JPS61159838A - Privacy telephone set - Google Patents

Abstract

PURPOSE:To obtain a privacy telephone set having a large privacy effect with simple constitution, by providing a cipher part having the second frequency converting means for obtaining a privacy signal by converting a frequency of an adding signal by the second local oscillating signal. CONSTITUTION:In case when a sound signal S1 being an object of privacy, which has been supplied to an input terminal 1 becomes a privacy signal S3 as shown in the figure,in a cipher part CAD consisting of a local oscillator 5, a frequency divider 6, multipliers 2, 4, and an adder 3, a signal component of the privacy signal S3 becomes frequencies f8, f9-f10, f11-f12, and f13-f14 as shown in the figure, but each frequency component of the privacy signal becomes a state that a frequency area of each frequency component is superposed each other in a complicated aspect, therefore, the privacy signal S3 becomes a signal whose meaning is unknown entirely in an aural sense. Also, the privacy signal S3 which has been generated by the cipher part CAD is transmitted through a suitable transmission line, and thereafter, the decoding processing is executed in a decoding part RAD, and the original signal is restored.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a confidential communication device that is effectively used in telecommunications, particularly in the transmission of voice and data by wireless communication.

(Prior art) Wireless communication methods have recently come to be applied to everyday general telecommunications.

There is an increasing demand for prevention of wiretapping in various information communications.

For example, in recent years, cordless telephone systems, i.e.
As telephones in which the tether of general subscriber telephones was replaced with a wireless line began to be put into practical use, it became possible to communicate with a connecting device connected to the telephone line via a wireless line. In addition to the desire to prevent eavesdropping on the wireless lines between telephones and telephones, it has also been recognized that there is a need for confidential communication devices to prevent eavesdropping on other communication devices that are used on a daily basis. It has come to be.

By the way, various methods have been known as technical means for concealing the contents of communication, such as a confidential method in which signal processing is performed on one frequency axis, and a confidential method in which signal processing is performed on one time axis. It is well known that

(Problem to be solved by the invention) However, in the various conventional secret message systems, if the structure is complex or the structure is simple, the secret signal is easily deciphered and the secret message effect is small. , etc., there was a need for a secret communication device that was simple in construction and had a large secret communication effect.

(Means for Solving the Problems) The present invention provides an encryption unit that generates a confidential signal by converting the frequency of an input signal that is targeted for confidential communication.

A secret speech device comprising a decryption section that converts the frequency of the secret speech signal generated by the encryption section and obtains a restored signal corresponding to the original secret speech target signal, comprising:
means for generating a first local oscillation signal; and first frequency conversion means for converting the frequency of the input signal that is kept confidential by the first local oscillation signal to obtain a first frequency-converted signal. , a means for obtaining an addition signal by adding the first frequency converting means and a DC voltage of a predetermined voltage value, and a means for obtaining an addition signal by adding the first frequency converting means described above and a DC voltage of a predetermined voltage value; and a second frequency converting means that converts the frequency of the addition signal using the second local oscillation signal to obtain a secret signal. an encryption unit; means for obtaining a restored second local oscillation signal corresponding to the second local oscillation signal from the secret signal supplied from the encryption unit; The secret signal is frequency-converted by a local oscillation signal, and the restored first frequency-converted signal and the restored DC voltage having a predetermined voltage value are added together, and the added signal is a third frequency conversion means for obtaining a corresponding restored addition signal; and subtracting a DC voltage of a predetermined voltage value from the restored addition signal to obtain a corresponding restored addition signal. means for obtaining a restored first frequency converted signal corresponding to the first local oscillation signal; and means for multiplying the restored second local oscillation signal by N to obtain a restored first local oscillation signal corresponding to the first local oscillation signal. The present invention provides a secret speech device comprising means for obtaining an oscillation signal and a decoding section comprising the fourth frequency conversion means capable of being restored.

('l & Examples) Hereinafter, specific contents of the secret communication device of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the confidential communication device of the present invention, and in this FIG. The audio signal S1 is an input terminal and is supplied to the input terminal 1 described above.
is applied to analog multiplier 2. In the following explanation, as shown in FIG. 3(a), it is assumed that the audio signal exists in a frequency band between a lower limit frequency f1 and an upper limit frequency f2, and the frequency f1 is, for example, 300 Hz, and the frequency f2 is, for example, 3 KHz.

