JPH10303882A - Enciphering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the reduction of cryptographic strength even when the quality of pseudo random number is adverse in the case of enciphering data while using the pseudo random number. SOLUTION: The elements of pseudo random number string B composed of 256 bytes are selected while defining the addresses and elements of the natural random number string A composed of 256 bytes having the almost uniform appearance frequency of respective numerical values as addresses and two selected elements are exchanged so that the pseudo random number string B is stirred by the natural random number string A. The new pseudo random number string of 256 bytes is prepared and by exclusively ORing this new pseudo random number string and data for the unit of 256 bytes, these data for the unit of 256 bytes are enciphered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an encryption method for encrypting data.

[0002]

2. Description of the Related Art Conventionally, in a facsimile apparatus, data obtained by reading a document is encoded by MH encoding, MR encoding, or the like, and then the encoded data is transmitted to a target facsimile apparatus. . In such communication between facsimile apparatuses, a technique is known in which encoded data is further encrypted and transmitted to a target facsimile apparatus in order to prevent the original data from being decoded from the transmitted encoded data. .

As an example of such an encryption technique, a technique of generating a pseudo random number and encrypting transmission data using the pseudo random number is proposed in Japanese Patent Laid-Open No. 2-249333.

The pseudo-random number is a kind of random number, and can be created, for example, by the following multiplication congruential method.

X _n = 16807X _n -1 (mod 2 ³¹ -1) where n is a natural number and X _n is the n-th element. Also,
mod indicates a modulo operation, and 16807 is a primitive root of 2 ³¹ -1.

More specifically, a predetermined number of times (for example, 256 times) is calculated using the above-described equation with a preset encryption key as an initial value, and the lower one byte is collected to form a set of pseudo-random numbers. create.

On the other hand, as the random numbers, besides the above pseudo random numbers, those called natural random numbers are also known. This natural random number is generated by the following method, for example. Prepare a roulette wheel with high precision eyes from 0 to 15, turn the roulette with a calm feeling, and record the number in hexadecimal (0-F). This is repeated a predetermined number of times (for example, 256 times) to form one natural random number sequence. Since the roulette is manufactured with high precision and the operator is mindless, there is no bias or periodicity in the appearance of the roulette.

In general, it is known that the appearance frequency of each numerical value is substantially uniform in natural random numbers, while the appearance frequency of each numerical value is sometimes biased in pseudo random numbers.

[0009] However, the above-mentioned Japanese Patent Application Laid-Open No. H2-224933 is disclosed.
In the technique described in Japanese Patent Publication No. 3, a single pseudo-random number is used for encryption of transmission data, so that the pseudo-random number is of sufficient quality as a random number (the appearance of each numerical value has no bias or periodicity). Otherwise, there is a problem that the encryption strength is reduced.

Although a technique of combining two types of pseudo random numbers to generate a new pseudo random number has also been proposed, in this case also, the pseudo random number used does not have sufficient quality as a random number as described above. Thus, there is a problem that the quality of the generated pseudo-random numbers also deteriorates.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and when data is encrypted using pseudo random numbers, even if the quality of the pseudo random numbers is poor, the encryption is performed. It is an object of the present invention to provide an encryption method capable of avoiding a decrease in strength.

[0012]

According to the conventional encryption method,
A pseudo-random number sequence generated by a single pseudo-random number sequence or a pseudo-random number sequence generated by combining two types of pseudo-random number sequences is used.
In the encryption method according to the invention described in 3, a new number sequence is generated by using a natural random number sequence and a pseudo random number sequence in which the appearance frequencies of the respective numerical values are substantially uniform, and the data is encrypted by the number sequence. And

According to the first aspect of the present invention, one of the pseudo random number sequence and the natural random number sequence generated based on a predetermined key is agitated by the other. That is, the pseudo random number sequence is agitated with the natural random number sequence, or the natural random number sequence is agitated with the pseudo random number sequence.

Although the details will be described later, the stirring here includes both the so-called stirring process and the so-called search process. The so-called stirring process corresponds to a first random number generation method of the first embodiment described later (see FIG. 4), and the so-called search process corresponds to a second random number generation method of the first embodiment described later (see FIG. 5). Equivalent to.

