Method for encoded communication between a track-bound vehicle and a track-side device, and devices for applying the method

Abstract

The invention relates to a method for coded communication between a track-bound vehicle (FZ) and a trackside device (SE1 ... SE6), in which several telegrams (T1, T2) are transmitted between the trackside device (SE1 ... SE6) and the track-bound vehicle (FZ). The telegrams (T1, T2) each have a data area for filling with user data and a code area for encoding the user data. At least one of the telegrams (T1, T2) is transmitted unencrypted such that the data area is filled with the unencrypted user data, which is then encoded using the code area. The telegram (T1, T2) containing the unencrypted user data is then transmitted in coded form, and the unencrypted user data is decoded after transmission using the code area.At least one of the telegrams (T1, T2) is transmitted in encrypted and encoded form such that the unencrypted user data is encrypted before the user data area is filled, and the user data area is filled with the encrypted user data, which is additionally encoded using the code area. Furthermore, the telegram (T1, T2) containing the encrypted user data is transmitted in encoded form. After transmission of the telegram (T1, T2), the encrypted user data is decoded using the code area, and then the encrypted user data is decrypted. The invention further comprises a track-bound vehicle (FZ), a trackside device (SE1 ... SE6), a computer program product, and a delivery device for the computer program product.

Description

[0001] The invention relates to a method for computer-aided coded communication between a track-bound vehicle and a trackside facility, in which several telegrams are transmitted between the trackside facility and the track-bound vehicle, wherein the telegrams each have a user data area for filling with user data, and a code area for encoding the user data.

[0002] Furthermore, the invention relates to a track-bound vehicle with a communication interface for a trackside device. The invention also relates to a trackside device with a communication interface for a track-bound vehicle.

[0003] Finally, the invention relates to a computer program product and a provisioning device for this computer program product, wherein the computer program product is equipped with program instructions for carrying out this method.

[0004] Trackside equipment includes balises, particularly those conforming to the ERTMS standard (Eurobalises). Each balise transmits a data set called a telegram. Depending on the balise, these telegrams have either 1023 bits or 341 bits. Of these, 830 or 210 bits, respectively, can be used as a data block for signaling applications. This data block is divided into 10-bit symbols, each represented by 11 bits after shaping and scrambling transformations (resulting in a block of 913 = 83 * 11 bits or 231 = 21 * 11 bits). The structure of a telegram using a Eurobalise as an example shows the encoded data bits (length depends on the balise): 913 bits (data: 830 bits with a total length of 1023 bits) or 231 bits (data: 210 bits with a total length of 341 bits). Control bits CB 3-bit Scramblingbits Sb 12-bit Additional shaping bits Esb 10-bit Checksum CheckBit 85-bit

[0005] When the balise is passed over, the telegrams are repeated cyclically. To protect against transmission errors, the payload is scrambled, the payload is substituted with codewords of varying Hamming distances, and a checksum is calculated. Since the checksum is only calculated after the payload has been substituted, the additional shaping bits are used to pad the checksum bits so that the entire telegram consists only of symbols of the chosen channel coding, with each transmitted symbol comprising 11 bits.

[0006] The payload consists of a header, followed by several message fields (packets) standardized in the ERTMS protocol, and finally the end-of-information packet (Packet 255). If the payload exceeds 830 bits, additional message fields can be transmitted via telegrams from subsequent balises within the same balise group. With up to eight balises per balise group, an ERTMS message can therefore contain up to 8 * 830 = 6640 payload bits (where each telegram must contain a header and the end-of-information packet 255).

[0007] Encryption of the transmitted data according to the ERTMS standard, and also during the transmission of telegrams by other trackside equipment, is not planned. This was deliberately omitted in the past in the interest of the fastest possible transmission, as rail vehicles pass over the balises at relatively high speeds, leaving little time for telegram transmission. On the other hand, there is an interest in making the communication between trackside equipment and the trackside vehicle as secure as possible.

[0008] The document GUO HUAQUN ET AL: "Protecting Train Balise Telegram Data Integrity 11, 2018 21ST INTERNATIONAL CONFERENCE ON INTELLIGENT TRANSPORTATION SYSTEMS (ITSC), IEEE, November 4, 2018 (2018-11-04), pages 806-811, XP033470223, DOI: 10.1109 / ITSC.2018.8569616 ISBN: 978-1-7281-0321-1 [accessed on 2018-12-07] describes ETCS (European Train Control System) as an automatic control system that manages the speed limit of a train. The balise on the ground is a passive device that is activated by a passing train and then communicates with the BTM (balise transmission module) attached to the train via telegrams. This paper describes attacks such as For example, the changing of the location information of the balise. This paper therefore proposes three security designs for verifying the data integrity of telegrams.

