specified by the transmission power. All devices that are set to the same frequency can be reached (Fig. 8). To increase the range, a repeater can be used, i.e. a terminal device installed in a vehicle is interposed and forwards the signal (Fig. 9). If the TETRA network cannot be reached (e.g. use in an area that is in a radio shadow), a vehicle can be used as Figure 8 Simple DMO conversation between two radios [23] Figure 9 Increasing the range using a repeater system [23] Gateway can be used. This means that the connection between the DMO and the TETRA network is bridged (Fig. 10). Figure 10 Connection to the TETRA network via gateway [23] Data services In analog radio, it is possible to send status messages between the vehicle and the control center using FMS (radio reporting system), for example to make an emergency call or to report ready for use. This gives the control center the opportunity to keep track of the deployment status of the vehicles, and radio traffic is also relieved [24]. TETRA takes on the option of sending status reports [3]. In contrast to analog radio, most of them are not fixed and can be freely defined depending on the organization, e.g. "Free on radio" or "Patient admitted". The transmission of short text data (SDS, Short Data Service) is also new. These are comparable to the SMS known from public mobile communications. However, they can also be "sent to groups, the control center or other IT applications" [5, p. 78]. In addition, larger amounts of data such as mug images or emergency doctor protocols from rescue equipment can be transmitted [7]. Because here large bandwidths

13 2 Terrestrial Trunked Radio (TETRA) - communication security 10 are necessary, the information is divided into data packets according to the TCP / IP protocol 16, as is the case with the Internet, and these are sent one after the other [5]. 2.4 Communication security The main requirement for the BOS digital radio system is secure communication. The aim should be to allow access only to authorized persons / organizations, the system should also be protected against manipulation and interference and the authenticity of the information should be guaranteed [26] General If a mobile device is switched on, authentication takes place in two directions: the network checks, on the basis of device addresses, whether the radio device has authorization, and the radio device checks whether the network is verified. Only then is the connection established and, depending on the security class used, the key is calculated. With TETRA, every device has at least one TSI (TETRA Subscriber Identity) that is permanently stored on the device and cannot be changed. The TSI is divided into ITSI (Individual TSI) and GTSI (Group TSI). The former assigns an individual call number to the device, which can be used for calls, for example. The latter is required for group calls [27]. The TSI consists of three parts (Figure 11): the Mobile Country Code (MCC), the Mobile Network Code (MNC) and the Short Subscriber Identity (SSI). The three-digit MCC is used to identify the country of origin (e.g. 262: Germany [19]), the MNC identification of networks within a country. A distinction is made between four types of SSI: Figure 11 Composition of the Individual TETRA Subscriber Identity (ITSI) [5] ISSI (Individual Short Subscriber Identity): Use in ITSI. It uniquely identifies a radio device within a network. GSSI (Group Short Subscriber Identity): Use in the GTSI. Talkgroups can be identified with it. ASSI (Alias ​​Short Subscriber Identity): Addressing external network participants. TETRA system addresses [27]. 16 Transmission Control Protocol / Internet Protocol, protocol group for the switching and transport of data packets in a network [25]

14 2 Terrestrial Trunked Radio (TETRA) - communication security 11 Figure 12 Composition of the Operativ-Tactical Address (OPTA) [5] Instead of the "radio call names" in analog radio (eg "Stephan 12/1"), other participants in the digital radio network join the Operativ -Tactical address (OPTA) recognized, which is automatically transmitted from the transmitter to the receiver with every radio connection. It comprises a maximum of 24 characters (Fig. 12). The first two digits identify the federal state, the following three the authority or organization, the next three the region and the remaining characters contain additional allocation digits depending on the organization, e.g. Call name, local branch / guard or function assignment. A distinction must be made between the spoken nickname, the OPTA and the representation of the transmitter in the display. For example, if a subscriber is addressed by radio, the sender's OPTA appears on the receiver's display (eg sender: "Stephan 12/1", OPTA as in Tab. 1) [28] BYPOLBASTEPHAN 1 2/0 1 Table 1 Example for a OPTA from "Stephan 12/1", an emergency vehicle of the Bamberg / Bavaria police force. Authentication TETRA supports the mutual authentication of the mobile station (MS) and the network so the TETRA system can prevent unauthorized access and the MS check whether the network is verified is. This can be used to prevent a so-called man-in-the-middle attack, for example. In this attack, a modified radio station is prepared into which the MS logs in, the encryption is canceled and an attacker can overhear or intervene in the radio traffic. Such deceptions are possible with GSM, as there is only one "control", TETRA, on the other hand, prevents this by checking each other's authorization. The connection is only established after authentication. DMO does not use authentication, since in this case the MS do not make any connections to the network [26] Key generation and management After the connection between the MS and the network has been established, the TETRA Authentication Algorithm 1 (TAA 1) is used to generate the key for the radio interface encryption ( English: Air Interface (AI) Encryption). There are three security classes used: Class 1: No AI encryption Class 2: Static key (SCK, Static Cipher Key)

