JPS6281145A - Data encryption method - Google Patents

Abstract

PURPOSE:To enhance the secrecy of ciphering by deciding the order of replacement from both of a key and an input data. CONSTITUTION:The key K is inputted externally and stored in a key register 1. A pseudo random number series generator 2 generates a pseudo random number series one after another according to the content of the key register 1. An address generator 3 inputs a pseudo random number generated by the pseudo randiom number generator 2 and an output data just before and generates an address of a data to be outputted next. The data in an input data buffer 4 designated by the address generated by the address generator 3 is outputted. The outputted data is inputted to a delay device 5 and becomes an input of the address generator of the next cycle. The operation above is repeated by 256 times being number of blocks in the input data buffer 4 to complete the ciphering processing to one input data.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a data encryption method for the purpose of concealing information or protecting data, and particularly to a method that makes it difficult for a third party to decrypt or modify the data. [Background of the Invention] Conventionally, a method is known in which input data is divided into blocks and encrypted or decrypted by exchanging the positions of each block. An example of applying this method to document images is the method disclosed in Japanese Patent Laid-Open No. 59-32243.

However, in conventional methods including the above example, the replacement order itself is an encryption key (hereinafter simply referred to as the key), or the replacement order determined by the key is used to perform the replacement, so different input data Also, the exchange is performed in a fixed order, resulting in a decrease in cryptographic strength and a disadvantage that a third party can easily decrypt or modify the data, resulting in a decrease in reliability.

Conventionally, as a method for increasing encryption strength, there is a feedback method, that is, a method of encrypting using a procedure depending on input data. According to this method, even if different input data are encrypted with the same key, it is generally difficult to decipher because the encryption procedures are different. However, in the encryption method using permutation, there is no known method that incorporates feedback.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a more reliable data encryption method.

[Summary of the invention]

In order to achieve the above object, the present invention realizes the above feedback and increases the encryption strength by determining the replacement order from both the key and the input data.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Figure 1 shows an encryption device.
is the parameter, and outputs the data obtained by encrypting the input data. The cryptographic conversion here is a swapping of the positions of input data. It is also assumed that the input data is encrypted every 256 bytes, and the block that is the unit of replacement consists of 1 byte. Of course, other combinations of the input data length and block length may be used.

First, prior to encryption, IIK is input from the outside,
Stored in key register l. The pseudo random number sequence generator 2 is
According to the contents of the key register 1, pseudorandom number sequences are generated one after another by, for example, the congruence method. The address generator 3 is
The pseudo-random numbers generated by the pseudo-random number generator 2 and the previous output data are input, and the address of the data to be output next is generated. However, when operating for the first time, it is assumed that the previous output data is 0.

It is assumed that input data divided into 256 bytes is stored in the input data buffer 4 prior to operation.

The data in the input data buffer 4 specified by the address generated by the address generator 3 is output. The output data is input to the delay device 5 and becomes the input to the address generator for the next cycle. The above operation is repeated 256 times for each block in the input data buffer 4, and the encryption process for one input data is completed. Next, new 256-byte input data is input, and after the contents of the input data buffer 4 are updated, the same operation is performed to perform the encryption process.

For unique decoding to be possible, the address generator 3 must generate each address from 0 to 255 once. FIG. 2 shows an example of an algorithm for generating such an address.

The pseudo-random number sequence generator 3 is assumed to generate a pseudo-random number rl of 0.0 or more and less than 1.0, and the 1-byte input data block bi is assumed to be an integer of 0 or more and 255 or less.

First, as an initialization, the sixth order (1) with bo set to O and the pseudo random number ri and the previous output data b ny are input. Here, 0.0≦rH<1.0°0≦b=−t≦255.

(2) j as mod(int(r1*(256i))+bi-1+2
56-i). int represents an integer, and mod (m, n) represents the remainder when m is divided by n. j is 0≦j≦256-i.

(3) Find the first smallest address among the addresses that have not been output so far.

(4) Output the address obtained in (3).

This process is repeated 256 times for i from 1 to 256. According to this algorithm, if rl is completely random, all permutation orders will occur with equal probability, so it is difficult to decipher it without knowing the key. Reliability is further improved because the parts are replaced differently. The process in Figure 2 is
It can be easily realized using a normal microprocessor or dedicated hardware.

Decoding is performed by exchanging the input data and output data in FIG. In other words, if you input the same key as when encrypting, the output of the address generator 3 will also be the same,
The data are sequentially stored in corresponding locations in the input buffer 4. 2
One decoding process is completed when the storage of 56 pieces of input data is completed.

However, in the case of decoding, the pseudo random number sequence and the previous input data are input to the address generator 3.

It goes without saying that higher encryption strength can be obtained by using the above encryption method in combination with another encryption method, such as a sum encryption method that takes an exclusive OR with a pseudo-random number sequence.

Further, in this embodiment, only one-dimensional replacement was considered, but when applied to image data, it is easy to use two-dimensional replacement, and exactly the same effect can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, even if the same key is used, different input data are encrypted using completely different permutations, so that a more reliable encryption method can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the encryption device, and FIG. 2 is a diagram showing the processing contents of the address generator 3 in FIG. 1. 1...Key register, 2...Pseudorandom number sequence generator. 3... Address generator, 4... Input data buffer, 5... Delay device. Broom Z eye

Claims (1)

[Claims] In a device that encrypts or decrypts input data by dividing input data into blocks and replacing the positions of each block in the order determined by the encryption key, the replacement order is determined from both the input data and the encryption key. A data encryption method characterized by: