WO2011144418A1

WO2011144418A1 - Method for the secure establishment of a security key via an unencrypted radio interface

Info

Publication number: WO2011144418A1
Application number: PCT/EP2011/056560
Authority: WO
Inventors: Rainer Falk; Steffen Fries
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-05-21
Filing date: 2011-04-26
Publication date: 2011-11-24
Also published as: DE102010021254A1

Abstract

When establishing communication connections in an ad-hoc network, the identity of a subscriber is typically checked in accordance with a predefined communications protocol and a common session key is established for the subsequent communication. The wireless communication normally takes place in said short period in an unencrypted manner via a radio interface, so that an invader can easily intercept the respective messages. For the secure establishment of a security key for a wireless communication connection via a radio interface, according to the invention the radio interface is checked for a presence of an interfering signal prior to the transmission according to predefinable test criteria, wherein an interfering signal is generated so that an outsider who does not know the interfering signal cannot decode the transmitted data. If an interfering signal is present, the key establishment message is used to establish the security key. If no interfering signal is present, the key establishment message is not used to establish the security key. Interception-protected transmission of a cryptographic key, a password or generally of a security parameter is thus enabled via an unencrypted radio interface.

Description

description

Method for the secure agreement of a security key via an unencrypted radio interface

The present invention relates to a method and a sys tem for the protected ^¬ agreement a security key for a wireless communication link over an unencrypted radio interface.

In ad hoc networks, also known as self-organizing networks be ^¬ records, more power stations will be able without a mediating central institution establish a radio link with each other. The connection between two stations takes place either directly or at greater distances via other similar stations that form relay stations for this connection. These self-organizing networks are, for example, local area networks (WLANs: Wireless Local Area Networks) according to one of the HIPERLAN, IEEE standards

802.11, IEEE 802.15.x, Bluetooth, ZigBee or Wireless HART. Such networks are used not only in the usual Internet and telecommunications sectors, but also in the field of inter-vehicle communication, such as, for example, systems for warning of danger or cooperative driver assistance systems.

A particular advantage of ad hoc networks lies in their great mobility and flexibility. At any location radio links between stations can be established without relying on fixed base stations or fixed radio network planning. Connections from a station to a destination station can be realized either directly or by means of relay stations over a variety of possible ways.

However, the flexibility and mobility of such networks impli ^¬ adorns a large number of logins between the individual subscribers of the network. This is after a given communication protocol usually verifies the identity of a subscriber and a common session key for subsequent communication verein ^¬ beard. In this short period, the Drahtloskommuni- done cation via a radio interface usually unverschlüs ^¬ rare, so that an attacker can listen to the messages in any problems.

The object of the present invention is therefore to specify a method with which data is transmitted securely via an unencrypted radio link.

According to the invention, this object is achieved by a method and a system having the features of claims 1 and 11. Advantageous developments of the invention are specified in the dependent claims.

In the inventive method for secure agreement of a security key for a wireless communication connection via a radio interface, a first subscriber generates a transmission signal for transmitting a

Key agreement message to a second Kommunikati ^¬ onsteilnehmer. Before the transmission, the radio interface is checked in accordance with predefinable test criteria for the presence of an interference signal. In the presence of the interfering signal, the key agreement message is used to negotiate the security key. If there is no noise, the key agreement message is not used for Vereinba ^¬ tion of the security key.

In one embodiment of the present invention, the checking of the interference signal is performed by the first communication subscriber and, if there is no interference signal, the key ^{agreement message} is not transmitted by the first communication participant.

According to a further embodiment of the present invention, the checking of the interference signal by the second commu- and if no interference signal is present, the transmitted key agreement message is discarded or not accepted by the second communication user.

According to another embodiment of the present invention, the checking of the interference signal by the first communica ^¬ nikationsteilnehmer is performed, and if there is no interference signal is present, the transmitted key agreement message discarded by the first communication party to the agreement of a key.

According to a further embodiment of the present invention, the checking of the interference signal is carried out by a third communication participant. From this third communication participants then the first communication participant and / or the second communication participants are informed about the presence or absence of the interference signal. According to a further embodiment of the present invention, the checking of the interference signal is at least partially carried out during the transmission of the key agreement message. According to another embodiment of the present invention, the predetermined test criteria of the interference signal comprise a signal strength of the interference signal, a location information of the interference signal which is detected for example via a removal ^¬ measurement or position determination of the interference signal transmitter, a direction information of the sturgeon ^¬ signal and / or a statistical Signal property of the interfering signal.

