JP3121981B2 - Terminal device for encrypted communication - Google Patents

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 performing cryptographic communication, and more particularly to an improvement in a method for securing 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 facsimile machines from the viewpoint of maintaining confidentiality of communication data. 2. Description of the Related Art In a conventional facsimile apparatus for performing encrypted communication, during transmission, original image data corresponding to a document to be transmitted is encrypted using, for example, a secret encryption key, and the encrypted data (hereinafter, referred to as “encrypted data”) is transmitted. Had been sent to the telephone line. Then, the receiving-side facsimile apparatus reproduces the received encrypted data into the original original image data based on the same secret encryption key as the transmitting side.

FIGS. 5 and 6 show a communication flow of a conventional facsimile apparatus for performing encrypted communication and the principle of encryption / decryption. First, referring to FIG. 5A, an original to be transmitted is read by a scanner of a facsimile apparatus on the transmission side, and is subjected to an MH (Modified Huffman) method and an MR (Modified R).
EAD, READ: Relative Element Address Designate) is used to perform compression encoding for facsimile communication. After that, the data is encrypted. As shown in FIG. 6A, data is encrypted by encrypting a plaintext P (original image data after compression encoding) with an encryption algorithm using a secret encryption key K, as shown in FIG. 6A. Data is created. Then, the created cipher text C is transmitted from the modem to the telephone line.

On the other hand, a receiving facsimile machine receives encrypted data transmitted from a telephone line via a modem, and plain texts the received text. Plain text P is shown in FIG.
As shown in (1), the ciphertext C is obtained by performing a plain culture algorithm process using the same secret encryption key K used for encryption. And this plain text P is shown in FIG.
As shown in B, the data is subjected to encoding and decompression for facsimile communication such as MH, MR, etc., converted into the original text, printed by a printer, and output.

[0005] Reading of a document to be transmitted is generally started from its upper end. For example, when transmitting a standard manuscript published by the International Telegraph and Telephone Consultative Committee (CCITT), the upper part of which is shown in FIG. 7, reading is started from area A. The area A is a blank area as shown in FIG. That is, the first transmitted ciphertext C
Is generally very likely that the plaintext P corresponding to the margin is an encrypted one.

[0006] Therefore, when the ciphertext C transmitted first is intercepted by a third party, the plaintext P corresponding to the known margin is obtained.
And the corresponding ciphertext C are disclosed to a third party, so there is a high possibility that the correspondence between the plaintext P and the ciphertext C, that is, the encryption algorithm is easily obtained. Therefore, the ciphertext C can be easily decrypted, and as a result, there is a problem that confidentiality of communication contents cannot be ensured.

[0007]

In order to cope with this, for example, a specific one of the document areas to be read first is specified.
It is conceivable that original image data corresponding to one or a plurality of pixels is set in advance, the set original image data is inverted in black and white, and then encrypted and transmitted. According to this technique, the ciphertext transmitted first is not a plaintext corresponding to the margin, and therefore cannot be easily decrypted.

However, in this technique, since the original image data corresponding to a specific pixel is inverted between black and white, the cipher text transmitted first is always constant. Therefore, even in the above technique, there is a high possibility that the encryption algorithm is known, so that the decryption may be easily performed. Therefore, an object of the present invention is to solve the above-mentioned technical problem 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, wherein encrypted data is transmitted to a receiving terminal device connected via a predetermined communication line. A reading device for reading a document to be transmitted and outputting original image data,
Among the original image data output from the reading unit, a data designating unit for randomly designating arbitrary original image data in the original image data up to a predetermined number of bits from the head, Black-and-white inverting means for inverting, and encryption means for creating encrypted data by performing predetermined encryption processing on the original image data output from the reading means including the original image data which has been black-and-white inverted by the black-and-white inversion means; Transmission means for transmitting the encrypted data created by the encryption means to a predetermined communication line.

[0010] The terminal device for encrypted communication according to the second aspect of the present invention is a terminal device of the original image data output from the reading means.
Arbitrary original in original image data up to the specified number of bits from the beginning
White inverts the image data by specifying a random sender terminal device that creates the encryption data Ri by the applying predetermined encryption processing to the original image data including the monochrome inverted original data
A terminal device for receiving the encrypted data from the device via a predetermined communication line, wherein the encrypted data received from the transmitting terminal device via the predetermined communication line. Decrypting the original image data before encryption by performing a predetermined decryption process on the original image data, and identifying the original image data which is randomly designated and black- and- white inverted from among the original image data restored by the decryption means. It is characterized by including data specifying means and black and white reversing means for inverting black and white of the original image data specified by the data specifying means.

[0011]

According to the configuration of the first aspect of the present invention, in the transmission-side terminal device, of 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 the original image data including the black-and-white inverted original image data is subjected to an encryption process to create encrypted data, and the created encrypted data is transmitted to a predetermined communication line.

