JP2007116753A - Encryption apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for verifying the security of encrypted data and also to provide a means for confirming the correctness of decrypted data. <P>SOLUTION: The encryption apparatus includes: an encryption section; a decryption section; and a random number property detection section, and detects the random number properties of the encrypted data and the decrypted data. Further, the encryption apparatus is configured such that the random number property detection section detects the entropy of the data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for detecting the security of encrypted data and the correctness of decrypted data in a stream cipher apparatus using continuous pseudo-random numbers, and a technique for detecting synchronization.

The overall configuration of a conventional stream encryption system using continuous pseudorandom numbers will be described with reference to FIG. 4, and the configuration of the encryption device will be described with reference to FIG.
The terminal device 10 is connected to the encryption device 50 at a communication speed of 60 kbps. The encryption device 50 is connected to a transmission line having a communication speed of 64 kbps through the line termination 30. Further, it is connected to a corresponding device of the same type connected to this transmission line.

  The terminal device 10 creates a communication text (plain text) and displays decrypted data (plain text) on a display (not shown). Details of the encryption device 50 will be described with reference to FIG. First, encryption will be described. The communication text (plain text) created by the terminal device 10 is sent to the encryption device 50 through a transmission path with a communication speed of 60 kbps. This communication text (plain text) is input to the multiplexing section 51 through the input / output section 21a. In the multiplexing unit 51, the encryption synchronization monitoring data created by the encryption synchronization monitoring unit 53 is added. The encryption synchronization monitoring data has a communication speed of 4 kbps.

  The communication text (plain text) and the encryption synchronization monitoring data in the multiplexing unit 51 are multiplexed data, and the communication speed is 64 kbps. This data is encrypted by the encryption unit 22 based on the pseudo random number generated by the pseudo random number generation unit 23a. The encrypted data is output as communication speed data of 64 kbps through the input / output unit 21b.

  Next, decoding will be described. Encrypted data from a corresponding device of the same type, which is input as communication speed data of 64 kbps through the input / output unit 21b, is decrypted by the decryption unit 24 based on the pseudorandom number generated by the pseudorandom number generation unit 23b. (It will be plaintext.) This plain text is divided by the dividing unit 52 into 4 kbps encryption synchronization monitoring data and 60 kbps communication text (plain text).

  The communication text (plain text) is supplied to the terminal device 10 through the input / output unit 21a, and the communication text (plain text) is displayed on the display. On the other hand, the encryption synchronization monitoring data is supplied to the encryption synchronization monitoring unit 53, and it is determined whether or not it is correctly decrypted. As a result of the determination, when the data is not correctly decrypted, the generation synchronization of the continuous pseudo random numbers between the corresponding devices is not matched. If the generation synchronization of the continuous pseudo random numbers between the corresponding devices is not matched, the encrypted data cannot be decrypted by the corresponding device. For this reason, the control which resets the generation | occurrence | production synchronization of a continuous pseudorandom number according to a predetermined procedure between corresponding apparatuses is performed. Each operation described above is controlled by a control program stored in a ROM (not shown) inside the control unit 26.

  As described above, the conventional encryption system has a problem that the encryption apparatus is not provided with means for verifying the security of the encrypted data and further means for confirming the correctness of the decrypted data.

  In addition, in a conventional encryption system, when a transmission line having a communication speed of 64 kbps is used, a transmission line capacity of 4 kbps is used in order to confirm generation synchronization of continuous pseudo random numbers. For this reason, there is a problem that the capacity for transmitting the communication text is reduced and it takes an extra time to transmit the communication text. For this reason, it is desired to provide a method and apparatus for confirming the generation and synchronization of continuous pseudo-random numbers while using all transmission lines with a communication speed of 64 kbps in communication text.

  Furthermore, since the encryption synchronization monitoring data needs to be able to reliably determine encryption synchronization between the corresponding devices, it is often fixed data, and there is a problem that it is easy to give a clue for analyzing the encryption data. Therefore, it is desired to provide an apparatus that performs cryptographic synchronization monitoring without exchanging fixed data.