The analog multiplier 2 receives the audio signal S1 supplied thereto as described above and the first local oscillation signal C outputted from the first local oscillation signal oscillator 5, which will be described later.
1 (see FIG. 4(b)) to obtain the frequency of the audio signal.

In Fig. 4, to facilitate understanding of the operation of signal processing in the encryption section, the audio signal to be kept secret is a sinusoidal waveform signal as shown in Fig. 4(a). In addition, the illustration and explanation are given assuming that the local oscillation signal C1 is a square wave as shown in FIG. 4(b). As is clear from its waveform, the output signal S2 from the analog multiplier 2 shown in FIG. The audio signal is unknown.

The frequency f of the first local oscillation signal C1 output from the first local oscillation signal oscillator 5 described above in the following description.
3 is for the lower limit frequency (30011z in some examples) and the upper limit frequency f2 (3KHz in some examples) of the audio signal, as shown in FIG. 3(b).
Frequency f3 (with the relationship f3=(fl+f2)/2
In some cases, it is said to be 1.65 KHz).

Analog multiplier 2 as shown in FIG. 4(e)
As shown in FIG. 3(c), the output signal S2 from the The above-mentioned upper sideband ranges from frequency f6 (according to the above examples, the frequency value is 1.95 KHz) to frequency $f7 (according to the above examples, the frequency value is 4.65 Hz). occupies a frequency band of , and the lower sideband has a frequency i4 (
If you follow the few examples above.

It occupies a frequency band from 1.35 KHz) to f5 (one frequency value is -1.35 KHz according to the above examples) (from 0 to -1.35 KHz in the lower sideband mentioned above). The part up to 35KHz is the state where the frequency is folded back at the zero position, that is, the frequency is from zero to 1.
．． It goes without saying that the signal exists in the range up to 35 KHz).

The adder 3 has the output signal S2 from the analog multiplier 2 as shown in FIG. The output signal (S2+Vb) as shown in FIG. 4(d) is supplied to the analog multiplier 4.

As mentioned above, the output signal from adder 3 (S2+vb)
is supplied to the analog multiplier 4, which is supplied with the first
The frequency f3 of the local oscillation signal c1 is set to 1/N (however, N
is a number other than 1...in some examples it is set to N; 4), and the frequency is f 3/N = f 8 (in some cases, the frequency f8 is said to be 412.5Hz) In the second local oscillation signal C2 and log multiplier 4,
The two signals supplied to it, namely the output signal (S2+Vb) as shown in FIG. 4(d)
is multiplied by the branched local oscillation signal c2 as shown in FIG. 4(e) by the signal C2, and the signal (
S2+Vb) is converted to generate a secret signal S3 as shown in FIG. The signal components of the secret signal S3 generated by the section CAD are as follows:
It shows the distribution on the frequency axis as shown in (e) of Figure 3 (note that in Figure 3, sideband waves caused by harmonics of the signal are shown to simplify the illustration and explanation). (not shown).

The frequency values of each frequency f4 to f7 in the signal shown in FIG. 3(c) multiplied by the analog multiplier 4,
The frequency value f8 of the branched local oscillation signal C2 shown in FIG. 3(d) is respectively f4+1 as in several examples.
．． 35KHz, f5 knee 1.35KHz, f6=1.
95KHz, f7=4.65KHz, f8=41
2.5 Hz, each frequency f shown in (e) of FIG.
9 to f14 are f9=1.7625K)lz, f
1G=-937.5Hz, f11=-1.5
375KHz, f12=-4,2375KHz, f
13=1.95KHz, f14=4°65KHz.

The part from the frequency projection to -4,2375 KHz in the lower sideband shown in (6) of Figure 3 is 1
A state in which the frequency is folded back at the zero position, that is.

It goes without saying that the frequency exists in the range from zero to 4.2375 KHz.

Therefore, when the audio signal S1 supplied to the input terminal 1, which is targeted for secret speech, is converted into the secret speech signal S3 as shown in FIG. 4(f) in the encryption unit CAD, As shown in FIG. 3(e), the signal components of the signal S3 have frequencies f8, f9~f10, f11~
f12. It will be f13 to f14.

