JPH1173102A - Secret key ciphering/deciphering method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize ciphering and deciphering of arithmetic code having high secrecy without reducing encoding efficiency by taking an initial value of a corresponding section as a ciphering key in a section dividing/selecting process. SOLUTION: The initial value of a corresponding section is taken as a secret key [0, 1-K), (K is a positive real number). When the initial value of the corresponding section is changed, a partial section obtained by dividing the corresponding section [0, 1-K) based on a symbol appearance probability P0, P1 of a symbol Xi is changed into a partial section A0', A1', and a coordinate of a code point C obtained from the result wherein the section dividing/selecting process is repeated is also changed. Therefore, in the case that the initial value [0, 1-K) of the corresponding section is not known, the arithmetic code is not correctly deciphered, the initial value [0, 1-K) is held as the secret key by the ciphering side and the deciphering side, thereby a cryptographic system is formed. Since the initial value of the corresponding section is optionally set within the range wherein a sectional width does not become negative on a straight line of the real number, the secrecy of a cipher is high and then the cipher is not easily decoded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secret key encryption method and a decryption method using arithmetic codes, and an apparatus therefor.

[0002]

2. Description of the Related Art With the spread of computer networks, various encryption methods have been proposed as techniques for protecting important information from attacks such as eavesdropping and obstruction by third parties. Encryption uses an encryption key to convert the original message into an encrypted message that is difficult for a third party to understand, and then converts the encrypted message into the original message using a decryption key. This is to prevent attacks by three parties. The encryption method is different from the secret key encryption method in which the sender and the receiver secretly share the same key, and the encryption key and the decryption key. The encryption key is made public and the decryption key is received. There is a public key cryptosystem that a person keeps secret.

On the other hand, arithmetic coding is known as a coding method for reversibly and efficiently compressing data. Arithmetic coding divides a corresponding section on a real line [0, 1) into unequal lengths according to the occurrence probability of a symbol to be coded, selects a corresponding section corresponding to the symbol, and recursively selects the corresponding section. The processing is repeated, and the coordinates in the obtained section are represented by at least a binary decimal distinguishable from other sections, and are used as codes as they are.
This arithmetic coding has been adopted as an international standard for the still image compression system.

By the way, as a method of encrypting data simultaneously with data compression, a method of encrypting an arithmetic code is, for example, one.
Proposed in 1999 by IEICE IT91-34, pp. 17-20, "Secret Key Cryptography Using Arithmetic Codes". In this method, the order of data symbols when the corresponding section on the real axis is divided in the order of data symbols is used as a secret key. Here, the order of the data symbols is, for example, in the case of a quaternary symbol {a, b, c, d}, dividing the corresponding section into a, b, c, d in the order of b, d, c , A in this order.

[0005]

However, in the above-described conventional secret key cryptosystem using an arithmetic code, when the number of symbols is small, such as a binary symbol {0, 1}, for example. Has a drawback that it is weak in brute force decryption because the number of combinations of symbol order is small. . For this reason, there is a problem that the coding efficiency is reduced.

[0006]

The present invention employs the following structure to solve the above problems. <Structure 1> Based on the symbol appearance probability of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that the information of interest can take. A segment division selecting step of selecting a subsection corresponding to the symbol of the information of interest from; In the section division selecting step, a secret key encryption method is characterized in that an initial value of the corresponding section is used as an encryption key.

<Structure 2> A method of decrypting an encrypted arithmetic code and decoding the arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-sections representing symbols that can be taken by the information of interest, and a sub-section selection step of selecting a sub-section corresponding to an arithmetic code from the plurality of divided sub-sections, An arithmetic code decoding step of decoding an arithmetic code on the basis of the set partial section, wherein the section division selecting step uses the initial value of the corresponding section as a decoding key. Method.

<Structure 3> A secret key encryption / decryption method characterized by having the secret key encryption method of Structure 1 and the secret key decryption method of Structure 2.

<Structure 4> Based on the symbol appearance probabilities of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing the symbols that the information of interest can take, and the plurality of divided sections are divided. A section division selection unit that selects a partial section corresponding to the symbol of the information of interest from the section,
An arithmetic code forming unit configured to form an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit, wherein the section division selecting unit uses an initial value of the corresponding section as an encryption key. A secret key encryption device characterized by the above-mentioned.

<Structure 5> An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-sections representing symbols which can be taken by the target information, and a section division selection unit for selecting a sub-section corresponding to an arithmetic code from the plurality of divided sub-sections, and An arithmetic code decoding unit for decoding an arithmetic code based on the divided sub-interval, wherein the interval division selecting unit uses an initial value of the corresponding interval as a decoding key. apparatus.

<Structure 6> A secret key encryption / decryption device comprising the secret key encryption device of Configuration 4 and the secret key decryption device of Configuration 5.

<Structure 7> An adaptive symbol appearance probability estimation step of adaptively estimating the symbol appearance probability of information of interest to be encoded based on the already encoded reference information sequence;
Based on the symbol appearance probabilities estimated in the adaptive symbol appearance probability estimation step, the corresponding section on the probability number line is divided into a plurality of sub-sections representing symbols that can take information of interest. A section division selecting step of selecting a subsection corresponding to the symbol of the information of interest from among the above, and an arithmetic code configuring step of configuring an arithmetic code of the information of interest based on the partial section selected in the section division selecting step. A secret key encryption method, wherein the adaptive symbol appearance probability estimation step uses an initial value of the symbol appearance probability as an encryption key.

<Structure 8> A method for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein the symbol appearance probability of information of interest to be decoded based on an already decoded reference information sequence An adaptive symbol appearance probability estimating step for adaptively estimating the symbol, and a symbol corresponding to the corresponding section on the probability number line representing the target information based on the symbol appearance probability estimated by the adaptive symbol appearance probability estimation step. A section division selecting step of dividing into a plurality of partial sections and selecting a partial section corresponding to an arithmetic code from the divided partial sections; and an arithmetic code based on the partial section selected in the section division selecting step. An adaptive symbol appearance probability estimating step, wherein the initial value of the symbol appearance probability is used as a decoding key. Decoding method.

<Structure 9> A secret key encryption / decryption method comprising the secret key encryption method of Structure 7 and the secret key decryption method of Structure 8.

<Structure 10> An adaptive symbol appearance probability estimating unit for adaptively estimating the symbol appearance probability of information of interest to be encoded based on the already encoded reference information sequence,
Based on the symbol appearance probability estimated by the adaptive symbol appearance probability estimation unit, the corresponding section on the probability number line is divided into a plurality of sub-sections representing symbols that can take information of interest. A section division selection unit that selects a subsection corresponding to the symbol of the information of interest, and an arithmetic code configuration unit that configures an arithmetic code of the information of interest based on the partial section selected by the section division selection unit,
The above-described adaptive symbol appearance probability estimating unit uses an initial value of the symbol appearance probability as an encryption key.

<Structure 11> An apparatus for decrypting an encrypted arithmetic code and decoding the arithmetic code, the symbol appearance probability of the information of interest to be decoded based on the already decoded reference information sequence An adaptive symbol appearance probability estimating unit for adaptively estimating a symbol, and a symbol corresponding to a corresponding section on a probability number line based on the symbol appearance probability estimated by the adaptive symbol appearance probability estimating unit. An interval division selecting unit that divides into a plurality of sub-intervals and selects a sub-interval corresponding to an arithmetic code from the divided plurality of sub-intervals; and an arithmetic code based on the corresponding interval selected by the interval division selecting unit. An adaptive symbol appearance probability estimating section, wherein the adaptive symbol appearance probability estimating section uses an initial value of the symbol appearance probability as a decoding key. .

<Structure 12> A secret key encryption / decryption device comprising the secret key encryption device of Structure 10 and the secret key decryption device of Structure 11.

<Configuration 13> Based on the symbol appearance probabilities of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that the information of interest can take, and a plurality of divided sections A section division selecting step of selecting a subsection corresponding to the symbol of the information of interest from the section, and an arithmetic code forming step of forming an arithmetic code of the information of interest based on the partial section selected in the section division selecting step. The section division selecting step includes shortening at least one of the plurality of partial sections, and converting at least one of the plurality of partial sections into the corresponding section according to the shortened section width. A secret key encrypting method, wherein the encrypting step is performed using the partial section as an encryption key.

<Structure 14> A method of decrypting an encrypted arithmetic code and decoding the arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-intervals representing symbols that can be taken as information of interest, and a sub-interval selection step of selecting a sub-interval corresponding to an arithmetic code from the plurality of divided sub-intervals, An arithmetic code decoding step of decoding an arithmetic code on the basis of the obtained partial section, wherein the arithmetic code decoding step shortens at least one of the plurality of partial sections and reduces the shortened section. According to the width, at least one of the plurality of partial sections is moved within the corresponding section,
A method for decrypting a secret key, comprising a decryption step of using a decryption key for an encrypted partial section.

<Structure 15> A secret key encryption / decryption method comprising the secret key encryption method of Structure 13 and the secret key decryption method of Structure 14.

<Structure 16> Based on the symbol appearance probabilities of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that the information of interest can take. A section division selection unit that selects a partial section corresponding to the symbol of the information of interest from the section,
An arithmetic code forming unit configured to form an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit, wherein the section division selecting unit determines at least one partial section of the plurality of partial sections. In accordance with a shortened section width, at least one of the plurality of sub-sections is moved within the corresponding section according to the shortened section width, and an encrypting section is provided which uses the partial section as an encryption key. Secret key encryption device.

<Structure 17> An apparatus for decrypting an encrypted arithmetic code and decoding the arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-intervals representing symbols that can take information of interest, and the sub-interval selection unit that selects a sub-interval corresponding to an arithmetic code from the sub-intervals selected by the sub-interval selection unit, An arithmetic code decoding unit for decoding an arithmetic code based on the partial interval, wherein the interval division selecting unit shortens at least one of the plurality of partial intervals, and according to the shortened interval width. A secret key decryption unit for moving at least one of the plurality of partial sections within the corresponding section and using the decryption key as a decryption key for the encrypted partial section. .

<Structure 18> A secret key encryption / decryption device comprising the secret key encryption device of Structure 16 and the secret key decryption device of Structure 17.

