JPH03293834A - Wiretap preventing system for facsimile communication - Google Patents

Abstract

PURPOSE:To prevent wiretap of facsimile communication by converting primary transmitted and received cipher parameters to secondary cipher parameters by using a predeterminate calculation formula and collating them with a cipher table to determine the ciphering system. CONSTITUTION:A primary cipher parameter generating part 13 performs the operation to convert random numbers Rn outputted from a random number generating means 12 to cipher parameters, and a secondary cipher parameter generating part 14 generates a secondary cipher parameter P based on a primary cipher parameter Pt generated in a local station and a primary cipher parameter Pr which is generated in a reception station and is added to a protocol control signal NSF and is transmitted. The conversion system corresponding to the secondary cipher parameter P is selected from the cipher table in a storage part 15, and the selected conversion system is indicated to an encoding/decoding part 3a. Thus, wiretap is impossible.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for preventing eavesdropping on facsimile communications, and in particular, it is possible to apply the method to prevent eavesdropping without bothering the operator. This invention relates to a facsimile communication eavesdropping prevention method that takes into consideration the productivity of facsimile machines.

(Prior Art) With the spread of facsimile communication, the problem of the contents of the communication being intercepted has arisen. Conventionally known forms of eavesdropping are as follows.

In FIG. 9, a wiretapping wireless transmitter 8103 is installed on the line connecting the transmitting station 101 and the receiving station 102.

The eavesdropping wireless transmitter 103 transmits and receives all signals between the transmitting station 101 and the receiving station 102 using the eavesdropping wireless receiver 104.
Send to. The dedicated adapter 105 is connected to the transmitting station 101.
At the same time as communication between the receiving station 102 and the receiving station 102 is started, the eavesdropping facsimile device M106 is called. The dedicated adapter 105 ignores the control signal from the eavesdropping facsimile device atlOδ, while transmitting the control signal from the transmitting station 01 to the eavesdropping facsimile device 106.

With such a wiretapping system, the wiretapping facsimile device 106 can receive image information sent from the transmitting station 101 in the same manner as when communicating directly with the transmitting station 101.

On the other hand, in order to prevent damage from eavesdropping, the following various measures have been taken.

First, in the method described in Japanese Patent Application Laid-Open No. 57-162574, an operator inputs encryption parameters at both the transmitting and receiving stations, and encodes/encodes according to the encryption parameters.
A decoding method is determined and communication is performed (conventional method a).

Furthermore, in the method described in Japanese Patent Application Laid-Open No. 61-93776, an initial identification signal NSS or NSF to which preset encryption/decoding method information is added is sent out, and the transmitting/receiving station uses the signal to determine the encryption/decoding method. The restoration method information is detected and communicated (conventional method b).

Furthermore, in the method described in Japanese Patent Application Laid-open No. 1-245765, two types of facsimile machines are used, one for a master station and one for a slave station, and the master station and slave stations communicate with each other to eavesdrop. We are trying to prevent this. That is, the plurality of slave stations in this system each have an encryption device using a separate method, and the master station is equipped with an encryption means using the same method as all the slave stations have. . As a result, the master station can identify the encryption means possessed by the slave station with which it communicates using the initial identification signal NSS or NSF. In other words, in this method, the master station automatically selects the encryption means installed in its own station that matches the encryption means of the identified slave station, and uses this to communicate. Yes (conventional method C).

(Problem to be solved by the invention) The above conventional method has the following problems.

In conventional method a, it is necessary to uniformly determine encryption parameters at both the transmitting and receiving stations in advance, and furthermore, there is a problem in that the operator is burdened with inputting the encryption parameters. Furthermore, if the encryption parameters are not changed frequently, there is a risk that the encryption parameters will be leaked to the outside. If the encryption parameters are known to an outside party, eavesdropping becomes possible by using a device of the same type as the receiving station as a facsimile device for eavesdropping.

Although the conventional system does not require the operator to input encryption parameters, eavesdropping is still possible if a device of the same type as the receiving station is used as a facsimile device for eavesdropping.

In conventional system C, it is difficult to prepare a device of the same model as the receiving station as a facsimile device for eavesdropping, so it is effective to some extent in preventing eavesdropping. However, it is necessary to provide a separate encryption means for each facsimile machine, which is problematic in that it is inefficient in producing facsimile machines and leads to an increase in costs.

An object of the present invention is to solve the above-mentioned problems, so that the operator does not have to bother inputting cryptographic parameters, and the productivity of a facsimile machine used to prevent eavesdropping is not impaired. An object of the present invention is to provide a method for preventing eavesdropping on facsimile machines.

(Means and Effects for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention provides a cryptographic table in which cryptographic parameters correspond to cryptographic methods, and a random number generating means to a transmitting station and The transmitting station and the receiving station transmit the primary cryptographic parameters determined by the numbers generated by the random number generating means at least for each communication, and the transmitting station and the receiving station transmit the transmitted and received primary cryptographic parameters. The first feature is that the encryption parameters are converted into secondary encryption parameters using a predetermined calculation formula, and the encryption method is determined by comparing the secondary encryption parameters with the encryption table.

