JPH07250252A - Terminal equipment for cipher communication - Google Patents

Abstract

PURPOSE:To secure the privacy of communicated contents by making deciphering due to the third person difficult by inverting the black and white of original image data at an n-th bit from the top of an original. CONSTITUTION:In response to the start of reading of the original to be transmitted at a reading part 1, a control part 3 accesses a real time clock(RTC) 9 and reads a number (n) of seconds. Then, the black and white of source image data corresponding to this read number (n) of seconds counted from the top of this original, namely, the source image data at the n-th bit from the top of the original are inverted. Thus, all the source image data including the black- and-white inverted source image data are compressed/encoded by the compression-encoding system of MH or MR at a transmitting function part 4, ciphered later by a cipher communication equipment 6 and applied to a modem 5 as ciphered data. Then, those data are transmitted through a network control unit(NCU) 7 to a public telephone line 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device for cryptographic communication, and more particularly to improvement of a method of ensuring confidentiality of communication contents.

[0002]

2. Description of the Related Art Conventionally, so-called cryptographic communication may be performed between a plurality of communication devices such as a facsimile machine from the viewpoint of maintaining confidentiality of communication data. In a conventional facsimile device for executing encrypted communication, at the time of transmission, original image data corresponding to a document to be transmitted is encrypted with, for example, a secret encryption key, and this encrypted data (hereinafter referred to as “encrypted data”) I was sending out to the telephone line. Then, the receiving side facsimile machine reproduces the received encrypted data into the original image data based on the same secret encryption key as the transmitting side.

FIG. 5 and FIG. 6 show the flow of communication of a facsimile apparatus for executing conventional encrypted communication and the principle of encryption / decryption. First, referring to FIG. 5A, a document to be transmitted is read by a scanner of a facsimile apparatus on the transmission side, and an MH (Modified Huffman) method and an MR (Modified R) method are used.
Compression coding for facsimile communication is performed by EAD, READ: Relative Element Address Designate) method or the like. After that, the data is encrypted. As shown in FIG. 6A, the data is encrypted by performing an encryption algorithm with a secret encryption key K on a plaintext P before encryption (original image data after compression encoding processing) to obtain a ciphertext C (encryption). It is achieved by creating Then, the created ciphertext C is sent from the modem to the telephone line.

On the other hand, the receiving side facsimile apparatus receives the encrypted data transmitted from the telephone line via the modem and flattens the received text. Plain text P is shown in FIG. 5B.
As shown in, the ciphertext C is obtained by performing the plain culture algorithm processing using the same secret encryption key K as that used for encryption. And this plaintext P is shown in FIG.
As shown in B, encoding / expansion for facsimile communication such as MH and MR is performed, the original sentence is corrected, and the document is printed and output by the printer.

By the way, reading of a document to be transmitted is generally started from the upper end thereof. For example, when a standard manuscript published by the International Telegraph and Telephone Consultative Committee (CCITT) shown in the upper part of FIG. 7 is transmitted, reading is started from the area A. This area A is a blank area as shown in FIG. That is, the ciphertext C that is transmitted first
In general, there is a very high possibility that the plaintext P corresponding to the blank space is encrypted.

Therefore, when the first transmitted ciphertext C is intercepted by a third party, the plaintext P corresponding to the known blank area is obtained.
Since the encrypted text C and the encrypted text C corresponding thereto are disclosed to a third party, there is a high possibility that the correspondence relationship between the plain text P and the encrypted text C, that is, the encryption algorithm is easily required. Therefore, there is a problem that the ciphertext C can be easily decrypted, and as a result, the confidentiality of the communication content cannot be secured.

[0007]

Therefore, in order to deal with this, for example, a specific area of the original area to be read first is specified.
It is conceivable to preset the original image data corresponding to one or a plurality of pixels, invert the set original image data in black and white, perform encryption processing, and transmit. According to this technique, the ciphertext transmitted first is not the plaintext corresponding to the blank space, so it should not be easily deciphered.

However, in this technique, since the original image data corresponding to a specific pixel is black-and-white inverted, the ciphertext transmitted first is always constant. Therefore, even in the above technique, since the encryption algorithm is likely to be known, there is a fear that the decryption may be easily performed. Therefore, an object of the present invention is to solve the above-mentioned technical problems and to provide a terminal device for encrypted communication capable of ensuring confidentiality of communication contents.

