JPH11112490A - Ciphering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make deciphering of a cryptogram difficult and to unnecessitate a program only for decoding on a data receiver side by transmitting a program for returning data as an arithmetic result in execution environment as a ciphering result with respect to data. SOLUTION: Intermediate code interpreting mechanisms VM 203 and 204 with respect to select-fixed program language are provided for each of a transmitting side computer 201 and a receiving side computer. The computer 202 holds execution environment information ENV 205 for deciphering. The computer 201 evaluate a message M210 desired to send by the copy ENV 209 of information ENV 205 by the mechanism VM 203 to generate such one program E211 as outputs the message M210. Then, the program E211 expressed by intermediate codes is sent to the computer 202 by a cryptogram.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing pre-processing before actual communication in order for computer users to exchange information with each other via a network in a safe and secure manner. In particular, the present invention relates to a method of encrypting and decrypting a communication message.

[0002]

2. Description of the Related Art Conventionally, in a network environment as shown in FIG. 13 in which a communication network such as a computer is connected, users 12, 13, and 14 who connect their computers to a network 11 are connected via the network 11,
Various information including product information can be obtained by WWW, net news, e-mail, etc., and trading can be performed using a credit card or electronic money. The problem in this case is that when the user 12 wants to exchange messages with the user 14,
1 may be intercepted by the third party user 13 while relaying the information to the third party.
There is a possibility that illegal acts such as falsification of data and transmission to the network 11 may be performed.

As a basic technique for solving this problem, there is an encryption technique. Conventionally, generally used encryption methods are as follows. First, the key K is shared between the sender and the receiver of the information using some means. After that, the plaintext M and the ciphertext C are mutually converted by the encryption conversion E and the decryption conversion D as follows, thereby performing the encryption communication.

[0004]

## EQU1 ## C = E (M, K), M = D (C, K). That is, D and E are given by M = D (E
(M, K), K).

[0005]

However, in the conventional encryption method, the encryption algorithm is fixed as can be seen from "Equation 1". For this reason, there has been a problem that the distribution bias of data (encryption result) resulting from the employed encryption algorithm is analyzed and used for decrypting the plaintext M.

Further, when one plaintext M is fixed, the ciphertext E obtained by encryption is always uniform regardless of the time of encryption, so that an attack that collects the ciphertext and uses it for decryption. Was possible.

On the other hand, in an environment using a network computer, a program for decryption cannot be stored because there is no temporary storage area such as a hard disk on the side that receives and decrypts a message. Further, in an environment where multiplatforms have advanced, the same user may use a plurality of machines having different computational capabilities, and it is difficult to process all of them using the same algorithm. Then, when a new encryption algorithm is devised, research on a decryption method corresponding thereto is also performed. For this reason, when security is particularly important as in an electronic money system, the encryption algorithm is periodically changed. However, this causes a problem that the system itself must be changed.

On the other hand, the principle that confidential data such as personnel data in a company can be accessed only by the human resources department and managers, and that only managers can see only those related to their subordinates. It is generally provided. As described above, in a company or the like, there is a case where the same data is desired to be displayed differently depending on a person accessing the same data. In such a case, conventionally, a method of preparing a password only for the type of presentation and teaching the password to the person concerned has been adopted. However, this makes it difficult to manage passwords, and also causes a problem that it is not possible to flexibly cope with a system change due to a change in job system or the like.

It is an object of the present invention to provide an encryption method and system in which it is more difficult to decrypt a ciphertext and does not require a dedicated program for decryption on the data receiving side.

[0010]

In order to achieve the above object, the present invention provides a program which uses a computer's execution environment as a key and returns specified data as a calculation result in the execution environment. The data is transmitted to the receiving side as an encryption result.

Specifically, first, one programming language is selected and fixed on the transmitting side and the receiving side. Each of the transmission side and the reception side is provided with an intermediate code interpreting machine VM for this program language, and the reception side holds one execution environment NV for decoding supplied from the transmission side. This is stored in an IC card or the like. On the transmitting side, a program generating device is provided, and for a message M to be transmitted using the program generating device, an intermediate code interpreting mechanism VM evaluates the message E in the execution environment ENV and outputs a program E that outputs the message M. Generate one. The transmitting side sends the program E to the receiving side as ciphertext.

The receiving side evaluates the program E in the execution environment ENV by the intermediate code interpreter VM, and
To restore.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a diagram showing the most basic system configuration for carrying out the present invention, in which a computer 201 on the transmitting side and a computer 20 on the receiving side are shown.
There are two.