Further, in the present invention, a cipher table in which cipher parameters correspond to encryption methods is provided in both the transmitting station and the receiving station, a random number generator is provided in the receiving station, and the receiving station uses the numbers generated by the random number generating means. The second feature is that the determined cryptographic parameters are sent to the transmitting station at least for each communication, and the transmitting station and the receiving station check the cryptographic parameters with the cryptographic table to determine the encryption method. .

In the present invention having the above configuration, the encryption parameters for determining the encryption method can be changed at least for each communication based on the numbers generated by the random number generation means, and the encryption parameters for determining the encryption method can be changed at least for each communication. Since at least the receiving station has an encryption method selection function, wiretapping using a device of the same type as the receiving station as a wiretapping facsimile device can be avoided.

The third feature of the present invention is that the primary encryption parameter or the encryption parameter is sent each time one page of image information is sent. As a result, the encryption method is changed each time the communication of one page of image information is completed, so even if the eavesdropping device's encryption method matches that of the receiving station, all the image information will be decoded. There is little chance of it happening.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 6 is a block diagram showing the hardware configuration of a facsimile machine according to a first embodiment of the present invention.

In the figure, a reading device 1 reads image information of a document. The read image information is compressed and encoded by the encoding/decoding circuit 3 and temporarily stored in the image memory 2. The accumulated image information is modulated by the modem 4 and sent to the network control unit f (NCU
)5 to the line. These modem 4 and NCU 3 are controlled by a communication control section 6.

On the other hand, the signal taken in from the line is demodulated by modem 4,
The image is stored in the image memory 2. The accumulated image information is decompressed by the encoding/decoding circuit 3, read out as appropriate, and recorded by the printing device 7.

The encoding/decoding method (hereinafter referred to as a conversion method) in the encoding/decoding circuit 3 is determined by the system control unit 8. A cryptographic table that associates various conversion methods with cryptographic parameters is stored in RAM10. The system control unit 8 determines communication parameters and encryption parameters, and selects a conversion method corresponding to the encryption parameters by referring to the encryption table. A specific example of the cipher table and a method for determining the cipher parameters will be described later.

The system control section 8 is composed of a microcomputer, and has the function of determining the conversion method as well as the function of controlling each of the above-mentioned components according to a predetermined program.

The program that operates the system control unit 8 is stored in the ROM 9.
is memorized.

The operation unit 11 is provided for inputting various commands, the management data, and dialed numbers of the other station.

Next, the encryption table will be explained. FIG. 7 is an example of a cipher table. As shown in the figure, the encryption table contains encryption parameters, conversion methods associated with them, and false conversion method information fi to be sent to the receiving station.
It consists of Six encryption parameters are set, and each of the parameters is associated with one of the conversion methods MH, MR, and MMR. In this example, the encryption parameter is 6.
Although the number is set, it goes without saying that the number is not limited to this.

In communications performed according to CCITT Recommendation T.30, conversion method information is added to the protocol control signal NSS. In this embodiment, in order to make the eavesdropping device recognize an incorrect conversion method, the false conversion method information fi, that is, information indicating a method different from the conversion method actually used, is added to the control signal NSS.

Next, the operation of this embodiment will be explained. FIG. 1 is a block diagram showing the main functions of a transmitting station for preventing eavesdropping, and FIG. 3 is a flowchart showing the transmitting and receiving operations of this embodiment.

In FIG. 1, the random number generation means 12 is equipped with a random number table,
An irregular number (random number) Rn is generated for each communication. The number Rn generated by the random number generating means 12 is for determining the cryptographic parameter, and has a number of digits greater than the number of digits of the cryptographic parameter, that is, at least 2 in this embodiment.
Equipped with a random number table of digits.

The primary cryptographic parameter creation section 13 performs calculations to convert the random number Rn output from the random number generating means 12 into the cryptographic parameter. For example, random number generation means 1
The two-digit number Rn generated from 2 is divided by the number n of cryptographic parameters, that is, "6", and the remainder is defined as the primary cryptographic parameter Pt. In this way, the random number generating means 1
Based on the numbers output from 2, unpredictable cryptographic parameters corresponding to the cryptographic table can be obtained for each communication.

The secondary cryptographic parameter creation unit 14 uses the primary cryptographic parameter pt created at its own station and the primary cryptographic parameter Pr created at the receiving station and sent out after being added to the protocol control signal NSF. Secondary encryption parameter P
is created. The secondary encryption parameter creation unit 14 performs the following calculations. For example, the primary cryptographic parameter p
The added value of t and the primary cryptographic parameter P'' is calculated, the number n of cryptographic parameters, that is, 6'' is subtracted from that value, and the absolute value is determined as the secondary cryptographic parameter P.

