EP2178235B1 - Verschlüsselung von Informationssignalen - Google Patents

Verschlüsselung von Informationssignalen Download PDF

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Publication number
EP2178235B1
EP2178235B1 EP08390001A EP08390001A EP2178235B1 EP 2178235 B1 EP2178235 B1 EP 2178235B1 EP 08390001 A EP08390001 A EP 08390001A EP 08390001 A EP08390001 A EP 08390001A EP 2178235 B1 EP2178235 B1 EP 2178235B1
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Prior art keywords
subbands
signal
subband
encryption
analysis
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French (fr)
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EP2178235A1 (de
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Anastasis c/o SignalGeneriX Ltd. Kounoudes
Demosthenis c/o SignalGeneriX Ltd. Doumenis
Nikolaos c/o SignalGeneriX Ltd. Doukas
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SignalGeneriX Ltd
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SignalGeneriX Ltd
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Priority to AT08390001T priority Critical patent/ATE527768T1/de
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Priority to CY20111101254T priority patent/CY1112183T1/el
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/04—Secret communication by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

Definitions

  • the invention relates to techniques for encrypting and decrypting information signals, for example digital voice signals. More particularly, the invention relates to the encryption and decryption of information signals based on polyphase filter banks.
  • voice encryption technologies are often provided as a separate unit (an 'add-on' device) to communication devices such as mobile phones.
  • an analogue voice signal is captured by a microphone, digitized and input into the encryption add-on.
  • the add-on outputs the encrypted voice signal to the mobile phone.
  • the encrypted signal is then transmitted via a mobile network to the receiving party, which may be another mobile phone.
  • the encrypted signal is provided to a decryption add-on, which reverts the encryption and outputs the decrypted signal, for example back to the mobile phone.
  • US 4,829,378 may be construed to disclose a signal transceiving system in which an input signal is split into two signals being decimated 2:1. In turn, the decimated two signals are each again split into two further signals, and the resulting four signals are coded for transmission.
  • the receiving end provides the exact reverse operations to the coding, decimating and splitting i.e., decoding, interpolation and summing.
  • Paper " Exact Reconstruction Techniques for Tree-Structured Subband Coders", Mark J. T. Smith et.al., IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. ASSP-34, no. 3, June 1986 may be construed to disclose a signal transceiving system similar to that of US 4,829,378 .
  • GB 1 465 923 may be construed to disclose a signal transmission method (and system) comprising splitting an input signal into subbands, replacing one of the subbands with an interference spectrum, and synthesizing the subbands into an output signal, so as to camouflage the transmitted signal.
  • the above methods may be applied to any kind of digital (or analogue) information signal including for example digital audio signals or digital voice or speech signals.
  • the signal subbands may be interleaved subbands.
  • the analysis and/or synthesis subband filters in both the above-outlined methods may be polyphase subband (component) filters.
  • the analysis subband filters may be chosen such that the product of all analysis subband filters is all-pass, i.e. an input information signal would pass a filter implementing the product of all analysis subband filters essentially unchanged.
  • the multiple analysis filters may be derived from a single prototype subband filter.
  • the configuration of the particular synthesis filter may be simplified.
  • the prototype subband filter may for example be a (proprietary or standardized) low pass finite impulse response filter.
  • the analysis / synthesis subband or component filters may be derived from the prototype filter using, e.g., a factorization technique.
  • the number of signal subbands can be varied in time.
  • the time variation (or non-uniformity) of the signal subbands may be selected according to a complexity of the information to be encrypted or decrypted, which may be based on a measure of an energy distribution of the input information signal in frequency.
  • the number of signal subbands may be chosen such that the bit distribution of the encoding is proportional to the complexity of information.
  • the analysis filters and correspondingly the synthesis filters may be adapted accordingly.
  • the encryption or decryption operation may comprise transforming the signal subbands into frequency subbands. For example, a Fourier transformation, Laplace transformation or Z-transformation may be performed. A corresponding inverse or back transformation may also be included in the encryption (decryption) operation.
  • the analysis transformation may be an inverse Fourier or Z-transformation, while the synthesis transformation is a corresponding back transformation.
  • the encryption or decryption operation may comprise a permutation of at least two subbands.
  • two or more frequency subbands may be permuted.
  • the permutation of subbands may be varied in time.
  • the subbands to be currently permuted may either be signalled from an encrypting device to a decrypting device, or the permutation may be controlled by a control scheme which is in the same way or similarly implemented in both devices.
  • a permutation of subbands may be based on a signal energy contained therein. For instance, the two subbands containing most of the signal energy may be permuted with each other. This permutation could be reverted in the decryption operation.
  • the encryption operation may comprise replacing at least one subband by noise.