As described above, by performing agitation on a natural random number sequence in which the appearance frequency of each numerical value is substantially uniform as a random number sequence to be stirred or a random number sequence to be stirred, even if the quality of the original pseudo random number sequence is poor, It is possible to generate a sequence having no bias or periodicity with respect to the appearance of each numerical value (that is, a quality as a random number (good random number quality)). Therefore, by encrypting data using a sequence of high random number quality, a decrease in encryption strength can be avoided and the encryption strength can be maintained at or above a predetermined level.

Similarly to the above, a method of generating a sequence of good random number quality using a natural random number sequence and a pseudo random number sequence, and encrypting data by this sequence of good random number quality, claims 2 and 3 are provided. Can be cited.

According to the second aspect of the invention, two natural random number sequences are selected from a plurality of natural random number sequences based on a pseudo random number sequence generated based on a predetermined key, and the selected two natural random number sequences are selected. One natural random number sequence is mixed with the other natural random number sequence. Then, the data is encrypted by the sequence obtained by the stirring.

According to the third aspect of the present invention, one natural random number sequence is selected from a plurality of natural random number sequences based on a pseudo random number sequence generated based on a predetermined key, and the selected one natural random number sequence is selected. A predetermined natural random number sequence other than the plurality of natural random number sequences is mixed in the sequence. Then, the data is encrypted by the sequence obtained by the stirring.

Next, in the invention according to the fourth aspect, a predetermined random number sequence (pseudo random number sequence or natural random number sequence) is expanded and searched by the elements of the pseudo random number sequence generated based on the predetermined key. The sequence obtained by this expanded search is exclusive-ORed by a certain number to generate a pseudo-random sequence. Then, the data is encrypted by the generated pseudo random number sequence.

By thus generating the pseudo-random number sequence by combining the expanded search and the exclusive OR operation, even if the original pseudo-random number sequence has some deviation or periodicity, the generated pseudo-random number sequence is generated. The random number sequence has almost no bias or periodicity, and a pseudo-random number sequence with good random number quality can be obtained. Therefore, by encrypting data using the pseudo-random number sequence having a good random number quality, it is possible to avoid a decrease in encryption strength and maintain the encryption strength at a predetermined level or more.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of an encryption method according to the present invention will be described below with reference to the drawings.

[First Embodiment] First, a first embodiment according to claims 1 to 3 described in the claims will be described.

[Structure of Facsimile Machine for Executing Encryption Based on Encryption Method] First, the structure of a facsimile machine for executing encryption processing will be described. As shown in FIG.
The facsimile apparatus 10 according to the present embodiment includes a CPU 12 for controlling the entire facsimile apparatus 10, a ROM 14 as a memory storing a program for operating the CPU 12, a RAM 16 as a memory for storing data necessary for the operation of the CPU 12, an operator. Operating unit 18 for receiving an input from the MFP and displaying the status of the facsimile machine 10, an image reading unit 22 including a CCD and the like, which reads a document and binarizes the read data, and binarizes the image with the image reading unit 22 An encoder 24 for compressing and encoding the encoded image information, a memory having a built-in memory, writing the image information encoded by the encoder 24 in the memory, and performing encryption processing on the image information in cooperation with the CPU 12 Processing unit 2
6. a decoder 28 for decoding the compression-encoded image information;
An image recording unit 30 that prints out image information on recording paper or the like; a modem line control unit 32 that is connected to a public line 34 and sends out image information to the public line 34; It is configured to include an image storage unit 20 for temporarily storing the image information received by the control unit 32, and these are mutually connected via a data bus 36.

[Transmission / Reception Operation of Facsimile Machine]
A basic transmission / reception operation of the facsimile machine 10 will be described.

First, the transmission operation will be described with reference to FIG. When a transmission instruction is received from the operation unit 18 in step 102 shown in FIG.
After the image information obtained by the reading is encoded by the encoder 24, the encoded image information is temporarily stored in the image storage unit 20.

In the next step 106, a pseudo random number of 256 bytes is generated based on a pseudo random number generating method described later. In the next step 108, the image information stored in the image storage unit 20 is stored in the data
The image data is transferred to the memory No. 6 and the transferred image information in units of 256 bytes is subjected to an exclusive OR operation with the 256-byte pseudo-random number, thereby performing encryption processing on the image information. Then, the encrypted image information is transferred to the modem line control unit 32, and in step 110, the encrypted image information is transferred to the ITU-
It is sent to the public line 34 in the G3 facsimile error collect mode of T. In this way, the image information is encrypted and transmitted to the intended facsimile machine.

