KR20180101870A - Method and system for data sharing using attribute-based encryption in cloud computing - Google Patents

Abstract

The present invention relates to a method for sharing data using an attribute-based encryption in a cloud computing environment and a system thereof, which always guarantee a cryptogram of a constant size. The method of the present invention comprises: a setup step of generating a master key (MK) and a public key (PK); a key generation step of generating a secret key (SK_u) and transmitting the same to a corresponding user terminal; a step of storing a unique value (c) and an ID (id_u) of a user (u) in an entire user ID table (T); an encryption step of transmitting a cryptogram (CT) to a cloud server; a cryptogram request step; and a decoding step.

Description

[0001] METHOD AND SYSTEM FOR DATA SHARING USING ATTRIBUTE-BASED ENCRYPTION IN CLOUD COMPUTING [0002]

The present invention relates to an apparatus and method for sharing data using attribute-based encryption in a cloud computing environment. More particularly, the present invention relates to an apparatus and method for sharing data using attribute-based encryption in a cloud computing environment, Data sharing using attribute-based encryption in a cloud computing environment that detects poetry And a system.

The present invention proposes a data sharing technique in a cloud computing environment using attribute-based encryption that always guarantees a certain size of ciphertext regardless of the number of attributes.

An ID-based password encrypts data based on a specific ID. The ID must match in order for the user to decode the data. This is unsuitable for data sharing in a multi-user environment. Attribute-based cryptography encrypts data based on multiple attributes (e.g., degree, age, gender, title, etc.). In order to decrypt the data, the user must satisfy attribute-specific conditions (eg, a master's degree, 35 years of age, male, or higher). This is suitable for data sharing in a multi-user environment. However, most attribute-based passwords are inefficient in terms of storage because the size of the data increases in proportion to the number of attributes. There is a technique for preventing illegal copying of the secret key by inserting the user's identity information (e.g., ID) into the secret key, but it is not suitable for detecting key leakage by restoring the identity information from the secret key.

In addition, the cloud server supports access control of data based on the user's ID. However, this method is not suitable for data sharing for a large number of users, since only the user having the corresponding ID can access the data. Although there are techniques that support granular access control based on multiple attributes, most existing schemes are inefficient in terms of storage because the size of shared data increases in proportion to the number of attributes. In a data sharing environment, a malicious user illegally leaks his / her secret key, thereby allowing an unauthorized third party to access the data.

Accordingly, in order to solve the above-described problems that may occur in the cloud computing environment, the size of the shared data can be kept constant regardless of the number of attributes, and the identity of the user who has leaked the secret key can be tracked More efficient data sharing techniques are needed.

KR 1464727 B1 KR 1593165 B1 US 8615668 B2 JP 5650630 B2

 J. Li, K. Ren, Z. Wan, Privacy-aware attribute-based encryption with user accountability, Information Security. Springer Berlin Heidelberg, (2009) 347-362.  Z. Liu, Z. Cao, D. Wong, White-box traceable ciphertext-policy attribute-based encryption supporting any monotone access structures, IEEE Transactions on, (2013) 76-88.  Z. Liu, Z. Cao, D. Wong, Blackbox traceable CP-ABE: How to catch people leaking their keys by selling decryption devices on eBay, 2013 ACM SIGSAC Conference on Computer Communications Security, 2013, pp. 475-486.

The present invention provides a data sharing method and system using attribute-based encryption in a cloud computing environment for attribute-based user access control and secret key leakage detection that can share data in various user environments will be.

,

∈Z_p를 선택하여 마스터키(MK) 및 공개키(PK)를 생성하는 셋업 단계, 상기 신뢰기관 서버가 상기 마스터키(MK), 상기 공개키(PK), 각각의 사용자(u)의 ID(id_u), 및 사용자(u)의 속성집합(L_u)을 입력으로 하고, k+2개의 임의의 a, c∈Z_p ^*, {r₁, r₂,…, r_k}∈Z_p를 선택하여 비밀키(SK_u)를 생성하고 해당 사용자 단말에 전송하는 키 생성 단계, 상기 신뢰기관 서버가 상기 비밀키(SK_u) 생성을 위해 선택한 고유의 값(c) 및 상기 사용자(u)의 ID(id_u)를 전체 사용자 ID 테이블(T)에 저장하는 단계, 상기 복수의 사용자 단말 중 어느 하나가 메시지(M)를 상기 공개키(PK) 및 접근제어를 위한 속성집합(W)을 입력으로 암호화하여 암호문(CT)을 생성하고 암호문(CT)을 클라우드 서버에 전송하는 암호화 단계, 상기 복수의 사용자 단말 중 어느 하나가 클라우드 서버에 암호문(CT)을 요청하고, 클라우드 서버로부터 암호문(CT)을 수신하는 암호문 요청 단계, 상기 복수의 사용자 단말 중 어느 하나가 수신한 암호문(CT)을 복호화하여 메시지(M)를 추출하는 복호화 단계를 포함하되, 상기 암호화 단계는, 임의의 t∈Z_p를 선택하고 대칭키(Key)를 생성하는 과정, 상기 대칭키(Key)를 이용한 대칭키 암호문(

)을 생성하는 과정, 및 상기 공개키(PK), 상기 접근제어를 위한 속성집합(W), 상기 대칭키 암호문(

)을 입력하여 상기 암호문(CT)를 생성하는 과정을 포함한다.Based encryption that always guarantees a certain size of ciphertext irrespective of the number of attributes in a data sharing system using attribute-based encryption including a plurality of user terminals, a cloud server, and a trusted authority server according to an embodiment of the present invention data sharing method, the trust authority server random g∈G _0,

,

∈ Z _p to generate a master key (MK) and a public key (PK), wherein the trusted authority server comprises a master key (MK), a public key (PK) (id _u), and to input the set of properties (L _u) of the user (u) and, k + 2 of any of the ^{_{a, c∈Z p *, {r}} 1, r 2, ... , r _k } ∈ Z _p to generate and transmit a secret key SK _u to the corresponding user terminal, a unique key c (k) selected by the trust agent server for generating the secret key SK _u ) and the user (u) of ID (id _u) the entire user ID table (T) the release step, any one of the plurality of user terminals, the message (M) for storing the key (PK), and access control (CT) to the cloud server by encrypting an attribute set (W) for inputting a ciphertext (CT) for inputting a ciphertext (CT) to the cloud server A ciphertext request step of receiving a ciphertext (CT) from a cloud server, and a decryption step of deciphering a ciphertext (CT) received by one of the plurality of user terminals to extract a message (M) , to select any t∈Z _p Generating a symmetric key (Key), a symmetric key cipher text using the symmetric key (Key) (

(PK), an attribute set (W) for the access control, a symmetric key cipher text

) To generate the ciphertext (CT).

A data sharing system using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention generates a master key (MK), a public key (PK), and a secret key (SK _u ) corresponding to each user ID A trusted authority server for managing the master key MK, the public key PK, the secret key SK _u and the entire user ID table T, a ciphertext (CT) a) if the transmission or receiving part of the decoding request to the ciphertext (CT) or partial decryption key (g _i ^{D ')} communication unit, a storage unit, and a ciphertext (CT) that stores the ciphertext (CT) for receiving the A cryptographic module for generating a ciphertext (CT) by encrypting a message (M), a decryption module for decrypting a ciphertext (CT), and a decryption module for decrypting the ciphertext , ≪ / RTI > and a cipher text (CT) Transmitting the key (g _i ^{D '),} and comprising: a plurality of user terminals equipped with a communication module for receiving a ciphertext (CT) or partial decoding value (A),