  • the noise has to be configured such that the output information signal is unrecognisable with high probability.
  • a corresponding decryption operation may comprise removing noise from at least one subband based on, for example, the detection that a noise level in a subband exceeds a predetermined threshold or the detection of a pre-defined, particular signature imprinted on the noise by the encryption operation.
  • the computer program product is executed on one or more computing devices, for example one or both of an encryption device and a decryption device.
  • the computer program product may be stored on a computer readable recording medium, such as a permanent or rewriteable memory within or associated with a computing device or a removable CD-ROM, DVD or USB-stick. Additionally or alternatively, the computer program product may be provided for download to a computing device, for example via a data network such as the Internet or a communication line such as a telephone line or wireless link.
  • the encryption (decryption) device may be adapted to the encryption (decryption) of voice or speech signals and may be particularly configured as an add-on device for mobile phones.
  • the communication device or system may comprise a mobile phone, wherein the encryption device and/or decryption device may be implemented as hardware, software, or a combination thereof.
  • Another implementation of the communication device comprises a headset connectable to a mobile phone.
  • the headset may be an external headset with processing capabilities for connection with a mobile phone via Bluetooth or a similar wireless connection technique.
  • any of the above-outlined devices may be implemented based on an FPGA (Field-Programmable Gate Array). Additionally or alternatively, at least a portion of a circuitry of any one of the above-outlined devices may be adapted for parallel processing. For example, the parallel processing may be realized based on the aforementioned prototype subband filter.
  • An implementation of the above-mentioned headset may comprise an encryption and/or decryption device implemented on an FPGA with parallel processing capabilities.
  • the techniques described below may not only be applied to encryption and decryption of digital voice or speech signals, but to any kind of audio signals or more generally information signals including, for example, video signals, facsimilie data, electronic files (file transfer) or electronic data. Besides that, the techniques described herein may not only be used in conjunction with digital signal processing, but also analogue signal processing.
  • an encryption and/or decryption device may also be implemented purely software-based depending on the processing capabilities of current or future general purpose processing hardware available for, e.g., mobile phones.
  • Fig. 1 illustrates an embodiment of a system 100 for the encryption and decryption of digital audio signals.
  • the system comprises an analogue audio input device 102, an Analogue-to-Digital(A/D) unit 104, an encryption device 106 and a cellular phone 108 in communication via a mobile network 110 with a receiving mobile phone 112, a decryption device 114, a Digital-to-Analogue (D/A) unit 116 and an analogue audio output device 118.
  • the audio input device 102 may be a microphone, while the audio output device 118 may be a loudspeaker.
  • the encryption device 106 may be a hardware add-on which may or may not be _ specifically adapted to the mobile phone 108.
  • the encryption device 106 may be connected to a conventional interface to the mobile phone 108, such as a headset interface as it is conventionally used for hands-free operation of mobile phones. In this way, the encryption device may replace a headset or may be connected in between the headset and the mobile phone.
  • the A/D-unit 104 may be provided on a common hardware with either one or both of the microphone 102 and encryption device 106 or may be provided as a stand-alone unit.
  • the audio input 102 may be a microphone integrated in mobile phone 108.
  • a user speaks into the audio input device 102, which generates an analogue electrical representation of the voice or speech input.
  • the electrical signal is provided to the AID-unit 104, which samples the signal and generates a digital representation 120 thereof.
  • the digital voice signal 120 is input to the encryption device 106, which encrypts the signal as will be described in detail further below.
  • the encrypted output signal 122 is provided to the mobile phone 108 in digital or analogue form. In the embodiment described here it is assumed that the encryption device 106 outputs digital encrypted voice signals.
  • the signal 122 provided to the mobile phone 108 is transmitted via the mobile network 110 towards the receiving party, i.e. mobile phone 112. From there, the received encrypted voice signal is forwarded 124 to the decryption device 114. It depends on the details of the implementation whether the received encrypted voice signal 124 is provided to the decryption device 114 in digital or analogue form. In the embodiment described here, it is assumed that the signal 124 is input to the decryption device as a digital signal.
  • the decryption device 114 decrypts the encrypted voice signal 124.
  • the decrypted voice signal 126 is fed to the D/A-unit 116 which provides an analogue representation of the audio signal 126 to the audio output 118.
  • the decryption device 114 may, for example, be connected in between the mobile phone 112 and a headset which includes the D/A-unit 116 and audio output 118.
  • the D/A-unit 116 may be implemented on a common hardware with the decryption device 114.
  • the audio output 118 may be a loudspeaker 118 integrated in mobile phone 112.
  • Any of the encryption device 106 and the decryption device 114 may, for example, be implemented on an FPGA platform and may, depending on the concrete operational environment, include A/D-converter and/or D/A-converter, although these are illustrated as separate units in Fig. 1 .
  • An encryption device (decryption device) may further comprise various connectors for microphone, earphones, USB port, Ethernet interface, RS-232 port, etc.
  • the encryption device 106 operates to encrypt digital information signals, more particularly the digital voice signal 120.
  • an input information signal may be an analogue signal.
  • An encryption device may then comprise an A/D-unit similar to A/D-unit 104 of Fig. 1 .
  • the input voice signal 120 is provided to the analysis filter bank 204, which operates to split the input voice signal 120 into a set of signal subbands.
  • the filter bank 204 is a polyphase filter bank comprising multiple analysis subband filters (component filters) generating a set of interleaved subbands. While in the example illustrated in Fig. 2 the input signal 120 is split into 16 subbands 220, in other embodiments a smaller or larger number of subbands may be configured.
  • the multiple analysis filters of the filter bank 204 may be derived from a single prototype subband filter, which may be a standardized or a proprietary lowpass finite impulse response (FIR) filter.
  • the desired number of analysis subband filters (polyphase component filters) may be derived therefrom by using a factorization technique.
  • step 304 at least one encryption operation is performed on one or more subband of the set of subbands 220 generated by the filter bank 204. Details on the encryption operations will be described with reference to Fig. 6 further below.
  • an encrypted set of subbands 222 is provided to the synthesis filter bank 218, which operates to synthesize the encrypted set of subbands 222 into the output voice signal 122.
  • the filter bank 218 may be configured similarly as the analysis filter bank 204, i.e. may also be a polyphase filter bank comprising multiple (synthesis) subband filters.
  • the synthesis filters are adjusted in a way complementary to the analysis filters of filter bank 204. Specifically, each of the synthesis filters is a product of all analysis filters of filter bank 204 except the analysis filter which corresponds in subband to the particular synthesis filter. The reasons for this choice will be discussed with reference to Figs. 8a-8d .
  • the permutation process may be easily reverted in the decryption device without the need for an extra signalling.
  • a permutation of the two subbands containing most of the signal energy Performing exactly the same processing in the decryption device would revert the permutation and would in this way decrypt the encrypted signal.
  • parameters for properly controlling a decryption may be signalled to the decryption device. Such signalling may be performed in-line, i.e. embedded within the encrypted information signal, or in any other way.
  • the noise generator 212 operates to replace at least one of the frequency subbands 226 by noise.
  • the noise may be, for example, white noise which may or may not be randomly generated.
  • An intensity of the noise has to be sufficient such that the speech signal becomes unrecognizable and that cryptoanalytic attacks on the encrypted information signal are prevented.
  • the noise intensity may be predetermined or may be controlled based on, for example, a signal energy measured from one or more of the subbands or the input information signal 120. For instance, the signal energies measured for controlling a permutation process may also be used for controlling the noise to be injected into the signal.
  • an in-line signalling may be imprinted on the noise in order that the decryption device may properly control a decryption, as discussed above.
  • Fig. 7 illustrates decryption operations which may be performed in the course of step 504 of Fig. 5 and which are described taking reference of the decryption device 114 of Fig. 4 . It is generally to be noted that many units and components of the decryption device 114 may operate similarly to the corresponding units and components of the encryption device 106 (in some embodiments, all units and components may operate similar). In particular, the filter banks 402 and 416 of device 114 may exactly correspond to the filter banks 204 and 218 of device 106.
  • the reverse permutation scheme will also be a fixed scheme, and may even be exactly the same scheme.
  • the component 408 may apply a similar scheme, however, some time synchronization would then be required between components 210 and 408.
  • a more extensive signalling would be required which indicates the momentary permutation configuration to the permutation component 408.
  • Such signalling mechanism may comprise in-line signalling, which may for example be imprinted on the noise by the noise generator 212 in Fig. 2 .
  • the noise remover 410 operates to remove noise from those subbands to which noise has been added by the noise generator 212 in the encryption device 106.
  • the noise remover 410 may replace noise by silence (zero signal energy) in these subbands.
  • the noise remover 410 has to detect the one or more subbands of the set of subbands 422 which contain noise.
  • the component 410 requires decision logic in this respect in order to decide whether a subband is filled, for example, by white noise.
  • Fig. 8b illustrates the system of Fig. 8a wherein the filter functions F(z) have been rearranged. Still, the system behaviour is all-pass. An identity matrix may be inserted at the point A indicated in Fig. 8b , which also leaves the operation of the system unchanged.
  • the proposed techniques allow implementing an encryption device, decryption device or combined device on a simplified circuitry with small footprint and which is straightforwardly connectable to a communication device such as a mobile phone and with minimal requirements on processing power, memory and/or power supply. No further external peripheral devices may be needed.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)

