JP2004350084A - Data exchange method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent leakage of confidential data, etc., as making management separating general disclosure data and the confidential data unnecessary. <P>SOLUTION: A transmitting origin A creates/manages a management table of a management ID for uniquely determining the transmitting contents with a shared key associated with the management ID about transmission data (S1, S2), encodes the confidential data among pieces of transmitting data by the shared key (S3), encodes its hash value by a private key of the transmitting origin A (S4) and transmits values by attaching the management ID to them by encoding them by a public key with a transmitting destination B (S5). The transmitting destination B decodes transmitted data by the private key (S6), transmits the management ID by encoding the public key of the transmitting origin A (S7) when the contents of the confidential data are desired to be learned, makes the shared key corresponding to the transmitted data be encoded and transmitted from the transmitting origin A (S8, S9) and decodes the confidential data by decoding of the shared key (S10, 11). Thus, the transmitting origin performs batch management of the general disclosure data and the confidential data and transmission of them and management separating the general disclosure data and the confidential data becomes unnecessary for the transmitting origin since learning of the confidential data by the transmitting destination is considered only when the transmitting origin approves or only when the learning is approved via a third party to which the management is entrusted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data exchange method for encrypting data with a public key (public key) or a shared key (shared key) when exchanging data via a network such as the Internet and preventing the data from being leaked.
[0002]
[Prior art]
2. Description of the Related Art In the case of buying and selling goods, sales contracts and the like are increasingly performed through a network. For example, as shown in FIG. 7, company A transmits sending data to company B via a network, and company B, which has received the data, sends reception data to company A via the network.
[0003]
In this case, the data exchanged via the network often includes an article number, a price, a quantity, a contract date, a scheduled delivery date, a delivery date, and the like that are set so that the articles can be distinguished on both sides. In some cases, the information may include list information of the configuration contents of parts and the like constituting the article.
[0004]
Here, data exchange via a network has problems such as leakage of information, impersonation of a party, denial of data exchange, and falsification of data. To prevent these, the following data encryption methods are used.
[0005]
(A) Public key cryptography Different keys (bit strings) are used for data encryption at the source and decryption of data at the destination.
[0006]
This method generates two types of keys, a public key and a secret key. The private key is stored only by the user who generated it, and is not disclosed to anyone. The public key is widely distributed to a potential sender of the data or deposited at a management center so that anyone can refer to it.
[0007]
In this method, the sender of the data encrypts the data with the public key, and the receiver can decrypt the data using the private key corresponding to the public key used for the encryption. Send it safely to the other party.
[0008]
In another use form, the data is used as an electronic signature for certifying that the sender of the data is who he or she is. With this digital signature, the sender encrypts the data with its own secret key and sends it to the other party, and the receiver decrypts it using the public key issued by the sender, and if this is correctly decrypted, the sender's private key To get proof that it was encrypted.
[0009]
(B) Secret Key Cryptography The same key (bit string) is used for data encryption at the source and decryption of data at the destination.
[0010]
More specifically, transposition processing that divides transmission data into fixed fixed-length blocks and replaces the position of character data for each block according to a certain rule, and character substitution that replaces character data with different characters based on a certain conversion table Combine processing and so on.
[0011]
This method, like the shared key encryption method, has relatively simple processing and can perform high-speed encryption and decryption. However, since the source and destination use the same key (common key encryption method), the key Management becomes important.
[0012]
It has been proposed to use the above-mentioned encryption method in, for example, an electronic contract method (for example, see Patent Document 1).
[0013]
In this electronic contract method, unique data (random number) is generated from the user terminal B that has received an indication of the conclusion of the contract and is encrypted with a common key with the user A, , The user A decrypts the unique data with the common key, encrypts the contract contents using the unique data as a key, transmits the encrypted contents to the user B, and applies for a contract to the user B. The user B knows the contract contents by decrypting the contract contents using the unique data as a key. Further, the user A transmits to the user B the authentication data obtained by converting the contents of the contract by a hash function determined by its own secret key.
[0014]
[Patent Document 1]
JP-A-10-240826
[Problems to be solved by the invention]
In performing the data exchange as shown in FIG. 7, the receiving side of the product requests the detailed information of the configuration as much as possible for reasons such as securing reliability at the time of resale. There may be a situation in which it is not desirable to easily give detailed configuration contents to the recipient of the product because the product itself is a product value and a company secret.
[0016]
This is remarkable when, for example, the ingredients cannot be judged from the appearance, such as raw materials of food, but the cooking contents can be generally understood from the raw material list. For example, FIG. 8 shows that the product data A alone does not indicate what the raw material is, but the raw material list “pig, cow, chicken, hump, shiitake mushroom” as shown in the product data B. ) Will give you hints on how to make a soup base.
[0017]
When exchanging data via a network, the above-mentioned public key encryption method or secret key encryption method can be used for data confidentiality. It is not possible to cope with data exchange when a detailed data portion is disclosed only to a specially permitted destination.
[0018]
In order to solve this problem, it is conceivable that the transmission source manages data by separating a data portion (for example, a soup element) that generally discloses transmission data and a data portion (for example, a raw material list) that keeps secret data. Data management in which data is separated from each other becomes complicated, the burden on the data manager increases, and confidential data may be erroneously disclosed.
[0019]
An object of the present invention is to provide a data exchange method that prevents leakage of confidential data while eliminating the need for separate management of general disclosure data and confidential data.
[0020]
[Means for Solving the Problems]
The present invention, in order to solve the above problems, to prevent data leakage and the like by encrypting with a public key cryptosystem and a shared key cryptosystem, the source collectively manages the general disclosure data and confidential data and transmits the data, The transmission destination knows the confidential data only when the transmission source permits it or when it is permitted through a third party who has outsourced management, and is characterized by the following data exchange method.
[0021]
(1) A method of exchanging data transmitted from a transmission source A to a transmission destination B via a network by a public key encryption method and a shared key encryption method to secure leakage, falsification, spoofing, and non-repudiation;
The transmission source A collectively transmits the general disclosure data and the confidential data DAT1 of the transmission data to the transmission destination B, and the confidential data DAT1 is a data exchange disclosed to the transmission destination B when the transmission source A permits. It is characterized by having a procedure.
[0022]
(2) The data exchange procedure includes:
The transmission source A creates and manages a management table including a management ID for uniquely determining a transmission destination B and transmission contents and a shared key associated therewith for the transmission data; Data DAT1 encrypted with the shared key and a hash value of the confidential data DAT1 encrypted with the secret key of the transmission source A are generated, and the transmission data in which the management ID is packaged is transmitted to the transmission destination B. And transmitting by encrypting with a public key between
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own secret key, encrypts the management ID obtained by the decryption with the public key of the transmission source A, and transmits the management ID to the transmission source A. And a procedure for
The source A decrypts the encrypted management ID transmitted from the destination B with its own secret key, and obtains the shared key obtained from the management table based on the decrypted management ID using the public key of the destination B. Has a procedure of encrypting and transmitting to the destination B,
The transmission destination B has a procedure of decrypting the encrypted shared key transmitted from the transmission source A with its own secret key, and a procedure of decrypting the secret data DAT1 using the decrypted shared key. I do.
[0023]
(3) The data exchange procedure includes:
The transmission source A creates and manages a management table including a management ID for uniquely determining a transmission destination B and transmission contents and a shared key associated therewith for the transmission data; Data DAT1 encrypted with the shared key and a hash value of the confidential data DAT1 encrypted with the secret key of the transmission source A are generated, and the transmission data in which the management ID is packaged is transmitted to the transmission destination B. And transmitting by encrypting with a public key between
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own private key, and uses the management ID obtained by the decryption and the encrypted transmission data with the public key of the transmission source A. Encrypting and transmitting to the source A,
The transmission source A decrypts the encrypted management ID and the transmission data transmitted from the transmission destination B with its own secret key, and transmits the transmission data with the shared key obtained from the management table based on the decrypted management ID. Decrypting the transmission data with the public key of the transmission destination B and transmitting the transmission data to the transmission destination B.
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own secret key, decrypts the hash value with the public key of the transmission source A, and decrypts the hash value and the decrypted hash value. Comparing the hash value of the secret data DAT1 with the hash value of the secret data DAT1 to confirm that the secret data has not been tampered with.
[0024]
(4) A method of exchanging data transmitted from the transmission source A to the transmission destination B via the network by public key encryption and shared key encryption to prevent leakage, falsification, spoofing, and non-repudiation.
