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EP0313029A1 - Dispositif de transmission brouillée de signaux analogiques - Google Patents

Dispositif de transmission brouillée de signaux analogiques Download PDF

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Publication number
EP0313029A1
EP0313029A1 EP88117419A EP88117419A EP0313029A1 EP 0313029 A1 EP0313029 A1 EP 0313029A1 EP 88117419 A EP88117419 A EP 88117419A EP 88117419 A EP88117419 A EP 88117419A EP 0313029 A1 EP0313029 A1 EP 0313029A1
Authority
EP
European Patent Office
Prior art keywords
code
signal
signals
concealment
teg
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP88117419A
Other languages
German (de)
English (en)
Inventor
Alfred Platt
Wolfgang Tschirk
Erik Dipl.-Ing. Mally
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG Oesterreich
Siemens AG
Original Assignee
Siemens AG Oesterreich
Siemens AG
Siemens Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AT278787A external-priority patent/AT393339B/de
Priority claimed from AT239288A external-priority patent/AT393055B/de
Application filed by Siemens AG Oesterreich, Siemens AG, Siemens Corp filed Critical Siemens AG Oesterreich
Publication of EP0313029A1 publication Critical patent/EP0313029A1/fr
Ceased legal-status Critical Current

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Classifications

    • 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 a device according to claim 1.
  • EP 136 681 describes a method for operating a device for the veiled transmission of analog signals. Protection against eavesdropping is provided in that the subscriber terminals generate the transmission code, but cannot evaluate it. The code is evaluated in the base stations, but they are not freely accessible. A subscriber terminal can therefore not be used to decrypt signals which are intended for another subscriber terminal.
  • the filters and modulators used to swap the frequency bands reduce the signal-to-noise ratio and high frequency requirements must be placed on them.
  • the manufacturing tolerance of the components reduces the quality of the signals after double concealment and unveiling if they are received by the second subscriber terminal.
  • the frequency band swapping can lead to the radio channel being overloaded, since the frequency spectrum does not have a uniform amplitude and the heights are raised in the radio part.
  • EP 28 688 describes a communication system in which audio frequency signals in the speech area are used to switch from clear to secret mode.
  • an audio frequency signal generator is acoustically coupled to the microphone of a telephone and offers a personal identification option.
  • the encryption key is not changed.
  • DE-OS 35 36 384 describes a radio system in which the signals to be veiled are predistorted and equalized after the veiling. In this way, the influence of a blurring frequency on the overdriving characteristic of the transmitted speech signal is eliminated.
  • the advantages of using the dynamic range in the transmission channel due to the elevation on the transmitter side are retained.
  • a de-emphasis downstream of the concealer and a pre-emphasis upstream of the de-concealer compensate for the height increase by means of the pre-emphasis already present on the transmitting side or the lowering of the de-emphasis existing on the receiving side.
  • the object of the invention is to prevent unauthorized eavesdropping by locating the band with the highest energy while improving the reproduction quality of a veiled transmitted signal. This is solved by claims 1 and 7.
  • the digital signal processing in the obfuscation circuit prevents loss of quality due to component tolerances in the frequency band swapping of speech signals.
  • the words remain easy to understand even if they are obscured by both subscriber terminals.
  • the concealment can be switched on or off at any time.
  • the heights are raised before the swap and lowered again after the swap. This facilitates retrofitting and prevents overdriving by raising the height in the subsequent radio section and makes it difficult to listen to the veiled signal, since the correct arrangement of the frequency bands can no longer be concluded due to the amplitude distribution.
  • the number of signal inputs and outputs of the obfuscation circuit is to be selected in accordance with the two-wire or four-wire transmission method. By using integrated circuits of digital technology, the obfuscation circuit is small and light.
  • the output value of the code transmitter is changed randomly and equally distributed at intervals of less than five seconds in order to make decoding more difficult with the aid of a frequency analysis.
  • the pilot tone transmitter is set to the center frequency of a band gap in the area of the audio frequency band and the audio frequency band is expanded to the higher frequencies by the width of the band gap.
  • the signal transmission is disguised independently of the switching signaling and the quality of the audio signal is not impaired.
  • the connection establishment does not require any modification. Switching to a different base station or a different voice channel with an upright connection between the subscriber terminals therefore does not influence the concealment.
  • the concealment circuit is included in a signal concealment unit that can be connected via an interface in the signal path to the subscriber terminal, to which a toggle switch and a function control display are available and / or a remote control for plugging the concealment is connected.
  • a signal concealment unit that can be connected via an interface in the signal path to the subscriber terminal, to which a toggle switch and a function control display are available and / or a remote control for plugging the concealment is connected.
  • the signal obfuscation unit is unplugged, the handset is plugged directly back into the handset and the cell phone remains functional.
  • the remote control it is possible to accommodate the signal concealment unit together with the handset in the trunk of a vehicle.
  • a signal concealment button is provided on a handset of the subscriber terminal in a mobile phone and the operation of the concealment is shown on a display of the handset.
  • the operation of the signal concealment during a conversation or a data transmission is possible with the least effort and the disturbance of the concentration, for example of a driver, is kept to a minimum.
  • a base station with digital signal processing is connected to a digital exchange and the output of the signal processor is connected directly to the output of the concealment circuit for digital forwarding of the received and unveiled signals, a conversion process from digital to analog signals is saved.
  • the voice or data signals can be forwarded directly to an ISDN exchange.
