JPH04304730A - Data ciphering device - Google Patents

Abstract

PURPOSE:To prevent a key data at a reception side from being different from a value expected by a sender in a secret key cipher communication system. CONSTITUTION:A revision key data 11 discriminated by a key data discrimination circuit 10 is inputted to a key data storage circuit 4, in which a key data is revised. In this case, a key data before the revision is inputted to a key data buffer circuit 12. After a sender side delivers a key data, its own ciphering key is revised and information representing the delivery of the same key data is ciphered by using a new key and the result is delivered. The cipher is decoded into a revised key data 11 by a ciphering decoding circuit 6 and the data is a revised key data equal to the data discriminated just before by the key data discrimination circuit 10. However, when the revised key data 11 is in error, the two revision key data are different from each other and the revised key data not expected by a sender is generated. Then a key data buffer circuit 12 detects the difference between the two revision key data and outputs the key data 13 before the revision to a key data storage circuit 4.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a data encryption device having a function of preventing the generation of key data not intended by the information sender due to transmission errors in a cryptographic communication system using a plurality of key data. It is something.

0002

[Background Art] In the field of digital communication, signals from information sources such as text, audio, and images are generally "1".
It is converted into a numeric string consisting of two values:
By modulating the carrier signal according to the value, it is sent out on a wireless or wired transmission path and transmitted to the destination. When transmitting information using the above transmission path, confidential information source data is encrypted on the information source side, decrypted on the receiving side at the destination, and then transferred from the original source. A so-called encrypted communication system is constructed to restore the signal. Cryptographic communication systems based on various principles have been proposed and put into practice, and one of the commonly used systems is called a secret key cryptographic system. Information from an information source that is encrypted and sent to a transmission channel cannot be decoded by a third party who does not know the rules by which the information was processed, and cannot be decoded by a third party who is aware of the rules. It can only be deciphered. Therefore, in the above secret key encryption method, it is important to protect the rules used for encryption, that is, the correspondence table of transposition and substitution, which are known to the sender and receiver, from being known to a third party. . Since the correspondence table of transpositions and substitutions is called a key, the above method is called a secret key cryptosystem.

FIG. 3 shows an example of a conventional decryption device in the private key cryptosystem, and in the figure, 1 indicates an input ciphertext;
2 is a ciphertext input circuit, 3 is a ciphertext, 4 is a key data storage circuit, 5 is a key data, 6 is a decryption circuit, 7 is a plaintext, 8 is a plaintext output circuit, 9 is an output plaintext, 10 is a key data discrimination circuit The circuit 11 is update key data.

Next, the operation will be explained. Input ciphertext 1
is received by the cipher input circuit 2, converts the input data into a format for processing by the cipher text 3, and inputs the input data to the cipher text 3. Here, the ciphertext 3 is decrypted by the key data 5 stored in the key data storage circuit 4, and the plaintext 7 is output as the output plaintext 9 via the plaintext output circuit 8. The plaintext 7 is also supplied to the key data discrimination circuit 10, which detects specific information included in the plaintext 7 and determines that it is key data delivery, and then transfers the detected update key data 11 to the key data storage circuit 10. Supply to 4. The key data in the key data storage circuit 4 is updated in this way, and the new data is used as the key data to the decryption circuit 4 from now on. On the sending side, after delivering the above key data, it also updates its own encryption key and performs encryption.
It has the function of updating the synchronized key data on the sending and receiving sides so that information is always transmitted.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned conventional device,
The key data discrimination circuit identifies new key data contained in the plaintext and generates updated key data to update the key data, but due to a transmission error (bit error) during encrypted transmission, the update is interrupted. This poses a problem in that the key data sent to the sender is different from what the sender recognizes, making it impossible to obtain the correct information even if the ciphertext is deciphered.

[0006] In order to deal with the above-mentioned conventional problems, the present invention restores and uses the previous key data even when the key data to be updated is not transmitted correctly, thereby preventing a key not intended by the sender. The present invention provides a data encryption device that prevents data generation.

[0007]

[Means for Solving the Problems] A data encryption device according to the present invention has a circuit for temporarily holding old key data when updating key data, and the updated key data is transmitted to the sender. If the key data is unintended, the erroneous key data is restored to the old key data.

[0008]

[Operation] In this invention, even if a transmission error occurs in the information for updating the key data, the circuit returns to the key data before updating, so that decryption is always performed using the key data recognized by the sender. It is what causes it to be done.

[0009]

[Embodiment] Embodiment 1 FIG. 1 is a block diagram of a data encryption device showing an embodiment of the present invention. In the figure, 1 is an input ciphertext, 2 is a ciphertext input circuit, 3 is a ciphertext, and 4 is a key. A data storage circuit, 5 is key data, 6 is a decryption circuit, 7 is plaintext, 8 is a plaintext output circuit, 9 is output plaintext, 10 is a key data discrimination circuit, 11 is update key data, 12 is a key data buffer circuit, 13 is pre-update key data.

The updated key data 11 determined in the key data determining circuit 10 is input to the key data storage circuit 4,
Key data is updated. At this time, the key data before update is input to the key data buffer circuit 12. After delivering the above-mentioned key data, the sending side also updates its own encryption key, and once again encrypts and delivers information that includes the delivery of the same key data using a new key. This code is decrypted by the decryption circuit 6 using the updated key data 11, and becomes updated key data that is the same as the one previously determined by the key data determining circuit 10. However, if the update key data 11 is incorrect, these two update key data generated by the key data discrimination circuit 10 will be different data, and update key data that is not intended by the sender at all will be generated. Therefore, the key data buffer circuit 12 detects the difference between these two updated key data and outputs the pre-updated key data 13 to the key data storage circuit 4. Therefore, since the ciphertext 3 is subsequently decrypted using the pre-update key data 13, the key data 5 can be set to a value within a range that the sender understands.

Although the above embodiment does not specify the operation of the key data buffer circuit, actual key data control depends on the configuration of the key data buffer circuit. FIG. 2 is an embodiment of a key data buffer circuit according to the present invention. In the figure, 14a is a first key data latch circuit;
15 is a first key data latch circuit output, 14b is a second key data latch circuit, 16 is a key data update detection circuit, 17 is a key data update detection circuit output, 18 is a key data comparison circuit, 19 is the key data comparison circuit output. The first and second key data latch circuits 14 input update key data to the key data storage circuit 4 through a key data update detection circuit 16.
The key data detection circuit output when detected is used as a clock to latch up, and when the second updated key data is input, the second updated key data and the first updated key data are latched. Then, the updated key data 5 and the data of the first key data latch circuit output 15 are compared by the key data comparison circuit 18, and when they do not match, the output of the second key data latch circuit is determined by the key data comparison circuit output 19. It is enabled, the pre-update key data 13 is output, and the value of the key data storage circuit 4 is returned to its original value.

0012

As described above, according to the present invention, an encryption key is delivered using a communication channel used for sending and receiving ciphertext, and a third party who intercepts the encryption key data itself can be decrypted and This provides a method that makes it impossible to know when the encryption key data is updated, and even in a communication system where key data cannot be delivered other than through the ciphertext communication path, it is possible to arbitrarily transmit the key via the ciphertext communication path. By delivering data, the key data is frequently updated, making it difficult for a third party who intercepts the communication channel to decrypt the encrypted key data, and the key data may be damaged due to transmission errors when updating the key data. This has the effect of making it possible to understand that the ciphertext is being processed using key data that is within the sender's knowledge even when the information is not transmitted correctly.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a partially detailed block diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a conventional embodiment.

[Explanation of symbols]

1 Input ciphertext 2 Ciphertext input circuit 3 Ciphertext 4 Key data storage circuit 5 Key data 6 Decryption circuit 7 Plaintext 8 Plaintext output circuit 9 Output plaintext 10 Key data discrimination circuit 11 Update key data 12 Key data buffer circuit 13 Key data buffer circuit output 14a First key data latch circuit 14b Second key data latch circuit 15 First key data latch circuit output 16 Key data update detection circuit 17 Key data update detection circuit output 18 Key data comparison circuit 19 Key data comparison circuit output

Claims (2)

[Claims] Claim 1: Key data for storing key data used when decoding a ciphertext in a data encryption device that receives a ciphertext encrypted by a secret key cryptosystem and decrypts it to obtain plaintext. a storage circuit; a decryption circuit that decrypts a ciphertext using data from the key data storage circuit; and a decryption circuit that detects specific characteristics included in the output of the decryption circuit and determines when to update new key data. a key data discrimination circuit that obtains key data and updates the data by supplying it to the key data storage circuit; A data encryption device comprising: a key data buffer circuit that temporarily holds a previous value in order to restore the previous value. 2. A key data buffer circuit comprising first and second key data latch circuits capable of preliminarily storing the output of the key data storage circuit in two stages;
A patent claim characterized by comprising a key data comparison circuit that compares the data held in the second key data latch circuit and controls to enable the data output of the second key data latch circuit if they differ. The data encryption device according to scope 1.