According to a further embodiment of the present invention, the predefinable test criteria of the interference signal comprise a

Check information transmitted between the first and the second communication subscriber, and on the basis of which each received by the first and second communication participants interference signal can be checked for its similarity.

According to a further embodiment of the present invention, the interference signal is determined by the second communication participant. From the received Schlüsselvereinbarungs ^¬ message the interference signal by the second Kommunikati ^{¬ on} participants signal processing technology is removed. The system according to the invention with a first and a second communication ^subscriber has means for protected agreement of a security key for a wireless communication connection via a radio interface. The means are designed such that the following steps are feasible:

The first communication subscriber generates a transmission signal for transmitting a key agreement message to the second communication participant. Before transmission, the radio interface is checked in accordance with predefinable test criteria with regard to the presence of an interference signal. In the presence of the interfering signal the key Vereinbarungs ^¬ message to declare the security key USAGE ^¬ det. If there is no noise, the Schlüsselvereinba ^¬ approximately message is not used to declare the Sicherheitsschlüs- sels.

In the following, possible embodiments of the method according to the invention and the system according to the invention will be described with reference to the attached figures. Show it:

FIG. 1 shows a schematic representation of a system according to the invention comprising a first and a second communication subscriber, as well as an interference signal transmitter, 2 is a schematic representation of a flow chart of a first embodiment of the method according to the invention, FIG. 3 is a schematic representation of a flow chart of a second embodiment of the method according to the invention,

FIG. 4 is a schematic representation of a flow diagram of a third embodiment of the method according to the invention,

Figure 5a, 5b in a schematic representation each one

Flowchart for a fourth and fifth embodiment of the method according to the invention.

1 shows a schematic representation of an inventive system with three communication nodes. Darge ^¬ represents are a first communication subscriber 101, a second communication subscriber 102, and a Störsignalsender 103th

The first communication user 101 functions as a transmitter, which transmits data via an unencrypted radio interface. The data may be a cryptographic key or parameters (nonce / random number) for generating a cryptographic key.

The second communication agent 102 is a receiver that receives the transmitted data. The interfering signal transmitter 103 is called a jammer and transmits an interference signal ("jam signal").

It can also be provided multiple Störsignalsender. Also, the receiver 102 itself may emit a jamming signal. Also, the transmitter 101, in addition to the actual data, additionally emit an interference signal. In addition, additional nodes ("monitoring nodes") can be provided in the network which detect an existing interference signal The detected data can be transmitted directly to the transmitter 101 and / or the receiver 102. Alternatively, the additional node performs a check of the interference signal and provides the result of the review to the transmitter 101 and / or the receiver 102.

FIG. 2 shows a schematic diagram of a flow chart of a first embodiment of the method according to the invention. First, a first communication part ^¬ participants generates a transmission signal for transmitting a key agreement message to a second communication terminal 201. Subsequently, the radio interface is monitored by the first communication subscriber 202. The monitored radio interface is checked by the first communication participants according to predetermined test criteria regarding a presence of a jamming signal 203. If a fault signal, the key agreement message is sent to the arrangement of the safety key 204. If there is no fault signal, the key agreement message is not sent to Vereinba ^¬ tion of the safety key and 205, the radio interface again monitors 202 after a predetermined period of time.

In the illustrated variant, the monitoring is carried out to an interference signal before sending. The data is sent when a sufficient interference signal is detected. In an alternative embodiment, the transmitter does not wait until there is a sufficient interference signal, but does not transmit the data in this case.

In another alternative embodiment, the transmitter monitors the interference signal during transmission of the Sendesig ^¬ Nals. FIG. 3 shows a schematic diagram of a flow chart of a second embodiment of the method according to the invention. First, a first communication ^¬ subscriber generates a transmission signal for transmitting a Schlüsselver- einbarungsnachricht to a second communication participant

301. Then, the first communication participant waits for a predetermined period of time 302, then sends the Keyring ^¬ selvereinbarungsnachricht 303 and again waits for a predetermined period of time 304th

The time period 302 and the time period 304 may be, for example, 10 ms, 1 s, 60 s. The time period 302 and the time period 304 may be the same length or different lengths. In parallel to the execution of the method steps 302 to 304, the radio interface 305 continuously monitored by the first Kommunikati ^¬ onsteilnehmer thus takes place in this variant, a monitoring of the radio interface by the transmitter during transmission and during a predeterminable time window, before and after the actual transmission ,

The monitored radio interface is checked 306 by the first communication ^¬ participants in accordance with predetermined test criteria for the presence of an interference signal. If an interference signal in accordance with the predetermined test criteria, the sent key agreement message for Vereinba ^¬ tion of the security key by the first Kommunikati ^{¬ on} participants marked as valid 307 If there is no interference signal, the transmitted key agreement message for the agreement of the security key by the first communication user is marked as invalid 308.