Claims (14)

  1. Verfahren zum Verschlüsseln von Informationssignalen, wobei das Verfahren die Schritte umfasst:
    - Aufspalten (302), auf der Grundlage einer Mehrzahl von Analyseunterbandfiltern (204), eines Eingabeinformationssignals (120) in einen Satz von Signalunterbändern (220);
    - Durchführen (304) eines Verschlüsselungsvorgangs bei einem oder mehreren Unterbändern des Satzes von Unterbändern; und
    - Synthetisieren (306), auf der Grundlage einer Mehrzahl von Syntheseunterbandfiltern (218), des verschlüsselten Satzes von Unterbändern (222) in ein Ausgabeinformationssignal (122),
    dadurch gekennzeichnet, dass
    - eine bestimmte Synthesefilterfunktion das Produkt aller Analysefilterfunktionen außer der Analysefilterfunktion ist, die im Unterband der bestimmten Synthesefilterfunktion entspricht.
  2. Verfahren zum Entschlüsseln von Informationssignalen, wobei das Verfahren die Schritte umfasst:
    - Aufspalten (502), auf der Grundlage einer Mehrzahl von Analyseunterbandfiltern (402), eines Eingabeinformationssignals (124) in einen Satz von Signalunterbändern (418);
    - Durchführen (504) eines Entschlüsselungsvorgangs bei einem oder mehreren Unterbändern des Satzes von Unterbändern; und
    - Synthetisieren (506), auf der Grundlage einer Mehrzahl von Syntheseunterbandfiltern (416), des entschlüsselten Satzes von Unterbändern (420) in ein Ausgabeinformationssignal (126),
    dadurch gekennzeichnet, dass
    - eine bestimmte Synthesefilterfunktion das Produkt aller Analysefilterfunktionen außer der Analysefilterfunktion ist, die im Unterband der bestimmten Synthesefilterfunktion entspricht.
  3. Verfahren gemäß Anspruch 1 oder 2,
    wobei das Produkt aller Analyseunterbandfilter (204, 402) ein Allpass ist.
  4. Verfahren gemäß zumindest einem der vorhergehenden Ansprüche,
    wobei die Mehrzahl von Analysefiltern (204, 402) aus einem einzelnen Prototypunterbandfilter abgeleitet wird.
  5. Verfahren gemäß zumindest einem der vorhergehenden Ansprüche,
    wobei der Verschlüsselungs- oder Entschlüsselungsvorgang ein Transformieren (602) der Signalunterbänder (220, 418) in Frequenzunterbänder (226, 422) umfasst.
  6. Verfahren gemäß zumindest einem der vorhergehenden Ansprüche,
    wobei der Verschlüsselungs- oder Entschlüsselungsvorgang eine Permutation (604) von zumindest zwei Unterbändern umfasst.
  7. Verfahren gemäß Anspruch 6,
    wobei die Permutation über der Zeit variiert wird.
  8. Verfahren gemäß zumindest einem der Ansprüche 1 und 3 bis 7,
    wobei der Verschlüsselungsvorgang ein Ersetzen (606) von zumindest einem Unterband durch Rauschen umfasst.
  9. Verfahren gemäß zumindest einem der Ansprüche 1 und 3 bis 8,
    wobei die Anzahl von Signalunterbändern über der Zeit variiert wird.
  10. Verfahren gemäß Anspruch 2,
    wobei, in dem Durchführungsschritt, der Entschlüsselungsvorgang ein Entfernen (706) von Rauschen aus zumindest einem Unterband umfasst.
  11. Computerprogrammprodukt, umfassend Programmcodeabschnitte zum Durchführen der Schritte des Verfahrens gemäß zumindest einem der vorhergehenden Ansprüche, wenn das Computerprogrammprodukt auf einem oder mehreren Computervorrichtungen ausgeführt wird.
  12. Verschlüsselungsvorrichtung (106) zum Verschlüsseln von Informationssignalen, umfassend:
    - eine Komponente (204), die eingerichtet ist, um auf der Grundlage einer Mehrzahl von Analyseunterbandfiltern ein Eingabeinformationssignal (120) in einen Satz von Signalunterbändern (220) aufzuspalten;
    - eine Komponente (206 - 216), die eingerichtet ist, um einen Verschlüsselungsvorgang bei einem oder mehreren Unterbändern des Satzes von Unterbändern durchzuführen; und
    - eine Komponente (218), die eingerichtet ist, um auf der Grundlage einer Mehrzahl von Syntheseunterbandfiltern den verschlüsselten Satz von Unterbändern (222) in ein Ausgabeinformationssignal (122) zu synthetisieren, dadurch gekennzeichnet, dass
    - eine bestimmte Synthesefilterfunktion das Produkt aller Analysefilterfunktionen außer der Analysefilterfunktion ist, die im Unterband der bestimmten Synthesefilterfunktion entspricht.
  13. Entschlüsselungsvorrichtung zum Entschlüsseln von Informationssignalen, umfassend:
    - eine Komponente (402), die eingerichtet ist, um auf der Grundlage einer Mehrzahl von Analyseunterbandfiltern ein Eingabeinformationssignal (124) in einen Satz von Signalunterbändern (418) aufzuspalten;
    - eine Komponente (404 - 414), die eingerichtet ist, um einen Entschlüsselungsvorgang bei einem oder mehreren Unterbändern des Satzes von Unterbändern durchzuführen; und
    - eine Komponente (416), die eingerichtet ist, um auf der Grundlage einer Mehrzahl von Syntheseunterbandfiltern den entschlüsselten Satz von Unterbändern (420) in ein Ausgabeinformationssignal (126) zu synthetisieren, dadurch gekennzeichnet, dass
    - eine bestimmte Synthesefilterfunktion das Produkt aller Analysefilterfunktionen außer der Analysefilterfunktion ist, die im Unterband der bestimmten Synthesefilterfunktion entspricht.
  14. System (100), umfassend die Verschlüsselungsvorrichtung gemäß Anspruch 12 und die Entschlüsselungsvorrichtung gemäß Anspruch 13, das insbesondere als eine Zusatzvorrichtung für Mobiltelefone eingerichtet ist.
EP08390001A 2008-10-17 2008-10-17 Verschlüsselung von Informationssignalen Active EP2178235B1 (de)

