JPS60208132A - Encoding and decoding system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A transmitter/transmitter comprising means for digitizing a digitalized analog signal, a pseudo-random code generator, and means for relatively synchronizing the two pseudo-random code generators.
This invention relates to an encryption and decryption method for analog narrowband clear signals including receiving stations.

In particular, this type of system has a pass band of about 0.3 to 3.8 KHz.
It is used as an encrypted audio method for analog audio signals.

Pseudo-random digital encryption schemes have already been proposed. In this type of method, it is not encrypted, that is, it is “clear”.
The encryption unit is also supplied with a pseudo-random bit stream, referred to as a "key", generated by a first pseudo-random hood generator. The encryption unit encrypts clear text data in response to a "key", such as clear data sequences of the same order and cryptic digital data encrypted by adding modulo-2 the "key" bits. Generate a bit stream This encrypted digital bit stream is transmitted via a cable or wireless link to a decoding unit. In the decoding unit, a second pseudo-random code generator generates a receiving key identical to the transmitting key. Generate ◇Use this reception key to decrypt the transmitted encrypted data.0Then, this decrypted data can be used for normal purposes.

In order for the encryption and decryption unit to function properly, the first and second pseudo-random code generators at each end of the wireless link must be identical and synchronized. That is, both hood generators must start at the same operating cycle point so that they generate the same "key" at each moment in time at each transmitting/receiving station.

This type of encryption method is described, for example, in U.S. Pat. No. 418
In the above-mentioned encryption method, the digitized audio signal is transmitted via a transmission path, and the bandwidth of this transmission path must be at least twice the passband width of the audio signal. There is a need to.

SUMMARY OF THE INVENTION An object of the present invention is to provide an encryption/decryption system of the above-mentioned type that requires only a narrow-bandwidth transmission channel, is simple in construction, and is suitable for miniaturization.

The encryption and decryption system according to the present invention comprises means for decomposing composite data into frames of a predetermined number of bits and dividing each frame into a number of packets of a predetermined number of bits; and means for inverting and synchronizing the spectra of the transmitted IL1 signal and the received signal,
and the pseudorandom code generator has a period consisting of (N+n) random bits, N bits of this period are used to control packet switching, and n bits are used to control spectrum inversion. It is characterized by the following.

In the present invention, the audio fin signal is digitally processed at the transmitting station and the receiving station, and the audio signal is transmitted through the transmission path in an analog form. Therefore, the encryption and decryption unit can be connected online to the existing non-encrypted link without any changes to the existing non-encrypted link. For example, a radiotelephone link can be converted into a covert link without any changes other than the online connection in the scheme according to the present invention. In a preferred implementation of the present invention, the spectrum inversion is controlled. The value of the number of bits n used for is set to n=1.

Furthermore, according to another preferred embodiment of the present invention, the value of n is set to n=
2, and also includes means for reading the bit packets from the Ldm s of each bit packet to its end, or vice versa. Digitize and divide the resulting digital signal into frames, each consisting of a predetermined number of bit packets.These packets are stored and later determined by the order of the packets within the frame under the control of a pseudo-random receiver food generator. These exchanged packets are always read 0 in one direction or in the opposite direction under the control of a pseudo-random code generator, then converted to an analog state by a digital-to-analog converter, and then spectrally inverted. It may or may not be done.

According to a further advantageous embodiment of the invention, the frequency of the carrier signal performing the spectrally inversion is the same as the frequency of the signal used to synchronize the pseudo-random code generator.

On the receiving (71) side, the analog signal is digitized by an analog-to-digital converter, and the obtained digital data is then stored in a memory in the form of packets. Under the control of a pseudo-random code generator, the receiving side Performs a packet exchange that is the opposite of the packet exchange that was performed, and then transmits the bits of the packet (depending on whether one side entered the memory directly row 11 or in the opposite direction). normal order, or ′
Ni! l1ts are stored in memory in reverse order. Finally, depending on whether spectrum inversion was performed on the transmitting side or not, the spectrum of the analog data obtained again is inverted or not inverted ◇ The packets L&N of each frame are Assume that N=8 and the frame duration T is 1'=53.38m5.
Number of packet exchanges N! is N1=8+=40820, and since each packet can be read directly or inversely and with or without spectrum inversion, the number of combinations is 2X2X81=161.
,280.