[0009] The object of the invention is to provide a method for coded communication between track-bound vehicles and trackside equipment, which can be standardized and meets a high security standard during transmission. Furthermore, the invention provides a track-bound vehicle and a trackside device suitable for using this method. Finally, the invention provides a computer program and a delivery device for this computer program with which the aforementioned method can be carried out.

[0010] This problem is solved according to the invention with the subject matter of the claim (method) specified at the outset in that at least one of the telegrams is transmitted unencrypted in such a way that the payload area is filled with the unencrypted payload data, which is then encoded using the code area, the telegram with the unencrypted payload data is transmitted in encoded form, and the unencrypted payload data is decoded after transmission using the code area. and that at least one of the telegrams is encrypted and transmitted in such a way that the unencrypted user data is encrypted before the user data area is filled, the user data area is filled with the encrypted user data, which is additionally encoded using the code area, the telegram with the encrypted user data is transmitted in code, the encrypted user data is decoded using the code area after the telegram has been transmitted, and then the encrypted user data is decrypted.

[0011] According to the invention, user data (for example, before standardized encoding) can be easily encrypted, for example with a block cipher (and padded bits to achieve the required format) or a stream cipher. For this to work, the sender and receiver (i.e., the trackside equipment and the track-bound vehicle) must have a common key.

[0012] The coded transmission standard itself does not need to be altered for the purpose of transmitting the encrypted information. From a technical point of view, the invention therefore only transmits different data than in the known method, namely the encrypted data, which may well have the same content. This means that an encrypted telegram, after decryption, can have identical content to a comparable unencrypted telegram. The content of a telegram is contained in the payload (more on this below).

[0013] Because the transmission of the telegram remains technically untouched, the intervention in the transmission standard, whose transmission is to be made more secure according to the invention, is kept to a minimum. This advantageously simplifies the approval process for an existing standard, which is often associated with considerable effort. Furthermore, no hardware-related modifications are required on the trackside vehicle or the trackside equipment. Encryption can be achieved by modifying the operating software, which involves significantly lower investment costs. The invention's mixed transmission of encrypted and unencrypted telegrams also advantageously allows for a phased introduction of the improved transmission method.A phased introduction means that a relevant section of track, which is equipped with trackside facilities capable of already using the method according to the invention, can also be used by track-bound vehicles that cannot decrypt encrypted telegrams. This is because unencrypted telegrams can be transmitted to such vehicles by the trackside facilities.

[0014] The modification according to the invention can be implemented, for example, for communication between Eurobalises and rail vehicles. However, the modification is not limited to this application. Wherever coded transmission between trackside equipment and track-bound vehicles is provided, it can be further enhanced by encrypting the information to be transmitted before encoding, in order to increase the security standard. In particular, this modification can be advantageous not only for rail vehicles, but also, for example, for vehicles (automobiles) that are bound to a specific route, such as a road, by means of autonomous operation.

[0015] The decoding step itself may not conform to the standard, as it is necessary to verify that all received telegrams are identical. In this case, the standard might need to be modified. However, at least the transmission itself can be carried out without modifying the standard, taking advantage of the inventive benefit. This would allow the standard to be extended, ensuring backward compatibility for unencrypted transmissions. Alternatively, decryption could be performed independently of the standard after decoding.

[0016] In principle, the direction of transmission is irrelevant to the process. Transmission occurs from a sender to a receiver. When transmitting a telegram between the trackside vehicle and the trackside equipment, the trackside vehicle can be the receiver and the trackside equipment the sender, or vice versa. Transmission can occur in only one direction (and optionally in the other direction at a later time), or it can occur simultaneously in both directions.

[0017] For the purposes of this invention, encoding is understood to mean a modification of the payload data within the payload area using the code area, which contains the necessary information for the encoding. Such encoding can, for example, be defined in a standard for transmitting the telegram and is therefore known per se. Consequently, such encoding cannot serve to restrict unauthorized access to the telegram, since the encoding can be traced.

[0018] In contrast, encryption within the meaning of the invention is understood to mean a modification of the user data using keys, whereby the encryption ensures protection against unauthorized access to the telegrams. The key must be available to both the sender and the receiver to guarantee encryption of the telegram and subsequent decryption. Known encryption methods can be used for this purpose.

[0019] In the context of the invention, "computer-aided" or "computer-implemented" can be understood as an implementation of the method in which at least one computer or processor performs at least one process step of the method.

[0020] The term "computer" covers all electronic devices with data processing capabilities. Computers can include, for example, personal computers, servers, handheld computers, mobile phones, and other communication devices that process data using a computer system, as well as processors and other electronic devices for data processing, which may preferably also be connected to a network.

