JPH07288514A - Communication equipment - Google Patents

Abstract

PURPOSE:To prevent ciphering algorithm security from being deteriorated by providing a ciphering communication section applying ciphering to an original in the forward direction and the reverse direction. CONSTITUTION:An operation section 5, a MODEM 8, an NCU 9, a scanner 11a, a print section 15a, a real time clock 16 and a CPU 2 are interconnected via a data bus 17, each component using the CPU 2 as a center functions like a ciphering communication section to cipher an original in the forward direction and the reverse direction and a process for ciphering communication in both the transmission and reception is programmed by a control section. A sender side sends a signal to a specific receiver by regularly changing the forward ciphering and the reverse ciphering such as forward ciphering for 1st time and reverse ciphering for 2nd time.... The rule of the ciphering direction change is determined in advance between a sender and a receiver. Furthermore, a counter being a program stores the communication sequence for the sender and the receiver, the sender side implements ciphering and the receiver implements decoding according to the predetermined rule and to the counter representing the past communication number of times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device for performing secret cryptographic communication such as a facsimile device having a cryptographic communication function, and more particularly to a communication device designed to improve confidentiality in cryptographic communication.

[0002]

2. Description of the Related Art In facsimile communication, various special communication can be optionally performed for communication between facsimile machines of the same manufacturer. Cryptographic communication is one of the special communications.

FIG. 8 shows the procedure of normal cipher communication in a facsimile machine. In FIG. 8A, 91
Numerals 94 to 94 are signal processing procedures on the transmitting side, and a document to be transmitted is first read by the scanner 91. At 92, the read image data is subjected to data compression such as MH, that is, encoding processing. Next, in order to perform secret communication on the compressed image data, an encryption process is performed at 93 using an encryption key, and the encrypted data is sent out from a facsimile machine as a transmission side modem 94.

As described above, conventionally, when performing encrypted communication using a facsimile apparatus, the image data read by the scanner 91 is encrypted and transmitted according to the order read by the scanner 91 without being processed as it is. Was there.

In FIG. 8B, reference numerals 95 to 98 are signal processing procedures on the receiving side, and 9 is the encrypted received data of the original received by the facsimile apparatus as the receiving side modem 95.
At 6, the ciphertext is decrypted using the same encryption key as the sender,
So-called flat culture processing is performed. The plain-text image data is decompressed at 97, that is, decoded to become the original image data, which is printed by the printer 98, whereby the original is taken out at the receiving side. The encryption key mentioned here is a kind of data.

FIG. 9 shows an example of a typical transmission original. The manuscript shown in the figure is a standard manuscript of CCITT (International Telegraph and Telephone Consultative Committee). As is clear from the manuscript M, most of the normal transmission manuscript is occupied by "white", that is, a white background portion in which characters and the like are not written.

Now, in the conventional facsimile apparatus,
Considering the portion first scanned by the scanner 91, in other words, the first portion of the transmitted data or the first encrypted portion, the first portion H of the document M is scanned first. Usually this head part H
Is often white. For this reason, when a conventional facsimile apparatus tries to send out some original, it can be said that the first part of the sent data is very likely to correspond to the data for all white.

FIG. 10 shows an example of a general encryption processing unit in a facsimile apparatus, (A) shows an example using the ECB mode, and (B) shows an example using the CBC mode. In any of the cases shown in FIGS. 10A and 10B, the ciphertext C is normally output to the plaintext P using the cipher key K as described above.

However, in the ECB mode, as shown in FIG. 10A, the image data to be encrypted and the encryption are 1:
1 corresponds. On the other hand, in the CBC mode, as shown in FIG.
0 (B), the example n-th when encrypting plaintext P _n, EOR of ciphertext C _n-1 and the plaintext P _n of one time before the
Take the (exclusive OR) and encrypt the result. In this case, since the ciphertext is not written in the first image data, an initial value secretly set in advance is used, and the initial value and the plaintext P ₁ are EORed.

[0010]

In the cryptographic communication as described above, since only the ciphertext C is usually exposed to the public, it can be said that the possibility of decrypting the cryptogram is extremely low. However, the first scan portion of the transmission data is often data for "all white" as described above. For this reason, in the ECB mode in which the image data and the encryption are in a 1: 1 correspondence, the document M is scanned by the scanner 91.
, The first part of the received encrypted data is found to be "white" encrypted, and the encryption algorithm lacks strength.

