DE102005051493A1 - Device for monitoring near-field communication with inductive transponders of electronic documents - Google Patents

Abstract

Write and read processes with integrated transponders can be monitored remotely by unauthorized persons. The object of the present invention is to prevent this. DOLLAR A The device for eavesdropping near-field communication (1) has a useful signal source (2) and an interference signal source (3) and at least one device (5) for generating a sum or difference signal from the useful signal and the interference signal for masking or erasing the Useful signal. DOLLAR A The device offers optimal bug-protected near-field communication without the need for encoding encryption of the communication channel by means of eliminating or influencing the content of signal-bearing alternating magnetic fields or radio waves outside a defined reading zone. DOLLAR A It enables the low-wall restriction of the communication area between a reading and / or writing device for transponders and transponder modules and preservation of privacy with contactless transfer of sensitive data.

Description

The The present invention relates to the technical field of Electrical engineering, in particular in communications engineering and data transmission technology. Transponder communication facilities can be over magnetic Alternating fields or radio waves read and partly described become. Passive transponders can also over the radio waves with the needed energy be supplied. The energy and data transmission occurs contactless via electromagnetic Waves. If no energy is transmitted, it remains the transponder is mute. While a read or write between a reader and a user Transponder creates a magnetic alternating field with suitable recipients (Radio receivers) also over longer distances can be captured, although the distance for reading a passive Transponders due to the maximum permissible power of the remote power supply restricted to a few inches to a maximum of meters. To prevent such hostile interception or to complicate is cause for the use of cost-intensive encryption methods and coding methods. Disclosed is a device for selectively preventing unwanted eavesdropping Near field communications between a reader and one or more Transponders. Preferably, these are passive inductive Transponder with near-field antennas. The device allows the selective (destructive) disorder of signal contents or signals electromagnetic waves or alternating magnetic field by a comparison with the prior art modified electrical circuit for near-field communication with inductive transponders. This makes the area easier to understand Communication between the reader antenna and transponder antenna restricted to the detection range of the reader, thereby a listening the signal outside absolutely impossible becomes. The core task is the protection of communication between readers and transponders by extinguishing or disturbing Additional signal radiation.

State of technology

to Securing and marking or logistic monitoring of products and Documents are increasingly becoming electronic components used. RFID (radio frequency identification) facilities are miniaturized components with, for example, CMOS technology manufactured semiconductor integrated circuits at the main terminals antennas for information transmission and possibly also contacted for power supply. The reading the RFID devices due to briefly referred to as transponder takes place preferably over Radio waves or alternating magnetic fields from a short distance.

Inductive working transponders require one Antenna coil of at least one turn, the different Form has. For example, the coil is circular, spiral, oval, or triangular and quadrangular with mostly rounded corners. A similar designed Antenna coil is at the communication device for reading or Describe the transponder required. With sufficient proximity of the two Coils the transponder enough energy from an alternating field record and perform the data communication. This happens through Modulation of the magnetic field comparable to a transformer without iron core.

Around a hearing protection to reach transponders are different possibilities been developed. Emphasis is put on encryption methods, where symmetric or asymmetrical encryption algorithms are used. Size key prevent any decryption possibility of the data, except the key falls in the wrong hands.

Becomes the private information is not transmitted but only reference numerals or reference numbers may be interrogated only be successful if an information carrier with the referenced information is present.

Changing the transmission channels (carrier frequency jump method) or time windows (time hopping) complicate the interception, since a plurality of transmission channels simultaneously bugged would have to be.

Ultra wideband transmission allows the reduction of data transmission on very small temporal windows (secretly defined temporal Ranges) and consequently very short pulse lengths.

Also Shielding of the entire communication path is, albeit consuming However, a practiced and proven anti-hearing protection.

Blocker tags (Blocking transponder), designed to hold a large number of transponder addresses can also be used as eavesdropping protection be used when this outside the communication zone to be ordered.