[0021] In the context of the invention, a "processor" can be understood to mean, for example, a converter, a sensor for generating measurement signals, or an electronic circuit. In particular, a processor can be a central processing unit (CPU), a microprocessor, a microcontroller, or a digital signal processor, possibly in combination with a memory unit for storing program instructions, etc. A virtualized processor or a soft CPU can also be understood as a processor.

[0022] In the context of the invention, a "storage unit" can be understood to mean, for example, a computer-readable memory in the form of a working memory (Random-Access Memory, RAM) or data storage device (hard drive or data carrier).

[0023] "Interfaces" can be implemented in hardware, for example via wired or wireless connections, and / or in software, for example as interaction between individual program modules or program parts of one or more computer programs.

[0024] The term "cloud" refers to an environment for "cloud computing" (also known as a computer cloud or data cloud). It describes an IT infrastructure that is made available via network interfaces such as the internet. This typically includes storage space, computing power, or software as a service, without requiring installation on the local computer using the cloud. The services offered within the framework of cloud computing encompass the entire spectrum of information technology and include, among other things, infrastructure, platforms, and software.

[0025] The term "program modules" refers to individual functional units that enable a program sequence of process steps according to the invention. These functional units can be implemented in a single computer program or in several communicating computer programs. The interfaces implemented here can be implemented in software within a single processor or in hardware if multiple processors are used.

[0026] According to the invention, it is provided that at least one of the telegrams transmitted with unencrypted user data is also transmitted as a telegram with encrypted user data of the same content.

[0027] It should be noted that the unencrypted user data naturally differs from the encrypted user data. However, this does not change the fact that the unencrypted user data can have the same content as the encrypted user data. Thus, "content" within the meaning of the invention refers to the information content of the user data that becomes accessible after decryption of the encrypted user data and then has the same content as the unencrypted user data transmitted in the corresponding telegram.

[0028] By transmitting a telegram with the same content in both encrypted and unencrypted form, it is possible for the telegram's content to be evaluated by both track-bound vehicles capable of decrypting the encrypted telegram (hereinafter referred to as equipped vehicles) and track-bound vehicles that do not (yet) possess the key (hereinafter referred to as unequipped vehicles). While the latter cannot use the encrypted telegram to verify whether the unencrypted telegram has been tampered with, the vehicle's operation can be ensured using the unencrypted telegram.

[0029] By sending telegrams with the same content, both encrypted and unencrypted, equipped vehicles can compare the contents of the identical telegrams after decoding and, if necessary, derive further steps from the comparison. For example, manipulations or errors in the unencrypted telegrams can be detected. It is also possible (though less likely) that the content of the encrypted telegram contains an error.

[0030] If tampering or an error is detected, a safety measure can be derived from this finding. This measure can also advantageously apply to unequipped vehicles that, for example, communicated with the affected trackside equipment within a specific time interval before the tampering was detected. Thus, decoding the coded telegrams makes train operations safer overall, including the operation of unequipped vehicles, even if telegrams with altered content concerning these unequipped trains can only be detected with a time delay. The safety measures can apply to individual trackside vehicles, trackside equipment, specific track sections, or even the entire operation, depending on the severity of the detected error(s) (in the form of deviations in the content of telegrams).

[0031] According to one embodiment of the invention, it is provided that First, the unencrypted user data is decoded after transmission using the code area, then the encrypted user data is decoded after transmission of the telegram using the code area, then the encrypted user data is decrypted.

[0032] This embodiment of the invention aims to improve the performance of decoding user data. The unencrypted user data is decoded first (before the encrypted version of the same content), since the decryption step can be omitted for the unencrypted data, thus providing earlier access to the content. This effect is particularly pronounced when the telegrams are received by a vehicle or trackside equipment that cannot yet decrypt the encrypted user data. Otherwise, these devices would have to resort to the unencrypted user data in a further step, which would result in an additional delay.

[0033] According to one embodiment of the invention, it is provided that First, at least one telegram containing unencrypted user data is transmitted, followed by the telegram containing the encrypted user data of the same content.

[0034] This allows for a significant performance gain when evaluating the transmitted user data at the recipient's end. This performance gain is achieved because the decoding of the unencrypted user data in the transmitted telegram can begin while the telegram containing the encrypted user data of the same content is still being transmitted. This would not be possible if the process were reversed.

[0035] According to one embodiment of the invention, it is provided that telegrams with encrypted and unencrypted user data are transmitted in alternating sequence.

[0036] This solves the problem that existing routes and track-bound vehicles already in operation (at least before an update) use a communication standard that does not yet allow for the decryption of the user data. By transmitting both encrypted and unencrypted user data in alternating sequences, both equipped and unequipped vehicles can extract the information required for operation from the user data of several different telegrams. The invention takes into account that only a limited time is available for data transmission between the trackside equipment and the track-bound vehicle as the latter passes by.

