WO2000064096A1

WO2000064096A1 - Encrypted communication system

Info

Publication number: WO2000064096A1
Application number: PCT/JP2000/002554
Authority: WO
Inventors: Junko Suginaka; Toshi Suzuki
Original assignee: Akita, Yasuo; Fujino, Shigeru
Priority date: 1999-04-19
Filing date: 2000-04-19
Publication date: 2000-10-26

Abstract

An encrypted communication system for data communication in an encrypted status. A transmission device and reception device are provided with pseudo-random number sequence generating means for generating the same pseudo-random number sequence based on key information. The transmission device interprets a pseudo-random number sequence based on a preset transposition rule to thereby specify a plurality of exchange positions for a bit-string in a regular text; a ciphered text is prepared by exchanging individual values between these exchange positions. An example of a transposition rule is such that, in a portion of a pseudo-random number sequence where '1' or '0' continues over at least 2 bits, the leading bit and the trailing bit of each continuous portion are specified as a set of exchange positions to exchange bit values to each other.

Description

Document Secure communication system

TECHNICAL FIELD The present invention relates to a secret communication system that communicates various data in a secret state.

BACKGROUND ART In recent years, various types of data have been transmitted and received via networks such as the Internet and Internet. At that time, in order to prevent important data from being leaked to a third party, various encryption methods have been proposed to keep the data to be transmitted and received confidential. In many of such encryption methods, a ciphertext is created by repeating a substitution process and a transposition process on a plaintext a predetermined number of times.

However, in various conventional encryption methods, a predetermined bit length such as a 4-bit length or a 6-bit length is used as a unit of the transposition process, and the transposition process is performed on a predetermined bit position. For this reason, in the conventional encryption method, the characteristic resulting from the transposition process remains in the ciphertext, which may be decrypted.

An object of the present invention is to provide a confidential communication system capable of eliminating a characteristic caused by transposition processing in a sent / received encrypted text.

DISCLOSURE OF THE INVENTION To achieve the above object, a secret communication system according to the present invention generates a pseudo-random number sequence based on predetermined key information, and generates the generated pseudo-random number sequence and a preset pseudo-random number sequence. Based on a fixed transposition rule, a plurality of exchange positions are specified for the bit string of the plaintext, and a transposition process of exchanging values between the plurality of exchange positions is performed. And transmitting and receiving the encrypted text between the transmitting device and the receiving device.

According to such a confidential communication system, the exchange position to be subjected to the transposition processing is specified based on the pseudo-random number sequence in the plaintext bit string, so that the exchange position changes continuously. Therefore, in the sent / received cryptogram, the characteristics caused by the transposition process are eliminated, and a high encryption strength can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall conceptual diagram of a secure communication system according to the present invention.

FIG. 2 is a configuration diagram of a pseudo random number generator.

FIG. 3 is an explanatory diagram showing an example of a pseudo random number sequence.

FIG. 4 is an explanatory diagram showing a plaintext blocking process.

FIG. 5 is an explanatory diagram showing an example of encryption processing (transposition processing) based on the transposition rule (1).

FIG. 6 is a conceptual diagram of the encryption processing shown in FIG.

FIG. 7 is an explanatory diagram showing an example of a decoding process (transposition process) based on the transposition rule (1).

FIG. 8 is an explanatory diagram showing a process of assembling a block of plaintext.

FIG. 9 is an explanatory diagram showing an example of an encryption process in which the transposition process is repeated a plurality of times. FIG. 10 is an explanatory diagram showing a process of extracting a pseudo-random number sequence used in each transposition process from a series of pseudo-random number sequences when the transposition process is repeated a plurality of times.

FIG. 11 is an explanatory diagram showing another example of extracting a plurality of pseudo-random number sequences from a series of pseudo-random number sequences.

FIG. 12 is an explanatory diagram showing an example of encryption processing (transposition processing) based on the transposition rule (2). FIG. 13 is an explanatory diagram showing an example of encryption processing (transposition processing) based on the transposition rule (3).

FIG. 14 is an explanatory diagram showing an example of encryption processing (transposition processing) based on the transposition rule (4).

FIG. 15 is an explanatory diagram showing an example of a process of specifying a set of exchange bit positions from a pseudo-random number sequence in an encryption process (transposition process) based on the transposition rule (5).

