WO2017064007A1

WO2017064007A1 - Network gateway bridging

Info

Publication number: WO2017064007A1
Application number: PCT/EP2016/074221
Authority: WO
Inventors: Timo Lothspeich; Andreas Mueller
Original assignee: Robert Bosch Gmbh
Priority date: 2015-10-15
Filing date: 2016-10-10
Publication date: 2017-04-20
Also published as: DE102015220003A1

Abstract

The invention relates to a method for generating a secret in a network (1) having at least two subscribers (10, 20, 30, 40), which are arranged in different network segments (11,12), comprising a switching exchange (50), wherein the different network segments (11, 12) can be connected to transmit data via the switching exchange (50), and comprising a network switching exchange bridging unit (60) for a direct physical and data-transmitting connection of the different network segments (11, 12). For the purpose of secret generation, the network switching exchange bridging unit (60) is operated in a bridging operating mode such that the network segments (11, 12) of the at least two subscribers (10, 20, 30, 40) are directly connected, both physically and in a data-transmitting manner.

Description

description

title

Network Gateway Bridging The present invention relates to a method for generating a secret in a network with at least two subscribers and to a network exchange bridging unit for direct data-transmitting connection of different network segments. State of the art

In the subsequently published DE 10 2015 207 220 A1, the applicant presented a method for generating a secret or key in a network, which uses a superimposition of signals of two subscribers on a common transmission medium. In this case, the network has at least a first and a second subscriber and a transmission channel between at least the first and the second subscriber. The first and second subscribers may each provide at least a first value and a second value to the transmission channel. The first subscriber or the second subscriber initiate a first subscriber value sequence or a second subscriber value sequence for transmission to the transmission channel which is largely synchronous with one another. On the basis of information about the first subscriber value sequence or the second subscriber value sequence and on the basis of an overlay value sequence resulting from a superposition of the first subscriber value sequence with the second subscriber value sequence on the transmission channel, the first subscriber or the second subscriber generate a shared secret or a common cryptographic one Key. Such a method is particularly well suited for communication systems which provide for transmission of dominant and recessive bits or correspondingly dominant and recessive signals, whereby a dominant signal or bit of a participant of the network prevails against recessive signals or bits. An example of this is CAN (Controller Area Network), in which the

This bus is accessed using bitwise bus arbitration, which uses dominant and recessive bits in this transmission method. Other examples are TT CAN, CAN FD, LIN and l ² C. However, the use of such a method is difficult in networks in which individual network segments are connected via exchanges (so-called gateways). In this case, there is no longer a shared by all participants transmission medium, but usually a common used transmission medium per network segment. Correspondingly, subscribers from different network segments are not easily able to establish a shared secret without the associated exchange or switching centers also becoming aware of it. Disclosure of the invention

According to the invention, a method for generating a secret in a network with at least two subscribers and a network switching center bridging unit for direct physical and data-transmitting connection of different network segments with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description. In particular, a network exchange bridging unit is a unit that is set up to bridge a switching center of a network.

In the context of the invention is for generating a secret in a network with at least two participants (eg, a control unit, a sensor o- an actuator, in particular a motor vehicle, an industrial plant, a Home automation network, etc.), which are arranged in different network segments, with a central office, wherein the different network segments are data transmitting connectable via the exchange, the use of a network switching center bridging unit for direct physical and data transmission connecting the different network segments for a key generation serving network communication proposed. For generating the key, the network switching center bridging unit is operated in such a way that the network segments of the at least two subscribers are connected directly to transfer data. This is also referred to below as the bridging operating mode. The invention is in principle also suitable for connecting more than two network segments (possibly with more than one network switching center bridging unit) to one another.

The solution presented enables the generation of a shared secret and cryptographic keys derived from the secret in network topologies in which the two respective communication partners are separated by one or more exchanges by bypassing the network participants by direct physical data connection for secret generation Switch (s) is made by the network switch bridging unit.

With the invention, it is thus possible to establish a shared secret between two different subscribers of a network, which can be used in particular for generating a symmetric cryptographic key. However, such a shared secret can in principle also be used for purposes other than cryptographic keys in the strict sense, e.g. as a one-time pad.

Particularly advantageously, the method can be used in a network in which there is a dominant value (physically: a dominant signal) that prevails when only one subscriber applies it on the transmission channel and a recessive value (physically: a recessive signal ), which only results on the transmission channel if both or all participants transferred value. Because of the clearly defined overlay rules, the subscribers of such a network can derive information about the genesis of the secret from the resulting overlay value sequences in a particularly simple manner.

Alternatively, the transmission of a recessive value of at least one of the subscribers can also be replaced by the fact that at this point the value sequence or, as one of the at least two possible values, nothing is transmitted. Advantageously, in addition to the bridging operating mode, the network switching center bridging unit also supports an operating mode in which the network segments are data-transmitting via the switching center. This operating mode is also referred to below as the inoperative operating mode and is used for normal or non-secret network communication (normal operation).

Conveniently, after the completion of the secret generation and for the nongeneration network communication, it is switched back to the inoperative mode of operation. Preferably, from the bridging mode of operation in accordance with a

Trigger condition switched to the inoperative operating mode. For example, the triggering condition may include timing and / or detecting the end of the network communication serving to generate the secret.

Advantageously, the network switching center bridging unit also supports an operating mode in which the network segments are not (so also not connected via the switching center) data-transmitting connected. This operating mode is also referred to below as a separating operating mode and can be used, for example, if an error is detected in a network segment.

The network switching center unit expediently has all the (active and passive) electrical components (eg connections, switches, terminal resistors, capacitors, etc.) in order to implement all operating modes supported by it according to a network standard.

Preferably, switching between any two of the operation modes supported by the network switch bridging unit is performed by one

Participant of the network, by the exchange and / or by a non-network unit (other, not integrated into the network component (eg diagnostic tester)) triggered. In this sense, the switching center expediently has a switching input interface via which a command triggering a switching process can be received.

The Umschalteingangsschnittstelle can be integrated, for example, in the network interface, so that a switching command can be configured, for example, as a network packet. In particular, but not exclusively, the triggering of a switching operation may be to receive a particular message or to receive a particular value in a given field (e.g., message identifier) in a message.

Preferably, the operation mode of the network exchange bridging unit automatically becomes dependent on an operating condition of the

Networked system. The system may be, for example, a vehicle, a facility, a building, etc. If the network is located in a vehicle, it is preferably provided that the operating mode of the network switching center bridging unit is dependent on the operating state of the vehicle (for example vehicle start, after-run or end-of-line

Programming) depends. In that case, it is possible, in particular, for the switching center (s) to be bridged with the start of the corresponding vehicle operating state, until the method for generating the secret has been completed. In addition, it is expedient for one of the at least two subscribers to check whether there is a direct physical communication connection between it and another of the at least two subscribers, in particular before the secret is generated. Do the participants already have a common key (and would like, for example, a re-keying, ie a renewal or refreshing of the shared key), the existing key can be used, for example, for a secure challenge-response procedure. A runtime and / or signal level measurement can, for example, provide information about whether an exchange is interposed or not.

Alternatively, the first party transmits a network message and the second party then inserts data into the same network message (e.g., in the payload). Namely, a gateway usually receives a complete message before it is forwarded on another channel. Therefore, and due to the tinnings, the insertion into the payload part is only possible if there is a direct physical connection between the first subscriber and the second subscriber (ie no switch is interposed).

In order to permit an assignment of the inserted data to the second subscriber, this data is preferably authenticated. Authenticated data may include a message signed with an already existing cryptographic key or just a signature. An already existing key may in particular have been generated at an earlier time from an earlier secret between the first and the second subscriber.

