Outsourcing decryption method for protecting revocable user attributes based on cloud environment data

Abstract

The invention discloses an outsourcing decryption method for protecting revocable user attributes based on cloud environment data, and belongs to the technical field of cloud computing security. The method comprises an initialization algorithm, an encryption algorithm, a key generation algorithm, an outsourcing decryption algorithm and an attribute revocation algorithm. The method is based on the cloud environment, public parameters are composed of a fixed number of group elements, an attribute set used for encryption is not limited, user revocation can be executed at each attribute level instead of a system level, and finer-grained user access control is achieved. In addition, user information is not leaked when whether the user is revoked or not and outsourcing decryption is judged, the scheme is proved to be safe under the complexity hypothesis of a composite number order group, and the result shows that the scheme is more efficient and more flexible under the scene of user management in the cloud environment through comparative analysis of the performance of similar schemes.

Description

Technical Field

[0001] The present invention relates to a security technology in a cloud environment, and in particular to a revocable user attribute outsourcing decryption technology. Background Art

[0002] Cloud server is an Internet-based model. Some enterprises or government departments upload data to the cloud service platform to achieve data sharing between their departments. When people enjoy the advantages of these new technologies and services, their concerns about data security and access control also arise. Semi-trusted cloud servers may be curious about the data they store, and unauthorized access by external users may also pose a potential threat to their data. People prefer to make their shared data accessible only to authorized personnel with their specified credentials. In order to prevent these potential threats in the cloud environment, it is usually necessary to adopt relevant knowledge of cryptography to store data in the cloud server in the form of ciphertext.

[0003] In recent years, the research on the efficiency and flexibility of attribute-based encryption and decryption has attracted the attention of scholars from all walks of life. The following research results have emerged in the aspects of outsourced decryption and revocable users. Green et al. proposed an outsourced ABE scheme, which outsourced most of the decryption costs to a trusted third-party server; Lai et al. proposed a verifiable outsourced ABE. Although it prevents data from being dropped, the scheme requires a large amount of decryption costs. Belguith et al. proposed an outsourced decryption scheme based on multiple authorizations. This scheme requires each authorization center to add its own master key to the key, so the encryption and decryption costs of the ciphertext increase. Deng et al. proposed an efficient attribute-based revocable signcryption scheme with outsourced decryption in cloud environments. It can not only outsource decryption, but also has the function of user revocation, but the communication and calculation design in the revocation stage are not efficient enough. The research on revocable ABE schemes can be divided into two types: indirect revocable ABE and direct revocable ABE; Wang et al. proposed an attribute-based direct revocable encryption scheme and its application in cloud storage environments, which realized the outsourcing revocation of users in cloud environments, but its decryption calculation overhead is large.

[0004] Most of the public parameters in the above schemes are composed of attribute-related components. When some user revocation schemes are designed, the public parameters related to the user set are also preset and fixed in advance. When a large attribute set or user set is added to the system, the selection of public parameters will become particularly large, thereby increasing the complexity of encryption and decryption; and when user-related parameters are designed into public parameters, the public parameters must be updated as users are updated. Summary of the invention

[0005] The technical problems to be solved by the present invention are that the encryption and decryption overhead of the authorization center is large, the communication and calculation involved in the revocation phase of the revocable outsourced user are not efficient enough, and the decryption of public parameters is complicated. In view of the shortcomings of the prior art, the present invention aims to provide an outsourced decryption method for revocable user attributes based on cloud environment data protection.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An outsourced decryption method based on cloud environment data protection with revocable user attributes, including: initialization algorithm Setup(λ), encryption algorithm Encrypt(PP,M,S1), key generation algorithm KeyGen(MSK,PP,(A,ρ)), outsourced decryption algorithm Decrypt out (CT,SK out ), attribute revocation algorithm

[0008] Preferably, in the outsourced decryption method based on cloud environment data protection revocable user attributes, the initialization algorithm Setup(λ) is:

[0009] Input security parameter λ, select composite order group G with order N=p1p2p3, where p1, p2, p3 are three completely different prime numbers, randomly selected H1:G→Z N , let U be the user set and S be the attribute set, where the attribute is represented by the attribute name att i and attribute value s i Composition, select MSK = α as the system master key, and then output the public parameters

[0010] The key generation center generates a random number u for each registered user ε ,for Assumptions Is att i User collection of attributes, Is att i The number of users of the attribute,

[0011] The key generation center sends the attribute user set to the cloud server, and the cloud server calculates The specific algorithm is as follows:

[0012] The cloud server calculates the polynomial function based on the attribute user set Finally, the coefficient calculated by Composition and attributes att i Related in are equal to

[0013] Preferably, in the outsourced decryption method based on cloud environment data protection revocable user attributes, the encryption algorithm Encrypt(PP,M,S1):

[0014] The encryption algorithm is executed by the data owner (DO), and the plaintext M and the attribute set S1 used for encryption are input. The attribute set S1 = {s1, s2, ..., s l}, Randomly select s,t1,…,t l ∈Z N , calculate C = Me (g, g) αs ,C0=g s , The data owner will ciphertext Upload to the cloud server,

[0015] The cloud server binds each attribute in the newly uploaded ciphertext CT in

[0016]

[0017] Preferably, in the outsourced decryption method based on cloud environment data protection revocable user attributes, the key generation algorithm KeyGen(MSK,PP,(A,ρ)):

[0018] The key generation center executes the algorithm to distribute keys to data accessors, inputs the public parameter PP, the linear secret sharing scheme LSSS matrix (A, ρ) and the master key MSK = α, and lets S2 be the attribute set composed of the attributes related to the private key SK, and A is composed of the attributes belonging to Z N The n×m matrix is ​​composed of elements of A, ρ represents the mapping function of a certain attribute to a row of matrix A, let i∈{1,…n}, use A i Let ρ(i) represent the attributes associated with this row by mapping ρ, and randomly select ω,r1,…,r n ,y1…y n ∈Z N and a random vector make i∈{1,…,n},α i Yes A i The secret value of the attribute corresponding to the row is calculated:

[0019]

[0020] The key generation center sends the private key SK={(A,ρ),u ε ,k0,ki,1 ,k i,2 ,k i,3 ,k i,4} i∈{1,…,n} Sent to the data accessor.

[0021] Preferably, in the outsourced decryption method based on cloud environment data protection revocable user attributes, the outsourced decryption algorithm Decrypt out (CT,SK out ): When the proxy server receives the partial key of the data access user When retrieving properties related to ciphertext, the proxy server will perform the following operations:

[0022] After the proxy server retrieves the requested ciphertext CT, it will ε and attribute att in S2 i Corresponding Substitution

[0023]

[0024] If one of the calculation results is not equal to 1, it means that the user's attributes are revoked and the calculation is terminated directly. Otherwise, continue to execute the following algorithm:

[0025] 1) If the attribute set S1 of the ciphertext satisfies the access structure (A, ρ), then partially decrypt the ciphertext, let ξ = (1, 0, ..., 0), is the attribute correspondence matrix in the S2 set, and calculates is a vector The value corresponding to the attribute in , where s i ∈S2

[0026]

[0027] where s i =ρ(i);

[0028] 2) The proxy server sends D to the data access user,

[0029] Decrypt(C,D,SK): The data access user executes the decryption algorithm, inserts k0 into D, and calculates

[0030]

[0031] Preferably, in the outsourced decryption method based on cloud environment data protection revocable user attributes, the attribute revocation algorithm When a user in the attribute user collection needs to be updated, the key authorization center will update the attribute user collection To the cloud server, the cloud server Recalculate polynomial function

[0032]

[0033] By calculating the coefficients above Constructs a property-related In the future, if the user is not revoked, the cloud server will use the newly calculated Re-encrypt the relevant ciphertext.

[0034] The beneficial effects of the present invention are:

[0035] 1. The present invention delegates the user revocation management to the cloud server, and implements the user's attribute key revocation without updating the user's private key and public key. The user's attribute-related keys that have not been revoked can still complete normal decryption work if they meet the access policy. Therefore, the revocation method of this solution makes user management more flexible;

[0036] 2. By adopting the improved KP-ABE scheme with unrestricted attributes, the technology of the present invention can reduce the size of the preset value of the public parameter, thereby improving the efficiency of encryption and decryption in disguise;

[0037] 3. After the improvement, the outsourced decryption function can be realized, and a large amount of decryption work can be handled by the proxy server, which improves the user's decryption efficiency. If this solution is applied to actual applications, it will greatly improve the user's encryption and decryption experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Basic flow chart of the present invention;

[0039] Figure 2 Comparison of operation time of encryption algorithm of the present invention;

[0040] Figure 3 Comparison of the running time of the decryption algorithm of the present invention. DETAILED DESCRIPTION