Thereafter, steps 106, 108 and 110 are repeated, and all image information is encrypted and transmitted to the intended facsimile machine. In the pseudo random number generation process of step 106, the pseudo random number is generated based on the plaintext of the previous block from the second time.

Next, the receiving operation will be described with reference to FIG. When the encrypted image information is received from the external facsimile machine in step 202 shown in FIG.
In 04, the received image information is converted into binary data by the modem line control unit 32 (that is, demodulated), and then transferred to the memory of the data processing unit 26.

At the next step 206, a 256-byte pseudo-random number is generated based on a pseudo-random number generation method described later. In the next step 208, the data processing unit 26
As in the case of transmission on the memory, the exclusive OR is performed on the demodulated 256-byte unit image information and the 256-byte pseudo random number, thereby decoding the image information. Then, in the next step 210, the decrypted 25
The 6-byte image information is stored in the image storage unit 20.

After that, steps 206, 208 and 210 are repeated to decode all the received image information, and the image storage unit 2
Store in 0. In the pseudo-random number generation process of step 206, the pseudo-random number is generated based on the previously decoded data in the second and subsequent times.

When all the received image information has been decoded and stored in the image storage section 20, the process proceeds to step 214, where the image information is taken out from the image storage section 20 and expanded by the decoder 28, and at the next step 216. The expanded image information is printed out on a recording paper or the like by the image recording unit 30.

[Operation of First Embodiment] Now, as an operation of the first embodiment, a random number generation method for generating a pseudorandom number used for encryption will be described.

First, a first random number generation method using so-called stirring processing will be described. (1) Generate a natural random number sequence in the following procedure. First, prepare a roulette wheel with 0 to 15 eyes that is manufactured with high precision, rotate this roulette wheel with a calm feeling, and record the eye in hexadecimal (0 to F). . This is repeated 256 times to form one natural random number sequence. Since the roulette is manufactured with high precision and the operator is mindless, there is no bias or periodicity in the appearance of the roulette.

(2) A pseudo random number sequence is created by the following multiplication congruential method. X _n = 16807X _n -1 (mod 2 ³¹ -1) (A) where n is a natural number and X _n is the n-th element.
Also, mod indicates a remainder operation, and 16807 indicates 2 ³¹ -1.
Is a primitive root of.

Using the encryption key preset from the operation unit 18 (see FIG. 1) as an initial value, 25 using the above equation (A).
The calculation is performed six times, and the lower one byte is collected to form one pseudo-random number sequence.

(3) A pseudo-random number sequence is created by mixing the 256-byte natural random number sequence generated in (1) and the 256-byte pseudo random number sequence generated in (2) in the following manner. .

The random number sequence (A) shown in FIG. 4 corresponds to the 256-byte natural random number sequence, and the random number sequence (B) corresponds to the 256-byte pseudo random number sequence generated in (2). Here, the element of the random number sequence (B) is selected using the address and the element of the random number sequence (A) as addresses, and these two elements are exchanged.

For example, the address 00H of the random number sequence (A)
(H means hexadecimal notation, the same applies hereinafter) and its element 03H
Are extracted, and the element at address 00H and the element at address 03H are exchanged in the random number sequence (B). Next, the address 01H of the random number sequence (A) and its element 02H are extracted, and the element of the address 01H and the element of the address 02H are exchanged in the random number sequence (B). Hereinafter, such element exchange is performed up to the address FFH of the random number sequence (A), thereby stirring the random number sequence (B) with the random number sequence (A).

A new pseudo-random number sequence is generated by the agitation described above. In the first random number generation method, since the pseudo-random number sequence is agitated with a natural random number sequence having no bias or periodicity in the sequence, the mixed pseudo-random number sequence (= the pseudo-random number sequence generated by (2)) Even if there is bias or periodicity, the generated pseudo-random number sequence hardly has bias or periodicity.

The facsimile apparatus 10 encrypts data by using a pseudo-random number sequence of good random number quality generated by such a first random number generation method. That is, by performing an exclusive OR operation on the 256-byte image information transferred to the memory of the data processing unit 26 and the 256-byte pseudo-random number generated by the first random number generation method, the encryption for the image information is performed. Process. Thus, the original pseudorandom number (=
Even if the pseudo-random number sequence generated in (2) has some bias or periodicity, it is possible to avoid a decrease in encryption strength in the encryption processing.