FIG. 16 is an explanatory diagram showing exchange processing in encryption processing (transposition processing) based on the transposition rule (5).

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 is an overall schematic diagram of a secret communication system according to the present invention.

The secure communication system according to the present invention includes a transmitting device 10 and a receiving device 20 that can be connected via a network 30 such as the Internet.

The transmitting device 10 includes a pseudorandom number sequence generating means 11 for generating a pseudorandom number sequence based on predetermined key information 40, and a blocking means 12 for dividing a plain text (original text) into blocks having a predetermined bit length. Encrypting means 13 for creating a ciphertext from the plaintext by performing a predetermined transposition process, which will be described later, on each block of the plaintext based on the pseudo-random number sequence, and a network 30 And transmission means 14 for transmitting to the reception-side device 20 via the communication device.

The receiving device 20 generates the same pseudo-random number sequence as the pseudo-random number sequence generating device 11 of the transmitting device 10 based on predetermined key information 40. Pseudo-random number sequence generating means 21 to be formed, and decoding means 23 for decoding a ciphertext for each block by performing a predetermined transposition process described later based on the pseudo-random number sequence. An assembly means 24 for assembling each block to obtain a plain text (original text) is provided.

In this embodiment, the transmitting device 10 and the receiving device 20 are constituted by a personal computer or the like. It is configured as a functional block realized by However, as long as the function of each of the above means can be fulfilled, each of the above means can be constituted by hardware such as a dedicated circuit.

Also, the transmitting device 10 and the receiving device 20 need not be dedicated devices for transmission or reception, but are desirably transmission / reception devices of a confidential communication system capable of both transmission and reception. In this case, as described later, the pseudo random number sequence generating means 11 and 21 used for the transmitting side and the receiving side can be shared by one means.

Hereinafter, each means will be described in detail. The pseudo random number sequence generating means 11 and 21 are provided for both the transmitting device 10 and the receiving device 20. The pseudo random number sequence generating means 11 and 21 have the same configuration. . Therefore, when a transmitting / receiving device having both functions of the transmitting device 10 and the receiving device 20 is configured, the pseudo random number sequence generating means 11 and 21 can be shared. The pseudo-random number sequence generation means 11 and 21 are specifically configured by software that realizes a function corresponding to a circuit for generating a pseudo-random number sequence generally called an M-sequence shown in FIG. 2 on a computer. ing. The pseudo-random number sequence generation means 1 1, 21 is provided with a k-number of Shift register Xi _{X l} ~x _k connected in series, the elements that serve as the exclusive OR calculator X OR, each shift register _{X l} ~x _k output caries Chi of the feedback terminal specified coefficients a ~! ^ exclusive OR of the specified output by is the input of the shift register evening x _k of the most upstream side, of most downstream side shift register pseudo-random number sequence shown from _{X l} in Figure 3 for example is adapted to be sequentially output.

The pseudo-random number sequence generated by the pseudo-random number sequence generation means 11 and 21 determines the sequence of the pseudo-random number sequence according to the exclusive OR of the outputs from the shift registers X i X k . That is, the feedback terminal designating coefficient Ai Ak is information indicating a procedure for generating a pseudo random number sequence.

The initial value X i to X _k applied to the shift register X it to X _k is the beginning of the k bits of the value of the pseudo-random number sequence, that is, a default value.

In this confidential communication system, the feedback terminal designation coefficient A i Ak and the initial value Xi Xk of the pseudo random number are used as the key information 40. Sender 10 and receive Each of the side devices 20 is provided with input means such as a keyboard for inputting the key information 40 by an operator, or receiving means for obtaining the key information 40 through a communication line or the like. Further, a storage means such as a memory for storing the input or obtained key information 40 is provided. The pseudo-random number sequence generating means 11 and 21 read the key information 40 stored in the storage means in this way, and generate a pseudo-random number sequence based on the key information 40.

It should be noted that various known pseudo-random number sequence generation means can be applied to the pseudo-random number sequence generation means 11 and 21 as long as the same pseudo-random number sequence can be reproduced according to the key information 40. Further, it may be constituted by hardware such as a dedicated circuit. As shown in FIG. 4, the blocking means 12 divides the plaintext data transmitted from the transmitting apparatus 10 to the receiving apparatus 20 into blocks each having a predetermined bit length (for example, 64 bit length). Perform the following processing. The plaintext data may be data input from an input means such as a keyboard or data read from a storage means such as a hard disk.