The test criterion used can be for the period

302, sending the key agreement message 303

As well as for the period 304 be different. Thus, during the time period 302 and / or the time period 304, for example, testing criteria that are difficult to verify may apply (signal strength, direction determination, determination of a randomness value (Entropy estimate) of the interference signal and compared with a threshold value), whereas during the period 394 is a simp ^¬ cher applies to-be-verified test criterion (such as monitors only the Sig nalstärke of the interfering signal).

According to a variant of the described embodiment, a third node carries out the continuous monitoring and communicates the monitoring and / or checking results to the transmitter.

FIG. 4 shows a schematic representation of a flow chart of a third embodiment of the method according to the invention. First, a first communication subscriber generates a transmission signal for transmitting a key agreement message and sends it to a second communication subscriber (not shown). Prior to receiving the key agreement message is waiting the second communica tion ^¬ subscriber for a predetermined period of time 401, then the key agreement message 402 receives and waits in turn for a predetermined period of time 403rd

Parallel to the implementation of method steps 401 to 403, the radio interface is continuously monitored by the second communicating party on 404. Thus, this variant takes place a monitoring of the radio interface by the receiver during the reception and during a pre-definable time window before and after the actual transmission. The monitored radio interface is checked 405 by the second communication participants ^¬ according to predetermined test criteria for the presence of an interference signal. If an interference signal in accordance with the predetermined test criteria, the received key agreement message for agreement of the security key by the second communication participants ^¬ participants marked as valid 406. If no interference signal is present, the received key agreement verification looks to 407 for the agreement of the security key by the second communication participant marked as invalid.

According to a variant of the embodiment described a third node through the continuous monitoring and divides the monitoring and / or verification resulting ^¬ nis with the receiver.

FIGS. 5a and 5b each show, in a schematic representation, a flow chart for a fourth and a fifth embodiment of the method according to the invention.

In this variant, after the sending of a key agreement message from the transmitter 501 to the receiver 502, an interference signal check information is determined by the transmitter 503 or the receiver 506. Subsequently, the determined interference signal check information is transmitted from the transmitter to the receiver 504 or from the receiver to the transmitter 507. The receiver 505 or the transmitter 508 can then use the transmitted interference signal check information to check whether both transmitter and receiver had the same or a sufficiently similar interference signal. Depending on the result of the check, the sent key agreement message is marked as valid or invalid.

The Störsignal-PrüfInformation can be done for example by recording the interference signal over a predetermined period. The interference signal can be communicated directly to the communication partner or derived parameters, such as a checksum or statistical measures (mean, standard deviation, Rice factor). This requires both the transmitter and the receiver to continuously store the interference signal for specified periods and, if necessary, compare to received patterns. Alternatively, one of the two communication participants can request a test sequence, which is recorded in this case. Another alternative is the processing tion of minimum and maximum values of the interfering signal per Inter ^¬ vall.

The interference signal can be generated for example by means of a pseudo-noise code. The pseudo noise code can be generated randomly or cryptographically by means of a key. It can be sent out a digital noise or a continuous (analog) noise. A realization of the jammer by a separate node has the advantage that a simple implementation is possible: A node does not necessarily have to send and receive simultane- ^ously . In particular, a further node, which is located in the same network as the receiving node, is suitable as a jammer. In general, it is also possible to provide a plurality of interference signal transmitters which transmit the same interference signal or different interference signals.

An essential aspect of the present invention is the verification of whether an interference signal is present or not. A key agreement message is then sent Bezie ^¬ hung as accepted when its transmission at an interfering signal is present, or was present, which satisfies the test criteria.

When transmitting a key agreement message, the amount of information sent out may depend on the quality of the present interference signal. Thus, for example, bit values can be transmitted at random in order to determine a key therefrom by means of a hash function, such as, for example, SHA-1, SHA256. In the case of a good-quality interference signal, for example, 128-bit or 512-bit random numbers are transmitted, whereas for a poor quality interference signal, 1024-bit or 8192-bit random numbers are transmitted.