The patent US 2005/0058292 a method and an apparatus for secure 2-way communication is presented. In this case, an encrypted by a noise signal RF carrier signal is used, whereby the message of the communication is no longer extractable without the same means elsewhere by eavesdropping devices. In particular, the experienced by a a noise signal ver keyed RF signal after the modulation by the transponder removal of the encryption. For encryption is an amplitude, a frequency or a phase modulation circuit or combinations thereof. The modulation components are a voltage-controlled oscillator for frequency generation and modulation of the frequency or phase and / or an adjustable amplifier for amplitude modulation. In addition, a two-part coding key can be transmitted, which can also be partially varied. A password is possible. An encryption algorithm is possible. Overall, a very complex security procedure with different complexity is described, which also has a removable encryption of the carrier signal. The disadvantage is the increased system overhead, the effort to generate the reader signal and to secure the information and the effort to extract the data information. Furthermore, the modulation and Störsignalaufbringung not independent of each other possible.

Another Disadvantage is the spread of the spectrum of the reader device, which official Authorizations could not be granted.

Task of invention

It should be a cost effective and user-friendly device that creates the radius for the authorized or unauthorized collection of transponder communication content on the Radius of the maximum effective communication distance between a Limited communication device (a reader) and a transponder. Thereby should a listening the communication content during the write or read sequence outside a defined zone impossible be made.

The protection request

The Task is by the subject invention solved, which is a device for monitoring near field communication with inductive transponders of electronic represents. It points this device is a useful signal source and a noise source and at least one device for forming a sum or Difference signal from the useful signal and the interference signal for masking or to extinction of the useful signal.

For transmission the useful signal and for superposition through the interference signal At least one near field antenna is provided. This has preferably the shape of a coil or conductor loop of wound wire or is as a printed circuit with at least one conductive layer a circuit board material or the like.

For education the sum or difference signal within the device can Advantageously, an electrical or an electronic adding circuit or an electrical or electronic subtraction circuit be provided.

alternative or in addition may also be a sum or difference signal through a device to the geometric overlay at least two magnetic fluxes or electro-magnetic waves are generated for formation.

In In this case, it is advantageous if at least one antenna with the output of the useful signal source or the output of the adding circuit for the Sum signal, for example, from useful and interference signal is connected, and at least one further antenna with the output of a noise source or with the output of a subtracting circuit for the differential signal, for example made of useful and Störsignalgebildet becomes.

Considered one the different mitigation a magnetic excitation with the distance, for example, from coil antennas different diameter and different signal amplitude, the excitement can be higher due to the useful signal at close range, as the excitation by the interfering signal. Conversely, in the far range the lower weakening of a Coil with larger diameter and with higher noise level for one Covering the Nutzsignalen serve.

From Of particular importance is the use of a means for local Decoupling at least one antenna - for the useful signal or for a sum or difference signal with the useful signal - compared to all other antennas the near-field communication device. This remedy can be an aid for orthogonal orientation of the antenna axes, for example orthogonally oriented printed circuit boards or air coils. But it can also be a magnetically highly conductive field concentrator, For example, an iron yoke or a ferrite core by the field concentration has a strong filtering near-field, whereas in the far-field the useful signal in the interference signal disappears. Also a combination of the use of a field concentrator with the right-angled orientation is an effective means of data reception in the near field. Magnetic shielding elements made of magnetically conductive material Like iron sheets represent another alternative or complementary Means for local decoupling.

To recover the original useful signal or a derived signal which due to the modulation by the An If, for example, the antenna impedance of the transponder carrying the communication message (eg the antenna current of the device for monitoring near-field communication protected against tapping), there are two possibilities. In the case of using an adder circuit for masking or canceling the modulated useful signal, the output of the adder circuit is advantageously connected to a first input of a subtracting circuit, and the output of the interfering signal source is connected to a second input of the subtracting circuit, and its output is connected to a signal evaluation circuit.

Becomes a subtraction circuit for the formation of the signal to mask or cancel the modulated useful signal conversely, an adder circuit is used to obtain the signal. In this case, the output of the subtraction circuit is connected to a first input connected to this adder circuit, and the output of the interfering signal source connected to a second input of the adder, and its Output connected to a signal evaluation circuit.