If the length of the plaintext data is less than the predetermined bit length, a block having the predetermined bit length may be created by adding arbitrary dummy data. The encryption means 13 interprets the pseudo-random number sequence generated by the pseudo-random number sequence generation means 11 based on a preset transposition rule, thereby performing a plurality of exchanges on the blocked plaintext bit string. A position is specified, and a transposition process is performed to exchange values between the specified plurality of replacement positions.

As the transposition rule, various rules can be used as described later. In this embodiment, the following transposition rule (1) is adopted.

(1) The pseudo-random number sequence is a binary value sequence, and in the part where 1 or 0 continues over 2 bits or more in this pseudo-random number sequence, the start bit position and the tail bit position of each continuous part are exchanged. And exchange each other's bit values.

The encryption means 13 is provided with input means such as a keyboard for the operator to input such transposition rules, or reception means for obtaining the same through a communication line or the like. In addition, storage means such as a memory for storing the input or obtained transposition rules are provided. The encryption means 13 reads out the transposition rule stored in the storage means in this way, and performs transposition processing (encryption processing) based on the transposition rule. FIG. 5 is an explanatory diagram showing a specific example of the transposition process based on the transposition rule (1). This example, plaintext, 6 4-bit string bit length was one block _{S o, SJ, S 2,} ..., a S _{6 3,} bit value of 0 or 1 is given to each bit. The pseudorandom number sequence also uses the first 64 bits as shown in FIG. The pseudo-random sequence is a plaintext bit sequence S. , S There S _2, ···, it will correspond by S _{6 3} and the first bit or al 1-one.

Then, if the pseudo-random number sequence of FIG. 5 is interpreted in order from the first bit based on the transposition rule (1), 1 is continuous at bit positions 0 to 2. For this reason, bit position 0 and bit position 2, which are the first bits, are specified as a pair of exchange positions. Then, S at bit position 0 of the plaintext. And S _{2 at} bit position 2 exchange bit values with each other.

Similarly, pseudo-random number sequence is 0 are continuous in the bit positions 3, 4, since the bit position 8, 9 0 is continuous, S ₃ and S _4, 3 ₈ and 3 ₉ of plaintext, one in each Bit values are exchanged.

By performing the above transposition processing up to bit position 63, the bit string of the plaintext having a length of 64 bits is written into the bit string of the plaintext having the same length of 64 bits.

The transposition process shown in FIG. 5 can be schematically represented as the same procedure as that of a so-called “Amidakuji”, as shown in FIG. That is, the bit positions corresponding to the plaintext and the encrypted text are connected by vertical lines, and a schematic diagram is created in which the vertical lines of the set of exchange positions are connected by horizontal lines. In this figure, the vertical line is traced downward from each bit position of the plain text, and when the start point of the horizontal line is reached, the end point of the horizontal line is shifted to the connected vertical line. To reach. The encryption process (transposition process) is a process of writing the bit value of each bit position of the plaintext into the bit position of the ciphertext reached as described above. For example, S in bit 0 of plaintext. Will be written in the second bit position of the ciphertext by the horizontal line.

When the transposition of the first block of plaintext is completed in this way, As described above, the same transposition process as described above is performed on the second block of the plaintext using the next 64 bits of the pseudo random number sequence. By performing such a transposition process on all the plaintext blocks, all the plaintexts are encrypted, and the same number of ciphertext blocks as the plaintext blocks are created. The transmitting means 14 and the receiving means 22 transmit and receive the text created by the encrypting means 13 via the network 30. Specifically, the transmitting means 14 and the receiving means 22 are composed of software for adding various information to the ciphertext according to a protocol on the network or the like, and hardware such as a modem device. When a transmitting / receiving device having both functions of the transmitting device 10 and the receiving device 20 is configured, the transmitting means 14 and the receiving means 22 are one transmitting / receiving means having both functions. Can be realized. The decryption unit 23 decrypts the received ciphertext based on the pseudo-random number sequence generated by the pseudo-random number sequence generation unit 21 and the transposition rule used by the encryption unit 13 Perform processing. In this embodiment, since the sentence is divided into blocks, the bit string of the sentence is decoded into a bit string of plain text for each block.