The false conversion method information fi and the primary encryption parameter pt read from the encryption table corresponding to the secondary encryption parameter P calculated by the secondary encryption parameter generation unit 14 are added to the protocol control signal NSS. and sent to the other station.

The encryption table is stored in the encryption table storage section 15, and the conversion method corresponding to the secondary encryption parameter P is selected from the encryption table in the storage section 15. The selected conversion method is instructed to the encoding/decoding section 3a, and the image information is compressed and transmitted according to the instructed method.

Also, the received image information is expanded according to the same method.

Next, the operation of this embodiment based on the above functions will be explained with reference to a flowchart.

′! In FIG. a3, in step S1, dial numbers input from the operation unit 11 are read.

In step S2, a calling signal is sent out based on the dialed digits.

In step S3, the receiving station's response to the paging signal is monitored. If there is a response, the process proceeds to step S4, where the protocol control signal NSF sent from the receiving station is analyzed to detect the primary cryptographic parameter Pr.

In step S5, the random number Rn output from the random number generating means 12 is read.

In step S6, a primary cryptographic parameter pt is calculated based on the random number Rn, and the number n of cryptographic parameters is subtracted from the sum of the primary cryptographic parameter pt and the primary cryptographic parameter Pr sent from the receiving station. The absolute value is set as the secondary encryption parameter P.

In step S7, false conversion method information fi corresponding to the secondary encryption parameter P is selected with reference to the encryption table.

In step S8, the primary encryption parameter pt and false conversion method information fi are added to the protocol control signal NSS and sent to the receiving station.

In step S9, a conversion method corresponding to the secondary encryption parameter P is selected from the encryption table.

In step S10, image information is compressed according to the selected conversion method.

In step S11, the compressed image information is sent to the line.

The above procedure will be explained by assigning specific numerical values and symbols and referring to a sequence diagram.

In FIG. 8, the receiving station that has received the paging signal from the transmitting station creates and sends the primary encryption parameter Pr. In this case, the number Rn generated from the random number generating means 12
For example, if is "28" and the number n of cryptographic parameters set in the cryptographic table is 6", the remainder of the calculation result of (28÷6), that is, "4" is the primary cryptographic parameter Pr.
obtained as.

Therefore, the primary encryption parameter Pr "4" is added to the protocol control signal NSF sent from the receiving station.

On the other hand, in the transmitting station, if the number Rn generated by the random number generating means 12 is, for example, "27°" and the number n of cryptographic parameters set in the cryptographic table is "6", (
The remainder of the calculation result of 27÷6), that is, "3" is obtained as the primary cryptographic parameter pt.

The transmitting station uses the primary encryption parameter P sent from the receiving station.
r "4" and the primary encryption parameter Pt calculated by the local station
The absolute value of the number obtained by adding "3" and subtracting the number n of cryptographic parameters "6" from the value "7", that is, 1", is defined as the secondary cryptographic parameter P.

Through the above procedure, the conversion method "MMR" of the encryption table corresponding to the secondary encryption parameter P is determined as the conversion method in the communication, and similarly, the false conversion method information fi from the encryption table becomes "MH", The transmitting station uses the primary encryption parameter Pt “3°” and the false conversion method information fi.
MH" is added to the protocol control signal NSS and sent to the receiving station.

The receiving station that receives the primary encryption parameter pt "3" and the false conversion method information fi MH calculates the secondary encryption parameter P using the same procedure as that performed at the transmitting station. The same secondary encryption parameter P that is obtained at the station, that is, 1'' is obtained, and the conversion method "MMR" corresponding to the secondary encryption parameter P is obtained from the encryption table.

In this way, the receiving station normally converts the received information into image information using the same conversion method "MMR" determined by the transmitting station, regardless of the conversion method "MH" received as the false conversion method information fi. It can be restored as

On the other hand, since the eavesdropping device reproduces the received information using the conversion method "MH" received as the false conversion method information fi, it cannot restore normal information.

In the first embodiment, 1 is transmitted from the transmitting station and the receiving station.
For the next cryptographic parameters pt and Pr, the output numbers of the random number generation means 12 are converted into numerical values less than or equal to the number of cryptographic parameters n, and then sent to the partner station.

However, the output number of the random number generating means 12, that is, the two-digit random number, may be sent as is to the partner station. In that case, the value obtained by adding the random numbers sent from each station is divided by the number n of cryptographic parameters, and the remainder is determined as the secondary cryptographic parameter P.

Furthermore, by configuring the random number generation means 12 to output numbers 1 to 6 irregularly, the output numbers of the random number generation means 12 are transmitted as they are, and the secondary encryption parameters are determined based on the output numbers. Obtainable. For example, a simple number generation means that outputs irregularly arranged numbers 1 to 6 in the order of the arrangement for each communication is provided at both the transmitting and receiving stations, and a secondary encryption is performed based on the numbers generated here. Just create the parameters. In this case, numbers are output with regularity according to the scheduled arrangement, but since the number generation means outputs numbers according to the number of communications executed in the past with each facsimile machine, it is actually unpredictable. Encryption parameters can be obtained.