Further, in the CBC mode, since the initial value is not known, even if the first image data is "white",
Since the plaintext P ₁ representing this “white” is also scrambled, it can be said that the strength of the encryption algorithm is higher than in the ECB mode, but the point that the first part of the transmitted data is “white” This is not different from the case of the ECB mode, and therefore, in any mode, the plaintext P
(All white data) and the ciphertext C for it are open. As described above, in the case of the conventional apparatus, since the specific plaintext and the ciphertext corresponding thereto are known, there is a problem in that the strength of this cipher considerably deteriorates.

The present invention has been made in view of the above problems, and in a communication device which constitutes a transmission / reception modem of a communication system for performing cryptographic communication, the leading portion of a normal document is almost "white" in most cases. It is an object of the present invention to provide a configuration in which effective measures are taken to prevent the strength of the encryption algorithm from being reduced due to the above.

[0013]

In order to achieve the above object, according to the present invention, when encrypting image data, a method of encrypting the image data according to the order in which the image is read by a scanner in the same manner as in the prior art (hereinafter, forward direction encryption In addition to the above), a method of encrypting the image data read by the scanner from the last data (hereinafter referred to as backward encryption) is adopted, and the original is encrypted in the forward and backward directions according to a predetermined process. I am trying.

In the first configuration of the present invention using such a method, an encryption communication unit having a function of encrypting a document in the forward direction and the backward direction is provided, and the encryption communication unit is used for both transmission and reception. A counter that indicates the number of times of communication with a specific partner device from the time of resetting, and a table that shows the rules that determine whether the encryption direction is the forward direction or the reverse direction for each communication number at the time of transmission. According to the counting operation of the counter and the corresponding encryption direction of the table, the encryption direction for each communication is selected,
In the selected direction, an encryption process is performed at the time of transmission, and a control means for performing a flat culture process at the time of reception is provided.

Further, in the second configuration of the present invention, the random data addition means for providing the reference data for selecting the encryption direction as the encryption communication unit having the function of encrypting the original in the forward direction and the backward direction. Then, at the time of transmission, the encryption direction is selected based on the data from the random data giving means, and the encryption process is performed in that direction, and at the time of reception, the plain culture process is first performed in the preset direction, and thereafter, When an error occurs in the decryption process, a control means for performing the plain culture process in a direction opposite to the setting direction is provided.

Further, in the third configuration of the present invention, the encryption communication unit has a flag indicating the encryption direction in the non-standard signal in the pre-communication procedure, and the encryption direction is arbitrarily set during transmission. To set the flag indicating that direction, perform encryption processing in the selected direction, and at the time of reception, refer to the flag sent first from the other device, and set the direction in accordance with the value indicated by that flag. It is supposed to be equipped with control means for performing cultural processing.

[0017]

According to the first configuration of the present invention, the transmitting side is
Forward encryption and backward encryption, for example, forward encryption for the first time, backward encryption for the second time, forward encryption for the third time, etc. for a specific recipient as the other party. And change it regularly before sending. The rules to be changed are predetermined between the sender and the receiver. In addition, the counter stores the number of times of communication with each other, and according to a predetermined rule and a counter indicating the number of past communication,
The sender performs encryption, and the receiver performs plain culture.

According to the second configuration of the present invention described above, the transmitting side arbitrarily selects forward direction encryption and reverse direction encryption based on the data from the random data adding means, and performs encryption to obtain image data. Send. The receiving side first performs plain culture on the received data, for example, in the forward direction. If the received data is encrypted in the reverse direction, this forward-direction plaintext will always result in an error in the next decryption step. On the receiving side, when such an error occurs, the plain culture is performed from the opposite direction.

According to the third configuration of the present invention, the transmitting side arbitrarily selects the forward direction encryption and the backward direction encryption, performs the encryption, and transmits the image data. Then, according to the selected direction, for example, if it is the forward direction, the bit as the flag is set to "1".
If it is in the opposite direction, the bit is set to "0" and communication is performed. Prior to the processing of the plain culture, the receiving side refers to the bit, and if it shows "1", for example, performs the plain culture from the opposite direction.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a facsimile apparatus which constitutes a transmission / reception modem of a communication system for performing encrypted communication in the CBC mode will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a facsimile apparatus according to the first embodiment of the present invention. In this figure, reference numeral 1 is a control unit composed of a microcomputer or the like, and controls the entire control. As shown in FIG. 2, the control unit 1 is composed of a CPU 2, a program ROM 3, a RAM 4 and the like. Further, the RAM 4 has a work area for performing encrypted communication, an encryption key storage area as one form of a memory area, a direction determination table, a counter, and the like.