<Structure 19> Based on the symbol appearance probabilities of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing possible symbols of the information of interest, and A section division selecting step of selecting a subsection corresponding to the symbol of the information of interest from the section, and an arithmetic code forming step of forming an arithmetic code of the information of interest based on the partial section selected in the section division selecting step. The section division selecting step includes an encryption step of shortening the corresponding section, dividing the shortened corresponding section into the plurality of partial sections, and using the plurality of partial sections as an encryption key. Secret key encryption method.

<Structure 20> A method of decrypting an encrypted arithmetic code and decoding the arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-intervals representing symbols that can take the information of interest, and a sub-interval selection step of selecting a sub-interval corresponding to an arithmetic code from the divided sub-intervals; An arithmetic code decoding step of decoding an arithmetic code based on the corresponding section, wherein the section division selecting step shortens the corresponding section, divides the shortened corresponding section into the plurality of partial sections, and performs encryption. A decryption step for decrypting the plurality of partial sections into decryption keys.

<Structure 21> A secret key encryption / decryption method comprising the secret key encryption method of Structure 19 and the secret key decryption method of Structure 20.

<Structure 22> Based on the symbol appearance probabilities of the information of interest to be encoded, the corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that the information of interest can take, and A section division selection unit that selects a partial section corresponding to the symbol of the information of interest from the section,
An arithmetic code forming unit configured to form an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit. A secret key encrypting apparatus, comprising: an encrypting unit that divides the plurality of partial sections and uses the plurality of partial sections as an encryption key.

<Structure 23> An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein a corresponding section on a probability number line is determined based on a symbol appearance probability of information of interest to be decoded. Is divided into a plurality of sub-intervals representing symbols that can take information of interest, and the sub-interval selection unit that selects a sub-interval corresponding to an arithmetic code from the sub-intervals selected by the sub-interval selection unit, An arithmetic code decoding unit for decoding an arithmetic code based on the partial interval, wherein the interval division selecting unit shortens the corresponding interval, divides the shortened corresponding interval into the plurality of partial intervals, and performs encryption. A decryption unit for decrypting the plurality of partial sections into decryption keys.

<Structure 24> A secret key encryption / decryption device comprising the secret key encryption device of Structure 22 and the secret key decryption device of Structure 23.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below using specific examples. << Specific Example 1 >><Secret Key Encryption and Decryption Method> FIG. 1 is a schematic explanatory diagram of a secret key encryption / decryption method of a specific example 1 according to the present invention, and FIG. FIG. 1B is a diagram illustrating a normal arithmetic coding method, and FIG. 1B is a diagram illustrating a method of encrypting an arithmetic code. In FIG. 1A and FIG. 1B, the symbol is a binary symbol of {0, 1} for ease of explanation. Also, it represents the i th symbol of the symbol sequence S to be coded in x _i, the partial sequences S _i to i-th symbol shall be represented by _{Si = x 1 x 2 ··· x} i.

As shown in FIG. 1A, the arithmetic coding is
First, the occurrence probability P0 and symbol x ₁ symbol x ₁ is the symbol 0 is based on the appearance probability P1 is a symbol 1, the corresponding interval [0,1) the subinterval A on the real line
0 [0, P0) and A1 is divided into [P0,1), the subinterval A0 when the symbol x ₁ is 0, the symbols x ₁
Is 1, the section A1 is selected. In FIG. 1A, the partial section A0 is selected. Then, the selected corresponding section A0 symbol x ₂ symbols 0 and partial section based on the first probability A00 and partial section A01
It is divided into partial intervals when the symbol x ₂ is 0 A00
And if the symbol x ₂ is 1 to select the subinterval A01. In FIG. 1A, the partial section A01 is selected. Thereafter, the section division selection processing is similarly repeated until the last symbol based on the appearance probability of each symbol, and a certain point C in the final section obtained as a result becomes a code.

As shown in FIG. 1B, in the secret key encryption / decryption method of the first embodiment, the initial value of the corresponding section is set to a secret key [0, 1-K), where K is a positive real number. It is assumed that.
When the initial value of the corresponding section is changed, the corresponding section [0, 1-K)
Are divided on the basis of the symbol appearance probabilities P0 and P1 of the symbol x _i into partial sections A0 ′ and A0 ′.
Since it changes to 1 ', the coordinates of the code point C obtained as a result of repeating the process of selecting the section division also change. For this reason, if the initial value [0, 1-K) of the corresponding section is not known, the arithmetic code cannot be correctly decoded, and the encrypting side and the decrypting side perform this initial value [0, 1-K]. ) Is held as a secret key to establish a cryptographic system. Since the initial value of the corresponding section can be arbitrarily set within a range in which the section width does not become negative on the real number line, the encryption is highly confidential and its decryption is not easy. Also, if K is made sufficiently small, it is possible to make the decrease in coding efficiency due to the change of the corresponding section almost negligible. In FIG. 1B, the arithmetic code is encrypted by changing the value on the coordinate 1 side of the corresponding section. However, the value on the coordinate 0 side of the corresponding section may be changed.
The values on both the side and the coordinate 0 side may be changed.

As described above, according to the secret key encryption / decryption method of the first embodiment, the initial value of the corresponding section is used as the secret key.
Therefore, encryption and decryption of highly confidential arithmetic codes can be realized without lowering the coding efficiency. Also, the arithmetic code can be encrypted without changing the algorithm of the arithmetic coding, and the encrypted arithmetic code can be decrypted and decrypted without changing the algorithm of the arithmetic decoding. .

<Secret Key Encrypting Apparatus> FIG. 2 is a block diagram showing the configuration of the secret key encrypting apparatus according to the first embodiment of the present invention. As shown in FIG. 2, the secret key encryption device according to the first embodiment includes an image memory 11, a register of interest 12, a reference buffer 13, a prediction state calculation unit 14, and a symbol appearance probability estimation unit 1.
5, an arithmetic code forming unit 16 and a code memory 17 are provided.

The image memory 11 stores the encoding target 2
A value image is stored. This binary image is encoded for each pixel in the order of scanning. The target register 12 holds a target pixel to be coded, and the reference buffer 13 holds a reference pixel column of m pixels referred to by the target pixel held in the target register 12. The prediction state calculation unit 14 calculates a prediction state of the pixel of interest based on the plurality of reference pixel columns held in the reference buffer 13 and outputs the prediction state to the symbol appearance probability estimation unit 15. When the number of pixels in the reference pixel column is m,
The prediction state of the target pixel is represented by 2 ^m state values that the reference pixel row can take. For example, if m = 8, the status value is 0
255.

The symbol appearance probability estimating unit 15 calculates, for each predicted state of the pixel of interest calculated by the predicted state calculating unit 14,
The symbol appearance probability P0 in which the pixel of interest is 0 and the symbol appearance probability P1 in which the pixel of interest is 1 are estimated. The division register 15a and the appearance frequency counter 15b
Having. The division register 15 a
Holds a division ratio (probability of appearance of symbol 1) P1 for dividing the corresponding section for each state value calculated by. The initial value of the division ratio P1 is set to 2 ^−Q (Q is a positive integer). The appearance frequency counter 15b counts the appearance frequency of the symbols 0 and 1 selected by the arithmetic code forming unit 16 described below for each prediction state calculated by the prediction state calculation unit 14. The symbol appearance probability estimating unit 15 reads the division ratio P1 corresponding to the state value of the reference pixel column calculated by the prediction state calculation unit 14 from the division register 15a, and outputs it to the arithmetic code forming unit 16. Further, the symbol appearance probability estimating unit 15 changes the division register 15a according to a change in the ratio of the symbol 1 based on the appearance frequency of the symbols 0 and 1 counted by the appearance frequency counter 15b.
^Is changed stepwise by a shift operation.

The arithmetic code forming section 16 divides the corresponding section based on the symbol appearance probability (division ratio) P1 estimated by the symbol appearance probability estimating section 15, and
2 is used to select a partial section corresponding to the symbol of the pixel of interest held in 2 to form an arithmetic code. The section register 16a, the code register 16b, and the secret key setting section 16
c. The section register 16a holds a symbol series AUG indicating the section width of the corresponding section on the probability number line, and the code register 16b stores a symbol series to be coded indicating the start point of the corresponding section (hereinafter, also referred to as code point). Say)
C is held. The section register 16a has the number of bits with the precision required for dividing the probability number line, and the sign register 16b has twice or more the number of bits as the section register 16a. The secret key setting unit 16 c
The initial value of the section width AUG of a is set to the encryption key (1-K).

The arithmetic code constructing section 16 includes a section register 16
The division ratio P1 is subtracted from the section width AUG held in a to obtain the section width AUG-P1 of the partial section of symbol 0. When the symbol of the pixel of interest is 0, the arithmetic code forming unit 16 retains the code point C as it is, and retains and encodes the section width AUG-P1 of the partial section of the symbol 0 in the section register 16a. When the symbol of the pixel of interest is 1, the arithmetic code forming unit 16 adds (AUG-P1) to the code point C so as to move the code point C to a partial section of the symbol 1, and C + (AUG- P1) is stored in the code register 16b, and the section width P1 of the partial section of the symbol 1 is stored in the section register 16a. The code register 16b has a shift-out function,
The symbol sequence overflowed during encoding is used as a code,
Output to the code memory 17. The code output from the code register 16b is stored in the code memory 17.

FIG. 3 is a flowchart showing the operation of the secret key encrypting apparatus of the first embodiment shown in FIG. First, the secret key setting unit 16c of the arithmetic code forming unit 16 sets the interval width AUG of the interval register 16a to (1-K) and sets the initial value of the code register 16b to 0 (step S1). Division ratio P1 of division register 15a
= 2 ^-Q (step S2). Next, the register of interest 12 and the reference buffer 13 are initialized, and the position of the pixel of interest is initialized (step S3).

Next, the pixel of interest is read from the image memory 11 and held in the register of interest 12, and a reference pixel sequence referred to by the pixel of interest is read from the image memory 11 and held in the reference buffer 13 (step S4). ). Next, the prediction state calculation unit 14 calculates the prediction state of the pixel of interest based on the reference pixel sequence held in the reference buffer 13 (step S5), and the symbol appearance probability estimation unit 15
As a result, the division ratio P1 corresponding to the prediction state is read from the division register 15a and output to the arithmetic code forming unit 16 (step S6).