Next, a second embodiment of the present invention will be described. In the second embodiment, the transmitting station determines the conversion method according to instructions sent from the receiving station. The hardware configuration of the facsimile machine of the second embodiment is the same as that of the first embodiment, and illustration thereof is omitted.

FIG. 2 is a block diagram showing the main functions of a transmitting station and a receiving station in a second embodiment for preventing eavesdropping, and FIGS. 4 and 5 are flowcharts showing transmitting and receiving operations in the second embodiment. be. In FIG. 2, the same symbols as in FIG. 1 indicate the same or equivalent parts.

In FIG. 2, the receiving station 2 determines the conversion method and instructs the transmitting station 1. The cryptographic parameter creation section 16 creates cryptographic parameters Pr2 based on the random number Rn generated by the random number generation means 12. The cryptographic parameter Pr2 is created using the same calculation method as the primary cryptographic parameter Pr.

The created cryptographic parameter Pr2 is sent to the cryptographic table storage unit 15 of the own station, and the cryptographic table storage unit 15 sends data indicating the conversion method corresponding to the input cryptographic parameter Pr2 to the encoding/decoding unit 3a. supply

Furthermore, the created cryptographic parameter Pr2 is added to the protocol control signal NSF and sent to the transmitting station 1. Similar to the receiving station 2, data indicating the conversion method corresponding to the input encryption parameter Pr2 is read from the encryption table storage unit 15 of the transmitting station 1 to the encoding/decoding unit 3a of the own station. Furthermore, from the cipher table storage unit 15 of the transmitting station 1,
False conversion information fi corresponding to the cryptographic parameter Pr2 is selected, and the conversion information fi corresponds to the protocol control signal NSS.
and is transmitted to the receiving station 2. The conversion information fi is for adjusting the format of the protocol control signal NSS, and the conversion information fj is ignored at the receiving station.

Incidentally, in the same way as explained in connection with the first embodiment, if the numbers generated by the random number generation means 12 are limited to numbers equal to or less than the number of cryptographic parameters set in the cryptographic table, the cryptographic parameters The generating unit 16 can be omitted and the output numbers of the random number generating unit 12 can be directly sent to the code table storage unit 15 of the own station and the transmitting station 1.

Further, the encryption tables provided in the receiving station 2 and the transmitting station 1 may be the same, but the encryption table provided in the receiving station 2 does not need to include false conversion method information.

Next, the operation of the second embodiment based on the above functions will be explained with reference to a flowchart. First, the operation of the transmitting station is as follows.

In FIG. 4, in step S21, dial numbers input from the operation unit 11 are read.

In step S22, a calling signal is sent out based on the dialed digits.

In step S23, the receiving station's response to the calling signal is monitored. If there is a response, the process proceeds to step S24, where the cryptographic parameter Pr2 is detected by analyzing the protocol control signal NSF sent from the receiving station.

In step S25, the false conversion method information fi corresponding to the encryption parameter Pr2 is read from the encryption table, added to the protocol control signal NSS, and sent to the receiving station.

In step S26, the conversion method corresponding to the encryption parameter Pr2 is read from the encryption table and instructed to the encoding/decoding section 15 of the local station.

In step S27, the image information is compressed according to the selected conversion method.

In step 328, the compressed image information is sent to the line.

On the other hand, the operation of the receiving station is as follows.

In FIG. 5, in step S31, a calling signal from a transmitting station is monitored, and if a calling signal is detected, it is determined that there has been reception, and the process proceeds to step S32.

In step S32, the random number Rn output from the random number generating means 12 is read.

In step S33, a cryptographic parameter Pr2 is calculated based on the random number Rn.

In step S34, the calculated encryption parameter Pr2
is added to the protocol control signal NSF and sent to the transmitting station.

In step S35, the conversion method corresponding to the encryption parameter Pr2 is selected with reference to the encryption table, and is instructed to the encoding/decoding section 15 of the own station.

In step 336, image information from the transmitting station is received and stored in the image memory 2.

In step S37, the received image information is decompressed according to the conversion method corresponding to the encryption parameter Pr2, and the printing device 7
Send to.

As explained above, in the second embodiment, the image information conversion method, that is, the encoding/decoding method, is determined based on the numbers output from the random number generation means at the communication station and the receiving station, and the communication is performed according to the method. will be held.

In the first and second embodiments described above, the encryption method is determined based on at least a command from the receiving station. In addition, the commands, that is, the encryption parameters, can be changed each time communication is made.

In the first and second embodiments described above, the encryption method is a conversion method that corresponds to encryption parameters, that is, an encoding/decoding method. An encryption method can be adopted in which the transmission rate is changed each time communication is made according to encryption parameters determined by prepared and generated random numbers.

That is, the encryption method is not limited to the encoding/decoding method, and may be other encryption methods.