Returning to FIG. 1, 5 is an operation unit and 6 is encoding /
A decryption circuit, 7 is an encryption / plain culture circuit that performs encryption when the facsimile machine operates as a transmission side, and performs plain culture when the facsimile machine operates as a reception side, 8 is a modem unit, and 9 is an NCU. (Network control device) 10 is a public telephone line. A reading unit 11 includes a scanner 11a that reads a document. An image processing unit 12 performs processing such as shading correction on the read image data. 1
3 is a transmission function unit, 14 is a reception function unit, and 15 is a recording unit having a printing unit 15a and the like. Further, 16 is a real time clock (RTC) for measuring communication time.

As shown in FIG. 2, the operation unit 5, the modem unit 8 and the NCU 9, the scanner 11a, the printing unit 15a, the real-time clock 16 and the CPU 2 described above are as shown in FIG.
As described below, the above-described configurations centered on the CPU 2 are connected through the data bus 17, and function as an encryption communication unit that encrypts a document in forward and backward directions. A process for encrypted communication is programmed in the control unit 1.

Next, in the case where the above-mentioned configuration functions as an encryption communication unit, the control unit 1 when operating as a transmission side
An example of the operation will be described with reference to the flowchart of FIG. First, before performing encrypted communication, in step # 5,
The counter C provided in the RAM 4 is reset.
The counter C indicates the number of times of communication with a specific partner device from the time of reset in both transmission and reception, and stores the number of times of communication with each other in both transmission and reception.

After that, a communication procedure such as reading an original with the scanner 11a and encoding it is performed, and whether or not the encrypted communication is based on the bit for the encrypted communication in the signal received in the procedure. A decision is made. And
When the encrypted communication is started in step # 10, first, in step # 15, the remaining amount of memory required for the encrypted communication is confirmed,
Next, at step # 20, the number of times of the counter C is read.
The number of times of the counter C indicates the number of times of communication with a specific recipient.

Then, in step # 25, the direction corresponding to the counter C, that is, the forward direction encryption for encrypting according to the order read by the scanner 11a and the backward direction for encrypting the image data read by the scanner 11a from the last data Either direction of encryption is referred to from the direction determination table of the RAM 4.

[0026]

[Table 1]

This direction determination table shows a rule which determines whether the direction of encryption is the forward direction or the reverse direction for each communication at the time of transmission. For example, as shown in Table 1 above, a counter is used. The forward and reverse directions are randomly set with respect to the value of C, and the rule to be changed is predetermined between the sender and the receiver.

Then, the control unit 1 selects the encryption direction for each communication according to the counting operation of the counter and the encryption direction indicated by the corresponding direction determination table,
When transmitting in the selected direction, encryption processing is performed. Therefore, for example, if the value of the counter C is 4 in step # 30, the encryption direction of the direction determination table is "normal", so the flow advances to step # 35 to perform encryption in the normal direction.
Further, for example, when the value of the counter C is 5, the encryption direction of the direction determination table is “reverse”, and therefore the step #
Proceed to step 40 to encrypt in the reverse direction.

After the original is encrypted, the value of the counter C is incremented by 1 in step # 45 in preparation for the next encrypted communication, and the transmission operation is performed in step # 50. For reception, the ciphertext sent is selected in accordance with the encryption direction indicated by the direction determination table corresponding to the counting operation of the counter C, and the encryption direction for each communication is selected. It will be processed in plain culture.

As described above, in the first embodiment of the present invention, according to a predetermined rule and a counter indicating the number of past communications,
The sender side performs encryption and the receiver side performs flat culture, but the rules of the direction determination table are known only to a specific sender / receiver, so the strength of the encryption algorithm increases dramatically. . In the present embodiment, the value of the counter C corresponds to the number of times of communication, but in the present invention, various changes can be made such as updating it every time the page of the document is updated.

4 and 5 show the flow of the transmitting operation (FIG. 4) and the receiving operation (FIG. 5) of the control unit 1 in the second embodiment of the present invention. Since the configuration of this embodiment is common to that of the first embodiment shown in FIGS. 1 and 2,
The description of the common configuration will be omitted.