15 2 Terrestrial Trunked Radio (TETRA) - communication security 12 Class 3: Dynamic key (DCK, Derived Cipher Key) [26], [6]. Figure 13 Encryption at the radio interfaces [5] Security class 3 is generally used in German BOS radio. Class 1 and 2 are mainly used by other professional users (security services, transport companies, energy providers, etc.), since the implementation of the technology used in class 3 is complex [30]. Especially in German digital radio, every device has a BOS security card (similar to a SIM card, Fig. 14) to ensure encryption and decryption in the devices. "The data and the necessary algorithms are located as an additional application on the BOS security card" [5, p. 101]. A key management system was developed which, on the basis of certificates, authorizes the end user to request and forward keys. The Federal Office for Information Security (BSI) loads the cryptographic algorithms and registration data into the security cards (initialization). The security cards are then assigned to a radio device (Figure 14 BOS security card [7]) or to a mobile or fixed person (personalization). The user can only dial into the TETRA network with an activated security card. In addition, data such as Group addresses, SDS messages or DMO frequencies can be safely saved. Similar to the GSM network, the BOS security card uses the PIN / PUK function 17. The OPTA is also stored on the card. Stolen or lost devices can be deactivated or blocked using the permanently assigned numbers. According to a decision by the federal and state governments, all data in the digital radio network must be encrypted end-to-end (this corresponds to security level 3). The prerequisite for encryption is the presence of a digital signal. To do this, the analog voice signal is first digitized (see 2.3.3: Digitization). These data are encrypted with key data generated by the security card [5]. Figure 15 Principle of encryption [5] In Schengen countries, authorities use the encryption algorithm 17 PIN: Personal Identification Number, PUK: Personal Unblocking Key. When switching on, the device asks for a PIN, which the user must use to unlock. If the entry is incorrect several times, the PUK is requested.

16 2 Terrestrial Trunked Radio (TETRA) - TETRA in Germany 13 TEA2 (TETRA Encryption Algorithm 2) used [6]. Many security agencies use algorithms for air interface encryption that are tailored to their needs. Several methods are possible for end-to-end encryption: An organization can use its own cryptography model or implement these cryptographic functions individually using the IDEA 18 or AES algorithm 19 in accordance with public standards 20 [26]. The doubly encrypted data packets are then transmitted to the recipient. With the key generator stored on the key card, the operator can decrypt the data packets again and thus transmit the signal again in acoustic or optical plain text. The keys are administered, assigned and regularly changed by the control centers [5]. 2.5 TETRA in Germany "Originally, digital radio should have gone into operation nationwide for the football World Cup in 2006. The costs have now risen to more than 900 million euros," wrote the North Bavarian News on March 15 Germany is currently being built. 4500 base stations are planned, of which were integrated into the network at the beginning of June. The network is already established in most of the federal states, but the structure is not yet fully completed [31] Background of the introduction of digital radio for the authorities and organizations with security tasks The new TETRA network should be available to all authorities and organizations with security tasks (BOS) Figure 16 Progress of network expansion in Germany in August 2013 [31] will be available nationwide. The cooperation of the organizations e.g. in the case of major incidents, this should be simplified. Due to the structure there would be a comprehensive network. The network is also protected against unauthorized access and manipulation, as 18 International Data Encryption Algorithm: An encryption algorithm that has long been considered secure. 19 Advanced Encryption Standard: A patent-free encryption algorithm that offers a high level of security. 20 No information is available about the encryption methods used in Germany.

17 2 Terrestrial Trunked Radio (TETRA) - TETRA in Germany 14 it uses end-to-end encryption in addition to radio interface encryption. The TETRA network enables both individual and group communication, and mission-related groups can be formed. With the trunked radio procedure, frequencies are used more economically without loss of voice quality. Another feature is the introduction of the emergency call button, with which the control center is contacted immediately. Depending on the equipment of the end devices, it is possible, for example, to transmit position data, send pictures or send status reports [31]. The network is independent of network operators and therefore free of charge in network operation [32] Disadvantages, criticism and resistance In Germany, both the population and users make arguments against digital radio. The main argument against TETRA is the risk to health. By using relatively low frequencies, a large number of symptoms and different clinical pictures are postulated, which have meanwhile been examined in several studies, but have not yet been able to demonstrate any concrete results, which may only have been prospective Long-term studies can be specified [34]. Another argument from critics is the financing of the TETRA project.The question is often asked whether an expansion of analog radio would have been more cost-effective, since the exact development of the costs is unclear, so far only rough estimates exist of the financial expenses of the project and of the outstanding costs for nationwide, area-wide use and maintenance and expansion of the existing infrastructure [35]. Various system-related failures are reported; the remaining regional radio shadows caused by the geographical conditions represent a specific problem [36]. Compared to other systems such as LTE or UMTS, the transmission speeds with TETRA are rather low. It can happen that the network is transmitting large amounts of data such as is overloaded by images and thus the normal radio communication is restricted [33]. Reconfiguration of groups, as would be necessary in the event of a disaster, for example, is time-consuming and can lead to delays [37]. There are also doubts about the security of the TETRA system, which was developed in the 1990s. Although end-to-end encryption is also used in Germany, it may be possible in the near future to manipulate the system with powerful computers [30].

18 3 Conclusion 15 3 Conclusion Only they themselves know which radio network the ancient gods would use to communicate, but there is a large repertoire of public and non-public solutions for mobile communications that is constantly evolving. New technologies that are becoming ever faster and more powerful are constantly appearing on the market for public mobile communications. There is already speculation about the successor to LTE and the extension LTE-Advanced, although LTE is still in the process of being networked [38]. The trend is still moving away from the classic personal computer towards smartphones and tablet computers. More and more applications and services that require higher transmission speeds are being developed for mobile devices [39]. However, the greatest weakness of mobile devices is still the power supply: high-resolution displays and fast computing power require a lot of energy. Smartphones have nevertheless found their place in everyday life, because you can be reached anywhere, have access to the World Wide Web at any time, so you can navigate or shop, watch films or play games and take advantage of a multitude of other options. Postcards were sent ten years ago, s or SMS were sent five years ago and these are now increasingly being replaced by social networks such as "Facebook" or "Twitter". With the miniaturized devices, the "computers in your pocket", you have access to all kinds of applications anywhere and anytime. The question of whether authorities and organizations with security tasks (BOS, e.g. police, fire brigade) also use the diverse possibilities of public mobile radio systems should is therefore justified. The special requirements made by professional mobile phone users focus on a high level of security against eavesdropping, which is currently only guaranteed by UMTS and LTE. The TETRA system, on the other hand, offers other important features through the option of an implemented BOS security card. In practice, when the BOS is used, a large number of short messages are sent, which require a quick call setup: The dialing process that is still required when using the public mobile network is reduced to pressing the talk button when using the BOS radio, which immediately activates a Connection is established. Only the TETRA network is able to form dynamic task forces in order to be able to quickly inform all forces involved. A BOS-specific network should, for example, offer the possibility of informing all forces in a radio traffic area about a search at the same time. The control centers play a key role here, as they coordinate operations and groups and manage status reports with the help of radio reporting systems. The control center has a priority function over other radio participants and receives higher-level emergency