,

∈Z_p를 선택하여 상기 마스터키(MK) 및 상기 공개키(PK)를 생성하고, 상기 마스터키(MK), 상기 공개키(PK), 각각의 사용자(u)의 ID(id_u), 및 사용자(u)의 속성집합(L_u)을 입력으로 하고, k+2개의 임의의 a, c∈Z_p ^*, {r₁, r₂,…, r_k}∈Z_p를 선택하여 상기 비밀키(SK_u)를 생성하고, 상기 비밀키(SK_u) 생성을 위해 선택한 고유의 값(c) 및 상기 사용자(u)의 ID(id_u)를 전체 사용자 ID 테이블(T)에 저장하며,The trusted authority server may use any g < RTI ID = _0.0 >

,

∈Z _p to generate the master key (MK) and the public key (PK), and the master key (MK), the public key (PK), the ID (id _u ) And the attribute set L _u of the user u are input, and k + 2 arbitrary a, c? Z _p ^* , {r ₁ , r ₂ , ..., , R _k} select ∈Z _p to generate the secret key (SK _u), and the unique value of the selected for generating the secret key (SK _u) (c) and _(u id) of the user ID (u) To the entire user ID table (T)

)을 생성하며, 상기 공개키(PK), 접근제어를 위한 속성집합(W), 상기 대칭키 암호문(

)을 입력하여 상기 암호문(CT)를 생성한다.The encryption module of the user terminal generates a symmetric key by selecting an arbitrary t∈Z _p , and generates a symmetric key cipher text using the symmetric key

(PK), an attribute set (W) for access control, a symmetric key cipher text

) To generate the ciphertext (CT).

According to the data sharing method and system using attribute-based encryption in the cloud computing environment according to the embodiment of the present invention, a detailed access control technique based on a plurality of attributes (e.g., degree, age, sex, Is applied to a cloud environment, data can be shared in various user environments.

In addition, according to the data sharing method and system using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention, the size of the shared data can be always maintained regardless of the number of attributes.

In addition, according to the data sharing method and system using attribute-based encryption in the cloud computing environment according to the embodiment of the present invention, the identity of the user who has leaked the secret key can be tracked using the secret key.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more fully understand the drawings recited in the detailed description of the present invention, a detailed description of each drawing is provided.
1 is a schematic diagram of a data sharing system using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention.
2 is a functional block diagram of the user terminal shown in FIG.
3 is a flowchart illustrating a data sharing method using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention.
Figure 4 is a more detailed illustration of the decoding step of Figure 3;
Figure 5 is a more detailed illustration of the tracking step of Figure 3;

It is to be understood that the specific structural or functional description of embodiments of the present invention disclosed herein is for illustrative purposes only and is not intended to limit the scope of the inventive concept But may be embodied in many different forms and is not limited to the embodiments set forth herein.

The embodiments according to the concept of the present invention can make various changes and can take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. It should be understood, however, that it is not intended to limit the embodiments according to the concepts of the present invention to the particular forms disclosed, but includes all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms may be named for the purpose of distinguishing one element from another, for example, without departing from the scope of the right according to the concept of the present invention, the first element may be referred to as a second element, The component may also be referred to as a first component.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like are used to specify that there are features, numbers, steps, operations, elements, parts or combinations thereof described herein, But do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings attached hereto.

를 겹선형 함수라 한다.First, a bilinear map and encryption schemes used in the present invention will be described. Let G and G _T be a group having a prime number of prime p, then a function satisfying the following condition

Is called a folded linear function.

와

에 대하여

을 만족한다.Bilinearity: arbitrary

Wow

about

.

을

만족하는 가 존재한다.Non-degeneracy:

of

Satisfaction exists.

에 대해서

를 계산하는 효율적인 알고리즘이 존재한다.Computability: arbitrary

about

There is an efficient algorithm to calculate

Hereinafter, a data sharing system using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention will be described in detail with reference to FIG. 1 and FIG.

FIG. 1 shows a data sharing system 10 using attribute-based encryption in a cloud computing environment according to an embodiment of the present invention, and FIG. 2 shows a functional block diagram of the user terminal shown in FIG.