More specifically, in this embodiment in which the transposition processing is performed according to the transposition rule (1), as shown in FIG. 7, the decoding is performed by exactly the same processing as the transposition processing according to the transposition rule (1). Processing can be performed.

The decoding means 23 is provided with input means such as a keyboard for the operator to input such transposition rules, or receiving means for obtaining the transposition rules via a communication line or the like. In addition, storage means such as a memory for storing the input or obtained transposition rules are provided. The decoding means 23 reads the transposition rule stored in the storage means in this way, and performs transposition processing (decoding processing) based on the transposition rule. In FIG. 6, which schematically shows the encryption process, the decryption is a process of following a vertical line upward from each bit position of the ciphertext.

Therefore, when a transmitting / receiving device having both functions of the transmitting device 10 and the receiving device 20 is configured, the above-mentioned encryption means 13 can be used also as the decryption means 23. Can be. As shown in FIG. 8, the assembling means 24 performs a process of assembling the plaintext divided into a plurality of blocks decrypted by the decrypting means 23 into a series of plaintexts. The plaintext assembled in this way is output to an output means such as a monitor, or written to a storage means such as a hard disk and used for various purposes. According to the above secret communication system, the exchange position to be transposed in the plaintext bit string changes continuously based on the pseudo-random number sequence. Therefore, features resulting from the transposition process are excluded from the sent and received encrypted text. Also, since the plaintext bit string is transposed and disturbed in bit units, high encryption strength can be obtained.

In addition, since the exchange position is identified based on the pseudo-random number sequence and the bit value at the exchange position is exchanged, the encryption is performed by a simple process, so that the load on the encryption and decryption processes is small and the speed is high. Can be achieved.

In addition, since the information specifying the pseudo-random number sequence generation procedure and the information indicating the initial value of the pseudo-random number sequence are used as key information, various pseudo-random number sequences can be generated. Can be obtained.

Further, according to the transposition rule (1), since all the exchange positions have the same 1-bit length, the encryption means 13 and the decryption means 23 can be configured to perform the same transposition processing. Further, when a transmitting / receiving device that performs both transmission and reception is configured, one unit can be used as the encryption unit 13 and the decryption unit 23.

Further, according to the transposition rule (1), since all the exchange positions have the same 1-bit length, the values of the bit positions other than the exchange position do not change. Therefore, in the transposition process, the bit positions other than the exchange position can be immediately written into the bit string of the cipher without storing in the buffer, and the processing load of the encryption means 13 and the decryption means 23 performing the transposition processing Can be reduced.

In addition, the pseudo-random number sequence of binary values is made to correspond one-to-one with the bit sequence of the plain text, and the exchange position is specified according to the pseudo-random number sequence. It is possible to manage. Therefore, the encrypted data can be transmitted to the receiving device 20 sequentially from the first bit. In addition, since the same applies to the decryption of encrypted text, high real-time performance can be obtained between the transmitting device 10 and the receiving device 20 by decrypting the received encrypted text in order from the first bit. it can.

In addition, since plaintext data is divided into a plurality of blocks, and each block is encrypted and decrypted, encryption and decryption are completed for each block. Therefore, the load on the encryption means 13 and the decryption means 23 can be reduced even for a large amount of plaintext data.

Also, since the plaintext data is divided into a plurality of blocks, transmission / reception processing can be performed for each block, and a bucket communication method can be easily supported. Next, a second embodiment of the secret communication system according to the present invention will be described. In the second embodiment, the encryption means 13 performs the transposition process based on the transposition rule (1) a plurality of times (three times) on each block of the plaintext to perform the secret culture. .

As described above, if the transposition processing in the above embodiment is schematically represented as the procedure of “Amidakuji” in FIG. 6, the encryption processing and the decryption processing in the second embodiment will be as shown in FIG. The transposition process represented by the horizontal line is performed over multiple stages (three stages).

In each transposition process, different portions cut out from the pseudo-random number sequence generated by the pseudo-random number sequence generation means 11 and 21 may be used. Specifically, as shown in Fig. 10, the pseudo-random number sequence is divided into blocks of a predetermined bit length (for example, 64 bit length) from the first bit, and each block is subjected to the first transposition of the first block. It may be used in order. Alternatively, as shown in FIG. 11, a plurality of blocks may be extracted from the pseudo random number sequence by shifting the leading bit position by n bits.