In this embodiment, the real time clock 16
Is made to function as random data giving means for giving reference data for selecting the encryption direction. Then, at the time of transmission, the forward direction encryption and the backward direction encryption are arbitrarily selected based on the data from the real-time clock 16, and the encryption processing is performed in that direction to transmit the image data. As a method of selection, in this embodiment, the value of the second of the real-time clock 16 immediately before communication is read, and if the read number of seconds is even, forward encryption is selected, and if it is odd, backward encryption is selected. is doing.

That is, in FIG. 4, after the transmission operation is started, the value "S" of the seconds of the real-time clock 16 is read in step # 105, and the value "S" is read in step # 110.
Is an even number or an odd number. For example, if S = 10, it is determined that it is an even number and the process proceeds to step # 115 to perform encryption in the forward direction. For example, if S = 11, it is determined that it is an odd number and the process proceeds to step # 120 to encrypt in the reverse direction.
It is transmitted in step # 125.

At the time of reception, the received data is temporarily R
Store in AM4. Then, for the first preset direction, that is, for the received data, first, the flat culture process is performed, for example, in the forward direction. When an error occurs in the subsequent decryption processing, the plain culture processing is performed in the direction opposite to the setting direction. That is, in FIG. 5, when the ciphertext is received, the data received in step # 205 is plainly written in the positive direction as stipulated.

Next, in step # 210, it is decrypted. If the data received at that time is encrypted in the reverse direction, if the data is encrypted in the forward direction, an error will always occur in the decryption step. To do. That is, the number of dots in one line after decoding does not match the specified value (for example, 1728 in the fine mode).

Therefore, if an error does not occur at the time of decryption in step # 215, it is directly followed by step # 230.
When the error occurs, the process proceeds to step # 220, the plain culture is redone, that is, the plain culture is performed from the opposite direction, and the decryption is performed in step # 225. And output.

In this embodiment, it is specified that the normal culture is performed in the normal direction first, but of course, the normal culture may be performed in the reverse direction first.

FIGS. 6 and 7 show the flow of the transmission operation (FIG. 6) and the reception operation (FIG. 7) of the control unit 1 in the third embodiment of the present invention. Since the configuration of this embodiment is common to that of the first embodiment shown in FIGS. 1 and 2,
Descriptions of portions having the same configuration will be omitted. In this embodiment, the nonstandard signal NSS in the pre-communication procedure has a flag (bit) indicating the direction of encryption.

Then, the control unit 1 arbitrarily selects an encryption direction at the time of transmission, sets a flag indicating the direction, performs encryption processing in the selected direction, and first transmits from the partner machine at the time of reception. The flag is referred to and the flat culture process is performed in the direction according to the value indicated by the flag.

That is, in FIG. 6, after the transmission operation is started, the encryption direction is selected. As the selection method, the value of the seconds of the real-time clock 16 immediately before communication is read in step # 305, the forward encryption is selected if the number of seconds read in step # 310 is even, and the backward encryption is selected if it is odd. To activate.

Then, according to the selected direction, for example, S
If it is = 10, it is determined that it is an even number, that is, the forward direction, and the process proceeds to step # 315 to set the bit to "1", and the forward direction encryption is performed at step # 320. Also, for example, S =
If it is 11, it is determined that it is an odd number, that is, the backward direction, the process proceeds to step # 325, the bit is set to "0", encrypted in the backward direction at step # 330, and transmitted at step # 335.

At the time of reception, the received data is temporarily R
Store in AM4. Then, as shown in FIG. 7, the bit of the non-standard signal NSS sent in step # 405 is referred to before the plain culture process, and if “0” is indicated, the process proceeds to step # 410. If you perform normal culture in the positive direction, and if it shows "1", for example, then step # 4
Proceed to step 15 and perform plain culture from the opposite direction. In either case, after that, decryption is performed in step # 420, and step # 42.
At 5, the output operation to the print unit 15a or the like is performed.

[0043]

As described above, the present invention is provided with the encryption communication unit having the function of encrypting the original in the forward direction and the backward direction according to the predetermined process. Specifically, in claim 2, the transmitting side performs forward encryption and backward encryption on a certain recipient as the other party based on the counting operation of the counter and the rule determined between the sender and the receiver in advance. The transmission is changed.