Referring to FIG. 1, a data sharing system 10 using attribute-based encryption includes a plurality of terminals 100, 200, and 300, a cloud server 400, and a trusted authority server 500.

Trusted authority server 500 may generate a master key (MSK) and a public key (PK). Also, the trustworthiness institution server 500 receives as input the master key MSK, the public key PK, the attribute set L _{u of the} user u, and the ID _u u of the user u, Lt; _{RTI ID = 0.0} > SK _u. &_Lt; / RTI >

The secret key (SK _u ) is transmitted to the terminal of the corresponding user. Trusted server 500 stores a random value c to select the generated secret key (SK _u) to the entire user ID table (T) with the private key (SK _u),.

Using the trusted party server periodically secret key (SK _u) received by key integrity (key sanity) check, and the secret key (SK _u) if leaked Leaked secret key (SK _u) to the user terminal And tracks the ID (id _u ) of the user who has leaked the secret key (SK _u ).

Each of the user terminals 100, 200, and 300 may communicate with the cloud server 400 or the trusted authority server 500 through a network. The network according to one embodiment includes a wide range of possible communication means such as an open Internet, a wired Internet network including a closed intranet, a wireless Internet communication network interlocked with a mobile communication network, and a computer network capable of various data communication .

One or more terminals of the user terminals 100, 200 and 300 generate a ciphertext (CT) by encrypting data (M, message), and transmit the ciphertext (CT) to the cloud server 400 for storage.

One or more terminals of the user terminals 100, 200 and 300 request a ciphertext (CT) to the cloud server 400 and decrypt the ciphertext (CT) received from the cloud server 400 to extract the message M .

The user terminal may request the cloud server 400 for partial decryption while the user terminal requests the cryptographic key (CT) to the cloud server 400. [

The cloud server 400 calculates and transmits the decoded first decoded value A to the user terminal, and the user terminal calculates the second decoded value B. [ The user terminal performs the remaining decoding using the second decryption value B and the first decryption value A received from the cloud server 400 and extracts the message M. [

When the cloud server calculates A and transmits it to the user terminal, the communication cost can be reduced and the calculation time can be shortened.

The cloud server 400 includes a communication unit for transmitting a ciphertext or partial decryption value A or a ciphertext or partial decryption key g _i ^{D '} And a partial decoding unit for partially decoding the cipher text and calculating a partial decryption value (A, or 'first decryption value') when receiving a partial decryption request for the ciphertext (CT).

Referring to FIG. 2, the user terminals 100, 200, and 300 include an encryption module 110, a decryption module 130, a communication module 170, a memory 180, and a control module 190.

The module used in the present specification may mean a functional and structural combination of hardware for carrying out the technical idea of the present invention and software for driving the hardware. For example, the module may mean a logical unit of a predetermined code and a hardware resource for executing the predetermined code, and does not necessarily mean a physically connected code or a kind of hardware.

The encryption module 110 of the user terminal encrypts the message M by performing an encryption algorithm under the control of the control module 190. At this time, the encryption module 110 generates a ciphertext (CT) using the public key PK, the attribute set W for access control, and the message M as input.

)를 반환한다.The decryption module 130 of the user terminal decrypts the ciphertext (CT) received from the cloud server 400 by performing a decryption algorithm under the control of the control module 190. Decryption module 130 has the public key (PK), the user of the secret key _(U SK), and the ciphertext (CT) as an input, a message (M) or decryption fails (

).

The communication module 170 of the user terminal can perform communication with the cloud server 400 or the trusted institution server 500 through the wired or wireless communication network under the control of the control module 190. [ For example, the communication module 170 may transmit a ciphertext (CT) or partial decryption key (g _i ^{D '} ) to the cloud server 400 over the network and may receive a ciphertext (CT) Can receive the value (A). In addition, when the trusted-institution server 500 requests the key-integrity check, the trust-agent server 500 may transmit the secret key SK _u of the user to the trusted-institution server 500.