[0009]

According to a first aspect of the present invention, there is provided a terminal device for encrypted communication according to claim 1, wherein encrypted terminal data is transmitted to a receiving side terminal device connected via a predetermined communication line. A reading unit for reading a document to be transmitted and outputting original image data,
Of the original image data output from the reading means, data specifying means for randomly specifying arbitrary original image data in the original image data up to a predetermined number of bits, and the original image data specified by the data specifying means are monochrome. A black-and-white inversion means for inverting, an encryption means for creating encrypted data by subjecting the original image data output from the reading means including the original image data black-and-white inverted by the black-and-white inversion means to a predetermined encryption process, and And a sending means for sending the encrypted data created by the encrypting means to a predetermined communication line.

According to a second aspect of the present invention, in a terminal device for encrypted communication, encrypted data created by subjecting original image data including black-and-white inverted original image data to a predetermined encryption process is transferred to a predetermined communication line. A terminal device for receiving from a transmission-side terminal device connected via a device, the encrypted data received from the transmission-side terminal device via the predetermined communication line is subjected to a predetermined decryption process and encrypted. Decryption means for restoring the original image data before conversion, data specifying means for specifying the original image data that has been black and white inverted among the original image data restored by this decoding means, and original image data specified by this data specifying means And a black and white reversing means for reversing black and white.

[0011]

In the structure according to the above-mentioned claim 1, in the transmitting side terminal device, among the original image data read by the reading means,
Arbitrary original image data in the original image data up to a predetermined number of bits from the beginning is randomly designated, and the designated original image data is inverted in black and white. Then, all original image data including the original image data that has been subjected to the black-and-white inversion is subjected to encryption processing to create encrypted data, and the created encrypted data is sent to a predetermined communication line.

On the other hand, in the receiving side terminal device, as in the configuration described in claim 2, for example, the received encrypted data is decrypted to restore the original image data, and among the restored original image data, The original image data, which has been subjected to black-and-white reversal, is specified by the transmission side terminal device. Then, the specified original image data is inverted in black and white. As described above, in the above configuration, since the original image data to be black-and-white inverted in the original image data up to the predetermined number of bits from the beginning is randomly specified, from the beginning of the encrypted data to be transmitted up to the predetermined number of bits. The encrypted data of is different for each communication. Therefore, it is possible to make it difficult for a third party to decipher the encrypted data, so that the confidentiality of the communication content can be ensured.

Further, in the receiving side terminal device, since the original image data which has been subjected to the black-and-white inversion at the transmitting side terminal device is again black-and-white inverted, the original image data corresponding to the transmission original can be accurately restored.

[0014]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the electrical configuration of a facsimile apparatus according to an embodiment of the present invention. This facsimile apparatus includes a reading unit 1 that is a reading unit that optically reads a document to be transmitted and outputs original image data. The original image data output from the reading unit 1 is given to the image processing unit 2 and subjected to predetermined image processing. The original image data subjected to the image processing is the control unit 3
It is given to the transmission function unit 4 via the and is subjected to compression encoding necessary for facsimile communication such as MH and MR. The original image data that has been subjected to this compression coding is given to the modem 5 via the control unit 3. Further, when performing encrypted communication, in the encrypted communication device 6 which functions as an encryption unit and a decryption unit, the compression-coded original image data is subjected to encryption processing to create encrypted data, and this is created. The encrypted data is provided to the modem 5. The compression-encoded original image data or encrypted data is transferred to the network controller (N
It is sent to the public telephone line 8 through the CU) 7.

The control unit 3 is provided with a real time clock (hereinafter referred to as "RTC") 9 for counting the number of seconds for updating the counting operation every N (for example, N = 60) seconds. The control unit 3 can read the number of seconds n (0 ≦ n ≦ 59) from the RTC 9 at an arbitrary timing, and the number of seconds n read is the original image data to be reversed in black and white as described later. Used when specifying.

The facsimile unit also includes an operation unit 1
0 is provided. A numeric keypad 1 for inputting numerical data such as a facsimile number of a transmission destination is input to the operation unit 10.
0a, a start key 10b for inputting a start signal of the facsimile apparatus, an encrypted communication key 10c for instructing encrypted communication, and the like. The above-described types of keys in the operation unit 10 are examples, and keys may be added or changed as necessary.