On the other hand, in the receiving terminal device, for example, the decrypted process is performed on the received encrypted data to restore the original image data, and of the restored original image data, The original image data that has been inverted in black and white is specified by the transmitting terminal device. Then, the specified original image data is inverted in black and white. As described above, in the above configuration, the original image data to be black-and-white inverted in the original image data up to the predetermined number of bits from the top is randomly specified. Is different for each communication. Therefore, it is possible to make it difficult for a third party to decrypt the encrypted data, so that the confidentiality of the communication content can be ensured.

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

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of a facsimile apparatus according to one embodiment of the present invention. The facsimile apparatus includes a reading unit 1 serving as a reading unit that optically reads a document to be transmitted, for example, and outputs original image data. The original image data output from the reading unit 1 is provided to an image processing unit 2 and is subjected to predetermined image processing. The original image data subjected to the image processing is transmitted to the control unit 3
To the transmission function unit 4 through which compression encoding necessary for facsimile communication such as MH and MR is performed. The original image data subjected to the compression encoding is supplied to the modem 5 via the control unit 3. Further, when performing cryptographic communication, the cryptographic communication device 6 functioning as an encryption unit and a decryption unit performs encryption processing on the compressed and encoded original image data to create encrypted data. The encrypted data is provided to the modem 5. Then, the compression-encoded original image data or encrypted data is transmitted to the network control device (N
CU) 7 to the public telephone line 8.

The control section 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 controller 3 can read the number of seconds n (0 ≦ n ≦ 59) from the RTC 9 at an arbitrary timing, and the read number of seconds n Used when specifying.

The facsimile apparatus also has 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
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 are arranged. The above-described types of keys in the operation unit 10 are merely examples, and keys may be added or keys may be changed as needed.

When the facsimile apparatus shown in FIG. 1 receives data, the data is provided to the modem 5 via the NCU 7. When the received data is simply original data compressed and encoded, that is, in the case of normal facsimile communication, the received original data is demodulated by the modem 5 and then decoded (decompressed) by the reception function unit 11. ) To restore the original original image data. Thereafter, the original image data is provided to the recording unit 12, and the original is printed on paper in the recording unit 12, so that the transmission original is reproduced.

On the other hand, if the received data is encrypted data, that is, in the case of encrypted communication, the received encrypted data is demodulated in the modem 5 and then decrypted in the encryption communication device 6, ie, Plain culture is given.
After that, in the receiving function unit 11, the original image data is decoded and the original image data is restored in the same manner as described above, and then printed on paper by the recording unit 12, and the transmitted original is reproduced.

In this embodiment, the control section 3 functions as a black-and-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 transmitting means. FIG. 2 is a flowchart showing a transmission operation in the facsimile apparatus 1 in the encrypted communication. The transmission operation in the encrypted communication is performed by setting a document to be transmitted by a user on a predetermined document table, inputting a facsimile number of a destination from the numeric keypad 10a, and further pressing the encrypted communication key 10c and the start key 10b. Be started.

In response to the start of reading of the document 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 head of the original, that is, the original image data of the nth bit from the head of the original is inverted in black and white (step S3).

All the original image data including the original image data that has been inverted in black and white is compression-encoded by the transmission function unit 4 using a compression encoding method such as MH or MR (step S).
4) An encryption process is performed in the encryption communication device 6 (step S5), and the encrypted data is given to the modem 5 as encrypted data. Then, it is transmitted to the public telephone line 8 via the NCU 7 (step S6).

FIG. 3 is a flowchart showing the receiving operation in the facsimile apparatus 1 in the encrypted communication. N
The encrypted data received via the CU 7 is demodulated by the modem 5 and then provided to the encryption communication device 6. In the encryption communication device 6, decryption processing is performed on the encrypted data (step P1), and the original image data before encryption is restored. The restored original image data before encryption is supplied to the receiving function unit 11 and decrypted (step P2), and the original image data is restored.

In the restored original image data, the n-th bit from the top is inverted in black and white, and if the transmitted original is reproduced as it is, only the n-th 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 of the original image data, and inverts the estimated original image data in black and white.

That is, from the original image data up to the Nth bit from the beginning, original image data showing a color different from the other N-1 bit original image data is searched (step P3), and as a result, there is original image data having a different color. If the original image data is identified as the original image data that has been black-and-white inverted on the transmitting side,
The specified original image data is inverted in black and white (step P4). As a result, the original image data before the black-and-white inversion on the transmission side can be accurately restored. Then, the original image data after the black-and-white inversion is given to the recording unit 12,
The transmitted document 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, the original image data of the nth bit from the head of the original is inverted between black and white. Can be sent instead. Therefore, decryption by a third party can be made difficult, so that it is possible to improve security of communication confidentiality.