The memory 180 of the user terminal may include a program memory and a data memory. Programs for controlling the operation of the first terminal 100 may be stored in the program memory. Data generated during the execution of the programs may be stored in the data memory.

The control module 190 of the user terminal controls the overall operation of the user terminal. That is, it can control operations of the encryption module 110, the decryption module 130, the communication module 170, and the memory 180.

Hereinafter, with reference to FIGS. 3 to 5, it is assumed that the access control for the shared data is supported based on the attribute value assigned for each user using the base data sharing system according to the embodiment of the present invention, This paper discusses the data sharing method using attribute-based encryption in a cloud computing environment.

3 is a flowchart illustrating a data sharing method using attribute-based encryption in a cloud computing environment using the infrastructure data sharing system shown in FIG. FIG. 4 is a more detailed view of the decoding step (S400) of FIG. 3, and FIG. 5 is a view showing the searching step (S500) of FIG. 3 in more detail.

을 가지며, 각각의 속성은

와 같이 세 가지 유형의 값 중 하나를 가진다. 예를 들어, +로 표기된 속성은 사용자가 해당 속성(A_i)을 가지고 있음을 나타내고, -로 표기된 속성은 사용자가 해당 속성(A_i)을 갖고 있지 않거나 해당 속성(A_i)이 사용자의 적절한 속성이 아님을 나타낸다. *로 표기된 속성은 사용자가 해당 속성에 무관함을 의미한다.In the present invention, the user selects one of the following k attributes

And each attribute has

And one of the three types of values. For example, the attribute indicated by + is the user and indicates that it has the property (A _i), - attributes stated in the user does not have the property (A _i) its properties (A _i) have the appropriate user's Attribute. An attribute marked with * means that the user is irrelevant to the attribute.

set up  step

,

를 선택하여 마스터키(MK)와 공개키(PK)를 각각 생성한다(S100).As a preliminary step for the user terminal to generate a ciphertext (CT) related to the message M, the trusted authority server 500 receives k as an input,

,

To generate a master key (MK) and a public key (PK), respectively (S100).

Key generation step

를 선택하여 아래와 같이 비밀키(SK_u)를 생성한다(S200).Trusted server master key (MK), a public key (PK), the set of properties of the user u (L _u), and _(u id) of the user ID u as input and, k + 2 of any

And generates a secret key SK _u as follows (S200).

을 만족한다. At this time,

.

은 전체 사용자 ID 테이블(T)에 저장된다.The secret key SK _u is issued to the user,

Is stored in the entire user ID table (T).

A unique value (c) is added to the secret key (decryption key) to allow the user to find identifiable information when the decryption authority is illegally shared.

Encryption step

A message M is encrypted at any one of the user terminals 100, 200, and 300 to generate a ciphertext (CT) (S300). The ciphertext (CT) generated at the user terminal is transmitted to the cloud server 400.

The user terminal generates a ciphertext (CT) using a public key (PK) and an attribute set (W) for access control.

를 선택하고, 아래와 같이 대칭키(Key, 일회성 대칭키)를 생성한다.Specifically,

And generates a symmetric key (Key, one-time symmetric key) as shown below.

Next, a ciphertext (CT) is generated as shown below.

는 일반적인 대칭키 암호를 이용한 대칭키 암호문(

)을 의미한다.At this time,

Symmetric key ciphertext using general symmetric key ciphers (

).

Decryption step

The user terminal requests the cryptographic text (CT) from the cloud server 400 and receives the cryptographic text (CT) from the cloud server 400. The user terminal having received the ciphertext (CT) from the cloud server 400 decrypts the ciphertext (CT) to extract the message M (S400).

