JPH0993242A - Data transmitter-receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To strengthen security against tapping by sending a ciphering text through a telephone line or the like. SOLUTION: When a transmitter side 1 transforms a plain text P to a ciphered text C at a ciphering transformation section 11, a key selection section 13 changes a ciphering key table at random in the unit of jobs for ciphering. Since the ciphering key table is optionally changed in the unit of jobs, even when ciphering data of the same line undergo tapping for a long period, it is difficult to analyze the ciphering method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission / reception device, and more particularly to a data transmission / reception device which encrypts transmission data and sends it out in order to maintain confidentiality of data communication.

[0002]

2. Description of the Related Art When data communication is performed using a telephone line or the like, it is necessary to prevent the contents of data from being read by a third party in order to maintain confidentiality. Therefore, there is a technique in which transmission / reception data is encrypted and transmitted on the transmission side and decrypted on the reception side.

FIG. 5 shows an example of this type of encryption / decryption device. Referring to FIG. 5, on the transmission side 1, the plaintext P which is the data to be transmitted is encrypted by the encryption conversion unit 1
At 1, the ciphertext C is generated using the encryption key table f and is transmitted from the data transmitting unit 12 via the communication network 2 such as a telephone line.

On the receiving side 3, the data receiving section 32 decrypts the data using the decryption key table f'to obtain the plaintext P. The decryption key table f'means an inverse conversion table of the encryption key table f.

Japanese Laid-Open Patent Publication No. 5-115013 discloses a facsimile in which a key table to be used is communicated among a plurality of key tables shared by all devices in order to determine a key table for encryption in facsimile communication. A method for automatically determining a combination of devices is disclosed.

[0006]

In the conventional encryption / decryption device shown in FIG. 5, since the fixed encryption key table f stored inside the transmission side 1 is used, a long time is required. There is a problem in that the encryption method is analyzed and the confidentiality of the data is lost when the encrypted data on the same line is illegally wiretapped.

In Japanese Patent Laid-Open No. 5-115013, an encryption key table is determined by a combination of facsimile devices that communicate each time, and information such as telephone numbers and passwords of both senders and receivers is used. In addition, since the encryption key table to be used is calculated and determined, calculation processing is required, and hardware and software for the calculation processing are also required.
There is also a problem that the cost cannot be reduced.

It is an object of the present invention to provide a data transmission / reception apparatus which has an extremely simple structure and further enhances the confidentiality of data.

[0009]

According to the present invention, there is provided a data transmission device for transmitting data in units of jobs, and encryption key selection means for selecting different encryption key tables for each job, and The encryption output by the encryption means includes an encryption means for encrypting the transmission data according to the selected encryption key table and a specific information generation means for generating information for specifying the encryption key table. And a specific information of the specific information generating means are transmitted.

According to the present invention, a receiving device for receiving data from the data transmitting device includes a decrypting means for decrypting the received encrypted data according to the contents of the decryption key table. A characteristic data receiving device is obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The operation of the present invention will be described. On the transmitting side, the encryption key table is changed and sent for each job, but at the same time, information specifying this encryption key table is also sent. By doing so, the encryption key table changes for each job each time, so that the data confidentiality can be further improved.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system block diagram of an embodiment of the present invention, and the same parts as those in FIG. 5 are designated by the same reference numerals. In the transmission side 1 of this embodiment, the key selection unit 13
The key selection unit 13 arbitrarily (randomly) selects an encryption key table for transmission data (plain text P) for each job, and the encryption conversion unit 11 selects the selected encryption. The plaintext P is encrypted using a key table.

On the receiving side 3, if the encryption key table is not specified at the time of decryption, the decryption cannot be performed. Therefore, the key selecting section 13 of the transmitting side 1 uses the inverse conversion of the selected encryption key table f. Decryption key table f'of
Is transmitted as the information for decoding.

Therefore, on the receiving side 3, the decryption conversion unit 32 decrypts the received data using the decryption key table f ', and the plaintext P is obtained.

