JPH09149025A - Cipher communication method and cipher communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the danger of leaking a cipher key and a common key to a third person and to easily perform use by changing the cipher key and a decipher key at a prescribed timing. SOLUTION: A common key conversion part 13A converts the common key inputted from a common key sharing part 11 to a new common key provided with two values p1 and p2. Then, a cipher key generation part 13B performs initialization to a logistic equation. The cipher key generation part 13B operates the logistic equation and obtains the cipher key from output and a ciphering processing part 13C performs a character conversion cipher processing. Then, the common key conversion part 23A converts the common key inputted from the common key sharing part 21 to the new common key provided with the two values p1 and p2. Then, a decipher key generation part 23B performs the initialization to the logistic equation. Then, the decipher key generation part 23B operates the logistic equation and obtains the decipher key from the output and a decipher processing part 23C performs a character conversion decoding processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryptographic communication method and a cryptographic communication system, and more particularly to a cryptographic communication method and a cryptographic communication system for performing cryptographic communication by decrypting a ciphertext encrypted on the transmitting side on the receiving side. Regarding

[0002]

2. Description of the Related Art A network service that provides services such as electronic mail by connecting computers installed in a distributed manner to each other has been commercialized. However, some networks have been constructed for academic purposes, and network security may not be fully considered. Therefore, eavesdropping, tampering, and spoofing are performed on network services, which is a problem. Here, taking e-mail as an example,
Explain wiretapping, tampering, and spoofing.

Eavesdropping means that a plain text, that is, a communication text (message) in a state where nothing is encrypted is read during delivery. Tampering means that the content of an email is changed during delivery. Tampering is performed at a relay node on the way when electronic mail is delivered via a plurality of relay nodes. Spoofing means that a malicious third party impersonates another person by forging the sender information when the information identifying the sender is not protected.

In order to solve such a problem, plaintext is encrypted. Common key cryptosystems, public key cryptosystems, and the like are known as encryption techniques. The common key encryption method is a method of performing encryption and decryption using a common key between communication parties. On the other hand, the public key cryptosystem is composed of a combination of each person's private key and public key.
This is a method in which the public key is known to others and the private key is known only to one person.

[0005]

When using the public key encryption method in the above-mentioned conventional technique, there is a drawback that the processing speed is lowered due to the huge amount of calculation. On the other hand, when the common key encryption method in the above-mentioned conventional technique is used, the processing speed does not decrease unlike the public key encryption method, but there is a possibility that the common key may be leaked to a third party during repeated communication. is there. This fear can be solved by making the encryption key (decryption key) random each time, but it is difficult to consider the actual operation because it is necessary for the communicators to prepare the same huge encryption key. .

The present invention has been made in view of the above circumstances, and provides a cryptographic communication method and a cryptographic communication system that are less likely to be leaked to a third party by a cryptographic key and a common key. The challenge is to provide.

[0007]

The present invention adopts the following means in order to solve the above-mentioned problems.

<First Cryptographic Communication Method> The first cryptographic communication method employs the following means in order to solve the above-mentioned problems. That is, the first cryptographic communication method is a cryptographic communication method for performing cryptographic communication by decrypting the ciphertext encrypted on the transmission side on the reception side, from the first chaotic vibration generator that outputs as chaotic vibration. A ciphertext is generated from plaintext by using the output value as an encryption key. And a second chaotic vibration generator having the same structure as the first chaotic vibration generator.
A decrypted text is generated from the encrypted text by using the value output from the chaos vibration generator as the decryption key (corresponding to claim 1).

Here, chaos (CHAOS) means regularity in randomness, and chaotic oscillation means that even a slight difference in initial value causes the value of the result to fluctuate greatly and individual predictions to be made. It means a phenomenon that makes it difficult. As an example of causing chaos oscillation, a logistic equation in a certain input value range is known. The plain text may be in any format such as a text format, a binary format, compressed data, encrypted data, and the like.

According to the first cryptographic communication method, the value output from the first chaotic vibration generator is used as the encryption key, and the value output from the second chaotic vibration generator is used as the decryption key. Here, since the first and second chaotic vibration generators have the same structure, the encryption key and the decryption key are the same. Moreover, since the encryption key and the decryption key generated by the chaotic oscillation have an infinite period, changing the encryption key and the decryption key at a predetermined timing may cause a third party to leak the encryption key and the decryption key. Is few. The predetermined timing is preferably synchronized with the timing of transmitting the ciphertext. Then, since the encryption key and the decryption key are automatically changed, they can be easily operated.