[0037] To minimize the probability of missing telegrams during transmission, the system can, for example, send a first telegram encrypted and then unencrypted, followed by a second encrypted and unencrypted telegram, then a third encrypted and unencrypted, and so on. Once all telegrams have been transmitted in both encrypted and unencrypted versions, the process can begin again with the first telegram, and so forth. If, for instance, the trackside vehicle passes the trackside equipment while the third telegram is being transmitted, the first and second telegrams can be received in the second transmission cycle.

[0038] The alternating order does not necessarily mean that unencrypted telegrams (U) and encrypted telegrams (V) must be sent alternately, i.e.: U, V, U, V...

[0039] Depending on whether you want to prioritize security or availability, you can also send other combinations, i.e., either more N (higher availability) or more V telegrams (higher security), e.g.: U, V, V, U, V, V... U, U, V, U, U, V... U, U, U, V, U, U, U, V...

[0040] In the latter examples, the changing order results in a repetition of sequences (namely U, V and U, V, V and U, U, U, V – other sequences are conceivable). However, the sequence to be repeated can also be changed during transmission as needed. Another possibility is to define the changing order without a repetition rule.

[0041] Typically, several telegrams are transmitted during a balise crossing. To achieve compatibility, the balise's transmission stream simply contains unencrypted telegrams (U) and encrypted telegrams (V) in alternating order, i.e., mixed and sequentially, e.g., alternately. Particularly with Eurobalises, which can transmit both long and short telegrams, sequences of three short telegrams can be selected to correspond to the transmission of a single long telegram. The effect described above, namely that as much data as possible is transmitted even with short transmission times (e.g., at high speeds of the track-bound vessel), can therefore be implemented particularly effectively with Eurobalises.

[0042] According to one embodiment of the invention, it is provided that in a sequence of telegrams, a proportionally higher number of telegrams with unencrypted user data than telegrams with encrypted user data are transmitted, wherein The payload areas of the unencrypted telegrams of the sequence are filled with different content, and at least one of the telegrams of the sequence transmitted with unencrypted payload is also transmitted as a telegram with encrypted payload of the same content.

[0043] These embodiments of the invention have the advantage that, with a limited available transmission time, for example when a track-bound vehicle passes over a balise as a trackside installation, a larger amount of data can be transmitted. This is because the transmission of unencrypted data can be faster than the transmission of unencrypted data. This is primarily due to the fact that the data must be encrypted before being sent, but also because encryption increases the amount of data and thus the required transmission time.

[0044] When dealing with the ratio of exclusively unencrypted telegrams on the one hand, and encrypted and unencrypted telegrams on the other, a technical compromise must be found that considers both the amount of data to be transmitted in relation to the available transmission time (data rate) and provides a sufficient means of detecting data manipulation or errors by comparing an encrypted telegram with an unencrypted telegram of the same content. The more telegrams are also sent encrypted, the more secure the transmission method becomes. The more telegrams are sent only unencrypted, the higher the achievable data rate.

[0045] According to one embodiment of the invention, it is provided that the user data of an encrypted telegram is compared with the user data of an unencrypted telegram of the same content after decoding.

[0046] As described above, the comparison serves to detect errors or manipulations of the user data in the telegrams. This ensures that the transmission process is sufficiently secure, even if some telegrams are sent unencrypted. Content discrepancies in unencrypted telegrams will be noticed promptly, allowing countermeasures to be taken and minimizing any impact on operational security.

[0047] According to one embodiment of the invention, it is provided that if the comparison reveals that the payload of the encrypted telegram differs from the payload of the unencrypted telegram of the same content, an error signal is generated and / or output.

[0048] The error signal thus serves as the basis for initiating further steps. These steps can consist of interpreting or evaluating the deviations of the telegram in question from its expected content. These steps can also include security-relevant reactions, as described in more detail above. The error signal is therefore the basis for the information technology processing that must follow the registration of an error or manipulation.

[0049] According to one embodiment of the invention, it is provided that several telegrams with different sized data areas are transmitted.

[0050] This makes it advantageously possible to select the size of the user data areas according to the amount of information to be transmitted. This is particularly beneficial in the case of encryption, as encrypting smaller amounts of data requires less time and computational effort, thus allowing transmission and decryption, and therefore the use of the data, to occur within a shorter time interval. This is especially relevant when data is to be transmitted via a beacon to a track-bound vehicle, as only a short time interval is available during the vehicle's passage over the beacon.

[0051] According to one embodiment of the invention, it is provided that the steps that The payload area is filled with the encrypted payload, which is additionally encoded using the code area; the telegram with the encrypted payload is transmitted in encoded form; the encrypted payload is decoded after transmission of the telegram using the code area; or the payload area is filled with the unencrypted payload, which is encoded using the code area; the telegram with the unencrypted payload is transmitted in encoded form; the unencrypted payload is decoded after transmission using the code area. carried out according to the ERTMS standard (European Rail Traffic Management System) applicable to the ETCS (European Train Control System) or the CBTC standard (Communication-Based Train Control) or the PTC standard (Positive Train Control).