을 반환한다. 사용자의 속성집합이 접근제어를 위한 속성집합을 만족한다면, 암호문(CT)을 복호하여 메시지(M)를 추출한다.First, the user terminal determines whether the attribute set L _u of the user satisfies the attribute set W for access control. If the attribute set L _u of the user does not satisfy the attribute set W for access control,

. If the attribute set of the user satisfies the attribute set for access control, the message (M) is extracted by decoding the ciphertext (CT).

에 대하여 아래와 같이 A_i를 계산한다. To decrypt the ciphertext (CT), the user terminal

, A _i is calculated as follows.

Next, the user terminal calculates B _i as follows.

Next, the user terminal calculates A _i / B _i as follows.

Next, the user terminal computes A / B as follows.

Alternatively, the user terminal calculates A / B by calculating the first decoded value A and the second decoded value B, respectively.

Next, the user terminal computes the following equation to restore the symmetric key.

를 복호하여 메시지(M)을 추출한다.After restoring the symmetric key, a symmetric key cipher

To extract the message (M).

는 공개적으로 알려져 있고 다른 암호문에도 재사용될 수 있다. 따라서, 사용자 단말이 클라우드 서버(400)에 암호문(CT)을 요청(S410)하는 동안 상기 사용자 단말이 부분복호키(

) 클라우드 서버(400)로 보내면서 클라우드 서버(400)에서의 부분 복호를 요청(S420)하는 경우 클라우드 서버(400)는 사용자를 대신하여 A_i 및 제1 복호값(A)을 계산할 수 있다. At this time, the first decryption value A can be calculated by the cloud server 400 (see FIG. 4). That is, the cloud server 400 can partially decrypt the cipher text on behalf of the user terminal. In the present invention

Is publicly known and can be reused in other ciphertexts. Therefore, while the user terminal requests (S410) a ciphertext (CT) to the cloud server 400, the user terminal transmits the partial decryption key

The cloud server 400 may calculate the A _i and the first decryption value A on behalf of the user when requesting the partial decryption in the cloud server 400 by sending it to the cloud server 400 in step S420.

The user terminal receives the first decryption value A from the cloud server 400 and calculates the second decryption value B to perform the remaining decryption and extract the message M at step S430.

When the cloud server calculates the first decryption value A and transmits it to the user terminal, the communication cost can be reduced and the calculation time can be shortened.

Tracking step

The trust institution server 500 tracks the ID of the original key owner by inputting the public key PK, the secret key SK _u received from the user terminal, and the entire user ID table T in operation S500. The trusted authority server 500 periodically requesting the key reliability periodically requests a key sanity check and responds to the user terminal. The specific tracking method is as follows.

As shown in FIG. 5, first, the trust authority server 500 requests the user terminal for a key sanity check (S510). The user terminal transmits the secret key (SK _u , user key) to the trust institution server 500 in response to the request of the trust institution server 500 (S520). Next, the trust authority server 500 confirms the received private key SK _u and tracks the original key owner's ID (S530).

The trusted authority server 500 tracks the ID of the original key owner as follows, with the public key PK, the secret key SK _u received from the user terminal, and the entire user ID table T as inputs.

The tracking method according to the present invention is suitable for frequent modification of user attributes. For example, in an online social network, a user creates groups by assigning different attributes and keys to their social contacts, and then assigns access policies based on the specified attributes. At this time, since the group is dynamic, the user attributes change over time.

Whether or not the secret key SK _u is illegally shared is determined by confirming whether the secret key SK _u is well formed and indicating that the secret key SK _u is the actual output through the key generation step KeyGen .

If the following expression is satisfied, it is determined that the secret key SK _u is well formed.

를 탐색한 후, 최종적으로

를 반환한다. 즉, 잘 형성된 비밀키(SK_u)로 확인된 경우 신뢰기관 서버(500)는 해당 비밀키(SK_u)에 상응하는

를 출력한다. 이때, 신뢰기관 서버(500)와 통신하는 사용자 단말의 아이디가 출력된 아이디와 일치하지 않는다면, 해당 비밀키가 유출되었다고 판단한다.If the above formula is satisfied, the trustworthiness server 500 checks the total user ID table T

And finally,

. That is, if it is confirmed with the well-formed secret key SK _u , the trusted-institution server 500 transmits the secret key SK _u corresponding to the corresponding secret key SK _u

. At this time, if the ID of the user terminal communicating with the trusted-institution server 500 does not match the output ID, it is determined that the corresponding secret key is leaked.

)를 반환한다. 이 경우, 신뢰기관 서버(500)는 사용자 단말이 전송한 비밀키가 키 생성 단계(KeyGen)에 의해 만들어진 것이 아니라 무작위로 생성한 값이며, 따라서 해당 사용자 단말은 합법적 사용자가 아니라고 판단한다.If the above expression is not satisfied, the trust authority server 500 stops searching for the secret key SK _{u and} returns a search failure

). In this case, the trusted-agent server 500 determines that the secret key transmitted by the user terminal is a randomly generated value, not created by the key generation step (KeyGen), and thus the corresponding user terminal is not a legitimate user.

A properly formatted decryption key (secret key) ensures that it works correctly in a properly configured decryption process.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: Data sharing system using attribute-based encryption
100, 200, 300: user terminal
400: Cloud server
500: Trusted authority server

Claims (8)

A data sharing method using attribute-based encryption that ensures a constant size of ciphertext regardless of the number of attributes in a data sharing system using attribute-based encryption including a plurality of user terminals, a cloud server, and a trusted authority server,
If the trusted authority server has any g ∈ G ₀ ,

,

∈ Z _p to generate a master key (MK) and a public key (PK);

The trusted authority server inputs the master key (MK), the public key (PK), the ID of each user ( _u ), and the attribute set (L _u ) of the user (u) + 2 arbitrary a, c? Z _p ^* , {r ₁ , r ₂ , ... , r _k } ∈ Z _p to generate a secret key SK _u and transmit it to the user terminal;

(At this time,

Lt; / RTI >
Storing the unique value (c) selected by the trusted authority server for generating the secret key (SK _u ) and the ID (id _u ) of the user (u) in the entire user ID table (T);
One of the plurality of user terminals encrypts the message M by inputting the public key PK and the attribute set W for access control to generate a ciphertext CT and transmits the ciphertext CT to the cloud server An encryption step for transmitting;
A ciphertext requesting step in which one of the plurality of user terminals requests a ciphertext (CT) from the cloud server and receives a ciphertext (CT) from the cloud server; And
And a decryption step of decrypting a ciphertext (CT) received by one of the plurality of user terminals to extract a message (M), the method comprising:
Wherein the encrypting step comprises:
Selecting an arbitrary t? Z _p and generating a symmetric key;

The symmetric key ciphertext using the symmetric key

); And
The public key (PK), the attribute set (W) for the access control, the symmetric key cipher text

And generating the ciphertext (CT) by inputting the ciphertext (CT)

A Data Sharing Method Using Attribute Based Encryption in Cloud Computing Environments. The method according to claim 1,
The decoding step includes:
If the user terminal

Calculating A _i with respect to A _i ;

If the user terminal

A process of calculating B _i relative;

Calculating A _i / B _i by the user terminal;

A step in which the user terminal calculates A / B;

Restoring the symmetric key satisfying the following equation: And

Wherein the user terminal transmits the symmetric key ciphertext using the restored symmetric key

) And extracting the message (M).
A Data Sharing Method Using Attribute Based Encryption in Cloud Computing Environments. The method according to claim 1,
The ciphertext requesting step and the decrypting step may include:
A step in which the user terminal requests a cipher text to the cloud server;
Transmitting a partial decryption key (g _i ^{D '} ) to the cloud server and requesting partial decryption while the user terminal requests the cipher text to the cloud server;
Wherein the cloud server replaces all

Calculating A _i with respect to A _i ;

Calculating a first decryption value (A) by the cloud server and transmitting the ciphertext (CT) and the first decryption value (A) to the user terminal;

If the user terminal

Calculating B _i and a second decoded value (B) with respect to the first decoded value;

A step in which the user terminal calculates A / B;

Restoring the symmetric key satisfying the following equation: And

Wherein the user terminal transmits the symmetric key ciphertext using the restored symmetric key

) And extracting the message (M).
A Data Sharing Method Using Attribute Based Encryption in Cloud Computing Environments. The method according to claim 1,
Using the trusted party server a secret key (SK _u) the secret key (SK _u) leakage when received by checking the key integrity (key sanity), and a secret key (SK _u) leaking from the user terminal Further comprising the step of tracking an ID (id _u ) of the user who has revealed the secret key (SK _u )
A Data Sharing Method Using Attribute Based Encryption in Cloud Computing Environments. The master key (MK), a public key (PK), and generating a secret key (SK _u) corresponding to each user ID, and the master key (MK), the public key (PK), the secret key (SK _u ), And an entire user ID table (T);
The communication unit receiving a ciphertext (CT) or partial decoding value (A) to send or ciphertext (CT) or partial decryption key (g _i ^{D ')} through a network, a storage to store the ciphertext (CT) unit, and the cipher text ( A partial decryption unit for partially decoding the cipher text and calculating a partial decryption value A when receiving a partial decryption request for the partial decryption value A; And
A decryption module for decrypting the ciphertext (CT), and a ciphertext (CT) or a partial decryption key (g _i ^{D '} ) via the network, (CT) or a partial decryption value (A), the user terminal comprising:
The trusted authority server,
Any g ∈ G ₀ ,

,

∈ Z _p to generate the master key (MK) and the public key (PK)

The master key (MK), the public key _{(PK), ID (id u} ) for each user (u), and a set of properties of the user _(u) (L u) as input and, k + 2 of any a, c? Z _p ^* , {r ₁ , r ₂ , ... , R _k} select ∈Z _p to generate the secret key (SK _u), and the unique value of the selected for generating the secret key (SK _u) (c) and _(u id) of the user ID (u) To the entire user ID table (T)

(At this time,

Lt; / RTI >
The encryption module of the user terminal comprises:
A symmetric key is generated by selecting an arbitrary t? Z _p , and a symmetric key cipher text

),

The public key (PK), the attribute set (W) for access control, the symmetric key cipher text

) To generate the ciphertext (CT)

Data Sharing System using Attribute - based Encryption in Cloud Computing Environment. 6. The method of claim 5,
The decoding module of the user terminal comprises:
all

Lt; _{RTI ID = 0.0} > _{Ai <} / _RTI > and _Bi ,

A _i / B _i and A / B are calculated,

Restores the symmetric key satisfying the following equation,

The symmetric key ciphertext (ciphertext) using the restored symmetric key

) And extracting the message (M)
Data Sharing System using Attribute - based Encryption in Cloud Computing Environment. 6. The method of claim 5,
When the user terminal sends a partial decryption key g _i ^{D '} to the cloud server and requests partial decryption while the user terminal requests a cryptographic key (CT) to the cloud server,
Wherein the partial decryption unit of the cloud server replaces all

For calculating A _i and the partial decoding value (A) and with respect to the to the user terminal sends the ciphertext (CT) and the partial decoding value (A), and

The decryption module of the user terminal

B _i , B, and A /

Restores the symmetric key satisfying the following equation,

The decryption module of the user terminal uses the restored symmetric key to generate the symmetric key ciphertext

) And extracting the message (M)
Data Sharing System using Attribute - based Encryption in Cloud Computing Environment. 6. The method of claim 5,
Using the trusted party server a secret key (SK _u) the secret key (SK _u) leakage when received by checking the key integrity (key sanity), and a secret key (SK _u) leaking from the user terminal (ID _u ) of the user who has leaked the secret key (SK _u )
Data Sharing System using Attribute - based Encryption in Cloud Computing Environment.

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