Each of the computers 201 and 202 has one common programming language selected and fixed. Further, the transmission side computer 201 and the reception side computer 202 respectively provide intermediate code interpreting machines (VM) 203, 20 for a selected and fixed programming language.
4 are provided. Also, the receiving computer 202
Holds one execution environment report (ENV) 205 for decoding supplied from the sending computer 201. This is stored and held in an auxiliary storage 206 such as a floppy disk or an IC card.

The transmission side computer 201 stores a program generation device 208 and a copy (ENV) 209 of the execution environment information (ENV) 205. A program (E) 211 that outputs a message (M) 210 by being evaluated by a copy (ENV) 209 of execution environment information by a code interpretation mechanism (VM) 203
Is generated.

The sending computer 201 sends the program (E) 211 expressed as an intermediate code to the receiving computer 202 as ciphertext. The receiving computer 202 evaluates the program (E) 211 which is a received cipher text with the interpreting mechanism (VM) 204 and the execution environment information (ENV) 205, and the same message (M) 212 as transmitted by the transmitting side. Get.

Here, the execution environment information includes the performance of the transmitting computer 201, the installation location, the transmitting computer 2
The contents of the information, such as variables or a set of variables arbitrarily set by the user No. 01, fluctuate and cannot be understood only by monitoring the network.

As described above, the message M210 is programmed using the execution environment information (ENV) 209 of the transmission-side component 201 as an encryption key, and
In this case, even if a third party attempts to eavesdrop, the information on the execution environment is unknown and fluctuates, making eavesdropping substantially difficult. The executable program E21
1 is transmitted, the receiving computer 202 only needs to have the intermediate code interpreting mechanism (VM) 204, and there is no need to prepare a specific compounding program. Therefore, even in a network computer that does not have a temporary storage mechanism such as a hard disk, the same encrypted communication as a computer that prepares various encryption algorithms can be performed.

FIG. 3 is a block diagram showing a case where a subprogram (F) 303 is added as a key held by the receiving computer 202 in addition to the execution environment information. In this case, the transmitted encryption code, program (E) 3
01, when evaluated by the interpreter (VM) 302, proceeds with the calculation while calling each other with the subprogram (F) 303, and the same message 30 transmitted by the sender is transmitted.
4 is restored.

The addition of the subprogram (F) 303 makes eavesdropping more difficult.

FIG. 4 is a diagram showing a configuration example of the program generation device 208. The device 208 receives the execution environment information (ENV) 401 and the message (M) 402 as inputs, and generates and outputs a program (P) 403 that returns M as a calculation result. For the sake of simplicity, here (ENV) 401 is ｛(x, 0),
It is assumed that the sequence is a sequence of pairs of variables and their values such as (y, 1), (z, 2)} (actually, a program counter or a return address counter may be provided). In the following description, it is assumed that this environment is bound to the global variable ENV, and a set of variables appearing in the ENV is bound to the global variable V. Also, a program database (DB) 40
It is assumed that the upper limit value of the key used for the search from 4 is bound to the global variable.

For simplicity, the following description will be made assuming that all variables take integer values. Message division device 406
Decomposes the message (M) 402 into a sum or product of several numbers. FIG. 4 shows an example of the dividing algorithm. In this example, in steps 415 to 417, a random number sequence ｛(T1, R
1), (T2, R2),. . . , (Tn, Rn), M
0)}, and M is calculated as T1 + R1 * (T2 + R2
* (... Tn + Rn * M0)))) and output as a division result S. Note that the random number R is generated by the random number generation device 410.

The synthesizing unit 407 searches the program database (DB) 404 for a program that returns each number of the result of the decomposition as a calculation result, replaces the program, and synthesizes as one program. Generally, a plurality of candidates are obtained as a search result, and one of them is selected at random. FIG. 5 shows an example of program data stored in the program database (DB) 404, FIG. 6 shows a DB search algorithm, and FIG. 7 shows a program synthesis algorithm.

In the program database (DB) 404, a plurality of programs having a plurality of key values as evaluation values corresponding to search keys 1 to N are stored. In FIG. 5, the key value 601 is “13”, and three types of programs 602, 603, and 604 that return “13” as a calculation result are stored.
The program 602 uses a library function fib, and its definition 605 is also stored in the program database (DB) 404. These programs are searched by the processing shown in steps 606 to 608 in FIG. 6, and one of the three program definitions is returned after local variable rewriting is performed.