[0052] All these standards stipulate data transmission between trackside facilities and trackside vehicles in coded form. Therefore, these standards benefit, as described above, from the additional encryption of a portion of the transmitted data, which can increase operational security.

[0053] According to one embodiment of the invention, the transmission takes place between a balise as a trackside device and the track-bound vehicle.

[0054] The advantages of applying the method according to the invention to balises have already been explained above.

[0055] According to one embodiment of the invention, it is provided that it is checked whether the balise belongs to a balise network, whereby the received data is then classified as reliable.

[0056] For the purposes of this invention, unlinked balises are understood to be balises that are not linked to other balises during transmission: These therefore offer a greater potential for unauthorized attacks. For example, hackers could delete a danger point or increase the permissible speed for a train.

[0057] Linked balises, unlike unlinked balises, are functionally connected to other balises within a balise group. This also means that an unauthorized attack can be detected even without the encrypted transmission of telegrams of the same content if the information sent by the balises does not fit the context of the balise group, i.e., does not fit the context that would be expected when the balises in question are traversed. Because the functionality of the balise group is known, it is possible (through a plausibility check) to deduce what information can be expected from a specific balise within the group and when this information is transmitted (depending on the balise's position within the group).

[0058] This makes it possible to equip preferably unlinked balises with encryption according to the invention. These are often retrofitted balises that are not integrated into a balise network. At the same time, the retrofit creates the opportunity to equip them from the outset with an encryption method according to the invention for the transmitted telegrams. The encrypted transmission then provides protection from which an unlinked balise particularly benefits. Outside of the balise network, such a balise would represent a vulnerability to unauthorized attacks due to the aforementioned factors.

[0059] The aforementioned problem is alternatively solved according to the invention with the subject matter of the claim (vehicle) specified at the outset by the fact that it is equipped to participate in a method for coded communication according to one of the preceding claims.

[0060] The aforementioned problem is also alternatively solved according to the invention with the subject matter of the claim (device) specified at the outset by the fact that it is equipped to participate in a method for coded communication according to one of claims 1 - 10.

[0061] The devices (i.e., vehicle and equipment) offer the advantages already explained in connection with the method described in more detail above. The statements made regarding the method according to the invention also apply accordingly to the devices according to the invention.

[0062] Furthermore, a computer program product with program commands for carrying out the said inventive method and / or its embodiments is claimed, wherein the inventive method and / or its embodiments can be carried out by means of the computer program product.

[0063] Furthermore, a provisioning device for storing and / or providing the computer program product is required. The provisioning device is, for example, a storage unit that stores and / or provides the computer program product. Alternatively and / or additionally, the provisioning device is, for example, a network service, a computer system, a server system, in particular a distributed, for example cloud-based, computer system and / or virtual computer system, which preferably stores and / or provides the computer program product in the form of a data stream.

[0064] The provision of the computer program product takes the form of a program data block as a file, in particular as a download file, or as a data stream, in particular as a download data stream. This provision can also, for example, take the form of a partial download consisting of several parts. Such a computer program product is, for example, read into a system using the provisioning device, so that the method according to the invention is executed on a computer.

[0065] Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same reference numerals and are only explained more than once to the extent that differences arise between the individual figures.

[0066] They show: Figure 1A schematic embodiment of the devices according to the invention (trackside equipment, track-bound vehicle) with their interactions, Figure 2 an embodiment of a computer infrastructure of the devices (trackside equipment, track-bound vehicle) according to Figure 1 as a block diagram, wherein the individual functional units contain program modules that can each run in one or more processors and the interfaces can accordingly be implemented in software or hardware, Figures 3 and 4 Examples of the transmission of encrypted and unencrypted short and long telegrams, depending on a time sequence t, Figure 5 An embodiment of the method according to the invention is shown as a flowchart, wherein the individual process steps can be implemented individually or in groups by program modules, and wherein the functional units and interfaces are defined according to Figure 2 are indicated by example.

[0067] In Figure 1 The track GL is depicted as a route on which a track-bound vehicle FZ travels in one direction FR. Furthermore, the track GL is equipped with trackside equipment SE1 ... SE6, which in the embodiment shown in the diagram... Figure 1 are designed as Eurobalises.

[0068] The trackside equipment SE1 and SE3 through SE6 form a group (VB) of trackside equipment. This trackside equipment may have been included in the initial track layout, for example, and is functionally related. Therefore, it will be referred to as linked balises. Trackside equipment SE2, for instance, may have been retrofitted at a later date to provide an additional reference point for locating the track-bound vehicle (FZ). However, this trackside equipment SE2 is not part of group VB and will therefore be referred to as an unlinked balise.