Then, the division ratio P1 is subtracted from the section width AUG held in the section register 16a by the arithmetic code forming section 16, and the section width (AU
GP1) is held in the section register 16a as AUG (step S7). Next, when the symbol of the pixel of interest held in the register of interest 12 is 0 (Step S
8, YES), the code point C is held as it is, and the partial section of the symbol 0 is selected.
A symbol series normalized according to the value of AUG held in a and overflowing from the code register 16b is output to the code memory 17 as a code (step S9). Next, the appearance frequency of the symbol 0 in the corresponding predicted state is incremented by 1 by the appearance frequency counter 15b, and the division ratio P1 held in the division register 15a as necessary.
Is updated (step S10).

On the other hand, when the symbol of the pixel of interest held in the register of interest 12 is 1 (step S8, N
O), AUG is added to code point C to select a partial section of symbol 1, and P1 is held in section register 16a. At this time, the symbol series normalized and overflowed from code register 16b is used as a code as a code memory. 17 is output. (Step S11). Next, the appearance frequency of the symbol 1 in the corresponding predicted state is incremented by one by the appearance frequency counter 15b, and the division ratio P1 held in the division register 15a is updated as necessary (step S12). Next, when the encoding of all the pixels to be encoded is not completed (step S13, NO), the position of the next pixel of interest is set (step S14), and the process returns to step S4. On the other hand, when the encoding of all the pixels to be encoded has been completed (step S13, NO), the processing is terminated.

As described above, according to the secret key encrypting apparatus of the first embodiment, the secret key setting unit 16c uses the section register 16
By setting the initial value of a to (1-K), the arithmetic code can be encrypted. Therefore, since K can be set arbitrarily, it is possible to encrypt an arithmetic code with high secrecy. Also, if the value of K is made sufficiently small, the decrease in coding efficiency can be made small enough to be ignored.

<Secret Key Decryption Apparatus> FIG. 4 is a diagram showing the configuration of the secret key decryption apparatus according to the first embodiment of the present invention. As shown in FIG. 4, the secret key decryption device is for decoding the arithmetic code encrypted by the secret key encryption device shown in FIG.
2, an image memory 23, a reference buffer 13, a predicted state calculation unit 14, and a symbol appearance probability estimation unit 15. The same components as those of the secret key encryption device shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The code memory 21 stores the encrypted and arithmetically encoded binary image data. The binary image data is read from the beginning of the code and input to the arithmetic code decoding unit 22. The arithmetic code decoding unit 22 decodes the input arithmetic code and stores it in the image memory 23.
In the reference buffer 13, an already decoded reference pixel sequence of m pixels referred to by a pixel of interest to be decoded by the arithmetic code decoding unit 22 is read from the image memory 23 and held.

The predicted state calculation unit 14 and the symbol appearance probability estimation unit 15 simulate the operation at the time of arithmetic coding. The prediction state calculation unit 14 calculates the prediction state of the target pixel to be decoded based on the reference pixel sequence held in the reference buffer 13 and outputs the prediction state to the symbol appearance probability estimation unit 15. The symbol appearance probability estimation unit 15
For each state value calculated in step 4, the symbol appearance probability of the pixel of interest to be decoded is estimated based on the division ratio P1 held in the division register 15a. The initial value of the division ratio P1 is set to 2 ^−Q (Q is a positive integer). Further, the symbol appearance probability estimating unit 15 counts the appearance frequency of the symbols 0 and 1 decoded by the arithmetic code decoding unit 22 using the appearance frequency counter 15b, and stores the divided frequencies held in the division register 15a. The ratio P1 is changed stepwise.

Arithmetic code decoding section 22 divides the corresponding section into symbol 0 and symbol 1 partial sections based on division ratio P 1 estimated by symbol appearance probability estimating section 15, and when the input code data is symbol 0 It is determined which of the sub-intervals of symbol 1 and symbol 1 are present, and the arithmetic code is decoded. The arithmetic code decoding unit 22 includes:
a, a code register 22b and a secret key setting unit 22c.

The section register 22a holds the symbol series AUG representing the section width of the corresponding section on the probability number line, and the code register 22b holds the code data C read from the code memory 21. It is. The section register 22a has the number of bits with the precision required for dividing the probability number line, and the sign register 22b has the section register 2
It has twice or more the number of bits of 2a. Secret key setting unit 22
c sets the initial value of the section width AUG of the section register 22a as the decryption key (K-1).

Arithmetic code decoding section 22 includes section register 2
From the section width AUG held in 2a to the division register 15a
Is subtracted, the section width AUG-P1 of the partial section of symbol 0 is obtained, the section width of the partial section of symbol 0 is subtracted from the code point C, and a subtraction value C− (AUG− P1), code data C is symbol 0 and symbol 1
It is determined which of the sub-sections is present. When C- (AUG-P1) ≧ 0, the arithmetic code decoding unit 22 determines that the code data C is in the partial section of the symbol 0, and holds C- (AUG-P1) in the code register 22b. At the same time, AUG-P1 is held in the section register 22a to decode the symbol 0. If the subtraction value C- (AUG-A1) <0, it is determined that the code data C is in the partial section of the symbol 1. The symbol 1 is decoded by holding the code data C of the code register 22b as it is and holding the section width P1 of the partial section of the symbol 1 in the section register 22a.

FIG. 5 is a flowchart showing the operation of the secret key decryption apparatus of the first embodiment shown in FIG. First, the section width AUG of the section register 22a is set to (1-K) by the secret key setting section 22c of the arithmetic code decoding section 22, and the code register 22b is initialized (step S2).
1) The division ratio of the division register 15a is initialized to P1 = 2− ^Q (step S22). Then, reference buffer 1
3 is initialized, and the position of the pixel of interest to be decoded in the image memory 23 is initialized (step S23).

Next, the code data stored in the code memory 21 is read from the beginning, and
2 is read out from the image memory 23, and a reference pixel row referred to by the pixel row of interest to be decoded is stored in the reference buffer 13 (step S2).
4). Next, the prediction state calculation unit 14 calculates the prediction state of the pixel of interest based on the reference pixel sequence held in the reference buffer 13 (step S25), and the symbol appearance probability estimation unit 15 responds to the prediction state from the division register 15a. The division ratio P1 is read out and output to the arithmetic code decoding unit 22 (step S26).

Next, the arithmetic code decoding section 22 subtracts the division ratio P1 held in the division register 15a from the section width AUG held in the section register 22a, and obtains the section width (AUG-P1) of the partial section of the symbol 0. ) Is AUG
Is stored in the section register 22a (step S2).
7) The section width AUG of the partial section of symbol 0 is subtracted from the code data C held in the code register 22b (step S28), and it is compared whether C-AUG ≧ 0 (step S29).

If it is determined in step S29 that the subtraction value C-AUG ≧ 0, it is determined that the pixel of interest to be decoded is in the partial section of symbol 0, and the subtraction value (C-AUG) is held in the code register 22b. Thus, the pixel of interest is decoded (step S30). Next, the appearance frequency of the symbol 0 in the corresponding predicted state is incremented by one by the appearance frequency counter 15b, and the division ratio held in the division register 15a is updated as necessary (step S31).

On the other hand, if the subtraction value C-AUG <0 in step S29, it is determined that the target pixel to be decoded is in the partial section of symbol 1, and the code data C of the code register 22b is held as it is. The section width P1 of the partial section of the symbol 1 is held in the section register 22a, and the pixel of interest is decoded (step S32). Next, the appearance frequency of the symbol 1 in the corresponding predicted state is incremented by one by the appearance frequency counter 15b, and the division ratio held in the division register 15a is updated as necessary (step S33).

Next, when decoding of all the code data is not completed (step S34, NO), the position of the next pixel of interest is set (step S35), and step S2 is performed.
Return to 4. On the other hand, if the decoding of all the code data is completed (step S36, YES), the process ends.

As described above, according to the secret key decryption apparatus of the first embodiment, the secret key setting unit 22c uses the section register 22
The initial value of a is set as the decryption key (1-K), and the arithmetic code encrypted with the encryption key (1-K) having the same initial value can be suitably decrypted.

Example 2 <Secret Key Encryption and Decryption Method> FIG. 6 is a schematic explanatory diagram of a secret key encryption / decryption method of Example 2 according to the present invention, and FIG. FIG. 6B is a diagram illustrating a normal arithmetic coding method without encryption, and FIG. 6B is a diagram illustrating a method of encrypting an arithmetic code. In FIGS. 6A and 6B, the symbols are binary symbols of {0, 1} for ease of explanation. FIG. 6A is the same as FIG. 1A, and a description thereof will be omitted.

As shown in FIG. 6 (b), the secret key encryption / decryption method of the second embodiment uses an arithmetic coding method for adaptively estimating the symbol appearance probabilities of 0 and 1 during arithmetic coding. In the method and the arithmetic decoding method, an initial value of an appearance probability of symbols 0 and 1 in arithmetic coding is used as a secret key. When the initial values P0 and P1 of the symbol appearance probabilities are changed to P0 'and P1', respectively, the symbols 0 and 1 divided from the corresponding section [0, 1) are obtained.
Are subsections A0 '[0, P0') and A
1 '[P0', 1), so that the coordinates of the code point C also change. Therefore, if the initial value of the symbol appearance probability estimation value is not known, the arithmetic code cannot be correctly decoded, and the encrypting side and the decoding side perform the initial value P0 ′ or P1 of the symbol appearance probability estimation value. ′ As a secret key, a cryptographic system is established. Since the initial value of the symbol appearance probability estimation value can be set arbitrarily,
The decryption is not easy. Further, if the difference between the estimated value and the initial value in the case of not encrypting is sufficiently reduced, the decrease in the coding efficiency due to the change of the corresponding section can be almost ignored.

As described above, according to the secret key encryption / decryption method of the second embodiment, the initial value of the symbol appearance probability estimated value is used as the secret key. Therefore, encryption and decryption of highly confidential arithmetic codes can be realized without lowering the coding efficiency. Further, the arithmetic code can be encrypted without changing the algorithm of the arithmetic coding, and the encrypted arithmetic code can be decoded without changing the algorithm of the arithmetic decoding.

