JP2546504B2 - Pre-encryption processing device and post-decryption processing device in encryption - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encryption / decryption device.

[0002]

2. Description of the Related Art DES (Sho 51-108701 cryptographic device, for example, "Modern cryptographic theory" written by Shinichi Ikeno and Kenji Koyama,
(Explanation in Chapter 3 of the Institute of Electronics, Information and Communication Engineers 1986)
The conventional cryptosystems, such as RSA and RSA (discussed in Chapter 6 of "Modern Cryptography" above), are divided into blocks by dividing plaintext into certain lengths, and each block is encrypted independently or sequentially. It is characterized by obtaining the ciphertext of the whole plaintext by doing.

Generally, in the conventional encryption system as described above, when an attempt is made to encrypt a large file or communication text, the plain text is divided into many blocks. These blocks are usually encrypted with the same key. If the plaintext of many blocks encrypted with such an identical key becomes known to the decryption person, there is a risk that it may be a clue to deduce the secret key.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to make it difficult in cryptographic systems to easily deduce the secret key even if both the ciphertext and the plaintext are known to the decrypter. It is to provide an encryption pre-processing device and a decryption post-processing device.

[0005]

According to a first aspect of the present invention, there is provided an encryption preprocessing device for inputting a plaintext string to be encrypted in an encryption preprocessing device for performing preprocessing of an input of an encryption device. A block unit that divides the input plaintext string into blocks by dividing it into predetermined lengths, a random number generator that repeatedly generates random bits, and each block that is blocked by the block unit. Inserting means for inserting a random bit generated by the random number generating means at a predetermined position, and output means for sequentially passing the block in which the random bit is inserted by the pre-inserting means to the encryption device. Is characterized by.

A decryption post-processing device according to a second aspect of the present invention is a decryption post-processing device that performs post-processing on an output of a decryption device for decrypting a ciphertext and outputs a plaintext, and outputs a plaintext string decrypted from the encryption device. Input means for receiving, blocking means for dividing the input plaintext string into blocks by a predetermined length, and a predetermined position from each block blocked by the blocking means. The present invention is characterized by including redundant bit removing means for removing bits and plaintext string output means for outputting the plaintext string processed by the preceding arrival redundant bit removing means as a final plaintext.

[0007]

The pre-processing and post-processing of encryption in the present invention will be described.

Generally, a cryptosystem is required not only to be able to infer a plaintext from a ciphertext but also to be unable to easily infer an encryption key from a set of a ciphertext and a plaintext.

In the pre-encryption processing apparatus and the post-decryption processing apparatus of the present invention, a redundant bit is inserted into the original plaintext to generate a plaintext that is actually input to the encryption apparatus. Since the bit string to be inserted can be generated immediately before the encryption processing in the same device as the device that performs the encryption, the possibility that the content will be leaked to a third party is significantly smaller than that of ordinary plain text. Therefore, even if the original plaintext is leaked, there is almost no possibility that the entire plaintext actually used for encryption is known, and as a result, a known plaintext attack is less likely to occur.

Further, it is not necessary to discuss the contents of the bit to be inserted with the receiver in advance, it is sufficient to discuss only the block length and the position of the bit to be added, and the information is kept secret. There is no need.
Therefore, the secret information that the sender and the receiver have to manage does not increase.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an encryption preprocessing device of the first invention, FIG. 2 shows an example of the configuration of a random number generating means used in the embodiment of FIG. 1, and FIG. An embodiment of the post-decoding processing device has been shown.

The encryption preprocessing device shown in FIG .
For encryption devices configured based on RSA and other methods
Security of the encryption device prior to encryption processing
The processing for performing is performed. The before encryption processing apparatus, the plaintext string input means 11, the blocking means 12, random number generation means 13, insertion means 14 and output means 15 Tona
Input is given to each means other than the random number generation means 13.
And perform a certain work to issue an output and wait for the next input
Repeat a series of actions to enter. Plaintext input means 11
Has the function of importing plaintext from the outside,
It has a function of passing the sentence to the blocking means 12. Bro
The conversion means 12 receives the plaintext from the plaintext input means 11.
Then, it is divided into a certain number of bits and passed to the inserting means 14.
You. The random number generation means 13 automatically generates a random number and inserts it.
Deliver to the means 14. The inserting means 14 is a blocking means
Block from 12 and random number from random number generating means 13
When you take it, insert a random number in a certain position of the block and output it.
Hand over to dan 15. The output means 15 communicates with the encryption device.
Interface function and receives from the insertion means 14.
Received block as an input to the encryption device.
Give it away.