Here, local variable rewriting means rewriting the name of a local variable in a program in order to prevent the usage of the local variable used during the calculation from being inferred from its naming. means. For example, program 60
In the case where “λ (x) ｛x ＾ 2-x + 1｝ (4)” of 3 is selected, x of the local variable is rewritten to a randomly selected variable name, for example, “swk1125”, and the actually returned program is , “Λ (swk1125) ｛swk1125
{2-swk1125 + 1} (4) ".

At the time of synthesizing by the synthesizing unit 407, a logical expression is generated by the logical expression generating unit 403, and the if sentence P
Are configured. That is, a program R to be returned as a result is placed in a corresponding branch of an if statement in accordance with the evaluation result of the generated logical expression in the execution environment information (ENV) 401,
Another branch contains a randomly generated polynomial.

The program of the database search result corresponding to Ti and Ri is Pa + Pb * as Pa and Pb.
By composing programs in the form of P in order, the entire program is synthesized. This synthesis is performed in steps 701 to 713 in FIG.

In FIG. 7, based on the division result S returned from the division device 407, each element (A, B) of this list is extracted in step 703, and then, in steps 704 and 705.
To search the database 404 and substitute it for Pa and Pb. Further, in steps 706 and 707, a random polynomial is generated and substituted into P.
At 7,709, a logical expression is generated and assigned to L. In steps 711 and 712, an if statement is constructed in accordance with whether the evaluation result is true or false in the given execution environment ENV. Finally, in step 713, the program R synthesized in step 702 is returned to itself.

The logical expression generator 403 randomly generates and returns a logical expression including a variable appearing in the execution environment information (ENV) 401. However, by considering “0” as false and values other than “0” as true, polynomials and the like related to variables are also considered as logical expressions. An example of the procedure for generating a logical expression is shown in step 80 in FIG.
1 to step 817 are shown. Steps 801 to 804
Logical operator generation subroutine randomly selects and returns a logical operator of and, or, =. The random polynomial generation subroutine simply generates and returns a random number when the order is n and the variable is “0” or S is empty (step 806).
Otherwise, in step 807, a polynomial of degree n-1 is generated by calling itself, substituted into a, and
Is substituted for x (step 808). Further, an n-th order polynomial composed of variables other than x is generated by calling itself, and substituted into b (step 809).
An nth-order polynomial ax + b is constructed based on these results and returned as the final result (step 810).

The ethical expression generation routine includes a given number L of logical operators using the following subroutines.
L that randomly generates a logical expression consisting of a variable list S
Is zero, a random polynomial is simply generated (steps 812 and 813). Otherwise, call itself and add a logical expression not containing the logical operator to left, n
A logical expression including one logical operator is generated in right (steps 814 and 815), and a logical operator op is randomly generated (step 816). As a final result, a logical expression in the form of left op right is obtained. Return (step 817). The above program synthesizing procedure is repeated a specified number of times k times. Program selection / correction device 411
Calculates a message almost correctly from the k programs synthesized in this way, and selects a program whose program is more complicated than a certain standard. "Almost correctly" indicates that the absolute value of the difference between the calculation result and the message is equal to or smaller than N. If the difference is not "0", a program database (DB) search is performed and the result is corrected.
The complexity of the program is calculated by applying appropriate weights based on the complexity of the network in a flowchart and the complexity of the logical expression at the branch point.

If a program that is more complicated than a certain standard cannot be found, a set of these programs is applied to a program mutator 409 to perform mutating operations such as partial exchange of program text, exchange of local variables, insertion of random text, and the like. , A new program is generated and applied to the selection / correction device 411 again. An example of the algorithm for program mutation is shown in FIGS.

In this algorithm example, expansion 1001 of arithmetic operations such as "*" and "+" is performed. Partial matching of the syntax trees of two synthesized programs is performed.
3. Definition expansion 1004 of library functions used in the program database (DB) 404, constants appearing in the program are bound variables in the program or execution environment information environment (ENV) 401 of the corresponding program database (DB) 404 Substitution 100 to replace
Mutational operations such as 5 are performed.

Hereinafter, this loop is repeated. If the request regarding the encryption strength is not so strong, an upper limit value may be set for the number of repetitions, and the process may be forcibly terminated at an appropriate timing. FIGS. 11 and 12 show flowcharts of the above series of procedures.

Step 1101 in FIG. 11 is a message division process, step 1102 is a program database search process, step 1103 is a logical expression generation process, and step 1104 is a program database search process.
105 indicates one of the generated logical expressions R1. Step 1201 in FIG. 12 shows a program selection correction process, and step 1203 shows a program variation process.
202 indicates a selection correction result, and 1204 indicates a mutation result program.