  In order to solve the above-described problem, a stream encryption apparatus that performs encryption and decryption based on continuous pseudo-random numbers includes an encryption unit, a decryption unit, and a randomness detection unit.

  The randomness detection unit is characterized by detecting the entropy of the decrypted data and detecting the entropy of the encrypted data.

  Furthermore, it is characterized by detecting the loss of encryption synchronization by detecting the entropy of the decrypted data. In addition, the security of the encrypted data is detected by detecting the entropy of the encrypted data.

  As described above in detail, the present invention produces an effect of determining the security of encrypted data by calculating the entropy value of the encrypted data. In addition, it is possible to determine the correctness of the decoded data by calculating the entropy value of the decoded data.

  With a simple configuration including the encryption unit, the decryption unit, and the randomness detection unit, it is possible to detect loss of encryption synchronization without reducing the communication speed of the communication text. Further, by calculating the entropy value of the encrypted and decrypted data in the random number detection unit, it is possible to detect loss of encryption synchronization without performing transmission / reception of fixed data for detection of encryption synchronization.

  The best mode for carrying out the invention will be described below by way of examples. 1 and 2, components having the same functions as those of the prior art described in FIGS. 3 and 4 are denoted by the same reference numerals. FIG. 2 is an overall configuration diagram of a stream cipher system using continuous pseudo-random numbers according to the present invention. Here, the output from the terminal device 10 is connected to the encryption device 20 at a communication speed of 64 kbps. Hereinafter, all transmission lines connected to corresponding devices of the same type are connected at a communication speed of 64 kbps.

  Details of the encryption device 20 will be described with reference to FIG. First, encryption will be described. The communication text (plain text) created by the terminal device 10 is sent to the encryption device 20 through a transmission path with a communication speed of 64 kbps. This communication text (plain text) is encrypted by the encryption section 22 through the input / output section 21a based on the pseudo random number generated by the pseudo random number generation section 23a. The encrypted data is output to the line termination 30 as communication speed data of 64 kbps through the input / output unit 21b.

  At the same time, the data encrypted by the encryption unit 22 is input to the random number detection unit 25. Here, the randomness detecting unit 25 verifies the security of the encrypted data according to the entropy principle described later. If it is determined that the verification result is not safe (not encrypted), the result is notified to the control unit 26 and encrypted by a control program stored in a ROM (not shown) of the control unit 26. The encryption failure is displayed on the display (not shown) of the control unit 26, and the encryption operation is stopped. Thereafter, in order to start the encryption operation again, after removing the cause of the encryption failure, the encryption operation is restarted by a predetermined procedure.

  Next, decoding will be described. Encrypted data from a corresponding device of the same type, which is input as communication speed data of 64 kbps through the input / output unit 21b, is decrypted by the decryption unit 24 based on the pseudorandom number generated by the pseudorandom number generation unit 23b. (It will be plaintext.) This plain text is supplied to the terminal device 10 via the input / output unit 21a, and the communication text (plain text) is displayed on the display.

  At the same time, the data decrypted by the decryption unit 24 is input to the randomness detection unit 25. The randomness detection unit 25 confirms the correctness of the decrypted data according to the entropy principle described later. As a result of the confirmation, if it is determined that the data has not been correctly decoded, the generation and synchronization of the continuous pseudo random numbers between the corresponding devices are not matched. For this reason, the encrypted data cannot be decrypted by the corresponding device, and control is performed between the corresponding devices to reestablish and synchronize the generation of continuous pseudo random numbers by a predetermined procedure. Each operation described above is controlled by a control program stored in the ROM inside the control unit 26.

  Here, the randomness detection unit 25 will be described. In general, data encrypted by an encryption device has a characteristic that randomness is high (random characteristics have no characteristic). The more ideal the encryption device, the higher the randomness (the greater the entropy of the information source). This is because the more characteristic the encrypted data is, the easier it is to analyze the encrypted data.

  A set of data with high randomness has a large amount of entropy of the information source (unencrypted data (plain data) has some characteristics and has a small entropy of the information source compared to the random number). Focusing on this point, it is possible to verify the security of the encrypted data by calculating the entropy size of the encrypted data.

