Method and system for small time key generation

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a technique for generating a small time key from a time key that enables decoding at a specific time, and more particularly to a technique for reducing the time unit of decoding time without increasing the number of time keys by the small time key.

【0002】

[Conventional technology]

In the present invention, a short-time key generation method and a management (transmission, storage, etc.) method will be described. Generally, if the time unit of the decoding time is reduced, the number of time keys to be managed increases, but by using the present invention, the time unit can be made smaller without increasing the number of time keys to be managed. ..

【0003】

The time key is used as a mechanism to prevent data from being decrypted until a certain time. This mechanism is based on a mechanism in which the time decryption key is kept secret until a specific time by the time key management station that manages the time encryption key and the time decryption key, and the time decryption key is released after the specific time. ing.

【0004】

In order to reduce the time unit of the decryption time under such a mechanism, it is necessary to generate many time keys corresponding to the time unit. For example, if the time unit is a daily time key, 365 time keys may be generated and managed in one year. (Time key for January 16, 1998, time key for January 17, 1998, etc.) However, if the time unit is reduced to one minute, it is necessary to generate and manage 525,600 time keys in one year. There is. (Time key for 10:28 am on January 16, 1998, time key for 10:29 am on January 16, 1998, etc.) In this way, manage to reduce the time unit of decryption time. The number of time keys to be used increases. Since the most secure system is required for managing time keys, it is desirable not to blindly increase the number of time keys. On the other hand, considering an application that uses a time key, the smaller the time unit of the decryption time, the more flexible the operation becomes.

【0005】

For time keys using asymmetric key cryptography, M. Kudo, "Secure Electronic Sealed-Bid auction Protocol with Public Key Cryptography," IEICE Trans. Fundamentals of Electronics, Communications and Computer Sciences, Vol. E81-A, No.1 , 1998. For time keys using symmetric key cryptography, see RL Rivest, A. Shamir, DA Wagner, "Time-lock puzzles and timed-release Crypto," MIT Laboratory for Computer Science, pp. 1-9, 1996 time-lock puzzles. It is stated in. Both documents describe the unit time key, and do not describe a method of generating a small time key from the unit time key of the present invention and reducing the time unit of decoding time without increasing the number of time keys.

【0006】

[Problems to be Solved by the Invention]

Therefore, an object to be solved by the present invention is to provide a method and a system for generating a small time key from a time key.

【0007】

Another challenge is to provide a method and system for encryption using a small time key and a unit time key.

【0008】

Another task is to provide a method and a system for transmitting a short time key and a unit time key.

【0009】

Another task is to provide a method and a system for decrypting encrypted data using a short time key and a unit time key.

【0010】

Another issue is to provide a time key server in which the short time key and the unit time key can be freely used by the user.

【0011】

Another task is to provide a time key management method and its system in which the time key management function does not need to manage a huge number of time keys using a small time key and a unit time key.

【0012】

[Means for solving problems]

In order to solve the above problem, a plurality of small time keys are generated within an hour unit. First, the unit-time decryption key immediately after the time unit is generated. Then, a one-way function is applied to the unit-time decryption key to obtain the final short-time key. The desired small-time key is obtained by applying a one-way function to the small-time key immediately before the desired small-time key. That is, the short-time keys are viewed in chronological order, and the short-time keys in the last order are generated forward. By doing so, even if a specific short-time key leaks to the outside for some reason, it becomes impossible to generate the previous short-time key in chronological order based on this. Furthermore, the unit-time decryption key is safe even if the short-time keys are released one after another.

【0013】

With the above configuration, it is possible to construct a time key server similar to an existing time server that generates a unit time key and a short time key. The user who uses the time key can build various applications by using the time key published from the time key server.

【0014】

For example, a network test system, an electronic sealed bidding system, and the like. When there are restrictions such as not being able to see or see specific data before the time, the entire data in which the specific part is encrypted in advance using the time key is distributed electronically in advance. By acquiring the time decryption key at a specific time, the contents of the specific data can be viewed.