<Secret Key Encrypting Apparatus> FIG. 7 is a block diagram showing the configuration of the secret key encrypting apparatus according to the second embodiment of the present invention. As shown in FIG. 7, the secret key encryption device according to the second embodiment uses the symbol appearance probability estimation unit 15 and the arithmetic code configuration unit 16 of the secret key encryption device according to the first embodiment shown in FIG. It is replaced with an estimation unit 31 and an arithmetic code construction unit 32. Note that the same reference numerals are given to the same components as those in the secret key encryption device of the first embodiment,
The description is omitted.

The symbol appearance probability estimating unit 31 is obtained by adding a secret key setting unit 31a to the symbol appearance probability estimating unit 15 of the first embodiment shown in FIG.
Sets the initial value of the division ratio P1 stored in the division register 15a to the encryption key 2- ^{(Q + K)} (K is an integer). Here, 2 ^-Q is the initial value of the division ratio P1 when not encrypting, and K is the encryption key. Symbol appearance probability estimation unit 1
5 is the predicted state calculation unit 14 by the secret key setting unit 31c.
Ratio P1 for each state value of the reference pixel column calculated by
Are set to the encryption key 2- ^{(Q + K)} , respectively, and are output to the arithmetic code forming unit 16.
In accordance with a change in the ratio of the symbol 1 based on the frequency of appearance of the symbols 0 and 1 counted by 5b, the division ratio P1 held in the division register 15a is changed stepwise by a shift operation.

The arithmetic code forming unit 32 is obtained by removing the secret key setting unit 16c from the arithmetic code forming unit 16 of the first embodiment shown in FIG. The symbol register AUG indicating the width of the corresponding section on the probability number line is held in the section register 16a, and its initial value is set to 1. Sign register 16b
Holds a symbol sequence C to be encoded representing the start point of the corresponding section, and its initial value is set to 0.

FIG. 8 is a flow chart showing the operation of the secret key encryption device of the embodiment 2 shown in FIG. First, the arithmetic code forming unit 32 sets the section width AUG of the section register 16a to 1 and sets the code register 16b
Is set to 0 (step S41), and the division ratio P1 of the division register 15a is set to P1 = 2 as the encryption key.
Initialized to- ^{(Q + 1)} (step S42). Hereinafter, steps S43 to S54 are the same operations as steps S3 to S14 shown in FIG. 3, and a description thereof will be omitted.

As described above, according to the secret key encrypting apparatus of the second embodiment, the secret key setting unit 31a controls the division register 15
The arithmetic code can be encrypted by setting the initial value of the division ratio P1 of a to 2 ^{− (Q + K)} . Therefore, since K can be set arbitrarily, it is possible to encrypt an arithmetic code with high secrecy. Also, if the value of K is made sufficiently small, the decrease in coding efficiency can be made small enough to be ignored.

<Secret Key Decryption Apparatus> FIG. 9 is a diagram showing the configuration of a secret key decryption apparatus according to the second embodiment of the present invention. As shown in FIG. 9, the secret key decryption device decrypts the arithmetic code encrypted by the secret key encryption device shown in FIG. The symbol appearance probability estimating unit 15 and the arithmetic code decoding unit 22 of the secret key decryption device are replaced with a symbol appearance probability estimating unit 31 and an arithmetic code forming unit 32, respectively. In addition,
The same components as those of the components of the secret key decryption device of the first specific example shown in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

The predicted state calculating unit 14 and the symbol appearance probability estimating unit 31 have the same configuration as the predicted state calculating unit 14 and the symbol appearance probability estimating unit 31 of the secret key encryption device shown in FIG. To simulate the behavior at the time of conversion. Secret key setting unit 31 of symbol appearance probability estimating unit 31
c denotes the initial value of the division ratio P1 stored in the division register 15a, which is the same as the decryption key 2- ^{(Q + K)} (where K is an integer).
Set to. Arithmetic code decoding section 33 is different from arithmetic code decoding section 22 of specific example 1 shown in FIG.
c, and based on the symbol appearance probability (division ratio) P1 estimated by the symbol appearance probability estimating unit 31, the code data C input to the code register 22b.
Is decrypted. The initial value of the section register 22a is set to 1.

FIG. 10 is a flowchart showing the operation of the secret key decryption apparatus according to the second embodiment shown in FIG. First,
The section width AUG of the section register 22a is set to 1 by the secret key setting section 22c of the arithmetic code decoding section 22, the code register 22b is initialized (Step S61), and the division ratio P1 of the division register 15a is set to the decryption key. As P1 =
It is initialized to 2- ^{(Q + K)} (step S62). Thereafter, steps S63 to S74 are the same operations as steps S23 to S34 shown in FIG. 5, and a description thereof will be omitted.

As described above, according to the secret key decryption apparatus of the second embodiment, the initial value of the symbol appearance probability (division ratio) P1 is set to 2 ^{− (Q + K)} by the secret key setting unit 31a. The arithmetic code encrypted with the encryption key 2- ^{(Q + K)} of the initial value can be suitably decrypted. In the secret key encryption device and the decryption device of the second specific example, the symbol appearance probability (division ratio) P1 is set by the secret key setting unit 31a.
Is set to P1 = 2− ^{(Q + K)} , but the method of setting the secret key is not limited to this. For example, first, an image is arithmetically encoded without encryption,
At this time, the final value of the probability estimation value may be set as the initial value of the probability estimation value of the next image to be encrypted. In this case, the first image itself becomes a secret key.

In the first embodiment, the initial value of the corresponding section is used as the secret key, and in the second embodiment, the initial value of the symbol appearance probability is used as the secret key. By configuring the encryption system using the two secret keys described above, it is possible to configure a more difficult encryption system. Examples 1 and 2
In the above, the arithmetic code of the binary image is encrypted, and the encrypted arithmetic code is decoded. However, the encoding target is not limited to the image, and may be a multi-level symbol sequence. Needless to say.

<< Embodiment 3 >><Encryption and Decryption Method of Private Key> FIG. 11 is a schematic explanatory diagram of a secret key encryption / decryption method of Embodiment 3 according to the present invention. For ease of explanation, the symbols are represented as {0, 1,
As a ternary symbol of 2｝, a partial sequence up to the i-th symbol of the symbol sequence S is represented by S _i , and the i-th symbol is represented by x _i . Further, representative of the occurrence probability symbol x _i is 0 the probability is P0 _i, 1 occurrence probability is P1 _i, 2 with P2 _i. The sub-interval selected at the time of encoding the (i-1) -th symbol x _{i -1} is represented by a corresponding interval AS _i-1 , and the corresponding interval AS _i-1 is represented by a symbol appearance probability P0 _i ,
The partial sections divided by the ratio of P1 _i and P2 _i are represented by A0 _i , A1 _i and A2 _i , respectively. Further, the section width of the corresponding section AS _i-1 is represented by AUGS _i-1 , and the section widths of the partial sections A0 _i , A1 _i and A2 _i are respectively represented by AUG
0 _i , AUG1 _i and AUG2 _i .

[0071] FIG. 11 (a) each symbol occurrence probability P0 _i symbols x _i-1 of the corresponding section AS _i-1 symbols x _i,
Depending on the ratio of P1 _i and P3 _i, the subintervals A0 _i , A1 _i
And is a diagram showing a divided state A2 _i. Ci _-1 represents the code point of symbol xi _-1 . As understood from FIG. 11A, the code point C _i-1 represents the start point of the corresponding section AS _i-1 selected based on the symbol x _i-1 .

The secret key encryption / decryption method of the third embodiment is as follows.
First, as shown in FIG. 11B, the partial sections A0 _i , A0
1 _i and A2 _i, the respective section widths AUG0 _i , AU
Subtracting the G1 _i and AUG2 respectively from _i constants K0, K1 and _{K2, AUG0 i '= AUG0 i} -K0, AUG1 i' = AUG1 i -K1, seeking AUG2 _i '= AUG2 _i -K2, subinterval A0 _i , A1 _i and A2 _i are shortened to subintervals A0 _i ′, A1 _i ′ and A2 _i ′, respectively.

Next, as shown in FIG. 11 (c), the constants K1, K2 and K3 are shifted to the starting point side in the corresponding section AS _i-1 , and the corresponding sections A0 _i ′, A1 _i ′ and A2
_i 'is moved to the end point side in the corresponding section AS _i-1 . In other words, the constants K1 to K3 are added to the code point C _i-1 of the corresponding section AS _i-1.
Is added to the code point C _i-1 of the symbol x _i-1
i-1 'transferred to, and reduce the corresponding section AS _i-1, truncated corresponding section AS _i-1' in partial section A0 _i ', A1 _i' has allocated and A2 _i '. Then, a partial section corresponding to the symbol x _i is selected from the partial sections A0 _i ′, A1 _i ′, and A2 _i ′ shifted in the positive direction on the probability number line, and the arithmetic code is encrypted.

As shown in FIG. 11C, the symbols x _i
Is 0, the code point C _i becomes C _i = C _i-1 ′ = K ≠ C _i-1 , and if the symbol x _i is 1, the code point C _i becomes C _i = AUG 0 _{i '+ K = AUG0 i +} K1 + K2 ≠ AUG0 i becomes, if the symbol x _i is 2, code point C _{i is, Ci = AUG0 i' + AUG1} i '+ K = AUG0 i + AUG1 i + K2 ≠ AUG0 i + AUG1 i becomes, In any case, the code point Ci moves in the positive direction on the probability number line, and the arithmetic code is encrypted.

Therefore, if the constants K1, K2 and K3 are not known, the encrypted arithmetic code cannot be correctly decoded, and the encrypting side and the decrypting side do not have the constants K1, K2 and K3.
An encryption system is established by holding 0 to K3 as a secret key. Since the constants K0 to K3 can be set to any real numbers, the secret of the encryption is high and its decryption is not easy. If each of the constants K0 to K2 is made sufficiently small,
The movement of the partial section does not substantially reduce the coding efficiency.