  • the invention further relates to a method according to claim 7, for use in devices according to one of claims 1-6.
  • This special shaping of the speech signal changes the spectral energy distribution so that its characteristics are lost. Not even a spectral analysis of the signal allows an unauthorized listener to draw conclusions about the code used for the frequency band exchange, since the veiled speech signal is in turn adapted to the shape of the natural speech signal.
  • the method according to the invention can also be used in already existing radio systems, since the disguised speech signal can be controlled in the same way as the non-disguised one.
  • Fig. 1 shows schematically the structure of a mobile phone system.
  • Both voice and data signals from mobile subscriber terminals TEG are transmitted to base stations BS by radio.
  • the called subscriber can have both a mobile subscriber terminal TEG and a stationary device that can be reached via telephone or data exchange.
  • the signals are concealed by coded frequency band swapping of four subbands. Since about 40% of the energy of human speech is in the range of 400 - 800 Hz, the spectral energy distribution is changed in a predistorter VV with 0 dB at 1000 Hz and 6 dB / octave.
  • a frequency band exchanger FBT exchanges the four bands for a code derived from a code generator CG from random numbers.
  • the energy spectrum of the veiled speech signal with interchanged and inverted frequency bands has an energy distribution similar to the clear speech signal.
  • An equalizer EZ lowers the heights of the veiled signal.
  • the high frequencies of the veiled speech signal are raised again in a transmitting part, thus producing an energy spectrum that is optimal for the transmitter.
  • the code is inserted into a band gap of the audio frequency band by a pilot tone transmitter PS after activation of the obfuscation circuit VS.
  • the band gap is about 200 Hz, and the upper part of the frequency band is shifted by this amount to higher frequencies.
  • a pilot tone receiver PE decrypts the code contained in the signal.
  • the veiled signal is in turn changed by the predistorter VV.
  • the order of the bands is in the frequency band exchanger FBT corrected according to the code and the equalizer EZ converts the energy distribution back to its original form.
  • This signal is forwarded to the called subscriber in clear text via switching centers. If the latter has also activated the concealment circuit VS of its subscriber terminal TEG for its radio link, its code transmitter CG generates a code that is independent of the subscriber terminal TEG of the calling subscriber.
  • the new concealment is carried out with the code of this subscriber terminal TEG in the same way as for the calling subscriber.
  • the concealment of the return channel from the base station BS to the subscriber takes place in the concealment circuit VS of the base station BS with the code stored in the pilot tone receiver PE.
  • the return signals are sent without pilot tone to the subscriber terminal TEG via predistorter VV, frequency band exchanger FBT and equalizer EZ. Since the encryption takes place with the same code that is used by the code transmitter CG to encrypt the other transmission direction, the subscriber terminal TEG does not require a pilot tone receiver PE.
  • the received return signals are unveiled via the predistorter VV with the code from the code transmitter CG in the frequency band exchanger FBT and converted back in the equalizer EZ.
  • the voice concealment takes place in the subscriber terminal TEG and the base station BS using digital signal processors DSP.
  • the inputs and outputs of the concealment circuits VS are equipped with analog / digital converters A / D.
  • the code is changed by the code transmitter CG at randomly distributed intervals of 0.8 - 4.2 seconds. Exchanging four frequency bands gives 384 possible codes. Since many of these combinations lead to signals with high residual intelligibility, only 256 codes are actually used.
  • the transmission of the pilot tone is constantly in the base station BS by decoupling of the audio frequency signal is monitored.
  • the obfuscation circuit VS is activated when a valid code is determined by the pilot tone receiver PE.
  • Fig. 2 shows the block diagram of the concealment circuit of the subscriber terminal. Encryption is activated by activating a relay R at the four inputs and outputs of the concealment circuit via the signal processor DSP. If the signal processor DSP fails, the relay R drops out and bridges the concealment circuit.
  • the signal to be concealed is present at the BE handset input. The signal is digitized in a coder / decoder module CD and pulse code modulated via a low-frequency adaptation NA.
  • the handset input BE is connected to a data bus DB and the signal processor DSP via a serial / parallel converter SP of an application-specific circuit IC. After the concealment, the signal is connected to the transmit output SA via the data bus DB, serial / parallel converter SP, coder / decoder module CD and low-frequency adaptation.
  • the signal passes through the concealment circuit from the transmit input SE to the handset output BA.
  • the procedural steps of predistortion, encryption and equalization are carried out for both transmission directions in the signal processor DSP.
  • the inputs and outputs are selected via a connection selection circuit AW, which is controlled by the signal processor DSP.
  • a clock generator TG in the IC circuit supplies the digital components with a central clock.
  • the obfuscation circuit of the base station is constructed essentially the same.
  • the relay R is omitted and the low-frequency adaptation NA is implemented for electrical isolation with transformer circuits.
  • the loop monitoring in the system is maintained with the help of a relay circuit.
  • the concealment circuit in the subscriber terminal can be built into the handset as an integrated version and operated via the handset. Retrofitting is made easier by a signal concealment unit as an additional device. It is plugged into the handset socket on the handset and has a socket for the handset itself.
  • the signal concealment unit contains an LED control signal and an actuation button. A remote control connection also enables them to be checked and operated when housed in the trunk of an automobile.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
EP88117419A 1987-10-21 1988-10-19 Dispositif de transmission brouillée de signaux analogiques Ceased EP0313029A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AT278787A AT393339B (de) 1987-10-21 1987-10-21 Vorrichtung zur verschleierten uebertragung analoger signale
AT2787/87 1987-10-21
AT239288A AT393055B (de) 1988-09-28 1988-09-28 Verfahren zur verschleierung von sprachsignalen
AT2392/88 1988-09-28