[0069] The trackside equipment of the VB system is less vulnerable to hackers and less prone to errors compared to the unlinked balise, represented by the trackside equipment SE2. This can be explained by the fact that the functional relationship means that the trackside equipment SE1 and SE3 ... SE6 are expected to transmit certain data that fits into the context of the driving activity of the track-bound vehicle FZ. A deviation from this is therefore noticed more quickly than with the unlinked balise, represented by the trackside equipment SE2. The trackside equipment SE2 thus benefits most from the inventive method of mixed encrypted and unencrypted transmission of telegrams. For example, it can be designed from the outset for the inventive method as part of a retrofit.

[0070] In Figure 2The trackside vehicle FZ and the trackside equipment SE2 are shown schematically. Data transmission takes place via a first interface S1, which is implemented as a radio interface. Therefore, the trackside equipment SE2 has a first antenna A1 and the trackside vehicle FZ has a second antenna A2.

[0071] The first antenna A1 is connected to a first computer C1 via a fourth interface S4. Furthermore, the first computer C1 can retrieve a key KEY from a first storage device SP1 via a fifth interface S5. The key KEY thus enables the decryption or encryption according to the invention of a telegram to be transmitted via the first interface S1 (in its function as a balise, the trackside device SE2 will preferably send the telegram to the track-bound vehicle FZ via the first interface S1).

[0072] The second antenna A2 is connected to a second computer C2 via a second interface S2. The second computer C2 can access a second storage device SP2 via a third interface S3, in which, among other things, a key KEY is stored. Thus, the trackside vehicle FZ and the trackside device SE2 each have a key KEY for decrypting and encrypting the telegram to be transmitted via the first interface S1.

[0073] Figure 3 Using the example of telegrams transmitted via Eurobalises, this demonstrates the advantage of transmitting several short telegrams (KT) instead of one long telegram (LT). Three short telegrams together equal KT, as shown in... Figure 3 As indicated, a long telegram (LT) - at least in terms of the amount of data to be transmitted.

[0074] The transmission of telegrams is in Figure 3represented as a band, corresponding to a temporal sequence along a time axis t. During the passage of the vehicle FZ over the trackside device (for example, SE2 as in Figure 2 (as shown) there is only a specific time window in which the two antennas A1 and A2 are close enough to each other for transmission to occur. This time window is called the REC transmission window and is shown in Figure 3 registered.

[0075] In the example according to Figure 3 The track-bound vehicle FZ is currently crossing the trackside facility SE2 at a speed at which, theoretically, four short telegrams KT could be transmitted. However, it shows Figure 3This also occurs when the REC transmission window opens while a short telegram KT is being transmitted, causing it to be cut off and unable to be evaluated by the route-bound vehicle FZ. The same applies to the fifth and final short telegram KT, which (at least partially) appears in the REC transmission window according to... Figure 3 The transmission window REC contains three fully transmitted short telegrams (KT) in between, each containing the same amount of information as a single long telegram (LT). Therefore, if the data from three short telegrams (KT) is repeatedly sent by the trackside device SE2, the complete information content of the trackside device SE2 can be transmitted within the transmission window REC.

[0076] This example serves only as an illustration of a transmission standard and can be implemented in any number of ways. However, this particular example will be used in the following discussion. Figure 4to be used to discuss a sequence of encrypted and unencrypted telegrams with respect to the length of the transmission window REC.

[0077] With regard to telegrams T1 and T2, Figure 3 Preferably, short telegrams according to the ETCS standard are used. However, any other telegrams can also be transmitted, for example long telegrams (LT) if the track-bound vehicle (FZ) is traveling slower, or telegrams of another transmission standard.

[0078] In Figure 4Two variants, V1 and V2, are shown for the targeted encrypted and unencrypted transmission of a first telegram T1 and a second telegram T2. In variant V1, the first telegram is sent unencrypted (T1U) and then encrypted (T1V). Subsequently, the second telegram is sent unencrypted (T2U) and then encrypted (T2V). The described sequence is then repeated, as shown in Figure 4 is specified.

[0079] Will now, as in Figure 3Assuming that only three telegrams can be fully transmitted within the REC transmission window, it becomes clear that the first telegram is transmitted both encrypted and unencrypted, and the second telegram is transmitted only in encrypted form. Therefore, if the trackside equipment is passed by an unequipped trackside vehicle, it cannot process the content of the second telegram T2, as there is no way to decrypt the second encrypted telegram T2V.

[0080] For such cases, the transmission sequence of sequences according to variant V2 is more suitable. Here, the first telegram is always transmitted unencrypted (T1U) and then encrypted (T1V), and then the second telegram is transmitted only unencrypted (T2U), and this sequence is then repeated.