19 3 Conclusion 16 calls. Systems such as TETRA offer the possibility of setting up a local task force independent of the network, for example to ensure stable communication even in the event of a disaster in a remote area [40]. TETRA is able to transmit image files and larger data packets, but only with the use of a very high network capacity. For this reason, emergency services often switch to cell phones to avoid loss of time. The TETRA terminals cannot access existing databases and information systems, e.g. the police, access and still have to consult the control center. For this reason, various organizations equip emergency vehicles with special computers that enable a connection to these databases via LTE, for example. As a result, operational processes are optimized in terms of time and personnel, as this relieves the workload on the control centers and the required information is immediately available to the emergency services on site [41]. The TETRA network introduced in Germany offers functions that are elementary for professional users and that are not supported by public networks. Nevertheless, it makes sense not to rely entirely on one system, but to take advantage of other technologies as well. For example, extensive data such as image files can be transmitted over high-performance public networks, while mobile computer systems carry out database queries. The criticism expressed about the TETRA system needs to be taken seriously, processed and openly discussed. Citizens and users should therefore be informed in detail and, in particular, prospective, scientifically proven studies should be promoted in order to reduce any potential health risks to a minimum. Work is already underway on a further development of TETRA, which is linked to LTE. The focus here is on increasing the transmission speed. The time frame required to develop the necessary technologies is still uncertain at the moment, as an agreement must first be reached on a suitable frequency range that can be used throughout Europe as far as possible [42]. With TETRA, a leap in technology has been made that does justice to the development of technology in recent years. But it is also necessary to keep up with the progress of communication systems and to continuously develop existing technologies. BOS users in particular, but also representatives from industry and transport companies, need a modern and reliable communication system that offers them protection for sensitive information and effective protection against attacks. The application-specific functions must be kept at the cutting edge of technology so that the existing infrastructures continue to run smoothly and our security is guaranteed.

20 Appendix A: Sources, Figures, Abbreviations, CD-ROM A Appendix A: Sources and Figures, Abbreviations, CD-ROM A.1 Bibliography [1] V. Jung / H.-J. Warnecke (Hrsg.): Handbuch für die Telekommunikation, 1st edition, Springer 1998 [2] B. Walke: Mobile radio networks and their protocols Volume 1. Basics, GSM, UMTS and other cellular mobile radio networks, 2nd edition, Teubner 2000 [3] B. Walke: Cellular networks and their protocols Volume 2. Trunked radio, cordless telephone systems, W-ATM, HIPERLAN, satellite radio, UPT, 2nd edition, Teubner 2000 [4] F. Bergmann / H.-J. Gerhardt (Hrsg.): Taschenbuch der Telekommunikation, Leipzig 1999 [5] P. Hartl / G. Merzbach: Digitalfunk, 2nd edition, Kohlhammer 2010 [6] ETSI EN: Terrestrial Trunked Radio; Voice plus data; Part 7: Security, V2.1.1, European Telecommunications Standards Institute 2001 A.2 Internet sources [7] Christiansen, Jens (2012): "TETRA (Terrestrial Trunked Radio)", (access:) [8] (oj): "Daten and facts about mobile communications in Germany ". (Access:) [9] Wikipedia (Ed., 2013): "Global System for Mobile Communications". (access:) [10] ETSI (Hrsg., o.j.): "Mobile technologies GSM". (Access:) [11] Wikipedia (ed., 2013): "Universal Mobile Telecommunications System", (access:) [12] (oj): "Mediengeschichte des 19. und early 20 Century: Telegraphy ". (Access:) [13] Wikipedia (Ed., 2013): "Telefonie". (access:) [14] Wikipedia (ed., 2013): "Funkechnik". (access:) [15] 3GPP (Ed., oj): "About 3GPP", (Access:) [16] 3GPP (Ed., oj): "LTE", (Access :) [17] 3GPP (ed., May 2012): "LTE-Advanced", (access:) [18] Wikipedia (ed., 2013): "Long Term Evolution", (Access:) [19] Wikipedia (Ed., 2013): "Terrestrial Trunked Radio" (Access:) [20] The TETRA + Critical Communications Association (Ed., Oj): ( Call:) [21] TETRA Industry Group (2013),