As described above, according to the secret key encryption / decryption method of the third embodiment, the partial section divided based on the symbol appearance probability is shortened, and the partial section is shortened according to the shortened section width. The partial section is moved in the positive direction within the corresponding section AS _i-1 to be used as a secret key. Therefore, it is possible to realize a highly confidential arithmetic code encryption and decryption method. In addition, encryption can be performed at the same time as arithmetic encoding without substantially lowering the encoding efficiency, and the encrypted arithmetic code can be decrypted and decrypted.

In the secret key encryption / decryption method of the third embodiment, all of the divided sub-intervals are shortened. I just need to get it. Further, all of the partial sections are moved in the positive direction in the corresponding section. However, some of the partial sections may be moved, or the partial sections may be moved in the negative direction. Good. in this case,
The moving section and the moving direction are also secret keys.
In general, arithmetic coding recursively repeats the interval division selection process by the number of symbols. Therefore, even if only some partial intervals are shortened or only some partial intervals are moved within the corresponding interval This is because any symbol corresponds to a shortened or moved partial section, and the arithmetic code is encrypted. Further, the encryption of the partial section does not need to be performed for all symbols to be coded, and may be performed, for example, for symbols in a symbol sequence in random order. In this case, the random order is also a secret key.

<Secret Key Encrypting Apparatus> FIG. 12 is a block diagram showing the configuration of a secret key encrypting apparatus according to the third embodiment of the present invention. As shown in FIG. 12, the secret key encryption device includes a symbol appearance probability estimation unit 41, a section register 42, a section calculation unit 43, a sign calculation unit 44, an encryption unit 45, and a sign register 46.

The symbol sequence S to be coded is input to the symbol appearance probability estimating unit 41 and the sign calculating unit 44. Symbol occurrence probability estimator 41, which estimates a symbol occurrence probability of a symbol x _i based on the previously symbol appearance probability to symbol x _i-1 encoded, with the appearance frequency counter 41a. Appearance frequency counter 41
“a” counts the appearance frequencies of 0, 1, and 2 of the symbols encoded by the sign operation unit 44 described later. Symbol appearing probability estimation section 41, the occurrence frequency counter 41a by counting symbol occurrence probability P of the symbol X _i based on the occurrence frequency of the symbol 0, 1 and 2
1 _i , P 2 _i and P 3 _i are calculated and output to the section calculation unit 43.

[0080] The interval register 42 is section width AUG _i-1 of the corresponding section AS _i-1 of the symbol X _i-1 is held, in the code register 46, code point representing the start point of the corresponding section AS _i-1 C _i-1 is maintained. The section calculation unit 43 calculates the symbol appearance probability P estimated by the symbol appearance probability estimation unit 41.
1 _i , P2 _i and P3 _i based on the interval register 42
From the corresponding section AS _i-1 to the partial sections A0 _i , A
1 _i and A2 _i interval width AUG0 _i, computes the AUG1 _i and AUG2 _i. The section calculator 43 also subtracts a constant K from the section width AUG2 _i to obtain AUG2 _i ′ = AUG2 _i −K, and shortens the partial section A2 _i to a partial section A2 _i ′.

The sign operation unit 44 receives the input symbol x
_i , the code point C held in the code register 46
_An arithmetic code is formed by adding the section width of the partial section calculated by the section calculating section 43 to _i-1 . The sign operation unit 44
If the symbol x _i is 0, and C _i = C _i-1, when the symbol xi is 1, and _{C i = C i-1 +} AUG0 i, if the symbol x _i is 1, C Let _i = C _i-1 + AUG0 _i + AUG1 _i . In the section register 42, the section widths AUG0 _i , AUG1 _i and AUG calculated by the section calculating section 43 are stored.
2 _i ′, the symbol x input to the sign operation unit 44
section width of the subinterval AS _i corresponding to _i is held.

The encryption unit 45 encrypts the arithmetic code by adding the constant K to the code point C _i calculated by the code calculation unit 44. If the symbol x _i is _{1, C i = C i-1} + K becomes, if the symbol xi is 1, when _{C i = C i-1 +} AUG0 i + K , and the symbol xi is 1, C _i = C _i-1 + AUG0 _i + AUG1 _i + K The arithmetic code encrypted by the encryption unit 45 is held in the code register 46. The code point C _i held in the code register 46 is equal to the code point C _i held in the section register 42.
Normalized as necessary with UGS _i , where
The overflowed symbol sequence is output as a code.

FIG. 13 is a flowchart showing the operation of the secret key encrypting apparatus of the third embodiment shown in FIG. First, the code point C _{i = 0 of} the code register 46 is initialized to 0, the section = interval width AUGS _{i = 0 of} the section register 42 is initialized to 1, and the symbol x _{i of the} symbol sequence S to be coded.
Is initialized to 0 (step S8).
1). Then, the index i is incremented by 1, the symbol x _i is inputted to the symbol occurrence probability estimation section 41 and the code calculation unit 44 (step S82).

Next, the symbol appearance probability estimating section 41 outputs symbols 0, 1 and 2 of the appearance frequency counter 41a.
Based on the count value of the occurrence frequency of the symbol occurrence probability of the symbol X _i P1 _i, P2 _i and P3 _i is estimated (step S83). Next, the section calculator 43 calculates the AUG held in the section register 42 according to the ratio of the symbol appearance probabilities P1 _i , P2 _i and P3 _{i to} the section width AUG.
0 _i , AUG1 _i and AUG2 _i (step S84), a constant K is subtracted from the section width AUG2 _i ,
AUG2 _i 'is obtained (step S85). Then, the code calculation unit 44, the section width corresponding to the input symbol x _i is the summed code calculation is performed (step S86), by the encrypting unit 45, and the constant K is added to the code point C code point C _i is encrypted (step S8
7).

Next, the section width corresponding to the symbol x _i input to the sign operation section 44 is held in the section register 42 as a new AUGS _i (step S88). Then, AUGS _i 0.5 held in the segment register 42
If smaller (step S89, YES), the AUG and code register 4 held in the section register 42
The code points C _i held in 6 are both shifted by one bit in the MSB direction, and at this time, the overflow symbol sequence is encoded and output from the code register 46 (step S90). Then, the process returns to step S89. On the other hand, if AUGS _i held in the section register 42 is 0.5 or more (NO in step S89), the process proceeds to step S91. If index i is less than the total number of symbols, the process returns to step S82, and If i exceeds the total number of symbols, the process ends.

As described above, according to the secret key encryption device of the third embodiment, the section width AUG2 _i of the divided partial section A2 _i is shortened by the constant K by the section calculation section 43, and A constant K is added to the code point C calculated by the code calculation unit 44 to encrypt the arithmetic code. Therefore, if the constant K and the shortened partial interval are not known, the encrypted arithmetic code cannot be correctly decoded. The constant K can be set to an arbitrary real number, and the partial section to be shortened can be set arbitrarily, so that the secret of the encryption is high and its decryption is not easy. Also, if the constant K is made sufficiently small, it is possible to make the decrease in coding efficiency due to the movement of the partial section negligible. Therefore, it is possible to provide a secret code encryption device for arithmetic codes which has high secrecy and can perform encryption simultaneously with arithmetic coding without substantially lowering coding efficiency.

<Secret Key Decryption Apparatus> FIG. 14 is a diagram showing the configuration of a secret key decryption apparatus according to the third embodiment of the present invention.
As shown in FIG. 14, the secret key decryption device decrypts the arithmetic code encrypted by the secret key encryption device shown in FIG.
2. Arithmetic code decoder 53, symbol appearance probability estimator 4
1, a section register 42, and a section calculation section 43.
The same components as those of the secret key encryption device shown in FIG. 12 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The code register 51 stores the encoded and arithmetically encoded code data sequence C from the beginning thereof. The decryption unit 52 subtracts K from the code data Ci _-1 held in the code register 51, and calculates (Ci _-1
−K) is deciphered as Ci ₋₁ . The arithmetic code decoding unit 53 decodes and outputs the code data C decrypted by the decryption unit 52.

The symbol appearance probability estimating section 41 and the section calculating section 43 simulate the operation at the time of arithmetic coding.
The symbol appearance probability estimation unit 41 includes an appearance frequency counter 41
counting the occurrence frequency of the decoded symbol by an arithmetic decoding section 53 by a, a symbol occurrence probability of symbols x _i to be decoded by the arithmetic decoding section 53 P
Estimate 1 _i , P2 _i and P3 _i . Section register 4
2, the section width A of the corresponding section AS _i-1 of the symbol X _i-1
UGS _i-1 is held. The interval calculation unit 43 determines the interval register 4 based on the symbol appearance probabilities P1 _i , P2 _i and P3 _i estimated by the symbol appearance probability estimation unit 41.
The corresponding section AS _i-1 held in the subsections A0 _i , A0
_1i and A2 _i so that the subintervals A0 _i , A
1 _i and A2 _i interval width AUG0 _i, computes the AUG1 _i and AUG2 _i. The section calculator 43 also subtracts a constant K from the section width AUG2 _i to obtain AUG2 _i ′ = AUG2 _i −K, and shortens the partial section A2 _i to a partial section AUG2 _i ′.

The arithmetic code decoder 53 compares the decrypted code data C with the section width calculated by the section calculator 43, and decodes the code data Ci _-1 . If C _i-1 <AUG0 _i is satisfied, the code data C is determined to be in the partial interval A0, and is decoded into the symbol 0. If AUG0 _i ≤C _{i -1} <AUG0 _i + AUG1 _i is satisfied, the coded data C is determined to be in the partial section A1 and is decoded into symbol 1. When AUG0 _i + AUG1 _i <C _i-1 is satisfied, the code data C _i-1 is divided into the sub-interval A2
And decodes to symbol 1.

Arithmetic code decoder 53 outputs code data C
_The section width indicating the lower limit of the section corresponding to the decoded symbol X _i is subtracted from _i−1, and the result is stored in the code register 51. When the decoded symbol is 0, the arithmetic code decoding unit 53 holds the code data C as it is, and when the decoded symbol is 1, the arithmetic code decoding unit 53 converts C _i−1 −AUG0 _i to C _i. and then, when the decoded symbol is 1 holds C _i-1 + a (AUG0 _i + AUG1 _i) to the code register 51 as C _i. Further, the interval register 42, among the calculated section width AUG0 _i, AUG1 _i and AUG2 _i 'by section calculator 43, the section width corresponding to symbol x _i input to the code calculating unit 44 a new section is held in the interval register 42 as the width AUGS _i.