[0081] It turns out that the REC transmission window is now sufficient to always receive the first telegram both encrypted and unencrypted, as well as the second telegram unencrypted (although the order may vary). Therefore, an unequipped, track-bound vehicle (FZ) can decode and process all data even without the possibility of decrypting the first telegram (T1).

[0082] However, the possibility of mixed operation of equipped and unequipped track-bound vehicles FZ is offset by the fact that the second telegram is never sent encrypted and an error investigation or investigation of manipulation attempts can only be carried out using the first telegram T1 according to the invention.

[0083] It is thus evident that the choice of the sequence of telegrams (encrypted, unencrypted) depends on the specific use case and a compromise must always be found to achieve the highest possible security while taking into account the technical conditions (equipped vehicles, unequipped vehicles, length of the REC transmission windows, speed of the vehicles when passing over the trackside equipment).

[0084] In Figure 5The process flow for transmitting telegrams is shown as a flowchart. The process begins with a START step and initially takes place in the sender S. After an initialization step INI, a query is performed to determine whether a high security level SEC should be selected for the telegram to be transmitted. If so, the key KEY is loaded from the storage device SP and used to encrypt the telegram in an encryption step CRYP. Subsequently, the telegram is encoded in an encoding step CODE and sent to the receiver R via interface S1.

[0085] In receiver R, a decoding step DECO takes place, followed by a decoding step DECR using the key KEY, which is loaded from the storage device SP. The telegram is then available there for further processing.

[0086] The storage devices SP in the transmitter S and in the receiver R are different storage devices. If the transmitter is the trackside device SE2 according to... Figure 2 , the storage device SP could, for example, be formed by the storage device SP1 and the storage device in the receiver by the storage device SP2.

[0087] If the query regarding the SEC security level is answered negatively, then during transmission, as in Figure 5 The encryption step CRYP and the decryption step DECR are omitted. Only the encoding step CODE, the transmission step TRN, and the decoding step DECO take place.

[0088] The sender S repeatedly performs a RECEND query to check if the transmission has ended. If so, the transmission is aborted in a STOP step. If not, the security level SEC query for the next telegram is performed again. Reference symbol list

[0089] Route-bound vehicle SE1 ... SE6 Route-side equipment GG track FR Direction of travel VB convoy A1 ... A2 Antenna SP1 ... SP2 Storage unit C1 ... C2 Computer S1 ... S5 Interface LTLong telegram KTShort telegram T1 ... T2Telegram T1U ... T2UUnencrypted telegram T1V ... T2VEncrypted telegram tTime RECTransmission window V1 ... V2Variant Sender Receiver START Start step INI Initialization step SEC Security level query KEY Key CRYP Encryption step CODE Coding step TRN Transmission step DECO Decoding step DECR Decryption step RECEND End of transmission query STOP Stop step

Claims

1. Method for encoded communication between a track-bound vehicle (FZ) and a track-side facility (SE1 ... SE6) designed as a balise, in which multiple telegrams (T1, T2) are transferred between the track-side facility (SE1 ... SE6) and the track-bound vehicle (FZ), wherein the telegrams (T1, T2) in each case • have a payload data region for filling with payload data, • have a code region for the encoding of the payload data, wherein at least one of the telegrams (T1, T2) is transferred in an unencrypted manner, such that • the payload data region is filled with the unencrypted payload data, wherein this is encoded using the code region, • the telegram (T1, T2) filled with the unencrypted payload data is transferred in an encoded manner, • the unencrypted payload data is decoded after the transfer, using the code region, wherein at least one of the telegrams (T1, T2) is transferred in an encrypted and encoded manner, such that • the unencrypted payload data is encrypted before the filling of the payload data region, • the payload data region is filled with the encrypted payload data, wherein this is additionally encoded using the code region, • the telegram (T1, T2) filled with the encrypted payload data is transferred in an encoded manner, • the encrypted payload data is decoded after the transfer of the telegram (T1, T2), using the code region, • after which the encrypted payload data is decrypted, wherein at least one of the telegrams (T1, T2) transferred with unencrypted payload data is also transferred as a telegram with encrypted payload data with the same content.

2. Method according to claim 1, characterised in that • first, the unencrypted payload data is decoded after the transfer, using the code region, • after which the encrypted payload data is decoded, after the transfer of the telegram (T1, T2), using the code region, • after which the encrypted payload data is decrypted.

3. Method according to claim 2, characterised in that • first, the at least one telegram (T1, T2) filled with unencrypted payload data is transferred, • after which the telegram (T1, T2) filled with the encrypted payload data with the same content is transferred.

4. Method according to one of the preceding claims, characterised in that telegrams (T1, T2) with encrypted and unencrypted payload data are transferred in an alternating order, in that telegrams transferred in an unencrypted manner and telegrams transferred in an encrypted manner alternate with one another.