  Further, when the received encrypted data is decrypted, it is possible to verify whether or not the decrypted data is correctly decrypted by calculating the entropy size of the decrypted data.

In general, the entropy of information sources (Shannon entropy) is, for example, information in which n types of characters appear at random with appearance frequencies (appearance probabilities) p ₁ , p ₂ ... P _n (Σp _i = 1). The source entropy H is
H = NΣp _i log ₂ (1 / p _i ) N: given by the number of characters in a certain range.

If it is assumed that 1 character is 8 bits and 256 characters are encrypted, assuming that the encrypted data is an ideal random number, the appearance frequency of each character is 1/256, and its entropy H ₀ is
H ₀ = 256 (1/256 log ₂ 256) = 8
Thus, it can be seen that the entropy of the information source is maximized and ideal encryption is performed.

This time, if the encrypted data of 256 characters is decrypted, and the 256 characters after decryption have the following appearance frequency,
・ Two types of characters 32 times each ( _pi = 32/256)
・ 4 types of characters 16 times each ( _pi = 16/256)
・ Eight kinds of characters 8 times each ( _pi = 8/256)
-64 types of characters once each ( _pi = 1/256)
The source entropy H is
H = 2 (32 / 256log ₂ 256/32) + 4 (16 / 256log ₂ 256/16) + 8 (8 / 256log ₂ 256/8)
+64 (1 / 256log ₂ 256) = 0.75 + 1 + 1.25 + 2 = 5
It becomes.

The entropy H is clearly a smaller value than H ₀ , and it can be seen that the 256 characters in this case have characteristics that are far from ideal random numbers. In other words, it is possible to determine that the encrypted data is correctly decrypted by calculating the entropy value and to determine that the encrypted data is safe. Further, when the decrypted data (plain text) has few features and is close to a random number, the entropy value takes a large value. Therefore, by setting the entropy value to 7 or more, for example, it is possible to determine that decoding has not been correctly performed.

Furthermore, in order to strictly calculate the entropy value that determines the security of the encrypted data or that it can be correctly decrypted, increase the number of samples of the encrypted or decrypted data for entropy calculation. (For example, 2 ¹⁶ characters) or 256 character samples are performed several times (for example, 5 times) at regular time intervals, and the average value of the entropy calculation values of each sample is used, so that more accurate judgment can be made. It is also possible to devise.

  According to the applicant, using a 64-kbps digital line, an encryption device is arranged oppositely via a line termination, and a digital telephone device (incorporated with a 64-kbps PCM voice encoding process) is connected as a terminal device of the encryption device. On the transmission side of the device, plain data is converted into voice encoded (64 kbps PCM) data, this data is encrypted and transmitted, and a test is performed to decode it on the reception side. The entropy value is calculated with 8 bits 256 characters. When the value is less than 7, the decryption is normally performed, and when the value is 7 or more, the decryption is abnormal (the encryption synchronization is lost).

The figure explaining the detail of the encryption apparatus of this invention The figure explaining the encryption system of this invention The figure explaining the detail of the conventional encryption apparatus A diagram for explaining a conventional cryptographic system

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Terminal device 20 Cryptographic device 21a Input / output unit 21b Input / output unit 22 Encryption unit 23a Pseudorandom number generation unit 23b Pseudorandom number generation unit 24 Decryption unit 25 Randomness detection unit 26 Control unit 30 Line termination

Claims (6)

In a stream cipher that performs encryption and decryption based on continuous pseudo-random numbers,
A stream encryption apparatus comprising: an encryption unit, a decryption unit, and a randomness detection unit.   The stream cipher apparatus according to claim 1, wherein the random number detection unit detects entropy of decrypted data.   The stream cipher apparatus according to claim 1, wherein the randomness detection unit detects entropy of encrypted data.   The stream cipher apparatus according to claim 1, wherein the random number detection unit detects entropy of encrypted data and decrypted data.   5. The stream cipher apparatus according to claim 2, wherein a loss of encryption synchronization is detected by detecting entropy of the decrypted data. 6.   The stream encryption device according to any one of claims 3 to 4, wherein security of the encrypted data is detected by detecting entropy of the encrypted data.

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