<Second Cryptographic Communication Method> The first cryptographic communication method may be configured as the following second cryptographic communication method. That is, the second cryptographic communication method is the same as the first cryptographic communication method, in which the common key sharing process of sharing the common key between the sender and the receiver while performing feedback communication between the sender and the receiver. It is provided. Then, in the ciphertext generation process, the value of the common key shared in the common key sharing process is used as an initial value of the input value to the first chaotic vibration generator. Further, in the decrypted text generation process, the value of the common key shared in the common key sharing process is used as an initial value of an input value to the second chaotic vibration generator (corresponding to claim 2). The common key may be shared at any time, but from the viewpoint of security, it is most preferably performed every time a ciphertext is transmitted.

According to the second cryptographic communication method, since the common key changes, the series of values output from the first chaotic vibration generator and the second chaotic vibration generator changes.
As compared with the first encrypted communication method, communication safety is improved.

<Third Cryptographic Communication Method> The second cryptographic communication method may be configured as the following third cryptographic communication method. That is, in the third cryptographic communication method, in the second cryptographic communication method, the common key sharing process is a first stage common key encryption process, a second stage common key encryption process, and a first stage common key decryption process. And a second stage common key decryption process (corresponding to claim 3).

(First Stage Common Key Encryption Process) In the first stage common key encryption process, the first stage encrypted common key is generated by encrypting the common key with the secret key of the transmitting side.

(Second-stage common key encryption process) In the second-stage common key encryption process, the first-stage encrypted common key generated in the first-stage common key encryption process is the secret key of the receiving side. The second-stage encrypted common key is generated by encrypting with.

(First Stage Common Key Decryption Process) In the first stage common key decryption process, the second stage encrypted common key generated in the second stage common key encryption process is decrypted by the secret key on the transmitting side. By doing so, the first-step decrypted common key is generated.

(Second-stage common key decryption process) In the second-stage common key decryption process, the first-stage decrypted common key generated in the first-stage common key decryption process is decrypted by the secret key on the receiving side. Then, the common key is decrypted.

<Fourth Cryptographic Communication Method> The second cryptographic communication method may be configured as the following fourth cryptographic communication method. That is, in the fourth cryptographic communication method, in the second cryptographic communication method, the ciphertext generation process includes a common key conversion process, a cryptographic key generation process, and an encryption process process (corresponding to claim 4). .

(Common Key Conversion Process) In the common key conversion process,
The common key is input and converted into a common key composed of two values.

(Cryptographic Key Generation Process) In the cryptographic key generation process,
An encryption key is generated based on the value output from the first chaotic vibration generator using two values of the common key converted in the common key conversion process as initial values of input values, and thereafter, the chaotic vibration generator. It is repeated to reset the value output from the above as an input value and to generate the encryption key based on the value output from the first chaotic vibration generator.

(Encryption process) In the encryption process,
The plaintext is encrypted using the encryption key generated in the encryption key generation process.

<Fifth Cryptographic Communication Method> The second cryptographic communication method may be configured as the following fifth cryptographic communication method. That is, in the fifth cryptographic communication method, in the second cryptographic communication method, the decrypted text generation process includes a common key conversion process, a decryption key generation process, and a decryption process process (corresponding to claim 4). .

(Common Key Conversion Process) In the common key conversion process,
The common key is input and converted into a common key composed of two values.

(Decryption Key Generation Process) In the decryption key generation process,
A decryption key is generated based on the value output from the second chaotic vibration generator using two values of the common key converted in the common key conversion process as initial values of input values, and thereafter, the chaotic vibration generator. The value output from the above is reset as an input value, and the decryption key is generated based on the value output from the second chaotic vibration generator.

(Decryption Process) In the decryption process, a process of decrypting the ciphertext is performed using the decryption key generated in the encryption key generation process.

<First Cryptographic Communication System> The first cryptographic communication system adopts the following means in order to solve the above-mentioned problems. That is, the first cryptographic communication system is a cryptographic communication system that performs cryptographic communication by decrypting the ciphertext encrypted on the transmitting side on the receiving side, in the ciphertext generating unit, the ciphertext transmitting unit, and the ciphertext receiving unit. And a decrypted text generator (corresponding to claim 6).

(Ciphertext Generation Unit) The ciphertext generation unit generates a ciphertext from a plaintext by using the value output from the first chaotic vibration generator that can be regarded as chaotic vibration, as a cipher key. The plain text may be in any format such as text format, binary format, compressed data, encrypted data, and the like.

(Ciphertext transmission unit) The ciphertext transmission unit transmits the ciphertext generated by the ciphertext generation unit to the receiving side.

(Ciphertext Receiving Section) The ciphertext receiving section receives the ciphertext from the transmitting side.

(Decrypted text generator) In the decrypted text generator, the value output from the second chaotic vibration generator having the same structure as the first chaotic vibration generator is used as the decryption key to receive the ciphertext. A decrypted text is generated from the ciphertext received in the process.

According to the first cryptographic communication system, the value output from the first chaotic vibration generator is used as an encryption key (ciphertext generator), and the value output from the second chaotic vibration generator is used. It is used as a decryption key (decrypted text generator). Here, since the first and second chaotic vibration generators have the same structure, the encryption key and the decryption key are the same. Moreover, since the encryption key and the decryption key generated by the chaotic vibration have an infinite period, changing the encryption key and the decryption key at a predetermined timing causes the encryption key and the decryption key to be leaked to a third party. There is little fear that it will happen. The predetermined timing is preferably synchronized with the timing of transmitting the ciphertext. Then, since the encryption key and the decryption key are automatically changed, they can be easily operated.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Regarding the Configuration of the Embodiment> FIG. 1 shows the configuration of the embodiment. The first communication device 10 has a fixed secret key (represented by symbol A in FIG. 2) and transmits a ciphertext generated based on a predetermined common key (represented by symbol K in FIG. 2). Is. This first communication device 10
The second communication device 20 is connected to the via a line 30. This second communication device 20 has a fixed secret key (see FIG.
, Which is represented by the symbol B in FIG. 2), and decrypts the ciphertext transmitted from the first communication device 10 based on the common key (K).
The first communication device 10 is a plurality of second communication devices 20.
May be connected to. In addition, the second communication device 20,
It may be connected to a plurality of first communication devices 10.

(Regarding Common Key (K)) Common Key (K)
Changes every time a ciphertext is transmitted. That is, the common key in this embodiment is thrown away every time. This is because even if the common key is leaked to a third party, it cannot be used for the next eavesdropping, falsification, spoofing, etc.
This is to improve communication safety. The common key (K)
May be fixed in advance between the first communication device 10 and the second communication device 20 if wiretapping, tampering, spoofing and the like are unlikely to occur.

(Regarding plaintext, ciphertext, encryption key and decryption key) The plaintext, ciphertext, encryption key and decryption key in this embodiment are each composed of a combination of 26 letters of letters A to Z, and Is assumed to be assigned numbers 0 to 25 in alphabetical order. For example, “D” is assigned “3” and “S” is assigned “18”.

(Regarding First Communication Device 10) The first communication device 10 is connected to the transmission / reception unit 12 connected to the line 30, the common key sharing unit 11 connected to the transmission / reception unit 12, and the transmission / reception unit 12. In addition, a ciphertext generation unit 13 connected to the common key sharing unit 11 is provided. The transmission / reception unit 12 transmits the encrypted information on the line 30 and receives the encrypted information on the line 30.

The common key sharing unit 11 functions to share a different common key between the first communication device 10 and the second communication device 20 each time, and the first-stage common key encryption unit 1
It has 1A and a first-stage common key decryption unit 11B. The first-step common key encryption unit 11A uses the common key (K) as the first key.
By encrypting with the secret key (A) of the communication device 10, a common key (represented by symbol K + A) that has been encrypted in the first stage is generated. The generated first-stage encrypted common key (K + A) is
It is transmitted to the second communication device 20 via the transmission / reception unit 12. The first-step common key decryption unit 11B receives the second-step encrypted common key (symbol K +) transmitted from the second communication device 20.
A first-step decrypted common key (represented by symbol K + B) is generated by decrypting A + B) represented by secret key A. The generated first-step decrypted common key (K + B) is used by the transmission / reception unit 1
2 to the second communication device 20.

The ciphertext generating unit 13 generates ciphertext from plaintext, and includes a common key converting unit 13A and a cipher key generating unit 13
B and the encryption processing unit 13C. The common key converting unit 13A inputs the common key (K) from the common key sharing unit 11 and applies the function of the hash function to generate a new common key (hereinafter, referred to as p1 and p2) (hereinafter referred to as a new common key). , A new common key). Where the hash function is
A predetermined one is set in advance. The encryption key generator 13B
It has a function of calculating the logistic equation represented by the equation (1), and performs the following processes 1) to 4). 1) Using the two values p1 and p2 of the new common key converted by the common key conversion unit 13A, y in Expression (1) when a = p1 and x = p2 is obtained. 2) modulo 256 modulo the value of y (mod
256) The value obtained by performing the calculation is used as the encryption key. 3) With the value of y as x, y in equation (1) is calculated. 4) Repeat steps 2) to 3) for the number of plain text characters. That is,
The encryption key is generated by the number of plaintext characters.