5. Method according to one of claims 1 to 4, characterised in that telegrams (T1, T2) with encrypted and unencrypted payload data are transferred in an alternating order, in that, in a sequence of telegrams (T1, T2), proportionally more telegrams (T1, T2) with unencrypted payload data are transferred than telegrams (T1, T2) with encrypted payload data, wherein • the payload data regions of the telegrams (T1, T2) transferred in an unencrypted manner of the sequence are filled with different contents, • at least one of the telegrams (T1, T2) transferred with unencrypted payload data of the sequence are also transferred as telegrams (T1, T2) with encrypted payload data with the same content.

6. Method according to claim 1, characterised in that the payload data of a telegram (T1, T2) sent in an encrypted manner, after decryption (DECR), is compared with the payload data of a telegram (T1, T2) sent in an unencrypted manner with the same content, after decoding (DECO).

7. Method according to claim 6, characterised in that in the event that the comparison reveals that the payload data of the telegram (T1, T2) sent in an encrypted manner deviates from the payload data of the telegram (T1, T2) sent in an unencrypted manner, then an error signal is generated and / or output.

8. Method according to one of the preceding claims, characterised in that multiple telegrams (T1, T2) with different sizes of payload data regions are transferred.

9. Method according to one of the preceding claims, characterised in that the steps in which • the payload data region is filled with the encrypted payload data, wherein this is additionally encoded using the code region, • the telegram (T1, T2) filled with the encrypted payload data is transferred, • the encrypted payload data is decoded after the transfer of the telegram (T1, T2), using the code region, • after which the encrypted payload data is decrypted, or • the payload data region is filled with the unencrypted payload data, wherein this is encoded using the code region, • the telegram (T1, T2) with the unencrypted payload data is transferred in an encoded manner, • the unencrypted payload data is decoded after the transfer, using the code region, are performed according to the ETCS standard or the ERTMS standard or the CBTC standard or the PTC standard.

10. Method according to one of the preceding claims, characterised in that it is checked whether the balise belongs to a balise group (VB), wherein the received data is then categorised as trustworthy.

11. Track-bound vehicle (FZ), having a second computer (C2) and a second storage facility (SP2), in which a key (KEY) is stored in a retrievable manner, with a communication interface (S1) for a track-side facility (SE1 ... SE6), characterised in that this is configured for participating in a method for encoded communication according to one of the preceding claims, in which multiple telegrams (T1, T2) between the track-side facility (SE1 ... SE6) and the track-bound vehicle (FZ) are transferred between the track-bound vehicle (FZ) and a track-side facility (SE1 ... SE6) designed as a balise, wherein the telegrams (T1, T2) in each case • have a payload data region for filling with payload data, • have a code region for the encoding of the payload data, wherein in at least one of the telegrams (T1, T2) • the unencrypted payload data is decoded after the transfer, using the code region, wherein in at least one of the telegrams (T1, T2) • the encrypted payload data is decoded after the transfer of the telegram (T1, T2), using the code region, • after which the encrypted payload data is decrypted, wherein at least one of the telegrams (T1, T2) transferred with unencrypted payload data is also transferred as a telegram with encrypted payload data with the same content.

12. Track-side facility (SE1 ... SE6), designed as a balise, having a first computer (C1) and a first storage facility (SP1), in which a key (KEY) is stored in a retrievable manner, with a communication interface (S1) for a track-bound vehicle (FZ), characterised in that this is configured for participating in a method for encoded communication according to one of claims 1 - 10, in which multiple telegrams (T1, T2) between the track-side facility (SE1 ... SE6) and the track-bound vehicle (FZ) are transferred between the track-bound vehicle (FZ) and a track-side facility (SE1 ... SE6) designed as a balise, wherein the telegrams (T1, T2) in each case • have a payload data region for filling with payload data, • have a code region for the encoding of the payload data, wherein at least one of the telegrams (T1, T2) • is transferred in an unencrypted manner, such that • the payload data region is filled with the unencrypted payload data, wherein this is encoded using the code region, • the telegram (T1, T2) filled with the unencrypted payload data is transferred in an encoded manner, wherein at least one of the telegrams (T1, T2) • is transferred in an encrypted and encoded manner, such that • the unencrypted payload data is encrypted with the key (KEY) before the filling of the payload data region, • the payload data region is filled with the encrypted payload data, wherein this is additionally encoded using the code region, • the telegram (T1, T2) filled with the encrypted payload data is transferred in an encoded manner, wherein at least one of the telegrams (T1, T2) transferred with unencrypted payload data is also transferred as a telegram with encrypted payload data with the same content.

13. Computer program product with program commands for performing the method according to one of claims 1 - 10.

Images