The invention will be explained below with reference to the drawings.

In FIG. 1, which shows the encryption device on the transmitting side, a microphone 1 picks up an audio signal with a bandwidth of about 800 to 3,800 Hz. The delta modulator 2 includes a matched filter 3.
be followed by Modulator 2 receives fE=a by clock 4
Controlled at a rate of 2 KHz.

The digital audio data stream is cut into a number of frames of 58.8 ms each, each frame being formed by 8 packets, each packet having a period of 6.66 m5 and 2
It consists of 18 bits. These packets are input to the main memory 5 via the microprocessor 6.

A pseudo-random code generator 7 is also connected to the microprocessor 6, which is controlled by a main clock 8 at a frequency of fH=8.2 MHz. The frequency fE is changed to the frequency f by the frequency divider 9 with a frequency division coefficient of 100.
Take it out from H.

The packets stored in the main storage device (memory) 5 are exchanged via the microprocessor 6 under the control of the pseudo-random code generator 7. The 0-exchanged packets are stored in the second storage device W1.
10, these exchanged packets are then input to a digital-to-analog (D/A) converter, such as a delta demodulator.
) O D converted into an analog signal by converter 11
/A converter 11 has a zero narrow band A P S K (Amplitude Co) which is followed by a low pass filter 12 .
ntrol phase Shiftxeying =
The following functions are realized by a low-speed modem (modulator/demodulator) 13 that uses a modulated carrier wave (amplitude control phase shift keying). Synchronization of the transmitter and receiver and maintenance of said synchronization during fading of the radio frequency transmission path during low-speed data transmission (this function is not used in the present invention).

The frequency f0 of the modem 18 is a frequency that performs spectrum inversion, and has a passband width of 300 to a, ao.

If it extends up to Hz, its frequency f. f. =3.
It is assumed to be 600H2.

The pseudo-random code generator 7 is a 5-bit shift register 71 that performs an appropriate ←-loop. Pseudo-random code generators are well known, and these can be found in, for example,
``Theory and Applications of Digital Signal Processing''
Application of Digital Si
Lawrence Earl Rabiner on pages 565-567 of gnalProcessing''
R, RABINER) and Bernat Gold (Ber
nard GOLD) NiJ: 'J is described.

Bits 1, 2, and 3 are used for packet exchange within a frame, bit 4 is used to control spectrum inversion operations, and bit 5 is used to control full inversion of packet read operations in memory IO.

register? ■ is shifted in the forward direction at a frame frequency of 18.75 H2.

Encrypted analog audio signal and carrier wave f.

are added together at analog AND-gate 14.

The resulting signal is fed to a spectrum inverter 15, which inverts the spectrum from 800 to 8,300 Hz for a frequency of 3.600 Hz. That is, inverter ■5 is 300 Hz and 8,8
The frequency component of 00Hz becomes the frequency component of 3.30o1 (z and 300H2).The spectrum inverter 15 is connected to the output terminal 16 of the darkening device on the transmitting side.This output terminal Fl 6 is connected to the subscriber Figure 2 shows a decryption device on the receiving side, and the input terminal 46 of this decryption device is connected to either the line or the radio frequency transmission line. An analog signal to be transmitted is supplied, and this analog signal is converted into an analog signal via a spectrum inverter 45.
A digital (A/D) converter 32 and a modem 48 are provided. A/D converter 32 includes a low-pass filter 38
be followed by A/D converter 82 may be a delta modulator.

The frequency of modem 43 is f. output (g is the frequency rH
A voltage controlled oscillator (
VCO) 47 and spectrum inverter 45. The output of the VCO 47 controls the A/D converter 32 at a frequency fE via a frequency divider 39.