The transmission source A collectively transmits the general disclosure data and the confidential data of the transmission data to the transmission destination B, and the confidential data is transmitted via a third party X entrusted by the transmission source A, or The third embodiment is characterized in that the third party has a data exchange procedure to be disclosed to the transmission destination B when permission is granted in the situation judgment.
[0025]
(5) The data exchange procedure includes:
The transmission source A encrypts, with the public key of the third party X, the transmission destination B and the management ID for uniquely determining the transmission destination B and the transmission content, and the shared key associated therewith, and transmits the encrypted data to the third party X. And generating a procedure in which the secret data DAT1 is encrypted with the shared key and a hash value of the secret data DAT1 is encrypted with the secret key of the transmission source A in the transmission data. And encrypting the transmission data with the public key between the transmission destination B and the transmission destination B, and transmitting the transmission data.
The third party X decrypts the management ID and the shared key encrypted and transmitted from the transmission source A with its own private key, and creates and manages a relation table between the decrypted management ID and the shared key. Has,
The transmission destination B decrypts the encrypted management ID and the transmission data with its own private key, and encrypts the decrypted management ID with the public key of the third party X to the third party X. Sending, and
The third party X decrypts the management ID encrypted and transmitted from the transmission destination B with its own private key, and transmits the shared key obtained from the association table based on the decrypted management ID to the transmission destination B. And transmitting to the transmission destination B after encrypting with the public key of
The transmission destination B decrypts the shared key encrypted and transmitted from the third party X with its own secret key, and transmits the secret data DAT1 transmitted from the transmission source A using the decrypted shared key. Decoding procedure.
[0026]
(6) The destination B decrypts the secret data DAT1 using the shared key and then decrypts the hash value using the public key of the source A, and the hash value and the hash value of the decrypted secret data DAT1 And confirming that the confidential data has not been tampered with by comparing
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
The data exchange method according to the present invention uses an encryption method based on a public key encryption method and a shared key encryption method (or a secret key encryption method) in order to keep the contents of transmission data secret.
[0028]
In the public key cryptosystem, as described above, a pair of two keys, a public key and a secret key, is used. Data encrypted using one key can be decrypted using another key. One of the two keys is stored as a secret key, and the other is made public as a public key.
[0029]
As shown in FIG. 6A, when data is transmitted from the transmitting side A to the receiving side B, the transmitting side A encrypts the data DAT1 with the public key PuB of the data PuB ( If (DAT1) is transmitted to the receiving side B, only the receiving side B having the corresponding secret key PrB can decrypt and view the content DAT1 and prevent leakage during communication.
[0030]
Also, as shown in FIG. 6B, if the transmitting side A encrypts the data DAT1 with its own secret key PrA and transmits it to B, the receiving side B decrypts the data DAT1 with A's public key PuA and decrypts the contents. If DAT1 can be taken out, it is known that the data is data encrypted by PuA, and it can be confirmed that the data is transmitted by the transmitting side A, thereby preventing spoofing and denial. be able to.
[0031]
Further, as shown in FIG. 6 (c), the transmitting side A obtains a hash function value H (DAT1) of the data DAT1 to be transmitted, encrypts it with the secret key PrA of A, and When the whole added to the end of DAT1 is encrypted with the public key of B and transmitted, the received B first decrypts the whole with its own private key PrB, and then decrypts the tail data with the public key PuA of A. To extract the hash value H (DAT1), compare it with the result of calculating the hash value H (DAT1) of the data transmitted from A, and confirm the coincidence, thereby preventing leakage, spoofing, denial, and falsification. can do.
[0032]
On the other hand, the shared key cryptosystem (or secret key cryptosystem) is, as described above, an encryption system in which encryption and decryption can be performed with one secret key, and this secret key is shared by both the transmitting side and the receiving side. However, if the sender encrypts with the secret key, and the receiver decrypts with the same secret key, only the sender and the receiver have the shared key. Can be prevented.
[0033]
The present invention makes it possible to conceal and certify the contents by using these encryption schemes, and to further enable data exchange that does not require separate management of general disclosure data and confidential data. Hereinafter, embodiments will be described in detail.