As is clear from (,) in Fig. 3, each frequency component of the confidential signal mentioned above is in a state where the frequency regions of the respective frequency components overlap in a complicated manner. S3 is a signal that is audibly incomprehensible, and this means that the encrypted signal S3 is obtained from the cipher unit CAD, and the secret signal S3 is well-privileged.

The secret signal S3 generated by the encryption unit CAD is transmitted via an appropriate transmission path, and then decrypted by the decryption unit RAD to restore the original signal.

Now, the secret signal S3 shown in FIG.
3. Voltage controlled oscillator 14, loop filter 15.1/N
Frequency divider 16 (where N is 1/N in the encryption section CAD)
The signal is supplied to an analog multiplier 10 and a phase comparator 11 in the decoding unit RAD, which are configured with the same value as N in the frequency divider 6).

The above-mentioned loop consisting of the phase comparator 11 → loop filter 15 → voltage controlled oscillator 14 → 1/N frequency divider 16 constitutes a phase locked loop (PLL). From the 1/N frequency divider 16 in the loop (PLL), the 1/N frequency divider 16 in the cryptographic section CAD
A divided local oscillation signal (second local oscillation signal) C as shown in FIG. 4(e) generated by /N frequency division l16
The restored branch local oscillation signal (restored second local oscillation signal) 02' (see (g) in the 4th @) corresponding to 2 is supplied to the analog multiplier 10, and the phase
Voltage controlled oscillator 1 in locked loop (PLL)
From 4 onwards, the signal in which the restored branched local oscillation signal (restored second local oscillation signal) 02' is multiplied by N, that is, the oscillator 5 of the first local oscillation signal in the encryption unit CAD. The first local oscillation signal CI generated by
(See Figure 4(b))
The local oscillation signal C1' (see (j) in FIG. 4) is supplied to the analog multiplier 13.

In the analog multiplier 10 to which the restored second local oscillation signal C2' is supplied, the input terminal 9 of the decoder RAD is
(f
) is frequency-converted from the secret signal S3, and the resulting first frequency-converted signal S2' is added to the restored DC voltage vb' having a predetermined voltage value. The restored addition signal (S2+Vb)'( (see (h) in FIG. 4) and supplies it to the subtracter 12 as a minuend signal.

Since the subtraction signal vb' shown as vb' in FIG. 4(h) is supplied to the subtracter 12 from the terminal 17, the output signal from the subtracter 12 is as shown in FIG. (i
) signal S2'=(S2+Vb)' as shown in
-Vb'') That is, the DC voltage vb' of a predetermined voltage value is subtracted from the restored addition signal to correspond to the first frequency-converted signal S2 generated by the encryption unit CAD described above. The restored first frequency converted signal 52' is output.

The restored first local oscillation signal C1 generated by the voltage controlled oscillator 14 in the phase-locked loop described above.
′ (see (j) in FIG. 4), the analog multiplier 13 is supplied with the restored first local oscillation signal C
I' and the restored first frequency converted signal S2'
A multiplication operation is performed, and as an output signal, a restored signal 81' as shown in FIG. 4(k) is sent to the output terminal 18 of the decoder RAD.

(k
) is the restoration signal 81″ shown in the dark area CA
An audio signal similar to the input signal S1 supplied to the input terminal 1 of D as a signal to be confidentially spoken.

The secret communication device of the present invention is constituted by an encryption section CAD and a decryption section RAD shown in FIG.

Encryption and decoding of audio signals can be performed satisfactorily.

FIG. 2 is a partial block diagram illustrating another configuration of the component for detecting the first local oscillation signal C1 component from the secret signal S3 supplied to the input terminal 9 of the decoding unit RAD. In the configuration shown in the second figure, a bandpass filter 118PF and a voltage comparator CO are provided between the input terminal 9 and the phase comparator 11 in the decoding unit RAD in FIG.
A circuit connected in series with the MP is provided, and with this configuration, desired signal components can be extracted satisfactorily without adversely affecting each signal component.