Next, a third embodiment of the present invention will be described in which the communication speed and transmission rate are changed according to cryptographic parameters determined by random numbers. This third embodiment is a modification of the second embodiment described above, and its hardware configuration is the same as that of the first and second embodiments, so illustration is omitted.

FIG. 10 is a functional block diagram of a third embodiment of the present invention, and FIGS. 12 and 13 are flowcharts showing transmission and reception operations of the third embodiment.

In FIG. 10, the same reference numerals as in FIGS. 1 and 2 indicate the same or equivalent parts.

In this example, the receiving station 2 determines the transmission rate and instructs the transmitting station 1.

First, in FIG. 10, in the cryptographic parameter creation section 16 of the receiving station 2, the random number Rn generated by the random number generating means 12
Create a cryptographic parameter P"2 based on.

The created cryptographic parameter Pr2 is sent to the cryptographic table storage section 21 of the local station. This cipher table storage unit 2
1, as shown in FIG. 11, the cryptographic parameters and
It consists of the actual transmission speed associated with this and false transmission speed information gi. In this example, 12 encryption parameters are set, and each parameter has a transmission rate of 9600.7200.4800 or 2400 [bp].
s] are associated with each other.

Returning to FIG. 10, the encryption table storage section 21 supplies the transmission speed control section 22 with data indicating the true transmission speed corresponding to the input encryption parameter Pr2.

The created cryptographic parameter Pr2 is added to the protocol control signal NSF and sent to the transmitting station 1.

Similar to the receiving station 2, the cryptographic table storage unit 21 of the transmitting station 1 supplies data indicating the actual transmission rate corresponding to the input cryptographic parameter Pr2 to the transmission rate control unit 22 of the own station. Further, a false transmission rate gi corresponding to the cryptographic parameter Pr2 is selected from the cryptographic table storage unit 21 of the transmitting station 1, and the false transmission rate gt is added to the protocol control signal NSS and transmitted to the receiving station 2. The transmission rate gi is for adjusting the format of the protocol control signal NSS, and the receiving station uses the transmission rate g.
i is ignored.

Note that the encryption parameter Pr2 may be determined by any method.

Further, as described in connection with the second embodiment, the encryption tables provided in the receiving station 2 and the transmitting station 1 may be the same, but the encryption table provided in the receiving station 2 may contain false conversion method information. You don't have to.

Next, the operation of the third embodiment based on the above functions will be explained with reference to a flowchart. The operation of the transmitting station is as follows.

In FIG. 12, dialing is performed in step S41, and if it is determined in step S42 that a response has been made from the receiving station, it is determined in step S43 whether or not an NSF signal has been received.

When the NSF signal is received, its contents are determined, and in step S44 it is determined whether the receiving station has the capability of encrypted communication. If there is no encrypted communication capability, step S4
The line is released in step 5, after which the process ends.

If the receiving station has cryptographic communication capability, the cryptographic parameter Pr2 is extracted from the received NSF in step S46.

In step S47, the encryption parameter Pr2 is applied to the encryption table (cipher table storage unit 21 in FIG. 10), and the actual transmission speed and false transmission speed gi are read out.

In steps 84g and S49, the actual transmission rate and the false transmission rate gi are stored.

In step S50, a false transmission speed is set in the additional information of the NSS.

In step S51, NSS is transmitted.

In step S52, the modem is set to the stored actual transmission speed.

In step S53, a TCP signal is sent.

In step S54, it is determined whether or not the CFR has been received. If the CFR is not received, that is, if the training is not successful, the process returns to step S43.

If the CFR is received, the process proceeds to phase C, and proceeds to image information transmission/reception processing.

On the other hand, the operation of the receiving station is as follows.

In FIG. 13, if the incoming call is confirmed in step S6i, a CHD is transmitted in step S62.

In step S63, cryptographic parameters Pr2 are created using an appropriate method.

In step S64, the created encryption parameter Pr2 is stored.

In step S65, as additional information of the NSF,
Set cryptographic parameter Pr2.

In step 366, the NSF is sent.

In step S67, it is determined whether the NSS has been received.

If reception of NSS is not confirmed, then in step 868 it is determined whether DC8 was received. DC3
If reception is confirmed, the mode becomes normal reception mode.

If reception of DC8 is not confirmed, it is determined in step S69 whether 3 seconds have elapsed since the processing in step S67 or 36g. If 3 seconds have not elapsed, the process moves to step S67, and if it has elapsed, the process moves to step S66.

If reception of the NSS is confirmed in step S67, it is determined in step S7 ( ) whether or not an encrypted communication instruction has been issued from the transmitting station. If an encrypted communication instruction has not been issued, normal reception is performed. mode.

If an encrypted communication instruction has been given, in step S71, the stored encryption parameter Pr2 is applied to the encryption table (cipher table storage unit 21), and the actual transmission speed is read out.

In step S72, the modem is set to the read transmission speed.

In step S73, the TC transmitted from the transmitting station is
P is received, and it is determined whether the training was successful.