Publications (1)

Publication Number Publication Date
EP0313029A1 true EP0313029A1 (fr) 1989-04-26

Family

ID=25598355

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88117419A Ceased EP0313029A1 (fr) 1987-10-21 1988-10-19 Dispositif de transmission brouillée de signaux analogiques

Country Status (1)

Country Link
EP (1) EP0313029A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995015627A1 (fr) * 1993-11-19 1995-06-08 Litef Gmbh Procede et dispositif de brouillage et de desembrouillage de la parole lors de la transmission de la voix

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3624297A (en) * 1969-04-21 1971-11-30 Motorola Inc Tone-controlled speech scrambler
FR2354005A1 (fr) * 1976-06-01 1977-12-30 Europ Handelsges Anst Procede et dispositif de chiffrement et dechiffrement d'information sonore
EP0028688A1 (fr) * 1979-11-07 1981-05-20 Crypto Aktiengesellschaft Installation pour la transmission de signaux de commande par un canal de parole
WO1981002234A1 (fr) * 1980-02-01 1981-08-06 Patelhold Patentverwertung Procede et dispositif pour la transmission protegee de signaux vocaux
DE3536384A1 (de) * 1985-10-11 1987-04-16 Siemens Ag Fm-funksystem zur verschleierten uebertragung von sprachsignalen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3624297A (en) * 1969-04-21 1971-11-30 Motorola Inc Tone-controlled speech scrambler
FR2354005A1 (fr) * 1976-06-01 1977-12-30 Europ Handelsges Anst Procede et dispositif de chiffrement et dechiffrement d'information sonore
EP0028688A1 (fr) * 1979-11-07 1981-05-20 Crypto Aktiengesellschaft Installation pour la transmission de signaux de commande par un canal de parole
WO1981002234A1 (fr) * 1980-02-01 1981-08-06 Patelhold Patentverwertung Procede et dispositif pour la transmission protegee de signaux vocaux
DE3536384A1 (de) * 1985-10-11 1987-04-16 Siemens Ag Fm-funksystem zur verschleierten uebertragung von sprachsignalen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
THE BELL SYSTEM TECHNICAL JOURNAL, Band 62, Nr. 1, Teil 1, Januar 1983, Seiten 47-61, American Telephone and Telegraph Co., Murray Hill, New Jersey, US; R.V. COX et al.: "Analog voice privacy systems using TFSP scrambling: full duplex and half duplex" *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995015627A1 (fr) * 1993-11-19 1995-06-08 Litef Gmbh Procede et dispositif de brouillage et de desembrouillage de la parole lors de la transmission de la voix
US5778073A (en) * 1993-11-19 1998-07-07 Litef, Gmbh Method and device for speech encryption and decryption in voice transmission

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