[0034]
(Embodiment 1)
FIG. 1 shows a data exchange procedure for pre-processing, encryption processing, and subsequent content verification of data transmission by a method in which a transmitting side manages a shared key.
[0035]
In the pre-processing, first, at the time of data transmission, the transmission side A sets a unique management ID for uniquely determining the transmission destination B and the transmission content DAT based on the transmission destination and the transmission contents (S1). A shared key with the transmission destination B is generated, and a relation table with the management ID is created (S2).
[0036]
FIG. 2 shows an example of a shared key management table. As data, there are data DAT1 and DAT2 to be transmitted to the transmission destination B, and when the data DAT1 is data to be transmitted to the transmission destination C (not shown), the management ID is ID_B_DAT1, ID_B_DAT2, and ID_C_DAT1 are set. The shared keys are Shk_B_DAT1, Shk_B_DAT2, and Shk_B_DAT1.
[0037]
Here, it is assumed that the data DAT1 is transmitted to the transmission destination B. At this time, the management ID is ID_B_DAT1, and the shared key is ShK_B_DAT1.
[0038]
Next, in the process of encrypting the transmission data DAT1 to the transmission destination B, the transmission data DAT1 is encrypted with the shared key ShK_B_DAT1 with reference to the shared key management table of FIG. 2 (S3). Further, a hash value Hash (DAT1) of the transmission data DAT1 is generated by encrypting the hash value Hash (DAT1) with the secret key PrK_A of the transmission source A (S4). The data is encrypted with the public key PuK_B of the destination B and transmitted (S5).
[0039]
In this example, the content of the transmission data has the data structure shown in FIG. For example, DAT1 is a raw material list of the above-mentioned product name "soup stock", and ID_B_DAT1 is a product "soup stock" itself or a product number.
[0040]
Next, the transmission destination B decrypts the reception data with the public key PuK_B serving as a secret key with the transmission source A to obtain all transmission data (S6). By this decryption, the transmission destination B can know the management ID (= ID_B_DAT1), but since only the transmission source A knows the shared key ShK_B_DAT1 with the transmission source A, the transmission destination B is transmitted by the transmission source A. Data (DAT1) cannot be known.
[0041]
In this state, if the transmission destination B needs to know the contents of DAT1 (content verification request is generated), the transmission destination B informs the transmitting side A of the situation and the transmission data management ID (= ID_B_DAT1) Is encrypted with the public key of the transmission source A and transmitted (S7). The transmission source A decrypts the management ID with the secret key (S8), and obtains the shared key Shk_B_DAT1 corresponding to the management ID from the shared key management table. The shared key is extracted and encrypted with the public key of the destination B and transmitted (S9).
[0042]
The destination B can know the shared key ShK_B_DAT1 by decrypting with the secret key (S10). The transmission destination B decrypts the data DAT1 using the shared key ShK_B_DAT1 (S11), and can know the contents of the data DAT1 transmitted by the transmission side A.
[0043]
Therefore, the transmission source A transmits the general disclosure data (for example, the raw soup) and the confidential data (for example, the raw material list) to the transmission destinations B and C without separate management, but transmits the confidential data to the transmission source A. With the consent of the destination B, only the transmission destination B can know.
[0044]
(Embodiment 2)
FIG. 4 shows a data exchange procedure of the present embodiment. This embodiment is different from the first embodiment in that the transmission destination B sends the data DAT1 encrypted with the shared key ShK_B_DAT1 back to the transmission side A instead of having the transmission side A disclose the shared key Shk_B_DAT1, and The point is that they are sent back after decryption on the side A.
[0045]
The transmission destination B encrypts the decrypted management ID (= ID_B_DAT1) and the data DAT1 encrypted with the shared key Shk_B_DAT1 using the public key of the transmission side A, and transmits the encrypted data DAT1 (S7 ′). The transmitting side A decrypts the data DAT1 with its own secret key (S8 '), decrypts the data DAT1 with the shared key obtained from the management table based on the decrypted management ID, and decrypts the data DAT1 with the public key of the transmission destination B. The encrypted data is transmitted (S9 ').
[0046]
The transmission destination B decrypts the transmitted data with the secret key (S10 ') and can know the contents of the data DAT1. At this time, the transmission destination B decrypts the hash value using the public key Puk_A of the transmission side A in order to confirm that the decrypted data DAT1 has not been falsified by the transmission side A (S12). It is checked whether the decrypted DAT1 has been falsified by comparing it with the hash value (S13).