If the training is not successful, the FTT is transmitted to the receiving station in step S74, and the process is continued in step S6.
Return to 3.

If the training is successful, the CFR is transmitted to the receiving station in step S75, and the process proceeds to phase C, where it proceeds to image information transmission and reception processing.

By the way, in such communication systems, the transmission speed is randomly set at the receiving station, so for example, if the line condition is poor, it may be difficult to set the transmission rate to a low speed, or conversely, if the line condition is good, it may not be possible to set the transmission rate to a low rate. Even if the transmission rate is low, the transmission rate may be set to a low value.

An embodiment for solving such problems will be described below.

FIG. 14 is a flowchart showing the receiving operation of the fourth embodiment of the present invention. The transmission operation of this fourth embodiment is as follows:
It is similar to the figure.

In addition, in FIG. 14, the same reference numerals as in FIG. 13 represent the same or equivalent processing, so a description thereof will be omitted.

In FIG. 14, if CHD is transmitted in step S62, N is set to 0 in step S81.

Next, in step S82, a random number R from 1 to 3 is generated.

In step S83, the N and R are added,
It is set to the cryptographic parameter Pr2. After that, the process moves to the process after step S64.

The cryptographic parameters are read out in step S71 using a table as shown in FIG.

If it is not determined in step S73 that the training has been successful, in step S84, N is set to 3.
is added.

Then, in step S85, it is determined whether N is greater than 9 or not.

If N is not greater than 9, the process is performed in step S83.
Return to Further, if N is larger than 9, step S86
The line is disconnected at , and the process ends thereafter.

As is clear from the above explanation, when the process shown in FIG.
600 [bpsl] is set, and the false transmission rate gi is set to 7200.4800 or 2400 [bE)S] (see FIG. 11).

Transmission rate 9600 [If training is not successful with bpsl, 3 is added to N, so the encryption parameter is set to one of 4 to 6, and the actual transmission rate? 200 [bpsl is also a false transmission rate g
As i, 9600.4800 or 2400 [bps
l is set.

Similarly, if the training is not successful at the above transmission rate, then the encryption parameter is set to 7-9 or 1.
It is set to one of 0 to 12, and 4800 or 2400 bpsl is selected as the actual transmission rate.

FIG. 15 shows a functional block diagram of the fourth embodiment of the present invention. In FIG. 15, the same reference numerals as in FIG. 10 refer to the same or equivalent parts.

In FIG. 15, the initial value of the count value N of the counter 31 is 0, and the training failure determination unit 34 described later
It is incremented by 3 from 0 depending on the training failure signal output from the training failure signal. In addition, the random number generation means 32
generates a random number R from 1 to 3.

The adder 33 adds the count value N and the random number R to obtain a cryptographic parameter Pr2, and outputs the result to the transmitting station 1.

At the transmitting station, the actual transmission rate is set based on this encryption parameter Pr2. This transmission rate is input to the transmission rate control section 22. In addition, the cryptographic parameter Pr2
A false transmission rate gi is read out based on and transmitted to the receiving station.

The image information transmission/reception control section 35 on the transmitting station side outputs TCP to the image information transmission/reception control section 35 on the receiving station.

The training failure determination unit 34 of the receiving station determines whether the training was successful based on the received TCP. If the training was not successful, counter 3
1 is incremented by 3. This count value N and the random number R are added again in the adder 33, and the addition result is output to the transmitting station as the cryptographic parameter Pr2.

Now, in the third and fourth embodiments, the transmission speed has been described as being determined only by random numbers generated on the receiving station side, but similarly to the first embodiment, both the transmitting station and the receiving station It goes without saying that more random numbers may be generated and used to determine the transmission rate.

In addition, the transmission speed has been explained as being selected from four types: 9600.7200.4800 and 2400 bpsl, but by adding the transmission speed of 12k and 14°4k bpsl, the actual transmission speed can be selected from the six types of transmission speeds. It is also possible to select the speed. The more types of transmission speeds to choose from, the lower the risk of eavesdropping.

Now, in each of the embodiments described above, the encoding method or the encryption method such as the transmission rate is set at least once using a random number generated on the receiving station side when communication is started. Next, when transmitting image information for a plurality of pages, a method for setting the encoding method or transmission speed for each page will be explained.

FIG. 16 is a functional block diagram of a fifth embodiment of the present invention. In FIG. 16, the same reference numerals as in FIG. 1 indicate the same or equivalent parts. This fifth embodiment is a modification of the first embodiment. Note that the hardware configuration of the facsimile machine of this fifth embodiment is the same as that of the first embodiment, so
Illustration is omitted.

In FIG. 16, each of the transmitting station and the receiving station generates 1
The next encryption parameter creation unit 13 generates the primary encryption parameter Pt.
Alternatively, Pr is determined, and the secondary cryptographic parameter creation section 14 creates a secondary cryptographic parameter P using Pt and Pr and the primary cryptographic parameter Pr or pt determined by the partner station.