The Result is in both cases a signal at the input of the Signalauswerteschaltung, which that from conventional unprotected Near field communication devices corresponds.

Well suitable and advantageous is the use of a random value generator for switching the noise source. The value of the generator is preferably a pseudo-random signal generator, from a stochastic signal of a noise signal generator or formed like.

Around identifying an interfering signal source complicate or the disorder To prevent other devices, it is advantageous that the interference signal source activated by the modulation signal of at least one transponder, controlled or formed. Once a modulation by a Transponder (backscattering signal) from a change detector of the subject invention is detected, the interfering signal source active. A watchdog circuit Hold on to it advantageously the source of interference active, until no detector signal arrives for a sufficiently long time. Also can the noise source Time Lag be activated, or the signal of the change detector itself serves as interference signal source with the help of a time delay element. Cheap is suitable for a shift register or the like, whereby the Signal at the output of the register again delayed with the mentioned means the useful signal is added or subtracted.

Finally, can it may be advantageous if the interfering signal source itself is the useful signal source, or equal to the useful signal source is or from the signal caused by the transponder antenna impedance modulation is formed, as possible decoupled antennas for the far field is destructively fed interferent. So can the Antennas that are not in close coupling with a transponder be driven inverted, or the winding sense of the coil unlike that of the payload antenna.

The Invention and possible Embodiments will be described below with reference to the figures. Show it:

1 shows the principle circuit diagram with the device 1 for monitoring near field communication and a transponder 6 ,

2 and 3 show possible arrangements and designs of the antennas.

4 to 12 show exemplary embodiments of the device for forming a sum or difference signal.

13 . 14 and 15 show possibilities for decoupling the antennas 43 and 44 especially for the near field.

16 outlined a possible recovery of the transponder (backscatter) information with electrical or electronic addition of interfering and useful signal.

17 outlined a possible recovery of the transponder (backscatter) information with electrical or electronic subtraction of interfering and useful signal.

18 and 19 show outline different jamming-educational types.

20 shows a possibility for generating a noise signal for deletion of the useful signal in the far field by destructive interference.

As in the 1 . 16 and 17 shown are two signal generators 2 . 3 for generating a useful signal and a noise signal possible. These may have the same or similar carrier frequency. The useful signal is usually suitable for the energy supply of the transponder and approved carrier signal of certain frequency and is provided by the generator 2 generated. This carrier signal is applied to a read-out transponder by the coupling of the near-field antenna 4 with the transponder antenna 61 transferred to the transponder, which thereby absorbs energy. The variation of the energy consumption eg by varying the input impedance of the transponder 6 is visible by a change in the primary coil current of the transformer formed by the antennas, whereby a Datentrans port to the device 1 is possible.

The second generator 3 serves the disturbance of the alternating magnetic fields or radio waves around or also within the communication distance. It generates a signal that has indefinite, ambiguous, and non-repetitive content. This useless information is only for the privacy of the communication process. Through the device 5 In order to form at least one sum or difference signal, an interference signal is added or subtracted from the useful signal. This can happen on the electrical level or on the magnetic level. In the second case, as in 1 indicated by dashed lines and in 20 shown is an additional antenna 44 provided for the interfering signal. Then the magnetic fields of the antennas are superimposed 43 . 44 additive. With opposite superimposition, the magnetic field components are extinguished. The geometric superposition of the magnetic fields or the radio waves is through the frame 53 symbolizes.

In 2 serve coil antennas 4 . 41 . 61 the energy and data transmission. When using a second antenna 44 , This should have a possible decoupled orientation to Nutzsignalantenne and transponder antenna.

3 shows another example of the design of the near-field antenna. Here, a printed circuit, one or more circuit board elements or carriers of metallic or conductive layers serves to form a loop antenna 42 or several frame antennas 43 . 44 ,

4 shows the switching symbol of an adding function 51 as they pass through the device 5 can be embodied. 6 shows an electrical embodiment by a power node. (Then the useful signal source 2 and the interfering signal source 3 in 1 a power source. 8th shows an electronic addition of two signals with an operational amplifier. These come from generators, for example in the form of an electrical alternating voltage for the useful signal and an irregularly pulsed second alternating voltage for the interference signal.