FIG. 2 shows an example of the encryption key table, and FIG. 3 shows a decryption key table for reverse conversion corresponding to the encryption key table shown in FIG. To briefly explain these key tables, in information processing, data is processed as numerical values in byte units (0 to 255). Therefore, in order to send a sentence, that is, a character sequence, as a sequence of continuous byte data. Need to be expressed. For example, in the case of English characters, the ASCII code system, which is an international standard, is used.
In the I code, 1 English character is assigned to 1 byte (0 to 255).

“Input” in FIG. 2 is 1 of the input character to be transmitted.
It is a numerical value in bytes, and "output" shows the converted numerical value at the time of encryption.

FIG. 3 shows the contents of the inverse-conversion decryption key table corresponding to the encryption key table of FIG. 2, and it can be seen that “input” and “output” in FIG. 2 are reversed. .

There are 25 types of such encryption key tables.
6! Since the key selection unit 13 has 25
6! Random selection is made for each job from the following key tables. This random selection can be easily realized by using a random number table or the like.

In the embodiment of FIG. 1, confidentiality is maintained by converting the encryption key table for the transmission data for each job, but since the decryption key table is transmitted at the same time as the encrypted data. In addition, the integrity of confidentiality cannot be guaranteed.

Then, a second embodiment as shown in FIG. 4 is obtained. 4, the same parts as those in FIG. 1 are indicated by the same symbols. In this embodiment, 256! An ID (identification) number for identifying each type of encryption key table is given in advance, and each ID of the encryption key table randomly selected by the key selection unit 13 is assigned as a key number. Instead of sending the encryption key table generated by the generation unit 14, only the ID information is sent together with the ciphertext C.

Therefore, on the receiving side 3, the decryption key table is selected by the decryption key selector 33 based on this ID information, and the received ciphertext C is decrypted and returned to the plaintext P.

By doing so, the encryption key table is never known to others, and the communication system becomes extremely confidential.

[0024]

As described above, according to the present invention, since the contents of the encryption key table are changed for each job, even if the encrypted data on the same line is illegally wiretapped for a long period of time,
It is difficult to analyze the encryption method, and by sending only the ID information of the encryption key table instead of sending the contents of the encryption key table, the confidentiality can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing an example of contents of an encryption key table.

FIG. 3 is a diagram showing an example of contents of a decryption key table for inverse conversion corresponding to the encryption key table of FIG.

FIG. 4 is a block diagram of another embodiment of the present invention.

FIG. 5 is a block diagram of a transmission / reception device having a conventional encryption / decryption function.

[Explanation of symbols]

 1 Transmitting Side 2 Line 3 Receiving Side 11 Encryption Converter 12 Data Transmitter 13 Key Selector 14 Key Number Generator 31 Data Receiver 32 Decryption Converter 33 Decryption Key Selector

Claims (6)

[Claims] 1. A data transmission device for transmitting data in units of jobs, comprising encryption key selection means for selecting a different encryption key table for each job, and transmission data according to the selected encryption key table. Encryption means for performing encryption of the encryption key table and specific information generation means for generating information for specifying the encryption key table, and an encrypted output by the encryption means and specific information of the specific information generation means. A data transmission system characterized in that it is adapted to transmit. 2. The data transmitting apparatus according to claim 1, wherein the specific information is contents of a decryption key table corresponding to the encryption key table. 3. The data transmitting apparatus according to claim 1, wherein the specific information is an identification number uniquely assigned to each of the encryption key tables. 4. A data receiving device for receiving data from the data transmitting device according to claim 1, further comprising a decrypting means for decrypting the received encrypted data in accordance with a decryption key table corresponding to the specific information. A data receiving device characterized by the above. 5. A data receiving device for receiving data from the data transmitting device according to claim 2, further comprising a decryption means for decrypting the received encrypted data in accordance with the contents of the decryption key table. And a data receiving device. 6. The data receiving apparatus according to claim 3, further comprising a decrypting means for decrypting the received encrypted data according to the contents of the decryption key table corresponding to the identification number. apparatus.