When the encrypted data including the black-and-white inverted original image data is received, since the black-and-white inverted original image data is again black-and-white inverted, the transmission original can be accurately reproduced. Although the embodiment of the present invention is as described above, the present invention is not limited to the above-described embodiment.
For example, in the above-described embodiment, the case where the facsimile machine 1 is applied as the terminal device has been described.
The present invention is not limited to a facsimile apparatus, but can be applied to any terminal apparatus capable of transmitting and receiving image data.

In the above embodiment, the receiving-side facsimile apparatus specifies the original image data which has been inverted in black and white,
Although the specified original image data is inverted between black and white, this processing is not necessarily performed, and the receiving facsimile apparatus may perform normal reception processing. The reason is that one pixel (dot) is actually about 0.1 mm (= 1/200 inch) in size. For example, if the original image data to be black-and-white inverted is one dot, only one pixel is surrounded. This is because even if reproduced with different colors, it can be practically ignored from the viewpoint of image quality disturbance.

Further, in the above embodiment, only the original image data of the nth bit from the head of the original is inverted between black and white.
For example, a predetermined number of bit group data starting from the head of the document or the n-th bit may be inverted in black and white.
Furthermore, in the above-described embodiment, an example has been described in which encryption is realized by applying a so-called ECB mode in which normal encryption is performed.
The C mode may be applied.

Referring to FIG. 4 more specifically,
The original image data before encryption, that is, the plaintext P ₁
0, encrypted data, that is, ciphertext C ₁
Is created. The created cipher text C ₁ is output as it is and is also provided to an exclusive OR unit 21 provided on the input side of the encryption unit 20. Next, plaintext P
_{When 2} is encrypted, it is not directly provided to the encrypting unit 20, but the exclusive-OR unit 21 performs an exclusive-OR operation with the ciphertext C _1, and after the operation, plaintext P ₃ of is given to the encryption unit 20. Ciphertext C ₂ created by the encryption unit 20, similarly to the ciphertext C _1, is outputted as it is also given to the exclusive OR unit 21.

As described above, since the encryption is performed while calculating the exclusive OR in order, if the encrypted data up to the Nth bit from the head of the document is different for each communication, the encrypted data thereafter is also transmitted. Will be different for each. Therefore, the decryption by a third party can be made more difficult.
Various other design changes can be made within the scope described in the claims.

[0031]

As described above, according to the terminal device for cipher communication according to the first aspect, since the original image data to be black-and-white inverted is specified at random, there is a high possibility that the original image data corresponds to the margin. Can be changed for each communication. Therefore, unlike the technique in which the initially transmitted encrypted data is always constant, decryption by a third party can be made difficult. Therefore, confidentiality of communication contents can be ensured.

According to the second aspect of the present invention, the terminal device for black and white inverted original image data is specified from the received encrypted data, and the specified original image data is again black and white inverted. Therefore, the original can be accurately reproduced.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a transmission operation in the facsimile apparatus in the encryption communication.

FIG. 3 is a flowchart illustrating a receiving operation in the facsimile apparatus in the encrypted communication.

FIG. 4 is a diagram illustrating an encryption process when a CBC mode is applied.

FIG. 5 is a diagram showing a communication flow of a conventional facsimile apparatus for executing 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]

 DESCRIPTION OF SYMBOLS 1 Reading part 3 Control part 5 Modem 6 Encryption communication device

Claims (2)

(57) [Claims] 1. A terminal device for transmitting encrypted data to a receiving terminal device connected via a predetermined communication line, wherein the reading device reads a document to be transmitted and outputs original image data. And data designating means for randomly designating arbitrary original image data in the original image data up to a predetermined number of bits from the original image data output from the reading means; and original image data designated by the data designating means. Black-and-white inverting means for inverting black and white, and encryption means for creating encrypted data by performing predetermined encryption processing on the original image data output from the reading means including the original image data which has been black-and-white inverted by the black-and-white inversion means. Transmitting means for transmitting the encrypted data generated by the encrypting means to a predetermined communication line. 2. An original image data output from a reading means.
In the original image data up to the specified number of bits from the beginning,
Of the original data by specifying randomly and tone reversal, the white <br/> black inverted original data transmission end to create encryption data Ri by the applying predetermined encryption processing to the original image data including
The encrypted data from the device via the predetermined communication line
A terminal apparatus for receiving the decryption to recover the unencrypted original data by performing a predetermined decryption process on the encrypted data received through the predetermined communication line from the sending terminal apparatus Means, of the original image data restored by the decryption means,
A data specifying means for specifying the randomly designated original image data which has been black-and-white inverted, and a black-and-white inverting means for black-and-white inverting the original image data specified by the data specifying means. Terminal device.