[0047]
In this embodiment, since the transmission destination B has received the hash value in advance, the transmission side A can know the contents of DAT1 without being falsified.
[0048]
(Embodiment 3)
In the present embodiment, a third party manages a shared key. In the first embodiment or the second embodiment, the sender A discloses the shared key in response to the request from the receiver B. However, depending on the situation, the sender A cannot manage the shared key completely, and may lose the shared key. May not be disclosed.
[0049]
In the present embodiment, in order to avoid this, the third party X manages the shared key. In the present embodiment, in order to be able to cope with the case where the transmission side A refuses the disclosure for an unreasonable reason, the third party X requests the transmission side A and the reception side B as necessary. It is also possible to perform arbitration for the public key and play a role of disclosing the shared key according to the result of the situation determination.
[0050]
FIG. 5 shows a data exchange procedure of the present embodiment. For data transmission, the same procedure (S1 to S5) as in the first or second embodiment is performed, and the encrypted data is transmitted to the receiving side (transmission destination) B, and the receiving side B decrypts with the secret key (S6). . In addition, the transmission side A encrypts the transmission ID ID_B_DAT1 and the shared key ShK_B_DAT1 with the public key of the third party X and transmits the third party X (S14). The third party X decrypts them with its own secret key (S15), and creates and manages an association table between the management ID and the shared key (S16).
[0051]
In this state, if the transmission destination B wants to know the contents, the transmission destination B encrypts the management ID (= ID_B_DAT1) with the public key of the third party X and transmits it to the third party X. Then, an inquiry is made for a shared key corresponding to the management ID (S17).
[0052]
In response to this inquiry, the third party X decrypts the management ID with its own secret key (S18), extracts the shared key ShK_B_DAT1 from the association table, encrypts this with the public key of the receiving side B, and (S19).
[0053]
The receiving side B decrypts the shared key ShK_B_DAT1 transmitted from the third party X with its own secret key (S20), decrypts the data DAT1 using this shared key (S21), and knows its contents. .
[0054]
When transmitting the shared key to the receiving side B, the third party X can determine whether to disclose the shared key to the transmitting side A. By disclosing the shared key ShK_B_DAT1 to the receiving side B when permitted by the transmitting side A in this inquiry, the security can be enhanced even when the key management is outsourced to the third party X.
[0055]
Further, in the present embodiment, when decrypting using the shared key ShK_B_DAT1, the receiving side B can confirm that the data has not been tampered with by decrypting the hash value using the secret key Prk_A.
[0056]
【The invention's effect】
As described above, according to the present invention, the transmission source collectively manages the general disclosure data and the confidential data and transmits the data, and when the transmission source permits the transmission source to know the confidential data, or outsources the management. Since it is only when permitted through three parties, the transmission source does not need to separately manage general disclosure data and confidential data.
[0057]
Further, since data is exchanged after being encrypted by the public key cryptosystem and the shared key cryptosystem, leakage of confidential data does not occur.
[Brief description of the drawings]
FIG. 1 is a data exchange procedure according to a first embodiment of the present invention.
FIG. 2 is an example of a shared key management table in the embodiment.
FIG. 3 is a transmission data structure in the embodiment.
FIG. 4 is a data exchange procedure according to the second embodiment of the present invention.
FIG. 5 is a data exchange procedure according to the third embodiment of the present invention.
FIG. 6 is a data exchange method using a public key and a shared key according to the present invention.
FIG. 7 is an image diagram of a conventional data exchange method via a network.
FIG. 8 is an image diagram showing the merits and demerits of content disclosure.