When the facsimile apparatus shown in FIG. 1 receives data, the data is given to the modem 5 via the NCU 7. When the received data is simply compression-coded original image data, that is, in the case of normal facsimile communication, the received original image data is demodulated by the modem 5 and then decoded (decompressed) by the reception function unit 11. ) Is performed, and the original image data is restored. After that, the original original image data is given to the recording unit 12, and is printed on the paper in the recording unit 12, so that the transmitted original is reproduced.

On the other hand, when the received data is encrypted data, that is, in the case of encrypted communication, the received encrypted data is demodulated by the modem 5 and then decrypted by the encrypted communication device 6, that is, A flat culture is given.
Then, in the receiving function unit 11, the original image data is decrypted to restore the original image data in the same manner as described above, and then the recording unit 12 prints the original image data on the paper to reproduce the transmitted original document.

In this embodiment, the control unit 3 functions as a black / white inverting means and a data specifying means. Also,
The control unit 3 and the RTC 9 function as data designating means. Further, the control unit 3 and the modem 5 function as sending means. FIG. 2 is a flowchart showing the transmission operation of the facsimile device 1 in the cryptographic communication. The transmission operation in this cryptographic communication is performed by the user placing a document to be transmitted on a predetermined document table, inputting the facsimile number of the other party from the ten key 10a, and further pressing the cryptographic communication key 10c and the start key 10b. Be started.

In response to the start of reading of the original to be transmitted by the reading unit 1 (step S1), the control unit 3
Accesses the RTC 9 and reads the number of seconds n (step S2). Then, the original image data corresponding to the read number of seconds n counted from the beginning of the original, that is, the original image data of the nth bit from the beginning of the original is inverted in black and white (step S3).

All the original image data including the original image data which has been subjected to black and white inversion is compression-encoded by the compression encoding system such as MH and MR in the transmission function unit 4 (step S).
4) The encryption processing is performed in the encryption communication device 6 (step S5), and the encrypted data is given to the modem 5. Then, it is sent to the public telephone line 8 through the NCU 7 (step S6).

FIG. 3 is a flow chart showing the receiving operation in the facsimile device 1 in the encrypted communication. N
The encrypted data received via the CU 7 is demodulated by the modem 5 and then given to the encrypted communication device 6. In the encrypted communication device 6, the encrypted data is decrypted (step P1) to restore the original image data before encryption. The restored original image data before encryption is given to the reception function unit 11 to be decrypted (step P2), and the original original image data is restored.

In the restored original image data, the nth bit from the beginning is reversed in black and white, and if the transmitted original is reproduced as it is, only the nth bit is reproduced in a color different from the original transmitted original. Becomes Therefore, in order to deal with this, the control unit 3 estimates the n-th bit original image data, and inverts the estimated original image data in black and white.

That is, of the original image data from the head to the N-th bit, original image data showing a color different from other N-1 bit original image data is searched (step P3), and as a result, there is original image data having a different color. For example, the original image data is identified as the original image data that was black and white inverted on the transmitting side,
The specified original image data is inverted in black and white (step P4). As a result, it is possible to accurately restore the original image data before the black and white inversion on the transmitting side. Then, the original image data after the black and white inversion is given to the recording unit 12,
The transmission original is reproduced by being printed on the paper in the recording unit 12 (step P5).

As described above, according to the facsimile apparatus of the present embodiment, since the original image data of the n-th bit from the beginning of the original is inverted in black and white, the encrypted data from the beginning of the original to the N-th bit is transmitted for each communication. You can send it by changing to. Therefore, it is possible to make it difficult for a third party to decipher, and it is possible to improve the security of communication confidentiality.

Further, when the encrypted data including the black-and-white inverted original image data is received, the black-and-white inverted original image data is black-and-white again, so that the transmitted original can be reproduced accurately. Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.
For example, in the above embodiment, the case where the facsimile device 1 is applied as the terminal device has been described.
Not limited to the facsimile device, any terminal device capable of transmitting and receiving image data can be applied.

Further, in the above-described embodiment, the original facsimile image data, which has been inverted in black and white, is specified in the receiving side facsimile device,
Although this specified original image data is inverted in black and white, this processing is not necessarily required to be performed, and the receiving side facsimile device may perform normal reception processing. The reason is that one pixel (dot) is actually about 0.1 mm (= 1/200 inch), and for example, if the original image data for black and white inversion is one dot, only one pixel is surrounded. This is because even if the colors are reproduced differently, it can be realistically ignored from the viewpoint of image quality disorder.

Further, in the above embodiment, only the n-th original image data from the beginning of the original is black-and-white inverted.
For example, a predetermined number of bit group data having the beginning or the n-th bit of the original may be inverted in black and white.
Furthermore, in the above-mentioned embodiment, an example in which a so-called ECB mode is applied to perform ordinary encryption to realize encrypted communication has been described. However, for example, a CB using an exclusive OR.
The C mode may be applied.

More specifically with reference to FIG. 4,
The original image data before encryption, that is, the plaintext P ₁ is the encryption unit 2
Encrypted with 0, encrypted data, that is, ciphertext C ₁
Is created. The created ciphertext C ₁ is output as it is, and is also given to the exclusive OR unit 21 provided on the input side of the encryption unit 20. Next, plaintext P
_{When 2} is encrypted, it is not given to the encryption unit 20 as it is, but the exclusive OR unit 21 calculates the exclusive OR with the ciphertext C _1, and after the calculation, The plaintext P ₃ is given to the encryption unit 20. The ciphertext C ₂ created by the encryption unit 20 is output as it is, and is also given to the exclusive OR unit 21, similarly to the ciphertext C ₁ described above.

As described above, since the encryption is performed by sequentially calculating the exclusive OR, if the encrypted data from the head of the original to the N-th bit is different for each communication, the encrypted data after that is also communicated. It will be different for each. Therefore, the decryption by a third party can be made more difficult.
Other various design changes can be made within the scope described in the claims.

[0031]

As described above, according to the terminal device for encrypted communication according to the first aspect, since the original image data to be reversed in black and white is specified at random, it is highly likely that it corresponds to the margin. The encrypted data sent to the can be changed for each communication. Therefore, unlike the technique in which the encrypted data transmitted first is always constant, it is possible to make decryption by a third party difficult. Therefore, the confidentiality of the communication content can be secured.

Further, according to the terminal device for encrypted communication of claim 2, the original image data subjected to the black-and-white inversion is specified from the received encrypted data, and the specified original image data is again subjected to the black-and-white inversion. As a result, the original document can be reproduced accurately.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a transmission operation of the facsimile device in encrypted communication.

FIG. 3 is a flowchart showing a receiving operation in the facsimile device in encrypted communication.

FIG. 4 is a diagram for explaining an encryption process when the CBC mode is applied.

FIG. 5 is a diagram showing a communication flow of a facsimile device for executing conventional encrypted communication.

FIG. 6 is a diagram for explaining the principle of conventional encryption / decryption.

FIG. 7 is a schematic view showing a part of a standard manuscript published by the International Telegraph and Telephone Consultative Committee (CCITT).

[Explanation of symbols]

 1 reading unit 3 control unit 5 modem 6 cryptographic communication device

Claims (2)

[Claims] 1. A terminal device for transmitting encrypted data to a receiving side terminal device connected via a predetermined communication line, the reading device reading a document to be transmitted and outputting original image data. A data designating means for randomly designating arbitrary original picture data among the original picture data up to a predetermined number of bits from the original picture data outputted from the reading means; and the original picture data designated by the data designating means. A black-and-white inversion means for black-and-white inversion, and an encryption means for creating encrypted data by subjecting the original-image data including the original-image data black-and-white inverted by the black-and-white inversion means to a predetermined encryption process. A terminal device for encrypted communication, comprising: sending means for sending the encrypted data created by the encrypting means to a predetermined communication line. 2. To receive encrypted data created by subjecting original image data including black-and-white inverted original image data to a predetermined encryption process from a transmission side terminal device connected via a predetermined communication line. And a decryption means for performing a predetermined decryption process on the encrypted data received from the transmission side terminal device through the predetermined communication line to restore the original image data before encryption. Of the original image data restored by the decryption means,
A terminal device for encrypted communication, comprising: a data specifying unit that specifies black-and-white inverted original image data; and a black-and-white inversion unit that black-and-white inverts the original image data specified by the data specifying unit.