FIG. 2 shows an example of the configuration of the random number generating means 13, which is a component of the encryption preprocessing device of the first invention.
In this example, DES encryption is performed using a time stamp in the computer as an encryption key and an initial constant as plaintext, and the ciphertext is regressed to repeatedly perform encryption. At this time, the leading 1 bit of the ciphertext is passed to the inserting means 14 as a random bit. The function as the random number generation means 13 is realized by performing encryption by the DES every time the insertion means 14 requests one random bit.

The post-decryption processing device shown in FIG .
In a cryptographic device configured based on SA or other method
Subsequent to the decryption process, the security of the encryption device is enhanced.
A process corresponding to the process of FIG. 1, which is a process for saving
Is to be applied. The decoder post-processing apparatus includes an input unit 3
1, blocking means 32, the redundant bit removing unit 33, Ri plaintext sequence output unit 34 Tona, each unit is given inputs
And perform a certain work to issue an output and wait for the next input
Repeat a series of actions to enter. The input means 11 is
It has the function of the interface with the encryption device.
Receive the output of the device and pass it to the blocking means 32
Have a function. Whether the blocking means 32 is the input means 31
When data is received from it, it is separated by a certain number of bits and redundant
It is delivered to the bit removing means 33. Redundant bit removing means 3
4 is from the block received from the blocking means 32
The bit at a fixed position is removed and received by the plaintext string output means 34.
Give it away. The plaintext string output means 34 is the redundant bit removing means 33.
The data received from the device is output to the outside of the device.

An example of the structure of each bit string in the above embodiment is shown in FIG. In FIG. 4, the original plaintext string represents the one already blocked by the blocking means 12. This block length does not necessarily have to match the block length unique to the encryption device. Original plaintext sequence (p
1, p2 ,. . . ) Is a plaintext string received by the plaintext string input means 11 from the outside and a plaintext string output by the plaintext string output means 33 to the outside in the above embodiment, and the plaintext for the cryptographic device is output from the output means 15 of FIG. 3 is a bit string that is handed to the encryption unit of and the handing to the input unit 31 of FIG. 3 from the decryption unit of the cipher chaining device. The portion drawn in black is inserted by the inserting means 14 and the redundant bit removing means 33 is inserted.
Corresponds to redundant bits removed in.

[0016]

According to the present invention, a random bit is inserted as redundant information in a predetermined position of a block to be encrypted, and the redundant bit can be generated completely independently of the other bits. If it is deciphered, there is no danger of it leaking to others. Therefore, in the selective plaintext attack, this bit becomes unknown information even for a decryption person who can make a known plaintext attack, which makes the decryption difficult. A legitimate recipient of the ciphertext does not need to know this redundant bit in advance at the time of decryption, and secret information to be shared does not increase. Therefore, the security of the conventional encryption method can be further enhanced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an encryption preprocessing apparatus of the first invention.

FIG. 2 is a block diagram showing an example of the configuration of the random number generating means in the first invention.

FIG. 3 is a block diagram showing an embodiment of a post-decoding processing device of the second invention.

FIG. 4 is a diagram showing an example of a structure of a bit string handled in the present invention.

[Explanation of symbols]

 11 Plain Text Sequence Input Means 12 Blocking Means 13 Random Number Generating Means 14 Inserting Means 15 Output Means 21 Encrypting Device DES 31 Input Means 32 Blocking Means 33 Redundant Bit Removing Means 34 Plain Text Sequence Output Means

Claims (2)

(57) [Claims] 1. An encryption preprocessing device for performing preprocessing of an input of an encryption device, input means for inputting a plaintext string to be encrypted, and input plaintext strings for each predetermined length. Blocking means for dividing into blocks, random number generating means for repeatedly generating random bits, and random numbers generated by the random number generating means at predetermined positions of each block blocked by the blocking means. An encryption pre-processing device in encryption, comprising: an inserting means for inserting a bit, and an output means for sequentially passing blocks in which random bits are inserted by the pre-inserting means to an encryption device. 2. A decryption post-processing device that performs post-processing on the output of a decryption device for decrypting ciphertext to output plaintext, and input means for receiving the decrypted plaintext sequence from the encryption device. Blocking means for dividing the plaintext sequence into blocks by dividing it into predetermined lengths, and redundant bit removing means for removing bits at predetermined positions from each of the blocks blocked by the blocking means. A decryption post-processing device for encryption, comprising plaintext string output means for outputting the plaintext string processed by the redundant bit removing means as a final plaintext.