Preferably, the at least one of the at least two network subscribers is arranged to select the type of network communication depending on the result of the check. Preferably, secret generation is started only when the network switch bridging unit is in the bridging mode of operation. Accordingly, it can be provided that a subscriber first issues a switching command to the network switching center bridging unit and subsequently checks its operating mode and only begins the secret generation if the switching operation was successful.

The invention is particularly well implemented in a CAN, TTCAN or CAN FD bus system. Here, a recessive signal level is displaced by a dominant signal level. The superimposition of values or signals of the Subscriber thus follows defined rules which the participants can use to derive information from the superimposed value or signal and the value or signal transmitted by them. Other communication systems such as, for example, LIN and I ² C are also well suited for use of these methods.

Alternatively, however, the method may also be implemented, for example, in a (possibly also wireless) network with amplitude shift keying, e.g. On-Off-Keying, are used. Here, too, the overlay is fixed by the participants as signals "transmission" and "no transmission" to choose from and the

Overlay signal corresponding to the signal "transmission", if one or both of the participants transmitted, and the signal "no transmission" corresponds, if both participants do not transmit. Preferably, a method for generating a secret based on a superimposition of dominant and recessive signals, for example, according to DE 10 2015 207 220 A1 is used, wherein the network at least a first and a second subscriber and a transmission channel between at least the first and the second subscriber having. The first and the second participant can each have at least a first

Add value and a second value to the transmission channel. The first subscriber or the second subscriber initiate a first subscriber value sequence or a second subscriber value sequence for transmission to the transmission channel which is largely synchronous with one another. On the basis of information about the first subscriber value sequence or the second subscriber value sequence and on the basis of an overlay value sequence resulting from a superposition of the first subscriber value sequence with the second subscriber value sequence on the transmission channel, the first subscriber or the second subscriber generate a shared secret.

In order to obtain an overlay value sequence, the transmission of values of different subscribers must have overlapping periods (ie be largely synchronous in the sense of this application), so that a superimposition of the individual signals of a signal sequence takes place on the transmission channel, in particular in particular such that the signal corresponding to the n-th logical value or bit of the first user is at least partially superimposed with the signal corresponding to the n-th logical value or bit of the second user. In each case, this overlay should be sufficiently long for the participants to be able to record the overlay or to determine the corresponding overlay value.

The superimposition value can be determined by arbitration mechanisms or by physical signal superposition. By arbitration mechanism is meant, for example, the case that a subscriber has applied a recessive level, but detects a dominant level on the bus and thus omits the further transmission.

From the resulting value sequence of the overlay (i.e., overlay value sequence) and its own value sequence (i.e., subscriber value sequence), the subscribers can then generate a key that is secret to an outside attacker. The reason for this is that the outside attacker, who for example can listen to the effective overall signals present on the shared transmission channel, only sees the superimposition of the value sequences, but does not have the information about the individual value sequences of the participants. Thus, the participants have more information that they can use against the attacker to generate a secret key.

A refinement of the method for generating a secret between the subscribers based on a superimposition of dominant and recessive signals requires that the first subscriber value sequence and the second subscriber value sequence each have a first subvalue sequence and a second subvalue sequence, wherein the second subvalue sequence results from the first subvalue sequence by inverting, ie by exchanging first values for second values and exchanging second values for first values. The first partial value sequence and the second partial value sequence can be transmitted one after the other. Alternatively, a preferred method is proposed in which the values of the first and the second partial value sequence are combined into a subscriber value sequence in a particularly sorted manner, whereby at least one value of the second partial value sequence already exists is transmitted before all values of the first partial value sequence have been transmitted. This makes it possible, already during transmission of the subscriber value sequence and receiving the overlay value sequence with the evaluation and Geheimbzw. Key generation to start. The solution will continue to be independent of buffer or cache memory sizes, as not complete partial value sequences must be stored before the evaluation and secret generation can be started.

A network switching center bridging unit according to the invention for the direct physical and data-transmitting connection of different network segments is, in particular in terms of programming, set up to carry out a method according to the invention.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below with reference to the drawing.