With such a configuration in which the transposition process is repeated a plurality of times, the transposition process can be easily performed on more bit positions in the bit string of the plain text.

Also, if the plaintext is divided into blocks of a predetermined bit length, and the encryption processing by transposing multiple times (three times) from the first block is completed sequentially, the encryption processing will be completed. Since the blocks can be transmitted in order, the real-time communication can be improved. Next, a third embodiment of the secret communication system according to the present invention will be described. In the third embodiment, the encryption means 13 performs a dark culture on each block of the plaintext by a transposition process based on the following transposition rule (2).

(2) The pseudo-random number sequence is defined as a binary value sequence, and in the portion of the pseudo-random number sequence that changes from 0 to 1, the bit position corresponding to 0 and the bit position corresponding to 1 are specified as a pair of exchange positions. Exchange bit values with each other.

FIG. 12 is an explanatory diagram showing a specific example of the transposition process based on the transposition rule (2). If the pseudo-random number sequence shown in FIG. 12 is interpreted in order from the first bit based on the above transposition rule (2), it changes from 0 to 1 at bit positions 4 and 5. Therefore, bit position 4 and bit position 5 are specified as a set of exchange bits. And with the S ₅ S ₄ and bit position 5 of the bit positions of the plaintext 4 is replaced bit values of each other. Similarly, the bit values are exchanged in the pair of bit positions 6 and 7 and in the pair of bit positions 9 and 10 to create a ciphertext.

In this way, even with the transposition rule (2), the exchange position in the bit string of the plaintext changes according to the pseudo-random number sequence, so that it is possible to obtain a ciphertext in which the features resulting from the transposition process have been eliminated.

Further, according to the transposition rule (2), since all the exchange positions have the same 1-bit length, the encryption means 13 and the decryption means 23 can be configured to perform the same transposition processing.

Note that, even when the transposition processing is performed according to the transposition rule (2), the transposition processing can be repeated a plurality of times as in the above-described second embodiment. The same applies to the following embodiments. Next, a fourth embodiment of the secret communication system according to the present invention will be described. In the fourth embodiment, the encryption means 13 performs a dark culture on each block of plaintext by a transposition process based on the following transposition rule (3). (3) The pseudo-random number sequence is converted into a binary value sequence, and the bit positions corresponding to consecutive 1s or 0s in the pseudo-random number sequence are respectively specified as a group of exchange positions, and adjacent exchange positions are exchanged in group units. .

FIG. 13 is an explanatory diagram showing a specific example of the transposition process based on the transposition rule (3). If the pseudo-random number sequence in FIG. 13 is interpreted in order from the first bit based on the transposition rule (3), bit positions 0 to 2 are consecutive. For this reason, bit positions 0 to 2 are specified as a group of exchange positions, as enclosed in FIG. Subsequently, 0s are consecutive in bit positions 3 and 4. Thus, bit positions 3 and 4 are also specified as a group of exchange positions. Then, have you a bit string of the plaintext, the S _Q to S ₂ of these bit positions 0 to 2, S _3, S ₄ bit positions 3, 4 is exchanged bit group basis.

Furthermore, in the pseudo-random number sequence, at bit position 5, there is only one 1. For this reason, bit position 5 is specified as an exchange position with one bit. Similarly, at bit position 6, there is a single 0. For this reason, bit position 6 is specified as an exchange position with one bit. Then, in the plaintext bit string, S ₅ at bit position ₅ and S _{6 at} bit position 6 are exchanged.

According to the transposition rule (3), the exchange position in the plaintext bit string changes according to the pseudo-random number sequence, so that it is possible to obtain a ciphertext in which the characteristics resulting from the transposition processing are eliminated.

In particular, according to the transposition rule (3), the bit length of each exchange position to be transposed changes according to the pseudo-random number, so that the transposition process can be diversified and the encryption strength can be further increased. Next, a fifth embodiment of the secret communication system according to the present invention will be described. In the fifth embodiment, the encryption means 13 performs a dark culture on each block of plaintext by a transposition process based on the following transposition rule (4).