FIG. 15 is a flow chart showing the operation of the secret key decryption apparatus of the third embodiment shown in FIG. First, the section width AUGS i = ₀ interval register 42 is initialized to 1, the index i of the symbols x _i of the symbol sequence S being decoded is initialized to 0 (step S10
1). Next, the index i is incremented by one, and the code data C is input to the code register 51 from the beginning (step S102).

Next, the symbol appearance probability estimating section 41 outputs the symbols 0, 1 and 2 of the appearance frequency counter 41a.
, The symbol appearance probabilities P1 _i , P2 _i and P3 of the symbol X _i to be decoded
_i is estimated (step S103). Next, the AUG stored in the section register 42 by the section calculation section 43
, The section widths AUG0 _i , AUG1 _i and AUG based on the ratio of the symbol appearance probabilities P1 _i , P2 _i and P3 _i
2 _i is calculated (step S104), and the section width AUG2
AUG2 _i 'is obtained by subtracting a constant K from _i (step S105).

Next, a constant K is subtracted from the code data Ci _-1 held in the code register 51 by the decryption section 52, and (Ci _-1- K) is made Ci _-1. It is released (step S106). Next, the code data C decrypted by the arithmetic code decoder 53 is compared with the section width calculated by the section calculator 43, and the symbol X
_i is decoded (step S107), and code data C
section width from _i-1 represents the lower limit of the interval corresponding to the decoded symbols X _i is subtracted, the code data C _i is held in the code register 51 (step S108).

Next, the section width corresponding to the symbol X _i decoded by the arithmetic code decoding section 53 is held in the section register 42 as AUGS _i (step S10).
9). Next, the AUGS stored in the section register 42
_{If i} is smaller than 0.5 (step S110, Y
ES), the AUGS _i held in the section register 42 and the code point C _i held in the code register 46 are both shifted by one bit in the MSB direction (step S11).
1). Then, the process returns to step S110. On the other hand, if AUGS _i held in section register 42 is 0.5 or more (NO in step S110), the process proceeds to step S112, and if index i is less than the total number of symbols,
Returning to step S102, if the index i exceeds the total number of symbols, the process ends.

[0096] Thus, according to the secret key decryption apparatus embodiment 3, the section calculator 43, the section width AUG2 _i of the divided corresponding section A2 _i with shortened by a constant K, the descrambling section 52 Subtracts the constant K from the code data C held in the code register 51 to decrypt the arithmetic code. Therefore, the arithmetic code encrypted by the secret key encryption device shown in FIG. 12 can be suitably decrypted.

<< Embodiment 4 >><Encryption and Decryption Method of Secret Key> FIG. 16 is a schematic explanatory diagram of a secret key encryption / decryption method of Embodiment 4 according to the present invention. For ease of explanation, the symbols are represented as {0, 1,
A ternary symbol 2}, represents the partial sequence of up to i-th symbol of the symbol sequence S in Si, represents the i th symbol x _i. Further, representative of the occurrence probability symbol x _i is 0 the probability is P0 _i, 1 occurrence probability is P1 _i, 2 with P2 _i. The sub-interval selected at the time of encoding the (i-1) -th symbol x _{i -1} is represented by a corresponding interval AS _i-1 , and the corresponding interval AS _i-1 is represented by a symbol appearance probability P0 _i ,
The partial sections divided by the ratio of P1 _i and P2 _i are represented by A0 _i , A1 _i and A2 _i , respectively. Further, the section width of the corresponding section AS _i-1 is represented by AUGS _i-1 , and the section widths of the partial sections A0 _i , A1 _i and A2 _i are AUG0 _i , AUG _i
UG1 _i and AUG2 _i .

[0098] FIG. 16 (a) the symbol x _i-1 of the corresponding section AS _i-1 to each symbol occurrence probabilities P0 _i symbols x _i,
Depending on the ratio of P1 _i and P3 _i, the subintervals A0 _i , A1 _i
And is a diagram showing a divided state A2 _i. Ci _-1 represents the code point of symbol xi _-1 . As understood from FIG. 16A, the code point C _i-1 represents the start point of the corresponding section AS _i-1 selected based on the symbol x _i-1 .

The secret key encryption / decryption method of the third embodiment is as follows.
As shown in FIG. 16B, a constant K is subtracted from the section width AUGS _i-1 of the corresponding section AS _i-1 of the symbol x _i-1 to obtain AUGS _i-1 ′ = AUGS _i-1 −K. , shorten the corresponding section AS _i-1 to the corresponding section AS _i-1 ', then the corresponding section AS _i-1 which was reduced, by the ratio of the symbol occurrence probability of a symbol x _i P0 _i, P1 _i and P3 _i subinterval A0 _i ', A1 _i' is to divide the and A2 _i '. Corresponding section AS _i-1 to corresponding section AS
_When it is shortened to _i-1 ', the sub-interval divided based on each symbol appearance probability also changes, so that the coordinates of the code point C _i-1 also change.

Therefore, if the constant K is not known, the arithmetic code cannot be decoded, and the encryption and decryption sides hold the constant K as a secret key, thereby establishing a cryptosystem. Since the constant K can be set to an arbitrary real number, the encryption is highly confidential and its decryption is not easy. Also, if the constant K is made sufficiently small, the decrease in coding efficiency due to the movement of the corresponding section can be ignored.

As described above, according to the secret key encryption / decryption method of Example 4, the corresponding section is shortened by the secret key K,
The section width of the partial section is used as a secret key. Therefore, it is possible to realize a highly confidential arithmetic code encryption and decryption method. In addition, encryption can be performed at the same time as arithmetic encoding without substantially lowering the encoding efficiency, and the encrypted arithmetic code can be decrypted and decrypted.
The encryption of the corresponding section does not need to be performed on all the symbols to be coded, and may be performed on, for example, symbols in a symbol sequence in random order. In this case, the random order is also a secret key.

<Secret Key Encrypting Apparatus> FIG. 17 is a block diagram showing the configuration of a secret key encrypting apparatus according to Embodiment 4 of the present invention. As shown in FIG. 17, the secret key encryption device includes a symbol appearance probability estimating unit 61, a section register 62, a section calculating unit 63, a sign calculating unit 64, and a sign register 65.

The symbol sequence S to be coded is input to the symbol appearance probability estimating unit 61 and the sign calculating unit 64. The symbol appearance probability estimating unit 61 estimates the symbol appearance probability of the symbol xi based on the symbol appearance probabilities up to the already encoded symbol xi-1 and has an appearance frequency counter 61a. Appearance frequency counter 61
“a” counts the appearance frequencies of 0, 1, and 2 of the symbols encoded by the sign operation unit 64 described later. The symbol appearance probability estimating unit 61 calculates the symbol appearance probability P of the symbol Xi based on the appearance frequencies of the symbols 0, 1 and 2 counted by the appearance frequency counter 61a.
1 _i , P 2 _i, and P 3 _i are calculated and output to the section calculation unit 63.

[0104] the interval register 62 are held corresponding section AS _i-1 interval length AUGS _i-1 of the symbol X _i-1 is the code register 65, code point representing the start point of the corresponding section AS _i-1 C _i-1 is maintained. The section operation unit 63 performs the AUGS _{i-1 of} the corresponding section AS _i-1 held in the section register 62.
AUGS _i-1 ′ = AUGS _i-1 −K is obtained from the following equation, and the symbol appearance probability P estimated by the symbol appearance probability estimating section 61 from the obtained section width AUG _i-1.
1 _i , P2 _i and P3 _i , the sub-interval A0
_i ′, A1 _i ′ and A2 _i ′ interval width AUG0 _i ′,
AUG1 _i ′ and AUG2 _i ′ are calculated, respectively.

The sign operation unit 44 receives the input symbol x
_i , the code point C held in the code register 46
The section width of the corresponding section calculated by the section calculation section 43 is added to _i−1 , and encryption is performed simultaneously with arithmetic coding. When the symbol x _i is 0, the sign operation unit 44 sets C _i = C _i-1, and when the symbol x _i is 1, sets C _i = C _i-1 + AUG1 _i ′, and the symbol x _i is in the case of 1 and _{C i = C i-1 +} AUG1 i '+ AUG2 i'. The encrypted arithmetic code is held in the code register 65.

In the section register 62, the section widths AUG0 _i , AUG1 _i and A calculated by the section calculating section 63 are stored.
UG2 _i 'among the section width of the subinterval AUGS _i corresponding to the symbol x _i input to the code calculating unit 64 AUGS
_i is kept. The code point C _i held in the code register 64 is normalized as necessary together with the AUG _i held in the section register 42, and at this time, a symbol sequence overflowing is output as a code.

FIG. 18 is a flow chart showing the operation of the secret key encryption apparatus of the embodiment 4 shown in FIG. First, the code point C of the code register 65 is initialized to 0, the interval width AUGS _{i = 0 of} the interval register 62 is initialized to 1, and the index i of the symbol xi of the symbol sequence S to be encoded is initialized to 0. (Step S121).
Then, the index i is incremented by 1, the symbol x _i is inputted to the symbol occurrence probability estimation section 41 and the code calculation unit 44 (step S122). Then
By the symbol occurrence probability estimation section 61, based on the count value of the frequency of occurrence of symbols 0, 1 and 2 of the occurrence frequency counter 61a, the symbol X _i symbol appearing probability P1
_i , P2 _i and P3 _i are estimated (step S12)
3).

Next, the AUGS _{i-1 of} the corresponding section AS _i-1 held in the section register 62 by the section calculation section 63
Is subtracted from, and AUGS _i-1 '= AUGS _i-1 -K is obtained (step S124). Next, from the section width AUGS _i-1 ′ obtained by the section calculation unit 63,
Symbol occurrence probability estimator symbol appearance probability estimated by 41 P1 _i, P2 _i and P3 _i ratio by partial section of A0 _i ', A1 _i' interval width of and A2 _i 'AUG0
_i ′, AUG1 _i ′ and AUG2 _i ′ are calculated (step S125).