(Effects) As is clear from the detailed explanation above, the confidential communication device of the present invention includes a cryptographic section that converts the frequency of an input signal to be confidential to generate a confidential signal, and an encryption section as described above. a decoder for converting the frequency of the secret signal generated by the system to obtain a restored signal of the original secret signal, the device comprising means for generating a first local oscillation signal; , a first frequency converting means for converting the frequency of an input signal that is a confidential target by the first local oscillation signal to obtain a first frequency converted signal; means for obtaining a summed signal by adding a DC voltage of a predetermined voltage value; an encryption unit comprising means for obtaining an oscillation signal; and a second frequency conversion means for converting the frequency of the addition signal using the second local oscillation signal to obtain a secret signal;
means for obtaining a restored second local oscillation signal corresponding to the second local oscillation signal from the secret signal supplied from the encryption unit; and the restored second local oscillation signal. The secret signal is frequency-converted, and the restored first frequency-converted signal and the restored DC voltage having a predetermined voltage value are added, and correspond to the above-mentioned addition signal. a third frequency conversion means for obtaining a restored addition signal; and a third frequency conversion means for subtracting a DC voltage of a predetermined voltage value from the restored addition signal to obtain a restored signal corresponding to the first frequency conversion signal. and means for obtaining a first frequency-converted signal corresponding to the first local oscillation signal, and multiplying the restored second local oscillation signal by N to obtain a restored first local oscillation signal corresponding to the first local oscillation signal. and a decoding unit comprising a fourth frequency converting means for frequency converting the restored first frequency converted signal using the restored first local oscillation signal to obtain a restored signal. Therefore, in the privacy device of the present invention, a high degree of privacy can be easily obtained by connecting two analog multipliers in series and employing a double frequency conversion method. That is, 1. When attempting to eavesdrop on a confidential signal encrypted by the confidential communication device of the present invention, it is impossible to obtain a restored signal unless a decryption unit having a configuration similar to that of the decryption unit in the confidential communication device of the present invention is used. However, if you try to eavesdrop and convert the frequency of the confidential signal using an analog multiplier, for example, the confidentiality will be completely maintained with only one frequency conversion operation, and if you try to eavesdrop twice Even if a frequency conversion operation is attempted, it is not possible to synchronize with the encryption time, so confidentiality can be maintained well. Furthermore, even if synchronization is achieved in the above case, it is impossible to decipher the secret signal unless the decoding promise for the first frequency conversion and the second frequency conversion at the time of encryption is known. As described above, the confidential communication device of the present invention has double or triple safety measures in spite of its simple circuit configuration, so that it can be effectively used as a confidential communication device in a wide range of technical fields.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the secret communication device of the present invention, FIG. 2 is a block diagram of a part of the decoding section, FIG. 3 is a frequency allocation diagram, and FIG. 4 is a signal waveform diagram. 1.9... Input terminal, 2.4.10, 13... Analog multiplier, 3... Adder, 5... Oscillator of first local oscillation signal, 6.16...1 /N frequency divider, 8, 18
...output terminal, 11...phase comparator, 12...subtractor, 14 voltage controlled oscillator, 15...loop filter, BPF...bandpass filter, COMP...voltage comparator, Part 3 Figure 1 ---CAD"-RAD

Claims (1)

[Claims] an encryption section that converts the frequency of the input signal that is the target of the secret message to generate a secret signal; a decoding unit for obtaining a restored signal; and means for generating a first local oscillation signal;
a first frequency conversion means for converting the frequency of the input signal to be confidential by the first local oscillation signal to obtain a first frequency conversion signal; means for obtaining an addition signal by adding the DC voltage of the voltage value;
(where N is a numerical value excluding 1) to obtain a second local oscillation signal; and a means for converting the frequency of the added signal by the second local oscillation signal to obtain a secret signal. 2
a cipher section comprising a frequency conversion means; and means for obtaining a restored second local oscillation signal corresponding to the second local oscillation signal from the secret signal supplied from the cipher section; The secret signal is frequency-converted by the restored second local oscillation signal, and the restored first frequency-converted signal and the restored DC voltage having a predetermined voltage value are added. a third frequency conversion means for obtaining a restored addition signal corresponding to the above-mentioned addition signal; and a third frequency converting means for obtaining a restored addition signal corresponding to the above-mentioned addition signal; means for obtaining a restored first frequency-converted signal corresponding to the frequency-converted signal; and means for multiplying the restored second local oscillation signal by N to correspond to the first local oscillation signal. means for obtaining a restored first local oscillation signal; and a fourth frequency converting the restored first frequency-converted signal using the restored first local oscillation signal to obtain a restored signal. A secret communication device comprising a decoding section comprising a conversion means.