[Mathematical formula-see original document] y = ax (1-x) (1) Note that the arithmetic expression is not limited to the logistic equation of Expression (1), and may be any expression that causes chaotic oscillation. .

The encryption processing unit 13C is a cryptographic key generation unit 13
Encrypt the plaintext using the encryption key generated in B. The encryption here is performed by a substitution encryption method. The substitution character encryption method is a method of replacing a plaintext with an encryption key by replacing a character with another character according to the value of the encryption key.
A specific example of the substitution encryption method is shown below. Here, the plain text is "SOCCER ...", and the encryption key is "DKAITL.
.. ”First, the first character“ S ”of the plaintext is associated with the first character“ D ”of the encryption key.“ S ”is“ 1 ”.
Since "8" is assigned and "3" is assigned to "D", "V" corresponding to "21" obtained by adding 3 to 18 is set as the first character of the ciphertext. , The second character “O” in plaintext is associated with the second character “K” in the encryption key, “14” is assigned to “O”, and “10” is assigned to “K”. Because 1
"Y" corresponding to 24 obtained by adding 10 to 4 is 2
The second character. Hereinafter, by repeating such an operation, “VYCLYD ...” Is generated as a ciphertext. Since the encryption key is generated by chaotic vibration, the cycle is infinite. Then, the ciphertext generated by the encryption processing unit 13C is transmitted to the second communication device 20 via the transmission / reception unit 12.

(Regarding Second Communication Device 20) The second communication device 20 is connected to the transmitting / receiving unit 22 connected to the line 30, the common key sharing unit 21 connected to the transmitting / receiving unit 22, and the transmitting / receiving unit 22. A decrypted text generation unit 23 connected to the common key sharing unit 21 is also provided. The transmission / reception unit 22 transmits the encrypted information on the line 30 and receives the encrypted information on the line 30.

The common key sharing unit 21 functions to share a different common key between the first communication device 10 and the second communication device 20 every time, and the second-stage common key encryption unit 2
It has a 1A and a second stage common key decryption unit 21B. The second-step common key encryption unit 11A transfers the first-step encrypted common key (K + A) transmitted from the first communication device 10 to the second-step common key
By encrypting with the secret key of the communication device 20, the second-stage encrypted common key (represented by the symbol K + A + B) is generated.
The generated second-stage encrypted common key (K + A + B) is
It is transmitted to the first stage communication device 10 via the transmission / reception unit 22. The second-stage common key decryption unit 21B uses the first communication device 1
The first-step decrypted common key (K + B) transmitted from 0 is decrypted with the secret key B to generate the common key (K).
Thus, by providing the common key sharing unit 10 of the first communication device 10 and the common key sharing unit 21 of the second communication device 20, the common key sharing between the first communication device 10 and the second communication device 20. It becomes possible to share (K).

The decrypted text generating unit 23 generates a decrypted text from the encrypted text transmitted from the first communication device 10, and has a common key conversion unit 23A, a decryption key generation unit 23B, and a decryption processing unit 23C. ing. The common key conversion unit 23A inputs the common key (K) from the common key sharing unit 21 and applies the function of the hash function to obtain two values (p1 and p2).
To a new common key (hereinafter referred to as the new common key). Here, the hash function is the same as the hash function set in the common key conversion unit 13A of the first communication device 10.

The decryption key generator 23B has a function of calculating the logistic equation represented by the equation (1), and performs the following processes 1) to 4). 1) Using the two values p1 and p2 of the new common key converted by the common key conversion unit 23A, y in the equation (1) when a = p1 and x = p2 is obtained. 2) modulo 256 modulo the value of y (mod
256) The value obtained by performing the calculation is used as the decryption key. 3) With the value of y as x, y in equation (1) is calculated. 4) Repeat steps 2) to 3) for the number of plain text characters. That is,
The decryption key is generated by the number of plaintext characters.