Each cipher table storage unit 15 stores the created 2
The actual encoding/decoding method is determined using the next encryption parameter P.

The image information transmitter/receiver controllers 52 of the transmitting station and the receiving station transmit and receive image information using the respective determined encoding/decoding methods.

The transmitting station also reads out the false encoding/decoding method fi based on the secondary encryption parameter P and sends it to the receiving station.

When the image information spans multiple pages, the transmitting station transmits the MPS after completing the transmission of one page's worth of image information. This MPS
The signal is input to the multi-page determination unit 51 of the receiving station,
be identified. By this identification of MPS, the random number generating means 12 is activated again in the receiving station, and the primary encryption parameter Pr
is created.

Also, at the transmitting station, the random number generating means 12 is activated again by the output of the MPS, and the primary cryptographic parameter pt is created.

After this, in the same way as described above, each station transmits its own primary encryption parameters to the other station, each creates secondary encryption parameters, and performs the encoding/decoding method again. It is determined.

In this re-determination, the transmitting station uses false encoding/
The decoding method fi is not output.

FIG. 17 is a flowchart showing the operation of the transmitting station among the operations of the fifth embodiment of the present invention.

In FIG. 17, the same reference numerals as in FIG. 3 refer to the same or equivalent parts, so a description thereof will be omitted.

In FIG. 17, after the processing from step S1 to Sll is completed, in step 5101, it is determined whether or not it is multi-page. If you don't have multivage,
The process ends.

If it is a multi-page, in step 5102, the random number Rn is read again in the same way as in step S5.

In step 5103, a primary encryption parameter pt is calculated based on the random number Rn.

In step 5104, the primary encryption parameter pt is added to the MPS and transmitted to the receiving station.

In step 5105, M
Analyze the CF and detect the primary encryption parameter Pr.

Then, in step 5106, using the primary encryption parameters Pt and Pr, the secondary encryption parameter P
Calculate. After that, the process moves to step S9.

FIG. 18 is a flowchart showing the operation of the receiving station among the operations of the fifth embodiment of the present invention.

In FIG. 18, first, in step 5111, a calling signal from the receiving station is monitored, and if a calling signal is detected, in step 5112, the random number generating means 12
Read the random number Rn output from .

Then, in step 5113, based on the random number Rn,
Calculate the primary encryption parameter Pr.

In step 5114, the primary encryption parameter Pr is placed on the NSF and transmitted to the transmitting station.

In step 5115, the N
Receive and analyze SS, and detect primary encryption parameter pt.

In step 5116, a secondary encryption parameter P is calculated from the primary encryption parameters Pt and Pr.

In step 5117, a conversion method (encoding/decoding method) corresponding to the secondary encryption parameter P is selected from the encryption table.

In step 5118, image information is received from the transmitting station and stored in the image memory.

In step 5119, the received image information is expanded according to the conversion method corresponding to the secondary encryption parameter P and output to the printing device.

In step 5120, it is determined whether it is multi-page, that is, whether the MPS has been output from the transmitting station. If it is not multi-page, the process ends.

If it is multi-page, in step 5121, M
Analyze PS and detect primary encryption parameter pt.

In step 5122, the random number generation means 12 generates a
Read the random number Rn to be added.

In step 5123, the random number Rn is used to
Next, calculate the encryption parameter Pr.

In step 5124, a secondary cryptographic parameter P is calculated from the primary cryptographic parameters pt and P'.

Then, in step 5125, the primary encryption parameter Pr is placed on the MCF and transmitted to the transmitting station, and then the process returns to step 5117.

Further, the processing procedure of the fifth embodiment of the present invention is as follows:
This will be explained with reference to the sequence diagram shown in FIG. In FIG. 19, the same reference numerals as in FIG. 8 represent the same or equivalent parts.

In FIG. 19, when the transmission of the image information of the first page is completed, the transmitting station uses a random number to set the primary encryption parameter pt.
is calculated, and the pt is added to the MPS and output.

The receiving station detects the primary encryption parameter pt from the MPS. At the same time, a primary encryption parameter Pr is calculated using a random number, and a secondary encryption parameter P is further calculated using the primary encryption parameters pt and Pr.

Then, the primary encryption parameter Pr is added to the MCF and output to the transmitting station.

At the transmitting station, the MCF is analyzed and the primary encryption parameter Pr
is obtained, and the secondary encryption parameter P is calculated using pt and Pr.

Here, assuming that the primary encryption parameter pt calculated at the transmitting station is "6" and the primary encryption parameter Pr calculated at the receiving station is "3", the method described in connection with the first embodiment According to , the secondary encryption parameter P is “3”
(6+3-6-3), and the encoding/decoding method is MR, as is clear from FIG.

Image information communication for the second page is performed using the encoding/decoding method determined in this manner.

Communication for the third and subsequent pages is performed in the same manner.

The primary encryption parameters Pr and pt sent at the beginning of communication are stored in the PIF (facsimile control field) of NSF and NSS, respectively, and the primary encryption parameters pt and P' sent out every time a page ends. teeth,
They are stored in the PIF of MPS and MCF, respectively.