【0015】

The time unit referred to in the present invention can be flexibly set. It may be in units of 1 day, 11 minutes, or 3 minutes. It can be selected as appropriate. By using the small time key of the present invention, the time key management function does not need to manage a huge number of time keys.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

The terms used in the examples are defined below. -Time key: A key for time-dependent encryption / decryption. When the decryption key for decrypting encrypted data is released after a specific decryption time, it is called a time key. The method of creating a time key and the method of encryption / decryption are the same as those of an asymmetric key (RSA, etc.) and a symmetric key (DES, etc.) in ordinary cryptography. -Small time key: A time key with a small time unit, which is a smaller time key with a smaller time unit created based on a time key with a larger time unit at the decryption time. Refers to the short-time key 11 and the short-time key 12 in FIG. -Time encryption key: An encryption key for time-dependent encryption without distinguishing between asymmetric keys and symmetric keys. -Time decryption key: Decryption key for time-dependent decryption without distinguishing between asymmetric key and symmetric key -Asymmetric time encryption key: Public key of asymmetric key for encrypting data -Asymmetric time decryption key: The private key of the asymmetric key for decrypting data -Symmetric time key: Symmetric key for encrypting / decrypting data -Encryption with asymmetric key encryption: When encrypting data with asymmetric key encryption, it means that the data is encrypted with a temporary symmetric key in advance and then the symmetric key is encrypted with the asymmetric key. -Time key management server (system): A special system with the purpose of managing time keys -Unit time key: The time key from which the small time key is created. In the present invention, it may be an asymmetric key or a symmetric key. Refers to the unit time key 1 and the unit time key 2 in FIG. -Time unit: The shortest time interval in which a unit time key or a short time key that is different from each other is generated. If the time unit of the unit time key is one day, it means that a different time key is generated for each day.

【0017】

The description method is defined below for use in the examples. M1 | M2: Concatenation of data M1 and data M2 PK_x : X asymmetric public key (normal signature verification public key, not time key) SK_x : X asymmetric private key (regular signing private key, not time key) PK_{x, t = t1} : X asymmetric time encryption key, decryption time is t1 SK_{x, t = t1} : X asymmetric time decryption key, decryption time is t1 K_X : X symmetric private key (normal encryption key, not time key) K_{X, t = t1} : X symmetric time key, decryption time is t1 {M} PK_x : Encryption of data M with X's asymmetric public key, or verification of signature on data M {M} PK_{x, t = t1} : Data M encryption with X asymmetric time encryption key {M} SK_x : Decrypting data M with X's asymmetric private key, or signing data M {M} SK_{x, t = t1} : Decryption of data M with X's asymmetric time decryption key {M} K_X : Data M encryption with X symmetric key {M} K_{X, t = t1} : Data M encryption with X symmetric time key {M} K^-1_{X, t = t1} : Decryption of data M with X symmetric time key f (M), f'(M): The value of the data M by the one-way functions f, f'. A one-way function is a function that has the property that it is computationally difficult to obtain the original argument M from a value. Hash function etc.

【0018】

Figure 7 shows a block diagram of the short-time key generation system. First, block 710 generates a unit-time decryption key. Next, in block 720, the value of the key of the last small time key in the time unit to which the small time key corresponds is calculated (generated) by applying a one-way function to the unit time decryption key. Then, the desired small time key is obtained by applying the one-way function to the small time key immediately before the small time key obtained in the block 730.

【0019】

Figure 8 shows a flowchart of how to generate a short-time key. First, in step 810, the value of the last small-time key in the time unit to which the small-time key corresponds is calculated by applying a one-way function to the unit-time decryption key. Then, by applying the one-way function to the small time key immediately before the small time key obtained in step 820, the obtained small time key is obtained. Next, it is determined in step 830 whether all the short-time key values have been calculated, and if NO, the process returns to step 820. If the judgment result is YES, the process ends.