[Explanation of symbols]
A: Sender (sender)
B: Transmission destination (reception side)
X: Third party

Claims (6)

In a data exchange method for securing leakage, falsification, spoofing, and non-repudiation of data transmitted from a source A to a destination B via a network by public key encryption and shared key encryption,
The transmission source A collectively transmits the general disclosure data and the confidential data DAT1 of the transmission data to the transmission destination B, and the confidential data DAT1 is a data exchange disclosed to the transmission destination B when the transmission source A permits. A data exchange method characterized by having a procedure. The data exchange procedure includes:
The transmission source A creates and manages a management table including a management ID for uniquely determining a transmission destination B and transmission contents and a shared key associated therewith for the transmission data; Data DAT1 encrypted with the shared key and a hash value of the confidential data DAT1 encrypted with the secret key of the transmission source A are generated, and the transmission data in which the management ID is packaged is transmitted to the transmission destination B. And transmitting by encrypting with a public key between
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own secret key, encrypts the management ID obtained by the decryption with the public key of the transmission source A, and transmits the management ID to the transmission source A. And a procedure for
The source A decrypts the encrypted management ID transmitted from the destination B with its own secret key, and obtains the shared key obtained from the management table based on the decrypted management ID using the public key of the destination B. Has a procedure of encrypting and transmitting to the destination B,
The transmission destination B has a procedure of decrypting the encrypted shared key transmitted from the transmission source A with its own secret key, and a procedure of decrypting the secret data DAT1 using the decrypted shared key. The method for exchanging data according to claim 1. The data exchange procedure includes:
The transmission source A creates and manages a management table including a management ID for uniquely determining a transmission destination B and transmission contents and a shared key associated therewith for the transmission data; Data DAT1 encrypted with the shared key and a hash value of the confidential data DAT1 encrypted with the secret key of the transmission source A are generated, and the transmission data in which the management ID is packaged is transmitted to the transmission destination B. And transmitting by encrypting with a public key between
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own private key, and uses the management ID obtained by the decryption and the encrypted transmission data with the public key of the transmission source A. Encrypting and transmitting to the source A,
The transmission source A decrypts the encrypted management ID and the transmission data transmitted from the transmission destination B with its own secret key, and transmits the transmission data with the shared key obtained from the management table based on the decrypted management ID. Decrypting the transmission data with the public key of the transmission destination B and transmitting the transmission data to the transmission destination B.
The transmission destination B decrypts the encrypted transmission data transmitted from the transmission source A with its own secret key, decrypts the hash value with the public key of the transmission source A, and decrypts the hash value and the decrypted hash value. 2. The data exchange method according to claim 1, further comprising: comparing the hash value of the secret data DAT1 with the hash value of the secret data to confirm that the secret data has not been tampered with. In a data exchange method for securing leakage, falsification, spoofing, and non-repudiation of data transmitted from a source A to a destination B via a network by public key encryption and shared key encryption,
The transmission source A collectively transmits the general disclosure data and the confidential data of the transmission data to the transmission destination B, and the confidential data is transmitted via a third party X entrusted by the transmission source A, or A data exchange method characterized by having a data exchange procedure to be disclosed to a destination B when permission is granted by a third party X in a situation judgment. The data exchange procedure includes:
The transmission source A encrypts, with the public key of the third party X, the transmission destination B and the management ID for uniquely determining the transmission destination B and the transmission content, and the shared key associated therewith, and transmits the encrypted data to the third party X. And generating a procedure in which the secret data DAT1 is encrypted with the shared key and a hash value of the secret data DAT1 is encrypted with the secret key of the transmission source A in the transmission data. And encrypting the transmission data with the public key between the transmission destination B and the transmission destination B, and transmitting the transmission data.
The third party X decrypts the management ID and the shared key encrypted and transmitted from the transmission source A with its own private key, and creates and manages a relation table between the decrypted management ID and the shared key. Has,
The transmission destination B decrypts the encrypted management ID and the transmission data with its own private key, and encrypts the decrypted management ID with the public key of the third party X to the third party X. Sending, and
The third party X decrypts the management ID encrypted and transmitted from the transmission destination B with its own private key, and transmits the shared key obtained from the association table based on the decrypted management ID to the transmission destination B. And transmitting to the transmission destination B after encrypting with the public key of
The transmission destination B decrypts the shared key encrypted and transmitted from the third party X with its own secret key, and transmits the secret data DAT1 transmitted from the transmission source A using the decrypted shared key. 5. The data exchange method according to claim 4, further comprising: decrypting. After decrypting the secret data DAT1 using the shared key, the destination B decrypts the hash value using the public key of the source A, and compares this hash value with the decrypted hash value of the secret data DAT1. 6. The method according to claim 5, further comprising the step of confirming that the secret data has not been tampered with.

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