Filter 88, vC047, pseudorandom code generator 37 and main memory 85 are connected to microprocessor 36. This microprocessor 36 includes a second memory 40.
, digital-to-analog (D/A) such as delta demodulators
) converter 4] and a spectrum inverter 45 are also connected. The spectrum inverter 45 is connected to the microprocessor 3
Receives a command from 6 to invert the spectrum or not (jf
At the same time, the frequency from the modem 48 is f. receive the carrier wave.

It is clear that there is a high degree of correspondence between the encryption device and the decryption device. Under the control of the five 7-lip flops of the shift register 871 included in the pseudo-random code generator 37, the decoder performs packet exchange opposite to the packet exchange performed on the transmitting side, and decodes the packet directly or inversely. The output terminal of the decoding device is connected to a speaker 31.

FIG. 8 shows an example of a circuit suitable for use as a spectral inverter, consisting of transistors 158, 15 whose emitters are interconnected to form a constant current source.
Circuits of this type comprising a differential amplifier formed by transistors 151 and 152 connected to the collectors of 4 are known, for example from Wiley Interscience (
L, J, GIAO published by WILEYINTER3OIENOE
“Difference Amplifiers” by OLETTO
rs), page 71, Figure 5.2.

The base of transistor 151 is connected to the output terminal of AND-gate 14 and the base of transistor 153 is connected to modem 13 . The command to invert or not invert the spectrum is provided by transistor 154, which shorts or disables transistor 153. The spectral inverter is connected to a low pass filter 155. The output terminal 16 of this filter forms the output terminal of the encryption device.

It goes without saying that the present invention is not limited to the above-mentioned examples, but can be modified in many ways. In particular, the packet exchange of the frame by the pseudo-random code generator may be 3 bits. It is also clear that more than 4 bits could be set aside for packet exchange to increase the number of combinations.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of an encryption device on the transmitting side; Figure 2 is a block diagram showing an example of a decoding device on the receiving side; Figure 3 is a block diagram showing an example of an analog spectrum inverter. It is a circuit diagram. [・Microphone 2・・A/D conversion 13・・Matched filter 4・・Clock 5・・Main memory 6・・Microprocessor 7・・Pseudo random hood generator 8・・Main click 9・・Branch unit 10・・・Second memory 11 ・D/A converter 12...
Low pass filter 13...Modem 14...Analog AND-gate 15 Spectrum inverter 81...Speaker 32...A/D converter 33 -Low pass filter 35...Main memory 86...Microprocessor 87 ... Pseudo-random code generator 39 ... Frequency divider 4o ... Second memory 41 - ... D/
A converter 48 ・Modem 45 ・Spectrum inverter 46 ・Input terminal 47 of decoding device ・Voltage controlled oscillator 71 ・Shift register (1
51, 152)...Differential amplifier (15s, 1.54)・Constant current source 165・・Low pass filter 371・・Shift register special i1H [1i person NV Philips Fluiran Penfabriken

Claims (1)

[Claims] L Means for digitizing the incoming clear analog signal/1IIf coded 7 program signal (2°32), a pseudorandom code generator (7°37), and generation of these two pseudorandom codes ""a (8, 37) respectively comprising means (13, 48) for relatively synchronizing the transmission/
In an encryption and decryption scheme for analog narrowband clear signals including receiving J stations, the scheme divides the composite data into frames of a predetermined number of bits, and each frame is divided into frames of a predetermined number of bits. A means for dividing into packets, a means for converting the packets of the frame, and a means for transmitting (
means (15, 45) for inverting and synchronizing the spectra of the g signal and the received signal, and said pseudo-random code generator (7, 37)
n) random bits, N bits of this period are used to control packet switching, and n bits are used to control spectrum inversion. conversion and decoding method. Claim 1 characterized in that l n=1.
Encryption and decryption method described in section. & n-2, and includes means for reading the bit packets from the beginning to the end of each packet, or in the opposite direction. conversion and decoding method. 4. The system according to claim 1, wherein the means for synchronizing the pseudo-random code generator comprises means for transmitting an audio frequency signal from a transmitting station to a receiving station, wherein the frequency of the audio frequency signal is An encryption/decryption method characterized in that (fo) is the same as an audio frequency used for spectrum inversion.