【0020】

In more detail, the steps to generate a short time key are described below. Step 1: Generate a unit-time decryption key with t = t2. More specifically, it generates a unit-time decryption key that is used in the next time unit (t = t2) after the corresponding time unit (t1 = <t <t2). Step 2: Calculate the key value of the last small time key in the time unit to which the small time key applies. The key value shall be the value obtained by applying the one-way function (f) to the unit-time decryption key value in step 1. Step 3: The key value of the short-time key immediately before the short-time key obtained in step 2 is the value obtained by applying the one-way function (f') to the obtained short-time key key value. To do. Step 4: Repeat step 3 until the corresponding time unit of the small time key begins.

【0021】

The method of encrypting using a small time key and a unit time key consists of the following steps. Step 1: When the time key user requests the time encryption key at decryption time t1, the time key management server applies the corresponding unit time encryption key PK._{x, t = t1'}To send. (For example, the unit-time encryption key is the unit-time key with the latest decryption time (t1') that does not exceed t1.) Step 1 is a step that should be selected when security is more important, and can be omitted. Step 2: The time key management server uses the small time key (K) for the message (M) sent by the user._{X, t = t1'}_') And {M} K_{X, t = t1''}To send. (For example, t1'' is the short-time encryption key after t1 and the first decryption time (t1'').) Note that the corresponding K_{X, t = t1''}Skip this step if you do not have or do not need it. Step 3: The user encrypts with the obtained unit time key as follows. {{M} K_{X, t = t}_1''} PK_{x, t = t1'}.. This is the encrypted data encrypted with the unit-time key and the short-time key. Note that step 3 above is a step to be selected when security is more important, and can be omitted.

【0022】

The method of managing (transmitting, storing, etc.) the short time key and the unit time key consists of the following steps. Step 1: The time key management server has a unit time decryption key (SK) at decryption time t11._{x, t = t11}) Is safely stored until time t11. Step 2: When the time key management server receives a decryption request for decryption time t11 after time t11, the unit time decryption key (SK) whose decryption time is t11._{x, t = t11}) Is sent. However, this step 2 is a selectable step and does not necessarily have to be performed. Select when safety is important. Step 3: The time key management server decrypts the decryption time (= t11 + n * stp) from the time key decryptor after time t11 by a multiple of the time unit (stp) of the small time key (n * stp). Applicable short time key (K) upon request_{X, t = t11 + n * stp}) Is sent. At this time, the small time key (K_{X, t =}_{t11 + n * stp}The value of) may be calculated using the step of 1. generating the small time key described above, or the value of the small time key stored securely in the time key management server is used. Step 4: The time key management server repeats step 3 until the time t21 of the next unit time key. Figure 3 shows how to manage the small time key and the unit time key along the time axis. Where SK at t = t12_{X, t = t11}, SK at t = t13_{X, t = t11}, SK at t = t22_{X, t = t21} Does not necessarily have to be sent. It can be selected as appropriate.

【0023】

The method of managing the small time key can be classified before and after the time when the small time key is released. For example, before publication, the value of the short time key may be stored and managed on the server. Alternatively, the server may calculate the value of the short-time key when requesting the short-time key without managing the value of the short-time key. After publication, there is no need to manage the value of the small time key. This is because the value of the short-time key can be uniquely obtained from the value of the unit-time decryption key using a one-way function (assuming it is open to the public).

【0024】

The method of decrypting encrypted data using a short-time key and a unit-time key consists of the following steps. Step 1: The time key decryptor has the encrypted data E and the unit time decryption key (SK) for decryption._{x, t = t1}₁), Small time key (K_{X, t = t1n}) Is obtained. Unit-time decryption key (SK_{x, t = t11}) Is a matter of choice. If the encrypted data is encrypted using the unit-time encryption key, the unit-time decryption key is also acquired. Step 2: Decryptor is {E} K^-1_{X, t = t1n}To calculate. However, K^-1_{X, t = t1n}= K_{X, t = t1n}.. This is the original encrypted data. In this step, if the encrypted data is data encrypted with a unit-time decryption key and a short-time key, the decryptor is {{E} SK._{X, t = t11}} K^-1_{X, t = t1n}To calculate.