In this way, in this fifth embodiment, cryptographic parameters (primary cryptographic parameters pt and Pr) are added to the post message command (MPS in this example) and its response command (MCF in this example), and these pt and Pr is used to calculate the secondary encryption parameter P and the encoding/decoding method is determined, or as in the second embodiment, only the encryption parameter Pr2 generated on the receiving station side is used. It may also be used to determine the encoding/decoding method.

Furthermore, it goes without saying that the method of changing the encoding/decoding method on a page-by-page basis can also be applied to a communication method of changing the transmission speed. That is, this fifth embodiment is applicable to any encryption method.

Now, when a facsimile device with the wiretapping prevention function is used as a wiretapping device, the wiretapping device ignores the false encryption method information output from the transmitting station at the start of communication, so every time one page is sent, Any encryption method may be used to reset the encryption method, but if a facsimile device that does not have the wiretapping prevention function is used as a wiretapping device,
Since the eavesdropping device operates using the false encryption method output from the transmitting station at the start of communication, if the reset encryption method matches the false encryption method, the image information will be decoded. . In such a case, the encryption method to be reset may be one excluding the false encryption method.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) At least the receiving station is involved in deciding the encryption method, and the encryption method is randomly selected from among multiple methods for each communication, so that the facsimile device in question during communication Eavesdropping is impossible even if the same type of device is used as a wiretapping device.

Further, the operation of selecting an encryption method for preventing eavesdropping can be performed automatically without bothering the operator.

Furthermore, there is no need to distinguish facsimile machines into master stations and slave stations in order to implement the eavesdropping prevention method.
The facsimile device can be efficiently produced.

(2) Also, when the image information to be communicated is multiple pages,
Since the encryption method is changed every time one page is transmitted, even if the eavesdropping device's encryption method matches that of the receiving station, there is little chance that all the image information will be decoded.

[Brief explanation of drawings]

FIG. 1 is a functional diagram showing the first embodiment of the present invention;
FIG. 2 is a functional block diagram showing the second embodiment of the present invention, FIG. 3 is a flowchart showing the operation of the first embodiment, FIGS. 4 and 5 are flowcharts showing the operation of the second embodiment, and FIG. Figure 6 is a block diagram of the hardware configuration of the facsimile machine.
Figure 7 is a chart showing an example of a cipher table, and Figure 8 is a diagram showing an example of a cipher table.
Sequence diagram showing the protocol control procedure of the embodiment, No. 9
The figure is a block diagram showing the eavesdropping method, Figure 10 is a functional block diagram of the third embodiment of the present invention, Figure 11 is a diagram showing another example of the encryption table, and Figures 12 and 13 are the third embodiment. FIG. 14 is a flowchart showing the transmission and reception operation of the example; FIG. 14 is a flowchart showing the reception operation of the fourth embodiment of the invention;
FIG. 5 is a functional block diagram of the fourth embodiment of the present invention, FIG. 16 is a functional block diagram of the fifth embodiment of the present invention, and FIGS. 17 and 18 are transmission and reception operations of the fifth embodiment of the present invention. A flowchart showing the operation, and FIG. 19 is a sequence diagram showing the protocol control procedure of the fifth embodiment. 3a... Encoding/decoding unit, 12. 32... Random number generation means, 13... Primary encryption parameter creation unit, 14.
...Secondary cryptographic parameter creation section, 15°21... Cipher table storage section, 16... Cryptographic parameter creation section, 2
2...Transmission speed control section, 31...Counter, 33.
... Addition section, 34... Training failure determination section, 3
5.52... Image information transmission/reception control unit, 51... Multi-page determination unit

Claims (3)

[Claims] (1) A cryptographic table in which the cryptographic parameters correspond to the cryptographic methods and a random number generation means are provided at both the transmitting station and the receiving station, and the primary cryptographic parameters determined by the numbers generated by the random number generating means are provided at the transmitting station. and the receiving station send each other at least for each communication, and the transmitting station and the receiving station convert the transmitted and received primary encryption parameters into secondary encryption parameters using a predetermined calculation formula, and convert the secondary encryption parameters into the encryption parameters. A facsimile communication eavesdropping prevention method characterized by determining an encryption method by comparing it with a table. (2) A cipher table in which encryption parameters correspond to encryption methods is provided at both the transmitting station and the receiving station, a random number generator is provided at the receiving station, and the receiving station is determined by the numbers generated by the random number generating means. A method for preventing eavesdropping on facsimile communications, characterized in that cryptographic parameters are sent to a transmitting station at least for each communication, and the transmitting station and receiving station compare the cryptographic parameters with the cryptographic table to determine an encryption method. . (3) The method for preventing eavesdropping on facsimile communication according to claim 1 or 2, wherein the transmission of the primary encryption parameter or the encryption parameter is performed each time transmission of image information for one page is completed.