[0109] Then, the code calculation unit 64, the section width corresponding to the input symbol x _i is summed code calculation is performed is held in the code register 65 (Step S
126). Then, the section width corresponding to symbol x _i input to the code calculating unit 64 is held in the interval register 62 as new AUGS _i (step S127). Then, AUGS _i 0.5 held in the segment register 42
If it is smaller (step S128, YES), both AUGS _i held in section register 62 and code point C _i held in code register 62 are shifted by one bit in the MSB direction. Is encoded and output (step S129). Then, the process returns to step S128.
On the other hand, if AUGS _i held in the section register 42 is 0.
If the number is 5 or more (step S128, NO), the process proceeds to step S130. If the index i is equal to or less than the total number of symbols, the process returns to step S122 and the index i
If the number exceeds the total number of symbols, the process ends.

As described above, according to the secret key encrypting apparatus of the fourth embodiment, the section width AUGS _i-1 of the corresponding section AS _i-1 is reduced by the constant K by the section calculating section 63, and the shortened section is obtained. The symbol appearance probabilities P1 _i , P2 _i and P estimated by the symbol appearance probability estimator 61 from the width AUGS _i-1 '
3. Divide by the ratio of _i and encrypt the arithmetic code. For this reason,
If the constant K is not known, the encrypted arithmetic code cannot be decoded. Since the constant K can be set to an arbitrary real number, the encryption is highly confidential and its decryption is not easy. Also, if the constant K is made sufficiently small, it is possible to make the decrease in coding efficiency due to the movement of the partial section negligible. Therefore, the secret is high,
It is possible to provide an arithmetic code secret key encryption device that can perform encryption at the same time as arithmetic encoding without substantially reducing encoding efficiency.

<Secret Key Decryption Apparatus> FIG. 19 is a diagram showing the configuration of a secret key decryption apparatus according to Embodiment 4 of the present invention.
As shown in FIG. 19, the secret key decryption device is for decoding the arithmetic code encrypted by the secret key encryption device shown in FIG. 17, and includes a code register 71, an arithmetic code decoding unit 72, The apparatus includes a symbol appearance probability estimating unit 61, a section register 62, and a section calculating unit 63. The same components as those in the secret key encryption device shown in FIG. 17 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The code register 71 receives a code data sequence C that has been encrypted and arithmetically coded from the beginning and holds the code data sequence C. The arithmetic code decoding unit 53 decrypts the code data Ci _-1 held in the code register 71,
Decode an arithmetic code.

The symbol appearance probability estimating section 61 and the section calculating section 63 simulate the operation at the time of arithmetic coding.
The symbol appearance probability estimating unit 61 includes an appearance frequency counter 61
counting the occurrence frequency of the decoded symbol by an arithmetic decoding section 72 by a, a symbol occurrence probability of symbols x _i to be decoded by the arithmetic decoding section 72 P
Estimate 1 _i , P2 _i and P3 _i . Section register 6
2, the section width A of the corresponding section AS _i-1 of the symbol X _i -1
UGS _i-1 is held. The section calculator 63 subtracts the constant K from the AUG _{i-1 of} the corresponding section AS _i-1 held in the section register 62 to obtain AUGS _i-1 ′ = AUGS _i−1 −K, and obtains the obtained section. From the width AUGS _i-1 ′, the sub-interval A0 is determined by the ratio of the symbol appearance probabilities P1 _i , P2 _i and P3 _i estimated by the symbol appearance probability estimator 61.
_i ′, A1 _i ′ and A2 _i ′ interval width AUG0 _i ′,
AUG1 _i ′ and AUG2 _i ′ are calculated, respectively.

Arithmetic code decoding section 72 includes code register 7
The code data Ci _-1 held in ₁ is compared with the section width calculated by the section calculator 43, and the code data Ci _-1 is decoded. If C _i-1 <AUG0 _i ′ is satisfied, the code data C _i-1 is divided into subinterval A
It is determined to be at 0 'and decoded to symbol 0. When satisfying _{AUG0 i ≦ C i <AUG0 i} '+ AUG1 i' , the code data Ci is subinterval A1 '
And decodes to symbol 1. If AUG0 _i ′ + AUG1 _i ′ <C _i−1 is satisfied, the code data C _i−1 is divided into the sub-interval A
It is determined to be at 2 'and decoded to symbol 1.

Arithmetic code decoder 53 outputs code data C
_The section width indicating the lower limit of the section corresponding to the decoded symbol X _i is subtracted from _i−1, and the result is stored in the code register 71. When the decoded symbol is 0, the arithmetic code decoding unit 53 sets C _i = C _i−1, and when the decoded symbol is 1, C _i = C _i−1 −AUG0 _i ′, and held in the sign register 71 as C _i = C _i−1 + (AUG 0 _i ′ + AUG 1 _i ′). The section register 62 stores the section width A calculated by the section calculating section 63.
Of UG0 _i ′, AUG1 _i ′ and AUG2 _i ′
Symbol x _i decoded by arithmetic code decoding section 72
Interval width corresponding to it is held in the interval register 62 as a new section width AUGS _i.

FIG. 20 is a flowchart showing the operation of the secret key decryption apparatus of the embodiment 4 shown in FIG. First, section width AUG interval register 62 is initialized to 1, the index i of the symbols x _i of the symbol sequence S being decoded is initialized to 0 (step S141).
Next, the index i is incremented by one, and the code data C is input to the code register 71 from the beginning (step S142). Then, the symbol occurrence probability estimation section 61, the occurrence frequency counter 61a based on the count value of the frequency of occurrence of symbols 0, 1 and 2, the symbol occurrence probability of symbols X _i to be decoded P1i, P
2i and P3i are estimated (step S143).

Next, the AUGS _{i-1 of} the corresponding section AS _i-1 held in the section register 62 by the section calculating section 63
AUGS _i-1 ′ = AUGS _i-1 −K is obtained from (step S144), and the obtained section width A
The symbol appearance probabilities P1 _i , P2 _i and P3 _i estimated from the UGS _i-1 by the symbol appearance probability estimating unit 61
, The subintervals A0 _i ′, A1 _i ′ and A2 _i ′
AUG0 _i ′, AUG1 _i ′ and AUG2
_i ′ are calculated (step S145). Then, the calculated section width by the code data C and the section calculator 63 which is held in the code register 71 by the arithmetic decoding section 72 are compared, the symbol X _i is output is decoded (step S146).

Next, the section width representing the lower limit of the section corresponding to the decoded symbol X _i is subtracted from the code data C and stored in the code register 71 (step S14).
7). Next, the section width corresponding to the symbol X _i decoded by the arithmetic code decoding section 72 is held in the section register 62 as AUGS _i (step S148). Next, the AUGS _i held in the section register 62 becomes 0.
If it is smaller than 5 (step S149, YES),
The AUG held in the section register 62 and the code point C _i held in the code register 71 are both shifted by one bit in the MSB direction (step S150). And
It returns to step S149. On the other hand, if AUGS _i held in the section register 62 is 0.5 or more (step S149, NO), the process proceeds to step S151, and if the index i is less than the total number of symbols, the process proceeds to step S14.
When the index i exceeds the total number of symbols, the process is terminated.

As described above, according to the secret key decryption apparatus of the fourth embodiment, the section width AUSG _i-1 of the corresponding section AS _i-1 is reduced by the constant K by the section calculating section 63, and the shortened section is obtained. The symbol appearance probabilities P1 _i , P2 _i and P estimated by the symbol appearance probability estimator 61 from the width AUGS _i-1 '
3 Divide by the ratio of _i and decrypt the arithmetic code. Therefore, the arithmetic code encrypted by the secret key encryption device shown in FIG. 17 can be suitably decrypted.

A program for executing the operations of the secret key encrypting device and the secret key decrypting device in each of the above specific examples is created and recorded on a recording medium such as a flexible disk, a hard disk, and a ROM. The color image encoding method and the decoding method can be realized. In this case, the device can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of a secret key encryption / decryption method according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a secret key encryption device according to a first embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of the secret key encryption device of the first specific example shown in FIG. 2;

FIG. 4 is a block diagram illustrating a configuration of a secret key decryption apparatus according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing an operation of the secret key decryption apparatus of the first specific example shown in FIG.

FIG. 6 is a schematic explanatory diagram of a secret key encryption / decryption method of Embodiment 2 according to the present invention.

FIG. 7 is a block diagram illustrating a configuration of a secret key encryption device according to a second embodiment of the present invention.

FIG. 8 is a flowchart showing the operation of the secret key encryption device according to the second embodiment shown in FIG. 7;

FIG. 9 is a block diagram illustrating a configuration of a secret key decryption device according to a second embodiment of the present invention.

FIG. 10 is a flowchart showing an operation of the secret key decryption apparatus of the second embodiment shown in FIG.

FIG. 11 is a schematic diagram illustrating a secret key encryption / decryption method according to a third embodiment of the present invention.

FIG. 12 is a block diagram illustrating a configuration of a secret key encryption device according to a third embodiment of the present invention.

FIG. 13 is a flowchart showing the operation of the secret key encryption device of the specific example 3 shown in FIG.

FIG. 14 is a block diagram illustrating a configuration of a secret key decryption apparatus according to a third embodiment of the present invention.

FIG. 15 is a flowchart showing the operation of the secret key decryption device of the third specific example shown in FIG. 14;

FIG. 16 is a schematic explanatory diagram of a secret key encryption / decryption method of Embodiment 4 according to the present invention.

FIG. 17 is a block diagram illustrating a configuration of a secret key encryption device according to a fourth embodiment of the present invention.

FIG. 18 is a flowchart showing the operation of the secret key encryption device of the specific example 4 shown in FIG.

FIG. 19 is a block diagram illustrating a configuration of a secret key decryption apparatus according to a fourth embodiment of the present invention.

FIG. 20 is a flowchart showing an operation of the secret key decryption apparatus of the fourth embodiment shown in FIG.