[Example]

Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 9 shows an overview diagram showing an embodiment of the hardware configuration of the system used in the present invention. System 100 includes a central processing unit (CPU) 1 and memory 4. The CPU 1 and the memory 4 are connected to the hard disk device 13 (or a storage medium drive device such as MO, CD-ROM23, or DVD) as an auxiliary storage device via the bus 2 via the IDE controller 25. Similarly, the CPU 1 and the memory 4 are connected to the hard disk device 30 (or a storage medium drive device such as MO28, CD-ROM23, DVD, etc.) as an auxiliary storage device via the bus 2 via the SCSI controller 27. The floppy disk device 20 is connected to the bus 2 via the floppy disk controller 19. The system 100 is a system that performs time key generation, time key management, time key encryption, time key decryption, and time key transmission / reception, and the time key management server has the same configuration.

【0025】

A floppy disk is inserted into the floppy disk device 20, and the floppy disk or the like, the hard disk device 13 (or a storage medium such as MO, CD-ROM, or DVD), and the ROM 14 are used as a CPU or the like in cooperation with the operating system. The code or data of a computer program for giving instructions and carrying out the present invention can be recorded and executed by being loaded into memory 4. The code of this computer program can be compressed or divided into multiple pieces and recorded on multiple media.

【0026】

System 100 may further include user interface hardware, a pointing device (mouse, joystick, etc.) 7 or keyboard 6 for input, and a display 12 for presenting visual data to the user. .. It is also possible to connect a printer via the parallel port 16 and a modem via the serial port 15. This system 100 can be connected to a network via a serial port 15 and a modem or a communication adapter 18 (Ethernet or Token Ring card) to communicate with other computers or the like. It is also possible to connect a remote transmission / reception device to the serial port 15 or the parallel port 16 to transmit / receive data by infrared rays or radio waves.

【0027】

The speaker 23 receives the audio signal D / A (digital / analog conversion) converted by the audio controller 21 via the amplifier 22 and outputs it as audio. In addition, the audio controller 21 A / D (analog / digital) converts the audio information received from the microphone 24, and makes it possible to take the audio information outside the system into the system.

【0028】

In this way, this system includes various home appliances such as ordinary personal computers (PCs), workstations, notebook PCs, palmtop PCs, network computers, and TVs with built-in computers, game machines with communication functions, telephones, and so on. It will be easy to understand that it can be carried out by a communication terminal having a communication function including a fax, a mobile phone, a PHS, an electronic notebook, etc., or a combination thereof. However, these components are examples, and not all of them are essential components of the present invention.

【0029】

1. Test system There is a time-dependent constraint as an example of the constraint when answering in a test or the like. For example, in the case of TOEIC, there is a restriction that the hearing test should be conducted for a few minutes from the start of the test, and the writing question page should not be viewed before that. In this way, if there is a restriction that you should not see specific data before the time, you can use the time key in advance to specify the specific part without distributing the specific data after a few minutes in real time via the network. If you encrypt the data, you can distribute the entire data including it electronically in advance. By acquiring the time decryption key at a specific time, the contents of the specific data can be viewed. In this case, if the time unit of the time key is one day, it will hinder the operation of the test system. If the time key is generated in minutes using the method of the present invention, the test taker can start the test at any time within one minute. Further, as an advantage of the present invention, it is not necessary to manage a huge number of time keys as a time key management function. A network test system using an electronic bulletin board system (Fig. 5) consists of the following steps. Step 1: Time key management server (administrator) 510 is the unit time decryption key (SK) at decryption time t11_{x, t = t11}) Is safely stored until time t11. The time key management server is the unit-time decryption key (SK) in the time unit next to the decryption time t11._{x, t = t21}A value obtained by applying a one-way function to the value of) (ft2 = f (SK)_{x, t = t21})) Safely store until time t11. Step 2: When the time key management server 510 passes the time t11, the unit time decryption key (SK) whose decryption time is t11 is displayed on the electronic bulletin board 520._{x, t = t11}) Is published. Step 3: When the time key management server 510 has passed the time (n * stp) which is a multiple of the time unit (stp) of the small time key from the time t11, the small time key (K) whose decryption time is t1n is displayed on the electronic bulletin board 520._{X, t = t1n}) Is published. Step 4: The time key management server 510 repeats step 3'until the time t21 of the next unit time key.