The decryption processing unit 23C has an encryption key generating unit 23B.
Decrypt the ciphertext using the decryption key generated in. The decoding here is performed by a substitution decoding method. The substitution substitution decryption method is a scheme similar to the substitution substitution encryption method, and is a method in which when a ciphertext is decrypted into a decryption text, a character is replaced with another character by the value of the decryption key. A specific example of the substitution character decoding method is shown below. Here, the ciphertext is "VYCLYD ..."
Then, it is assumed that the decryption key is "DKAITL ...". First, the first character “V” of the ciphertext is replaced with the first character “D” of the decryption key.
Correspond. Since “21” is assigned to “V” and “3” is assigned to “D”, 21
“S” corresponding to “18” obtained by subtracting 3 from is the first character of the decrypted text. Next, the second character "Y" in the ciphertext
To the second character "K" of the decryption key. "Y"
"24" is assigned to, and "1" is assigned to "K".
Since "0" is assigned, "0" corresponding to 14 obtained by subtracting 10 from 24 is set as the second character of the decrypted text. By repeating such an operation, "SOCCER .. "is generated.

(Operation of Embodiment) Next, as the operation of the embodiment, the first communication device 10 and the second communication device 2
The common key sharing operation performed between 0s, the encryption processing operation performed by the first communication device 10, and the decryption processing operation performed by the second communication device 20 will be described.

(Common Key Sharing Operation) FIG. 2 is a sequence diagram showing the common key sharing operation. First, the first communication device 10
Uses the common key (K) as the secret key (A) of the first communication device 10.
By encrypting with the common key (K +
A) is generated (step 201). Next, the first communication device 10 transmits the first-stage encrypted common key (K + A) generated in step 201 to the second communication device 20 (step 202). The second communication device 20 is the first communication device 1.
The first stage encrypted common key (K + A) received from 0
The second stage encrypted common key (K + A + B) is generated by encrypting with the secret key (B) of the second communication device 20 (step 203). Next, the second communication device 20 uses the second-stage encrypted common key (K +) generated in step 203.
A + B) is transmitted to the first communication device 10 (step 20).
4).

The first communication device 10 decrypts the second-step encrypted common key (K + A + B) received from the second communication device 20 with the secret key (A) to obtain the first-step decrypted common key (K + B). Is generated (step 205). Next, the first
The communication device 10 transmits the first-step decrypted common key (K + B) generated in step 205 to the second communication device 20 (step 206). The second communication device 20 receives the first-step decrypted common key (K + B) received from the first communication device 10.
Is decrypted with the secret key (B) to generate a common key (K) (step 207).

(Encryption Processing Operation) FIG. 3 is a flow chart showing the encryption processing operation of the embodiment. First, the common key conversion unit 13A converts the common key input from the common key sharing unit 11 into a new common key having two values (p1, p2) (step 301). Next, the encryption key generation unit 13B
Sets initial values for the logistic equation.
That is, a = p1 and x = p2 are set in the equation (1) (step 302). Then, the encryption key generation unit 13B
Calculates the logistic equation and obtains the encryption key from the output y (step 303).

Here, step 30 is performed for the number of plaintext characters.
It is determined whether or not 3 is repeated (step 304).
If it is determined in step 304 that "it has not been repeated", the output y of the logistic equation is substituted for x (step 305), and the process returns to step 303. When it is determined in step 304 that “it has been repeated”, the encryption processing unit 13C performs the substitution encryption process (step 30).
6).

(Decoding Processing Operation) FIG. 4 is a flow chart showing the decoding processing operation of the embodiment. First, the common key conversion unit 23A converts the common key input from the common key sharing unit 21 into a new common key having two values (p1, p2) (step 401). Next, the decryption key generation unit 23B sets initial values for the logistic equation. That is,
In the equation (1), a = p1 and x = p2 are set (step 402). Then, the decryption key generation unit 23B computes the logistic equation to obtain the decryption key from the output y (step 403).

Here, step 4 is performed by the number of characters in the ciphertext.
03 is repeated (step 40)
4). When it is determined in step 404 that “not repeated”, the output y of the logistic equation is substituted for x (step 405) and the process returns to step 403. When it is determined in step 404 that “it has been repeated”, the decoding processing unit 23C performs the substitution decoding processing (step 406).

[0050]

According to the first to fifth cryptographic communication methods and the first cryptographic communication system, since the encryption key and the decryption key generated by the chaotic oscillation have infinite cycles, the encryption is performed at a predetermined timing. By changing the key and the decryption key,
There is little risk that the encryption key and common key will be leaked to a third party. Further, according to the first to fifth encryption communication methods and the first encryption communication system, the encryption key and the decryption key are automatically changed, respectively, so that there is an effect that they can be easily operated. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a sequence diagram showing a common key sharing operation of the embodiment.