5 shows the switching symbol of a subtraction function 52 for the device 5 , In 7 the electrical subtraction is represented by a current node wherein the phase position of the interference signal is rotated by 180 degrees (signal inversion). In 9 An electronic subtracter is shown. Normally, the electronic and electrical circuits are still adjusted power output stages. Becomes a subtraction function 52 is used, the energy is strongly attenuated at the same frequency of the useful and interference signal. At the same amplitude even extinguished. Then no data transmission can take place. If a similar frequency is used, a beat occurs, with the difference frequency, thereby generating energy supply pulses. If they are too short, the complete information can not be transferred. Additional switching on and off of the Störsignalfrequenzgebers at irregular intervals cause an interference signal, which leads to high security against eavesdropping.

If the addition or subtraction of the signals by two antennas, one serves as a coupling antenna for the transponder and the second as a noise antenna can as a device 5 also simple connections with decoupled antennas are used, as in 10 shown. Depending on the orientation of the antennas to each other, there is a geometric addition or subtraction of useful and interfering field components.

The 11 and 12 show the function diagram when, for example, the sum signal of an adder 51 fed from useful signal and interference signal of an antenna and the difference signal of a subtractor 52 a further antenna is supplied, whereby the transponder modulates a signal changed by means of a noise source. By subtraction of sum and difference signal can be easily recover the modulation signal.

13 shows a possible means 7 for decoupling the magnetic fluxes: the orthogonal arrangement of the loop antennas 42 , one of which is the Nutzsignalantenne 43 and one the jamming antenna 44 is.

Another possible means 7 for decoupling is the guidance of the magnetic flux in highly magnetically conductive materials, as in 14 explained. In this case, the iron yoke is preferably formed by laminations 72 on the one hand, the field concentration for the useful signal, and on the other hand, the decoupling of the two windings 43 . 44 for data traffic via the transponder 6 and noise generation via antenna 44 for the environment.

15 shows the possibility of shielding 73 the field antenna 43 from the interference field antenna 44 as a decoupling device 7 ,

Becomes the sum signal of the adder 51 the communication antenna 4 fed, provides a subtractor 54 , as in 16 shown a simple signal recovery option for further processing in the signal evaluation circuit 8th ,

In 17 the principle is reversed, with the difference signal of the subtractor 52 the communication antenna 4 is fed and via the adder 55 the signal for further processing in the signal evaluation 8th is produced.

18 . 19 shows a part of the 1 . 16 or 17 wherein the generation of the interference signal by a "random" signal from the signal evaluation circuit 8th used to control a switch, transmission gate or amplifier. This results in a noise signal with pseudo information content low redundancy. As a random value generator 9 can serve a noise source with window discriminator or a pseudo-random generator or the time-shifted modulation signal of the transponder.

The latter is in 19 outlined. For the time shift, a time delay element 112 or a shift register 113 serve. But it can also be a monoflop activated by the transponder modulation. This switches on (retriggerable or not) the interference signal source for a limited time or off.

In 20 Finally, an embodiment is shown, wherein the signal of the useful signal source is tapped and amplified supplied to the Störsignalpfad. As a result, with suitable control, a partial to complete extinction of the communication signal outside the near field can be effected.

1

Near-field communication device with privacy protection

2

useful signal source

3

interference signal source

4

near field antenna

41

Kitchen sink made of wound wire

42

Loop antenna, formed by the conductive Layer of a printed circuit

43

antenna for the Useful signal or for a sum signal of useful and interference signal

44

antenna for the noise or for a difference signal from useful and interference signal

5

contraption to form a sum or difference signal

51 55

adders

511

electrical adder

512

electronic adder

52 54

subtraction

521

electrical subtracting circuit

522

electronic subtracting circuit

53

contraption to the geometric overlay at least two magnetic fluxes or electro-magnetic waves

6

transponder

61

Transponder antenna

7

medium for local antenna decoupling

71

medium for the right-angled orientation of the antenna axes

72

field concentrator (Ferrite, iron core)

73

magnetic conductive shroud

8th

signal evaluation (typical reader evaluation circuit)

9

Random value generator

10

change detector

11

control circuit

111

watchdog circuit (Watchdog)

112

Time delay element

113

shift register

12

amplifier

Claims (11)

Contraption ( 1 ) for tamper-proof near-field communication with inductive transponders ( 6 ) of electronic documents, characterized in that the device ( 1 ) a useful signal source ( 2 ) and an interfering signal source ( 3 ) and at least one device ( 5 ) for forming a sum or difference signal from the useful signal and the interfering signal for masking or for extinguishing the useful signal. Apparatus according to claim 1, characterized in that for transmitting the useful signal and for superposition by the interference signal at least one near-field antenna ( 4 ) is provided, which is preferably in the form of a coil ( 41 ) or conductor loop made of wound wire or as a printed circuit ( 42 ) is performed with at least one conductive layer of a printed circuit board material or the like. Device according to one of claims 1 and 2, characterized in that as device ( 5 ) for the formation of the sum or difference signal an electrical ( 511 ) or electronic ( 512 ) Adder ( 51 ) and / or an electrical ( 521 ) or electronic ( 522 ) Subtraction circuit ( 52 ) is provided. Device according to at least one of claims 1 to 3, characterized in that a device ( 53 ) is provided for the geometric superposition of at least two magnetic fluxes or electro-magnetic waves to form at least one sum signal or at least one difference signal. Device according to claim 4, characterized in that the device ( 53 ) by at least one antenna ( 43 ) with the output of the useful signal source ( 2 ) or with the output of the adder circuit ( 51 ) and at least one further antenna ( 44 ) with the output of the interfering signal source ( 3 ) or with the output of the subtraction circuit ( 52 ) is formed. Device according to claim 5, characterized in that it comprises a means ( 7 ) for local decoupling at least one antenna ( 43 ) compared to all other antennas ( 43 . 44 ) of the device ( 1 ), preferably means ( 71 ) for the orthogonal orientation of the antenna axes, a magnetically highly conductive field concentrator ( 72 ), for example an iron yoke or a ferrite core and / or a magnetic shielding element ( 73 ) made of magnetically conductive material, for example made of sheet iron. Device according to at least one of claims 1 to 6, characterized in that the output of the adding circuit ( 51 ) with a first input of a subtractor circuit ( 54 ), and the output of the interfering signal source ( 3 ) with a second input of the subtraction circuit ( 54 ), and whose output is connected to a signal evaluation circuit ( 8th ) connected is. Device according to at least one of claims 1 to 6, characterized in that the output of the subtracting circuit ( 52 ) with a first input of an adder circuit ( 55 ), and the output of the interfering signal source ( 3 ) with a second input of the adder circuit ( 55 ), and whose output is connected to a signal evaluation circuit ( 8th ) connected is. Device according to at least one of claims 1 to 8, characterized in that the interference signal source ( 3 ) by a random value generator ( 9 ) whose value is preferably formed of a pseudo-random signal generator, a stochastic signal of a noise signal generator or the like. Device according to at least one of claims 1 to 9, characterized in that the interference signal source ( 3 ) by the modulation signal (backscattering) of at least one transponder ( 6 ) via a change detector ( 10 ) is activated, controlled or formed, preferably as a control circuit ( 11 ) a watchdog (watchdog) 111 ), a time delay element ( 112 ), a shift register ( 113 ) or the like is used. Device according to at least one of claims 5 to 10, characterized in that the interference signal source ( 3 ) is the useful signal source, or equal to the Nutzsignalquelle, or by means of at least one amplifier ( 12 ) or the like is formed from the signal caused by the transponder antenna impedance modulation, wherein as far as possible decoupled antennas ( 43 . 44 ) for the far field are destructively fed interferent.