Further, in claim 3, at the time of transmission, an encryption direction is selected on the basis of the data from the random data adding means and the encryption processing is performed in that direction, and at the time of reception, it is first written in the preset direction. When an error occurs in the subsequent decoding process after the processing, the plain culture process is performed in the direction opposite to the setting direction.

Further, in claim 4, the direction of encryption is arbitrarily selected at the time of transmission, the flag indicating the direction of encryption is set in the non-standard signal in the pre-communication procedure, and the encryption processing is performed in the selected direction. In addition to the above, when the reception is performed, the flag transmitted from the other device is first referred to, and the control means for performing the flat culture processing in the direction according to the value indicated by the flag is provided.

As described above, according to the present invention, in the same manner as the conventional method, the forward direction encryption for encrypting in the order of reading by the scanner and the backward direction encryption for encrypting the image data read by the scanner from the last data are performed. Since the original is encrypted from the forward and reverse two directions by the encryption algorithm using, when the encrypted communication is performed in the CBC mode, the transmission data amount can be transmitted without any change. , The plaintext / ciphertext pair is not known, and the cipher strength does not decrease.

Even if the same document is repeatedly transmitted due to an error or the like, the image data at the beginning differs every time the image is transmitted, so the encryption strength is further increased, and for example, the beginning portion of a normal document is almost In the case of 1, it is possible to effectively prevent a decrease in the strength of the encryption algorithm due to being "all white".

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing the configuration of a facsimile apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a specific state of the control unit and a connection state with other components.

FIG. 3 is a flowchart showing an operation example regarding transmission of a control unit.

FIG. 4 is a flowchart showing an operation example regarding transmission of a control unit in the facsimile apparatus according to the second embodiment of the present invention.

FIG. 5 is a flowchart showing an operation example regarding reception of the control unit.

FIG. 6 is a flowchart showing an operation example regarding transmission of a control unit in the facsimile apparatus according to the third exemplary embodiment of the present invention.

FIG. 7 is a flowchart showing an operation example regarding reception of the control unit.

FIG. 8 is a block diagram showing a procedure of normal cipher transmission in a general facsimile apparatus.

FIG. 9 is a plan view showing an example of a transmission document.

FIG. 10 is a block diagram showing an example of an encryption processing unit in a general facsimile apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 control part 2 CPU 3 ROM 4 RAM 5 operation part 6 encoding / decoding circuit 7 encryption / plain culture circuit 8 modulation / demodulation part modem 9 NCU 11 reading part 11a scanner 12 image processing part 13 transmission function part 14 reception function part 15 Recording unit 15a Printing unit 16 Real-time clock

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04L 9/12 // H04N 1/44

Claims (5)

[Claims] 1. A communication device constituting a transmission / reception modem of a communication system for performing encrypted communication, comprising a cryptographic communication unit having a function of encrypting a document in a forward direction and a backward direction according to a predetermined process. Communication equipment characterized by. 2. The encryption communication unit has a counter that indicates the number of times of communication with a specific partner device from the time of resetting during both transmission and reception, and a direction in which encryption is performed for each number of times of communication during transmission. A table indicating a rule deciding which of the directions is to be selected, and the encryption direction for each communication is selected according to the counting operation of the counter and the encryption direction corresponding to the table, and the selected direction The communication device according to claim 1, further comprising a control unit that performs encryption processing at the time of transmission and performs plain culture processing at the time of reception. 3. The encryption communication unit, random data giving means for giving reference data for selecting an encryption direction, and at the time of transmission, selects an encryption direction based on the data from the random data giving means. Control that performs encryption processing in the same direction, and first performs plain culture processing in the preset direction at the time of reception and then performs the plain culture processing in the opposite direction to the above setting direction when an error occurs in the subsequent decryption processing The communication device according to claim 1, further comprising: 4. The encryption communication unit has a flag indicating an encryption direction in a non-standard signal in a pre-communication procedure, and at the time of transmission, arbitrarily selects an encryption direction and sets a flag indicating the direction. It is characterized by comprising control means for performing encryption processing in the selected direction, and at the time of reception, referring to the flag transmitted from the other device first and performing the flat culture processing in the direction according to the value indicated by the flag. The communication device according to claim 1. 5. The communication device according to claim 1, wherein the communication device is configured as a facsimile device having a CBC mode encrypted communication function.