FIG. 3 is a flowchart showing the encryption processing operation of the embodiment.

FIG. 4 is a flowchart showing a decoding processing operation of the embodiment.

[Explanation of symbols]

 10 ... 1st communication apparatus 11 ... Common key sharing part 11A ... 1st step common key encryption part 11B ... 1st step decryption part 12 ... Transmission part 13 ... Ciphertext generation part 13A・ ・ Common key conversion unit 13B ・ ・ Cryptographic key generation unit 13C ・ ・ Encryption processing unit 20 ・ ・ ・ Second communication device 21 ・ ・ ・ Common key sharing unit 21A ・ ・ Second stage common key encryption unit 21B ・ ・Second stage common key decryption unit 22 ... Reception unit 23 ... Decryption text generation unit 23A ... Common key conversion unit 23B ... Decryption key generation unit 23C ... Decryption processing unit 30 ... Line

Claims (6)

[Claims] 1. In a cryptographic communication method for performing cryptographic communication by decrypting a ciphertext encrypted on the transmission side on the reception side, a value output from a first chaotic vibration generator that can be regarded as chaotic vibration is used. A ciphertext is generated from a plaintext by using it as an encryption key, and a value output from a second chaotic vibration generator having the same structure as the first chaotic vibration generator is used as a decryption key. A cryptographic communication method characterized by generating a decrypted text. 2. A common key sharing process for sharing a common key between the transmitting side and the receiving side while performing feedback communication between the transmitting side and the receiving side, wherein the common key sharing is performed in the ciphertext generating process. The value of the common key shared in the process is used as an initial value of the input value to the first chaotic oscillation generator, and the value of the common key shared in the common key sharing process is used in the decrypted text generation process. The cryptographic communication method according to claim 1, wherein the cryptographic communication method is used as an initial value of an input value to the second chaotic vibration generator. 3. The common key sharing step comprises: a first-step common key encryption step of generating a first-step encrypted common key by encrypting the common key with a secret key of a sender; Second-stage common key encryption process for generating a second-stage encrypted common key by encrypting the first-stage encrypted common key generated in the first-stage common key encryption process with a secret key on the receiving side And a first-stage common key decryption for generating a first-stage decrypted common key by decrypting the second-stage encrypted common key generated in the second-stage common key encryption process with a secret key on the transmitting side. And a second-step common key decryption step of generating the common key by decrypting the first-step decrypted common key generated in the first-step common key decryption step with a secret key on the receiving side. The cryptographic communication method according to claim 2, wherein 4. The ciphertext generation step includes two steps, a common key conversion step of inputting the common key and converting the common key into a common key composed of two values, and a common key converted in the common key conversion step. Generating an encryption key based on a value output from the first chaotic vibration generator with the value as an initial value of an input value, and thereafter resetting the value output from the chaotic vibration generator as an input value; And an encryption key generation process that repeats generating an encryption key based on the value output from the first chaotic vibration generator, and a process of encrypting a plaintext with the encryption key generated in the encryption key generation process. The encryption communication method according to claim 2, further comprising an encryption processing step to be performed. 5. The decrypted text generation step includes two steps, a common key conversion step of inputting the common key and converting the common key into a common key composed of two values, and a common key converted in the common key conversion step. Generating a decryption key based on the value output from the second chaotic vibration generator with the value as an initial value of the input value, and resetting the value output from the chaotic vibration generator as an input value thereafter; And an encryption key generation process that repeats generating a decryption key based on the value output from the second chaotic vibration generator, and a process of decrypting a ciphertext with the decryption key generated in the encryption key generation process. The encryption communication method according to claim 2, further comprising a decryption processing step to be performed. 6. In a cryptographic communication system for performing cryptographic communication by decrypting a ciphertext encrypted on the transmitting side on the receiving side, a value output from a first chaotic vibration generator that can be regarded as chaotic vibration is output. A ciphertext generation unit that generates a ciphertext from plaintext by using it as a ciphertext, a ciphertext transmission unit that transmits the ciphertext generated in the ciphertext generation process to a receiving side, and a ciphertext from the transmission side. The ciphertext received in the ciphertext reception process by using the value output from the ciphertext reception unit that receives the ciphertext and the value output from the second chaotic vibration generator having the same structure as the first chaotic vibration generator. A cryptographic communication system, comprising: a decrypted text generation unit that generates a decrypted text from a text.