[Explanation of symbols]

 Reference Signs List 11 Image memory 12 Register of interest 13 Reference buffer 14 Prediction state calculation unit 15 Symbol appearance probability estimation unit 15a Division register 15b Appearance frequency counter 16 Arithmetic code configuration unit 16a Section register 16b Code register 16c Secret key setting unit 17 Code memory

Claims (24)

[Claims] 1. A corresponding section on a probability number line is divided into a plurality of sub-sections representing symbols that can be taken by information of interest based on a symbol appearance probability of the information of interest to be encoded. A section division selecting step of selecting a partial section corresponding to the symbol of the information of interest from among the steps, including an arithmetic code configuring step of configuring an arithmetic code of the information of interest based on the partial section selected in the section division selecting step, In the section division selecting step, a secret key encryption method is characterized in that an initial value of the corresponding section is used as an encryption key. 2. A method for decrypting an arithmetic code by decrypting an encrypted arithmetic code, the method comprising the steps of:
A section division selecting step of dividing the corresponding section on the probability number straight line into a plurality of partial sections representing symbols that can be taken by the information of interest, and selecting a partial section corresponding to an arithmetic code from the plurality of divided partial sections; An arithmetic code decoding step of decoding an arithmetic code based on the partial section selected by the section division selecting step, wherein the section dividing selecting step sets an initial value of the corresponding section as a decoding key. A secret key decryption method characterized by the following. 3. The secret key encryption method according to claim 1 and claim 2.
And a private key decryption method. 4. A corresponding section on a probability number line is divided into a plurality of partial sections representing symbols that can be taken by the information of interest based on a symbol appearance probability of the information of interest to be encoded. A section division selecting unit that selects a partial section corresponding to the symbol of the information of interest from among them, and an arithmetic code configuring unit that configures an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit, The secret key encrypting apparatus, wherein the section division selecting unit uses an initial value of the corresponding section as an encryption key. 5. An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, comprising the steps of:
A section division selecting unit that divides a corresponding section on the probability number line into a plurality of subsections representing symbols that can take information of interest, and selects a subsection corresponding to an arithmetic code from the plurality of divided subsections; An arithmetic code decoding unit that decodes an arithmetic code based on the partial section selected by the section division selecting unit, wherein the section division selecting unit sets an initial value of the corresponding section as a decoding key. A secret key decryption device characterized by the above-mentioned. 6. The secret key encryption device according to claim 4, and claim 5.
And a secret key decryption device. 7. An adaptive symbol appearance probability estimating step of adaptively estimating a symbol appearance probability of information of interest to be encoded based on an already encoded reference information sequence, and an adaptive symbol appearance probability estimating step. Based on the determined symbol appearance probability, the corresponding section on the probability number line is divided into a plurality of sub-sections representing symbols that can take information of interest, and among the plurality of divided sub-sections, the section corresponding to the symbol of the information of interest falls. A section division selecting step of selecting a partial section; and an arithmetic code configuring step of configuring an arithmetic code of the information of interest based on the partial section selected in the section division selecting step. A secret key encryption method, wherein an initial value of a symbol appearance probability is used as an encryption key. 8. A method for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein a symbol appearance probability of target information to be decoded is adapted based on a previously decoded reference information sequence. Based on the symbol appearance probability estimated in the adaptive symbol appearance probability estimation step, the corresponding section on the probability number line represents a plurality of symbols that can take the information of interest. A section division selecting step of dividing into a plurality of partial sections and selecting a partial section corresponding to an arithmetic code from a plurality of divided sections, and decoding an arithmetic code based on the partial section selected in the section division selecting step An adaptive symbol appearance probability estimating step, wherein an initial value of the symbol appearance probability is used as a decoding key. Method. 9. The secret key encryption method according to claim 7, and claim 8.
And a private key decryption method. 10. An adaptive symbol appearance probability estimating unit for adaptively estimating a symbol appearance probability of target information to be encoded based on an already encoded reference information sequence, and an adaptive symbol appearance probability estimating unit. Based on the determined symbol appearance probability, the corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that can take information of interest, and a partial section corresponding to the symbol of the information of interest among the divided partial sections , And an arithmetic code configuring unit that configures an arithmetic code of the information of interest based on the sub-interval selected by the interval division selecting unit. The adaptive symbol appearance probability estimating unit includes a symbol A secret key encryption device, wherein an initial value of an appearance probability is used as an encryption key. 11. An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein a symbol appearance probability of target information to be decoded is adapted based on a reference information sequence already decoded. An adaptive symbol appearance probability estimating unit for dynamically estimating, based on the symbol appearance probabilities estimated by the adaptive symbol appearance probability estimating unit, A section division selecting unit that divides into sub-sections and selects a sub-section corresponding to an arithmetic code from a plurality of divided sub-sections, and decodes an arithmetic code based on the corresponding section selected by the section division selecting unit An adaptive symbol appearance probability estimating unit, wherein an initial value of the symbol appearance probability is used as a decoding key. 12. A secret key encryption / decryption device comprising: the secret key encryption device according to claim 10; and the secret key decryption device according to claim 11. 13. A corresponding section on a probability number line is divided into a plurality of partial sections representing symbols that can be taken by the attention information based on a symbol appearance probability of the information of interest to be encoded. A section division selecting step of selecting a partial section corresponding to the symbol of the information of interest from among the steps, including an arithmetic code configuring step of configuring an arithmetic code of the information of interest based on the partial section selected in the section division selecting step, In the section division selecting step, at least one of the plurality of partial sections is shortened, and at least one of the plurality of partial sections is included in the corresponding section according to the reduced section width. A method for encrypting a secret key, comprising the step of moving and using a partial section as an encryption key. 14. A method for decrypting an arithmetic code by decrypting an encrypted arithmetic code, comprising the steps of:
A section division selecting step of dividing the corresponding section on the probability number straight line into a plurality of partial sections representing symbols that can be taken by the information of interest, and selecting a partial section corresponding to an arithmetic code from the plurality of divided partial sections; An arithmetic code decoding step of decoding an arithmetic code based on the partial section selected by the section division selecting step, wherein the arithmetic code decoding step includes at least one partial section of the plurality of partial sections. A deciphering step in which at least one of the plurality of sub-sections is moved within the corresponding section according to the shortened section width, and is used as a decryption key of the encrypted sub-section. A method for decrypting a secret key, comprising: 15. A secret key encryption / decryption method comprising the secret key encryption method according to claim 13 and the secret key decryption method according to claim 14. 16. A corresponding section on a probability number line is divided into a plurality of sub-sections representing symbols that can be taken by the information of interest based on the symbol appearance probabilities of the information of interest to be encoded. A section division selecting unit that selects a partial section corresponding to the symbol of the information of interest from among them, and an arithmetic code configuring unit that configures an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit, The section division selecting unit shortens at least one of the plurality of partial sections and, according to the shortened section width, sets at least one of the plurality of partial sections within the corresponding section. What is claimed is: 1. A secret key encrypting apparatus, comprising: an encrypting unit that moves and uses a partial section as an encrypting key. 17. An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein the arithmetic code is decoded based on a symbol appearance probability of information of interest to be decoded.
A section division selecting unit that divides a corresponding section on the probability number line into a plurality of partial sections representing symbols that can take information of interest, and selects a partial section corresponding to an arithmetic code from the divided partial sections; An arithmetic code decoding unit that decodes an arithmetic code based on the partial section selected by the division selecting unit, wherein the section division selecting unit shortens at least one of the plurality of partial sections, Having a decryption unit that moves at least one of the plurality of partial sections within the corresponding section according to the shortened section width and uses the partial section as a decryption key for the encrypted partial section. A secret key decryption device characterized by the above-mentioned. 18. A secret key encryption / decryption device comprising the secret key encryption device of claim 16 and the secret key decryption device of claim 17. 19. A corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that can be taken by the attention information based on the symbol appearance probabilities of the information of interest to be encoded. A section division selecting step of selecting a partial section corresponding to the symbol of the information of interest from among the steps, including an arithmetic code configuring step of configuring an arithmetic code of the information of interest based on the partial section selected in the section division selecting step, The section division selecting step includes an encryption step of shortening the corresponding section, dividing the shortened corresponding section into the plurality of partial sections, and using the plurality of partial sections as an encryption key. Secret key encryption method. 20. A method for decrypting an arithmetic code by decrypting an encrypted arithmetic code, the method comprising the steps of:
A section division selecting step of dividing a corresponding section on the probability number straight line into a plurality of partial sections representing symbols that can take information of interest, and selecting a partial section corresponding to an arithmetic code from the divided partial sections; An arithmetic code decoding step of decoding an arithmetic code based on the corresponding section selected by the division selecting step, wherein the section division selecting step shortens the corresponding section and sets the shortened corresponding section to the plurality of A method for decrypting a secret key, comprising a decryption step of dividing the plurality of partial sections into decryption keys for use as the decryption keys of the plurality of partial sections. 21. A secret key encryption / decryption method comprising the secret key encryption method according to claim 19 and the secret key decryption method according to claim 20. 22. A corresponding section on the probability number line is divided into a plurality of partial sections representing symbols that can be taken by the information of interest based on the symbol appearance probabilities of the information of interest to be encoded. A section division selecting unit that selects a partial section corresponding to the symbol of the information of interest from among them, and an arithmetic code configuring unit that configures an arithmetic code of the information of interest based on the partial section selected by the section division selecting unit, The section division selecting unit includes an encrypting unit that shortens the corresponding section, divides the shortened corresponding section into the plurality of partial sections, and uses the plurality of partial sections as an encryption key. Private key encryption device. 23. An apparatus for decrypting an arithmetic code by decrypting an encrypted arithmetic code, wherein the arithmetic code is decrypted based on a symbol appearance probability of information of interest to be decoded.
A section division selecting unit that divides a corresponding section on the probability number line into a plurality of partial sections representing symbols that can take information of interest, and selects a partial section corresponding to an arithmetic code from the divided partial sections; An arithmetic code decoding unit that decodes an arithmetic code based on the partial interval selected by the division selecting unit, wherein the interval division selecting unit shortens the corresponding interval and sets the shortened corresponding interval to the plurality of segments. A decryption unit that divides the data into partial sections and uses the decrypted keys as the decryption keys of the plurality of partial sections. 24. A secret key encryption / decryption device comprising the secret key encryption device of claim 22 and the secret key decryption device of claim 23.