(4) The pseudo-random number sequence is converted into a binary value sequence, and the pit positions corresponding to consecutive 1s are specified as a group of exchange positions in the pseudo-random number sequence, and adjacent exchange positions are exchanged in group units. FIG. 14 is an explanatory diagram showing a specific example of the transposition process based on the transposition rule (4). If the pseudo-random number sequence shown in FIG. 14 is interpreted in order from the first bit based on the transposition rule (4), bit positions 0 to 2 are consecutive. For this reason, bit positions 0 to 2 are specified as a group of exchange positions, as enclosed in FIG. Subsequently, bit position 5 of the pseudo-random number sequence is 1. Thus, bit position 5 is specified as the next exchange position. Then, in the bit string of the plaintext, these S at bit positions 0 to 2 are set. ~ S ₂ and S _{5 at} bit position 5 are swapped in units. Further, bit positions 7 and 10 of the pseudo random number sequence are 1. Therefore, bit position 7 and bit position 10 are each specified as an exchange position. Then, in the plaintext bit string, S ₇ at bit position ₇ and S i at bit position 10. Is exchanged.

Even according to the transposition rule (4), the exchange position in the bit string of the plaintext changes according to the pseudo-random number sequence, so that it is possible to obtain a ciphertext in which the characteristics due to the transposition process are eliminated.

In particular, according to the transposition rule (4), the bit length of each exchange position to be transposed changes according to the pseudorandom number, so that the transposition process can be diversified and the encryption strength can be further increased. Next, a sixth embodiment of the secret communication system according to the present invention will be described. In the sixth embodiment, a dark culture is performed on each block of plain text by a transposition process based on the following transposition rule (5).

(5) Each random value of the pseudo-random number sequence is an integer value including 0 that is less than the bit length of the plain-text bit sequence, and the bit positions corresponding to each of the two random numbers from the beginning of the pseudo-random number sequence are written in plain text. It is specified as a set of exchange positions in the bit sequence of, and the bit value of each exchange position is exchanged.

FIG. 15 is an explanatory diagram showing a specific example of a pseudo-random number sequence used for performing transposition processing according to the transposition rule (5). In this embodiment, the plaintext is treated as a block having a length of 64 bits at bit positions 0 to 63, and accordingly, each random value of the pseudo-random number sequence is one of integer values of 0 to 63. Take. Each random value of the pseudo-random number sequence Indicates the bit position of the exchange position in the plaintext bit string. Then, the bit positions indicated by each of the two random numbers from the beginning of the pseudo-random number sequence are used as a set of exchange positions, and the m-th random number value of the pseudo-random number sequence is used for transposing the first block of the plaintext.

FIG. 16 is an explanatory diagram showing a specific example of the transposition processing according to the transposition rule (5). The exchange of the first set of exchange positions specified by the pseudo-random number sequence in FIG. ) Is shown. That is, in the pseudo-random number sequence shown in FIG. 15, since the first random value is 6 and the second random value is 18, bit position 6 and bit position 18 are specified as a pair of exchange positions. Therefore, in the plaintext bit string, the bit value of S ₆ at bit position ₆ and the bit value of S i ₈ at bit position 18 are exchanged.

Hereinafter, the same operation is performed for each of the m-th random number values from the beginning of the pseudo-random number sequence, thereby generating a cryptogram for the first block. The second block may be sequentially encrypted in the same manner for the third and subsequent blocks using the m + 1 to 2m-th random numbers of the pseudo-random sequence.

Even according to the transposition rule (5), the exchange position in the bit string of the plaintext changes according to the pseudo-random number sequence, so that it is possible to obtain a sentence in which the characteristics resulting from the transposition process are eliminated.

In particular, according to the transposition rule (5), it is easy to set bit positions apart from each other in the plaintext bit string as a set of exchange positions, so that the transposition process is diversified and the encryption strength is further increased. be able to. As described above, the present invention has been described with reference to the embodiment. However, the confidential communication system according to the present invention is not limited to the above embodiment, and may be configured as follows.

(1) In the above embodiment, the transposition rules (1) to (5) are described, but the transposition rule is not limited to these. That is, any transposition rule can be adopted as long as a plurality of exchange positions can be uniquely specified for a plaintext bit string based on a pseudo-random number sequence.