【0030】

In FIG. 5, the time key management server 510 creates a unit time key for each day and a small time key for each minute, and publishes the unit time key and the small time key on the electronic bulletin board 520 every minute. When the test organizer 530 requests to take the test from the test taker X, a part of the test questions is encrypted with a short-time key, and then the whole test question is sent to the test taker X. In this case, Candidate X needs to be prepared to start the test, for example, 5 minutes after receiving the data. Five minutes after receiving the data, obtain the short-time decryption key that encrypts the first problem page from the electronic bulletin board 520. This allows Candidate X to start the exam. In addition, 40 minutes after the start of the test, the short-time decryption key that encrypts the next section is obtained from the electronic bulletin board 520. This allows Candidate X to begin the exam in the next section. Candidate Y can start the exam in minutes regardless of the convenience of Candidate X or the organizer.

【0031】

2. Electronic sealed bidding system Electronically sealed bidding is a system in which a bid is placed in a special electronic envelope that is not opened until a specific time. Use the time key and time key as a special electronic envelope. In bidding, it is necessary to keep the bid amount safe so that it will never be decrypted until the decryption time. In order to reduce the time unit of the decoding time, a unit time key and a small time key are used by the method of the present invention. As a result, for example, the opening time can be determined in units of one minute, and bidding rules can be flexibly set. By using the present invention, the time unit of the decryption time can be reduced, but the number of keys that need to be managed by the time key management station does not increase. Figure 6 illustrates an example of an electronic sealed bidding application. The bidder X620 obtains the unit-time encryption key and the short-time encryption key at the decryption time t1 from the time key management station 610 to encrypt the bid amount, and encrypts the bid amount. Send the encrypted bid amount to the bid management station 650. The bid management station 650 decrypts the encryption information transmitted from each bidder after the decryption time t1 by using the unit-time decryption key and the short-time decryption key acquired from the time key management station 610. If all bids can be decrypted, the cheapest price will be the winning bid. The successful bid result will be announced by the Bid Management Bureau 650.

【0032】

[Effect of the invention]

By using the small time key of the present invention, the time unit of the decryption time can be reduced without increasing the number of time keys managed by the time key management server. In Fig. 4, the time key that the time key management server should manage between t11 and t31 is SK._{x, t = t11}, SK_{x, t = t21}Only. Small time key K_{X, t = t12}, K_{X, t = t13}, K_{X, t = t22}, K_{X, t = t23}Does not need to be managed. Because the small time key K_{X, t = t12}, K_{X, t = t13}Is SK_{x, t =}_t21This is because after the time (t21) when the value of is published, it can be easily calculated by the one-way function (f, f'). Also, similarly, the small time key K_{X, t = t22}, K_{X, t = t23}Is SK_{x, t = t31}After the time (t31) when the value of is published, it can be easily calculated by the one-way function (f, f'). On the other hand, at time (t12), the small time key K_{X, t = t1}If 2 is published, the unit time decryption key SK from the value of this short time key_xIt is difficult to calculate the value of, t = t21 due to the nature of the one-way function. Therefore, the unit-time decryption key is safe even if the short-time keys are released one after another.

【0033】

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the time relationship between a unit time key and a small time key.

[Figure 2]

It is a figure which shows the generation method of a small time key.

[Fig. 3]

It is a figure which shows the method of managing a small time key and a unit time key along a time axis.

[Fig. 4]

It is a figure which shows the relationship between a small time key and a unit time key.

[Fig. 5]

It is a figure which shows the example of the network test system.

[Fig. 6]

It is a figure which shows the example of the electronic seal bidding application.

[Fig. 7]

It is a block diagram which generates a small time key.

[Fig. 8]

It is a flowchart which generates a small time key.

[Fig. 9]

It is an embodiment of the hardware configuration used in the present invention.