It can be provided a jammer that emits the receiver known interference signals. The jammer can part of the receiver or transmitter or realized as a separate node in the network. The light emitted from this jammer noise is superimposed on the übertra from the transmitter ^¬ related data. An attacker who is not aware of the interference signal can not obtain the data or only with complex reception technology.

The interference signal can be tested by the sender and / or the receiver. In principle, it is also possible that a third node of the network performs such monitoring of the interference signal and notifies the receiver and / or transmitter of the test result.

Possible test criteria for the interference signal are, for example:

- A sufficient signal strength.

- A localization information of the interfering signal transmitter, which is determined for example via a distance measurement or Positionsbe ^¬ mood. Here, the Störsignaleen- the example, be located in a particular area or at a certain distance to the network node.

- Direction information of the interfering signal transmitter. Here is to be determined, a corresponding interference signal, for example, at a reception with directivity in each ^¬ the segment or in a minimum number of segments.

- A statistical signal property of the interfering signal. Here ^¬ in the interfering signal is to have, for example, sufficient to maturity ^¬ which can be determined by an auto-correlation function of the received interference signal.

The monitoring of the interfering signal is usually done before sending. The monitoring can also be done after sending or during transmission. Monitoring during transmission can be done continuously or in short transmission pauses.

A receiving node of the network, which knows the interference signal, can eliminate the interference signal. An outsider, the does not belong to the network, does not know the interference signal and therefore can not decode the transmitted data or only with high reception costs. By the invention, the safety is thus improved in the transmission over a non-secure ^¬ radio interface as a transmitted security parameters will only be used when actually existed a suitable noise signal during its transmission.

Thus, protection is possible even without encryption of the transmitted data. This is easy to implement when multiple wireless nodes are available, such as multiple wireless access points, multiple nodes of a wireless WiFi mesh network, an ad hoc network or sensor network ^¬ plant.

Claims

claims

A method for secure agreement of a security key for a wireless communication connection via a radio interface, wherein

a first communication user generates a transmission signal for transmitting a key agreement message to a second communication user,

characterized,

that the radio interface is checked according vorgeb ^¬ cash test criteria regarding a presence of a jamming signal prior to transmission,

- in the presence of the interfering signal the key Vereinbarungs ^¬ message to the agreement of the safety key verwen- det is,

- in any presence of the interfering signal the Schlüsselvereinba ^¬ approximately message is not used to declare the Sicherheitsschlüs ^¬ sels.

2. The method of claim 1, wherein

the checking of the interference signal is performed by the first Kommunikati ^¬ onsteilnehmer and / or the second communication subscriber.

3. The method of claim 1, wherein

the interference signal is checked by a third communication user.

4. The method according to any one of claims 1 to 3, wherein

the checking of the interference signal at least partly currency ^¬ rend the transmission of the key agreement message is taken before ^¬.

5. The method according to any one of claims 1 to 4, wherein

the predetermined test criteria of the interference signal a signal strength ^¬ comprise a location information, direction information, and / or statistical signal properties.

6. The method according to any one of claims 1 to 5, wherein

the predetermined test criteria of the interference signal comprise a test information that is transmitted between the first and the second communication participant, and on the basis of which the respectively received interference signal to its similarity is ^{ver ¬} bar.

7. The method according to any one of claims 1 to 6, wherein

the interference signal is determined by the second communication participant,

- And the interference signal is signal processing technology removed by the second communication participant from the received key agreement message.

8. The method according to any one of claims 1 to 7, wherein

in any present interference signal is Schlüsselvereinba ^¬ approximately message is not transmitted by the first communication node.

9. The method according to any one of claims 1 to 7, wherein

if there is no interference signal, the transmitted key ^¬ agreement message is rejected by the second communication part ^¬ takers.

10. The method according to any one of claims 1 to 7, wherein

present in any interference signal, the transmitted key is discarded ^¬ agreement message by the first communication part ^¬ contractor for the agreement of a key.

11. System comprising a first and a second communication participant, comprising means for protected agreement a security key for a wireless Kommunikationsver ^¬ bond have over a radio interface, wherein the

the first communication ^user generates a transmission signal for transmitting a key ^{agreement message} to the second communication user,

characterized in that before the transmission, the radio interface is checked in accordance with predefinable test criteria with regard to the presence of an interference signal,

- in the presence of the interfering signal the Schlüsselvereinbarungs- message to the agreement of the safety key USAGE ^¬ det is,