(2) In the above embodiment, the plaintext is divided into blocks of a predetermined bit length before the encryption process is performed. However, such blocking is not necessarily performed, and starting from the first bit of the plaintext bit string. You may encrypt sequentially. (3) In the above embodiment, as the key information, the feedback specification coefficients A _{Q to} A _k and the random number initial value that specify the procedure for generating the M sequence are used.However, if the information can specify the pseudo-random number sequence, Any information can be used.

(4) In the above embodiment, the pseudo random number sequence generating means 11 and 21 included in the transmitting device 10 and the receiving device 20 are devices having the same configuration, but based on the key information. As long as the same pseudorandom numbers can be generated, pseudorandom number generation means 11 and 21 having an arbitrary configuration can be used.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a transposition process is performed on a plaintext bit string according to a pseudo-random number sequence as a secret communication system that transmits and receives data over a network in a secret state. As a result, it is possible to provide a system that eliminates characteristics caused by the transposition process.

Claims

The scope of the claims

1. A confidential communication system that performs communication in a concealed state,

Pseudo-random number sequence generating means for generating a pseudo-random number sequence based on predetermined key information; and a plurality of exchange positions for a plaintext bit sequence based on the generated pseudo-random number sequence and a predetermined transposition rule set in advance. Encrypting means for generating a ciphertext from the plaintext by performing a transposition process of identifying and exchanging values between the plurality of exchange positions;

Transmitting means for transmitting the cryptogram,

The receiving side

Receiving means for receiving the ciphertext;

Pseudo-random number sequence generation means for generating the same pseudo-random number sequence as the pseudo-random number sequence generation means on the transmitting side based on the predetermined key information;

A secret communication system, comprising: decoding means for decoding a received cipher text based on the generated pseudo-random number sequence and the transposition rule.

2. A transmitting-side device used in a confidential communication system that performs communication in a secret state,

A transmission unit for transmitting the ciphertext to a reception-side device; and a transmission-side device for a secret communication system.

3. The transmission-side apparatus for a confidential communication system according to claim 2, wherein the predetermined key information is a confidential communication system including information for specifying a pseudo-random number sequence generation procedure. The transmitting device of the stem.

4. The transmitting device of the confidential communication system according to claim 2, wherein the predetermined key information includes information indicating an initial value of a pseudo-random number sequence.

5. The transmitting device of the confidential communication system according to claim 2, wherein the encrypting means repeats the transposition process a predetermined number of times using a different pseudo-random number sequence.

6. The transmitting device of a confidential communication system according to claim 5, wherein the different pseudo-random number sequence is a different part of a series of pseudo-random number sequences.

7. The transmitting device of a confidential communication system according to claim 2, wherein the transposing process specifies a set of exchange positions at which values are exchanged with respect to a plaintext bit sequence according to a pseudo-random number sequence. A transmitting-side device of a confidential communication system for exchanging values for each set of exchange positions.

8. The transmitting device of a confidential communication system according to claim 2, wherein all the exchange positions have the same bit length.

9. The transmitting device of a confidential communication system according to claim 8, wherein the exchange positions are all 1-bit length.

10. The transmitting device of the confidential communication system according to claim 2, wherein the exchange position has a variable bit length.

11. The transmitting device of the confidential communication system according to claim 2, The transposition process associates a plaintext bit string with a binary-valued pseudo-random number sequence on a one-to-one basis from the first bit, and corresponds to a bit position where a predetermined feature set in the pseudo-random number sequence is recognized. A transmitting-side device of a secret communication system for specifying a bit position of a plaintext as the exchange position.

12. The transmitting device of the confidential communication system according to claim 2, further comprising a block creating unit that divides a plaintext bit string into blocks having a predetermined bit length, wherein the encrypting unit includes: A transmitting-side device of a secret communication system that performs the transposition process.

1 3. A computer-readable recording medium in which a program for operating a computer is recorded as a transmission-side device used in a secure communication system that communicates in a confidential state.

A pseudo-random number sequence generation function for generating a pseudo-random number sequence based on predetermined key information; and a plurality of exchange positions for a plaintext bit sequence based on the generated pseudo-random number sequence and a predetermined transposition rule set in advance. By performing a transposition process of identifying and exchanging values between the plurality of exchange positions, an encryption function of creating a ciphertext from the plaintext, and a computer-readable program recording a program for realizing Possible recording medium.