As an application, a single ciphertext having a plurality of decoding methods can be created. Assuming that there are n different types of opponents now, each has a different execution environment ENV
1,. . . , ENVn are held as decryption keys. Each different message M1,. . . ,
When it is desired to transmit Mn, as an initial program, for example, a polynomial F (M1) * (x-ENV2) *. . . . *
(X-ENVn) +. . . + F (Mn) * (x-ENV
1) *. . . * (X-ENV (n-1)), and the program selection condition is "Return Mi to ENVi. (I =
1,. . . , N)] and the same procedure as in the case of one message may be performed. Here, F is an initial generation program for one message.

In this way, in particular, the designated keys ENV1,. . . , ENVn, the same message can be sent to other recipients, and decryption is not allowed to other recipients. The recipients that can be decrypted can be determined when the sender encrypts.

Therefore, for example, even if there is no receiver having ENVn and instead wants to permit decryption to a person having ENVn + 1, the above-described method can be applied to ENVn + 1.
1,. . . , ENVn−1, ENVn + 1, the work such as exchange of the decryption key becomes unnecessary, and the key management work is remarkably reduced.

[0038]

As described above, the use of the encryption method of the present invention makes it unnecessary to have a dedicated program for decryption on the data receiving side. This is useful when you want to In particular, since the receiver does not need to hold the algorithm used for decoding in advance, it can be easily changed by the judgment of the sender.

Further, by using the encryption method of the present invention, the complexity of the program to be transmitted can be changed according to the use environment. In other words, in an environment without machine power,
In an environment where encryption strength is low but encryption speed is fast and machine power is strong, encryption with high encryption strength but slow encryption speed can be selected. The receiving side only needs to have an evaluator in the programming language, and a dedicated decoding program is not required. For this reason, the encryption algorithm can be changed only by the transmission side, and the encryption strength can be changed according to the environment of the receiver side.

Further, in the encryption method of the present invention, the number of encryption methods corresponding to one plaintext is infinite, and it is difficult to decrypt the data by collecting the ciphertext. In fact, it is generally known that it is impossible to mechanically determine whether two programs return the same calculation result (Rice's theorem). It is considered extremely difficult to break.

When not only the execution environment but also a subprogram is included as a key, the encryption code is not completed as a program without this subprogram.
It is more difficult to decipher.

Further, in the encryption method according to the present invention, it is possible to prepare a plurality of decryption methods corresponding to one ciphertext, and it is possible to receive different messages depending on the recipients by sending the same ciphertext. Becomes possible.

Further, it is possible to specify a recipient group that is allowed to decrypt the data at the time of encryption, and the management of the decryption key is significantly reduced.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a system configuration diagram showing an embodiment when a key includes a subprogram.

FIG. 3 is a functional block diagram illustrating a configuration example of a program generation device.

FIG. 4 is a diagram illustrating an example of an algorithm for dividing a message.

FIG. 5 is a diagram showing an example of data storage in a program database.

FIG. 6 is a diagram illustrating an example of an algorithm of a program database search.

FIG. 7 is a diagram illustrating an example of an algorithm of program synthesis.

FIG. 8 is a diagram illustrating an example of an algorithm for generating a logical expression and generating a random polynomial.

FIG. 9 is a diagram illustrating a method of program mutation.

FIG. 10 is a diagram illustrating a method of program mutation, as in FIG. 9;

FIG. 11 is a diagram for explaining the overall procedure of program generation.

FIG. 12 is a diagram illustrating a procedure after program selection correction.

FIG. 13 is a conceptual diagram of a network and its users.

[Explanation of symbols]

210: transmitting computer, 202: receiving computer, 203, 204: interpreter of intermediate code, 20
5, 209: execution environment information, 206: auxiliary storage device, 2
08: a program generation device; 303: a subprogram;
210, 212... Message, 406... Message dividing device, 404.

Claims (3)

[Claims] 1. A cipher, wherein a program for returning specified data as a calculation result in the execution environment using a program execution environment by a computer as a key is transmitted to a receiving side as an encryption result for the specified data. Method. 2. A program which uses a program execution environment and a specific subprogram as keys and returns specified data as a calculation result while calling each other with the subprogram in the environment as an encryption result for the specified data. An encryption method for transmitting to a receiving side. 3. The encryption method according to claim 1, wherein the program is in a code format executable by a receiving side.