In the first random number generation method,
The pseudo random number sequence generated in (2) is the random number sequence (A) in FIG.
In addition, the natural random number sequence generated in (1) may be made to correspond to the random number sequence (B) in FIG. 4, respectively, and a new pseudo random number sequence may be generated by agitating the natural random number sequence with the pseudo random number sequence. . Even in this case, even if the original pseudo random number sequence has some bias or periodicity, the generated pseudo random number sequence has almost no bias or periodicity, and a pseudo random number sequence with good random number quality can be obtained.

Next, a second random number generation method using a so-called search process will be described. Since the procedure for generating the natural random number sequence and the pseudo random number sequence is the same as the first random number generation method,
Description is omitted.

The random number sequence (A) shown in FIG. 5 corresponds to a 256-byte natural random number sequence, and the random number sequence (B) corresponds to a 256-byte pseudo random number sequence. Here, the element of the random number sequence (B) is selected using the element of the certain address of the random number sequence (A) as the address, and the element of the selected random number sequence (B) is set as the element of the certain address.

For example, since the element of the address 00H of the random number sequence (A) is 03H, the address 03 of the random number sequence (B) is
The element C3H of H is selected, and the selected element C3H is set as the element of the address 00H. Next, since the element of the address 01H of the random number sequence (A) is 02H, the element C2H of the address 02H of the random number sequence (B) is selected, and this selected element C2H is set as the element of the address 01H. Further, since the element of the address 02H of the random number sequence (A) is FFH,
Select the element CFH of the address FFH of the random number sequence (B),
The selected element CFH is set as the element of address 02H. Hereinafter, by selecting such an element up to the address FFH of the random number sequence (A), the random number sequence (A) is searched for the random number sequence (B).

Thus, a new pseudo-random number sequence is generated. In the second random number generation method, the pseudo-random number sequence is agitated with a natural random number sequence having no bias or periodicity in the sequence, so that the agitated pseudo-random number sequence (= original pseudo-random number sequence) exhibits some bias and periodicity. Even if it has, the generated pseudo-random number sequence has almost no bias or periodicity.

In the facsimile apparatus 10, since the data is encrypted by using the pseudo random number sequence having good random number quality generated by the second random number generating method as described above, the original pseudo random number has some deviation or periodicity. , It is possible to avoid a decrease in encryption strength in the encryption processing.

In the second random number generation method, the pseudo-random number sequence corresponds to the random number sequence (A) in FIG. 5, and the natural random number sequence corresponds to the random number sequence (B) in FIG. A new pseudo random number sequence may be generated by searching for a natural random number sequence. Even in this case, even if the original pseudo random number sequence has some bias or periodicity, the generated pseudo random number sequence has almost no bias or periodicity, and a pseudo random number sequence with good random number quality can be obtained.

As a modified example of the first and second random number generation methods, a random number generation method of generating a new pseudo random number sequence using a plurality of natural random number sequences and a pseudo random number sequence as described below is also effective. It is.

(S1) 256 natural random number sequences are prepared by the procedure shown in (1) of the first random number generation method.

(S2) A pseudo random number sequence is generated by the procedure shown in (2) of the first random number generation method, and the pseudo random number sequence is used in order from the beginning to obtain two natural random numbers from 256 sets of natural random number sequences. Select a column.

(S3) The first random number generation method or the second random number generation method
By mixing one of the selected two natural random number sequences with the other, a new pseudo random number sequence is generated.

The pseudo-random number sequence generated in this way has almost no bias or periodicity, and a pseudo-random number sequence with good random number quality can be obtained.

In the above (S2), two natural random number sequences are selected. However, three or more natural random number sequences are selected, two of them are taken out in order, and the stirring of (S3) is repeated. Thus, a new pseudo-random number sequence may be generated.

Further, in the above (S2), one natural random number sequence is selected from the 256 sets of natural random number sequences by using the pseudo random number sequences in order from the beginning, and the selected one natural random number sequence and the previously generated natural random number sequence are generated. In another natural random number sequence, a new pseudo random number sequence may be generated by mixing one with the other.

[Second Embodiment] Next, a second embodiment according to the invention described in claim 4 will be described. Note that the configuration of the facsimile apparatus and the transmission / reception operation in the second embodiment are the same as those in the first embodiment, and a description thereof will be omitted.

A random number generating method for generating a pseudo random number used for encryption will be described as an operation of the second embodiment with reference to FIG.