Brief description of the drawings

Figure 1 shows schematically a network with four subscribers, a central office and a central office bridging unit, as may be the basis of the invention.

FIG. 2 schematically shows three different operating modes of the switching center bridging unit from FIG. 1.

Embodiment (s) of the invention

In Figure 1, a network 1, as it may be based on the invention, shown schematically and schematic diagram. The network is realized as a two-wire network and has four network subscribers 10, 20, 30 and 40, which are partially networked. se are connected directly and partially via an exchange 50 data transmitting. In this case, the network subscribers 10 and 20 and the switching center 50, which are directly connected to one another in data transmission, form a first network segment 1 1, and the network subscribers 30 and 40 and the switching center 50, which are connected to one another in a data-transmitting manner, form a second network segment 12. The switching center 50 is set up to connect the network segments 11 and 12 in a data-transmitting manner. Furthermore, a network exchange bridging unit 60 is looped in between the network segments 11, 12 and parallel to the exchange 50. In particular, a network may be broken at the dashed connections to loop in the network switch bridging unit 60. For example, the network switch bridging unit 60 may have four network interfaces. Referring now to Figure 2, wherein different modes of operation of the network switch bridging unit 60 are illustrated by different routing, the operation will now be described. However, the network switch bridging unit 60 has all the active and passive electrical components (eg, ports, network switches, switches, terminators, capacitors, inductors, logic devices)

(e.g., μΡ, ASIC), etc.) in order to realize the operation modes according to a network standard.

In particular, the network switch bridging unit 60 is configured to operate in a first inoperative mode of operation and a second, bridging mode of operation. In the example shown, the network interface bridging unit 60 is further configured to operate in an optional third, disconnecting mode of operation.

The inoperative mode of operation is illustrated in Figure 2.1. In the inoperative mode of operation, the network interface bridging unit 60 has no effect, so that the network segments 1 1 and 12 are data transmitting via the central office 50. The bridging mode of operation is illustrated in FIG. 2.2. In the bridging mode of operation, the network segments 1 1 and 12 are connected directly physically and data-transmitting, with the switch 50 being bridged.

The separating operating mode is illustrated in FIG. 2.3. Finally, in the disconnecting mode of operation, the network switch bridging unit 60 is switched so that the network segments 1 1 and 12 are not data-communicatively connected to each other, but are terminated at the corresponding terminal, for example, by a terminating resistor.

To initiate a mode change, the reception of a particular message or the receipt of a particular value in a given field in a message over the network is particularly, but not exclusively, suitable. In this sense, a switching input interface is integrated in at least one of the network interfaces, preferably one or both of the network interfaces connected to the network segments 11, 12. It is understood that this integration is advantageously done on the software side; However, a hardware implementation is also possible.

The example of a CAN network can result in the following advantageous sequence:

Initially, the network 1 is in the normal state or normal mode, wherein the network exchange bridging unit 60 according to FIG

2.1 is in inoperative mode of operation. Here, the network switch bridging unit 60 forwards all messages it receives, expediently not making any changes. The network switch bridging unit 60 receives a special one

Switching message, which is realized, for example, by a message with a specific message identifier, and switches to the bridging operating mode according to FIG. 2.2. This can be done so fast that the remainder of the switching message (ie after the message identifier) already contains data for the secret message. or to verify the operating mode. Alternatively or additionally, the messages following the switching message may contain data for checking the operating mode or for generating the secret.

Finally, in response to a triggering condition, it is automatically switched back to the inoperative operating mode, wherein the triggering condition may include a timing and / or a switching command and / or the detection of the end of the secret communication network communication. The end of the secret generation serving network communication can be particularly easily recognized, if all the secret generation serving network communication is handled in the switching message, or alternatively, if the entire secret generation serving network communication is sent in switching messages, after transmitting each switching message automatically again is switched back to the inoperative operating mode.

Claims

Expectations

1 . Method for generating a secret in a network (1)

with at least two participants (10, 20, 30, 40) which are arranged in different network segments (1 1, 12),

with an exchange (50), the different network segments (1 1, 12) being connectable via the exchange (50) for data transmission, and

with a network switching center bridging unit (60) for direct physical and data-transmitting connection of the different network segments (1 1, 12),

wherein, to generate secrets, the network exchange bridging unit (60) is operated in a bridging operating mode in such a way that the network segments (11, 12) of the at least two participants (10, 20, 30, 40) are directly connected physically and for data transmission.

2. The method according to claim 1, wherein for network communication that does not serve to generate secrets, the network switching center bridging unit (60) is operated in an inoperative operating mode in such a way that the network segments (11, 12) are connected via the switching center (50) for data transmission.

3. The method according to claim 2, wherein the bridging operating mode is automatically switched to the inoperative operating mode in accordance with a triggering condition.

4. The method according to claim 3, wherein the triggering condition comprises a timeout and/or a switching command and/or detecting the end of the network communication used for secret generation.

Method according to one of the preceding claims, wherein the network switching center bridging unit (60) is operated in a separating operating mode such that the network segments (1 1, 12) are not connected for data transmission.

Method according to one of the preceding claims, wherein switching between two of the operating modes supported by the network switching center bridging unit (60) is carried out by a subscriber (10, 20, 30, 40) of the network, by the switching center (50) and / or by someone external to the network unit is triggered.

Method according to one of the preceding claims, wherein the operating state of the network switching center bridging unit (60) is automatically set depending on an operating state of a system comprising the network (1).

Method according to one of the preceding claims, wherein one of the at least two participants checks whether there is a direct physical communication connection between it and another of the at least two participants.

9. The method according to claim 8, wherein the one of the at least two participants selects the type of network communication depending on the result of the check.

10. The method according to claim 8 or 9, wherein the one of the at least two participants carries out a transit time and / or signal level measurement to check whether a direct physical communication connection exists between it and the other of the at least two participants.

1 1 . The method of claim 8, 9 or 10, wherein one of the at least two participants transmits a network message, the other of the at least two participants inserting data into the same network message when a There is a direct physical connection between the at least two participants.

2. Method according to one of the preceding claims, wherein a first participant (10) and a second participant (30) of the at least two participants (10, 20, 30, 40) each transmit at least a first value and a second value to a common transmission channel the first and second participants (10, 20, 30, 40), whereby to generate the secret, the first participant (10) has a first participant value sequence and the second participant (30) has a second participant value sequence for transmission on the transmission channel that is largely synchronous with one another cause and wherein the first participant (10) the secret based on information about the first participant value sequence and based on an overlay value sequence resulting from a superposition of the first participant value sequence with the second participant value sequence on the transmission channel and the second participant (30) the secret on the basis of Generate information about the second participant value sequence and based on the overlay value sequence.

3. The method according to claim 12, wherein a state corresponding to the first value is established on the transmission channel when both the first and the second participant initiate a transmission of the first value via the transmission channel, and a state corresponding to the second value is established when the first or the second participant or if both initiate a transmission of the second value via the transmission channel.

4. The method according to claim 12 or 13, wherein the first participant value sequence and the second participant value sequence each have a first partial value sequence and a second partial value sequence, the second partial value sequence emerging from the first partial value sequence by exchanging first values for second values and second values for first ones Values can be exchanged.

15. The method according to claim 14, wherein the transmission of at least one value of the second partial value sequence on the transmission channel is initiated before the transmission of all values of the first partial value sequence on the transmission channel has been initiated.

16. Network switching center bridging unit (60) for direct physical and data-transmitting connection of different network segments (1 1, 12), which is set up to carry out a method according to one of the preceding claims.

17. Network exchange bridging unit (60) according to claim 16, with a switching input interface via which a command triggering a switching process between two operating modes can be received.

18. Network exchange bridging unit (60) according to claim 17, wherein the switching input interface is integrated into a network interface.