Priority Applications (3)

Application Number Priority Date Filing Date Title
AT08390001T ATE527768T1 (de) 2008-10-17 2008-10-17 Verschlüsselung von informationssignalen
EP08390001A EP2178235B1 (de) 2008-10-17 2008-10-17 Verschlüsselung von Informationssignalen
CY20111101254T CY1112183T1 (el) 2008-10-17 2011-12-16 Κωδικοποιηση πληροφοριακων σηματων

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EP08390001A EP2178235B1 (de) 2008-10-17 2008-10-17 Verschlüsselung von Informationssignalen

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EP2178235B1 true EP2178235B1 (de) 2011-10-05

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Publication number Priority date Publication date Assignee Title
US9935604B2 (en) * 2015-07-06 2018-04-03 Xilinx, Inc. Variable bandwidth filtering
GB2589492B (en) * 2018-07-10 2022-05-25 Cirrus Logic Int Semiconductor Ltd A system and method for performing biometric authentication

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1465923A (en) * 1973-04-03 1977-03-02 Siemens Ag Camouflaged speech signal transmission systems
CA1288182C (en) * 1987-06-02 1991-08-27 Mitsuhiro Azuma Secret speech equipment
US4829378A (en) * 1988-06-09 1989-05-09 Bell Communications Research, Inc. Sub-band coding of images with low computational complexity

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ATE527768T1 (de) 2011-10-15
EP2178235A1 (de) 2010-04-21

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