As shown in FIG. 6, a random number sequence A and a random number sequence B having a 4-byte element at one address are created in advance. Of these, the random number sequence A is created using a pseudo random number sequence generated based on a predetermined encryption key. The random number sequence B is created using either a pseudo random number sequence or a natural random number sequence. For example, the first random number sequence generation method and the second random number sequence generation method described above are applied to one address with 4
By executing it once, a random number sequence having 4-byte elements at one address can be created.

(1) One element of random number sequence A (4 bytes)
Is decomposed into four by one byte, and four elements (4 bytes) of the random number sequence B are searched using the decomposed one byte as an address of the random number sequence B (so-called expanded search is performed).

For example, when the element of the address 00H of the random number sequence A is 02H, 03H, FEH, FFH, the element of the address 02H (00H, 01
H, 02H, 03H), address 03H element (10
H, 11H, 12H, 13H), elements of address FEH (20H, 21H, 22H, 23H), and address F
The element of FH (30H, 31H, 32H, 33H) is searched.

(2) Exclusive OR is performed on each of the data obtained by the enlarged search with the corresponding bytes. The exclusive OR operation result (4 bytes) is used as new pseudo-random number sequence data.

In the above example, the corresponding 00H, 10H, 2
An exclusive OR is performed between the data of 0H and 30H, and 00H
Get H. Similarly, the corresponding 01H, 11H, 21H,
Exclusive-OR is performed on the data of 31H to obtain 00H. Further, exclusive OR is performed between the corresponding data of 02H, 12H, 22H, and 32H to obtain 00H. Furthermore, exclusive OR is performed between the corresponding data of 03H, 13H, 23H, and 33H to obtain 00H. The four bytes (00H, 00H, 00H, 00
H) is the element of the address 00H of the new pseudo-random number sequence.

(3) A new pseudo-random number sequence is obtained by repeating the expanded search of (1) and the exclusive OR operation of (2).

As described above, by generating a pseudo-random number sequence by combining an extended search and an exclusive OR operation,
Even if the pseudo-random number sequence A has some bias or periodicity, the generated pseudo-random number sequence has almost no bias or periodicity, and a pseudo-random number sequence with good random number quality can be obtained.

In the facsimile apparatus 10, the data is encrypted by using the pseudo-random number sequence of good random number quality generated by such a random number generation method. That is, the data processing unit 2
The exclusive OR of the 256-byte image information transferred to the memory No. 6 and the 256-byte pseudo-random number generated by the above-described random number generation method performs an encryption process on the image information. As a result, it is possible to avoid a decrease in encryption strength in the encryption processing.

In the above first and second embodiments, the example in which the encryption method according to the present invention is applied to the facsimile apparatus is shown. However, the encryption method according to the present invention can be applied to data other than the facsimile apparatus. It can be applied to all devices that transmit and receive.

[0066]

According to the present invention, even if the quality of the pseudo-random number sequence from which the sequence is generated is poor, a sequence with good random number quality can be generated. The strength can be maintained at or above a predetermined level.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a facsimile apparatus according to first and second embodiments.

FIG. 2 is a flowchart showing a processing routine of a transmission operation in the facsimile apparatus of FIG. 1;

3 is a flow chart showing a processing routine of a receiving operation in the facsimile apparatus of FIG.

FIG. 4 is a diagram showing an outline of a first random number generation method in the first embodiment.

FIG. 5 is a diagram illustrating an outline of a second random number generation method in the first embodiment.

FIG. 6 is a diagram illustrating an outline of a random number generation method according to a second embodiment.

[Explanation of symbols]

 10 Facsimile machine 12 CPU 26 Data processing unit

Claims (4)

[Claims] 1. An encryption method characterized by encrypting data with a sequence obtained by mixing one of a pseudo-random number sequence and a natural random number sequence generated based on a predetermined key with the other. . 2. A natural random number sequence is selected from a plurality of natural random number sequences based on a pseudo random number sequence generated based on a predetermined key, and one natural random number sequence of the selected two natural random number sequences is selected. An encryption method characterized in that data is encrypted by a sequence obtained by stirring with another natural random number sequence. 3. A natural random number sequence is selected from a plurality of natural random number sequences based on a pseudo random number sequence generated on the basis of a predetermined key, and the plurality of natural random number is selected by the selected one natural random number sequence. An encryption method characterized by encrypting data with a sequence obtained by agitating a predetermined natural random number sequence other than a sequence. 4. A pseudo-random number sequence obtained by enlarging and searching a predetermined random number sequence with elements of a pseudo-random number sequence generated based on a predetermined key. An encryption method characterized by encrypting data with a random number sequence.