[0041] The following is combined with Figure 1-3 The technical method of the present invention is further described in detail:

[0042] Step 1: Build a security system. Input security parameter λ, select a composite order group G with order N = p1p2p3, where p1, p2, and p3 are three completely different prime numbers, and randomly select H1:G→Z N , let U be the user set and S be the attribute set, where the attribute is represented by the attribute name att i and attribute value s i Composition, select MSK = α as the system master key, and then output the public parameters

[0043] Step 2: The key generation center generates a random number u for each registered user ε ,for Assumptions Is att i User collection of attributes, Is att i The number of users of the attribute,

[0044] Step 3: The key generation center sends the attribute user set to the cloud server, and the cloud server calculates

[0045] Step 3-1: The cloud server calculates the polynomial function based on the attribute user set

[0046] Step 3-2: Cloud server calculation coefficient Composition and attributes att i Related in are equal to

[0047] Step 4: The data owner (DO) executes the encryption algorithm, inputs the plaintext M and the attribute set S1 used for encryption, where the attribute set S1 = {s1, s2, …, s l}, i∈[1,l], randomly select s,t1,…,t l ∈Z N , calculate C = Me (g, g) αs ,C0=g s , Ciphertext Upload to the cloud server.

[0048] Step 5: The cloud server binds each attribute in the newly uploaded ciphertext CT in

[0049] Step 6: The key generation center distributes keys to data accessors, inputs public parameters PP, linear secret sharing scheme LSSS matrix (A, ρ) and master key MSK = α, let S2 be the attribute set composed of attributes related to the private key SK, A is composed of attributes belonging to Z N The n×m matrix is ​​composed of elements of A, ρ represents the mapping function of a certain attribute to a row of matrix A, let i∈{1,…n}, use A i Let ρ(i) represent the attributes associated with this row by mapping ρ, and randomly select ω,r1,…,r n,y1…y n ∈Z N and a random vector make i∈{1,…,n},α i Yes A i The secret value of the attribute corresponding to the row is calculated:

[0050]

[0051] Step 7: The key generation center sends the private key SK={(A,ρ),u ε ,k0,k i,1 ,k i,2 ,k i,3 ,k i,4} i∈{1,…,n} Sent to the data accessor.

[0052] Step 8: The proxy server receives the partial key of the data access user When retrieving properties related to ciphertext, u ε and attribute att in S2 i Corresponding Substitution

[0053]

[0054] Step 8-1: If the calculation result is not equal to 1, it means that the user's attributes are revoked and the proxy server directly terminates the calculation;

[0055] Step 8-2: The calculation result is equal to 1. If the attribute set S1 of the ciphertext satisfies the access structure (A, ρ), then the proxy server partially decrypts the ciphertext and sets ξ = (1, 0, ..., 0). is the attribute correspondence matrix in the S2 set, and calculates is a vector The value corresponding to the attribute in , where s i ∈S2

[0056]

[0057] where s i =ρ(i).

[0058] Step 9: The proxy server sends D to the data access user.

[0059] Step 10: The data access user executes the decryption algorithm, inserts k0 into D, and calculates

[0060]

[0061] Step 11: When a user in the attribute user set needs to be updated, the key authorization center will update the attribute user set To the cloud server, the cloud server Recalculate polynomial function

[0062]

[0063] By calculating the coefficients above Constructs a property-related

[0064] Simulation experiment:

[0065] The simulation experiment uses Java programming language, jpbc2.0 encryption library, the experimental platform is i5 2.5GHz CPU, 8GB memory, and the operating system is Windows 10. The development tool is IntelliJ IDEA, and the JDK version is 1.8. In the experimental setting, the A-curve with a 160-bit group-order symmetric elliptic curve is used, and its base element size is 512-bit. According to the above settings, when using different numbers of attributes (10-50) for encryption and decryption, the experimental results of the running time are as follows Figure 2 , Figure 3 As shown, according to Figure 2 , Figure 3 It can be intuitively reflected that the encryption and decryption operation time of this scheme is better than that of scheme (Wang H, Zheng Z, Wu L, et al. New directly revocable attribute-based encryption scheme and its application in cloudstorage environment), scheme (Han D, Pan N, Li K CA traceable and revocable ciphertext-policy attribute-based encryption scheme based on privacyprotection) and scheme (Li Q, Zhu H, Ying Z, et al. Traceable ciphertext-policyattribute-based encryption with verifiable outsourced decryption in ehealthcloud).

[0066] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features of the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0067] The present invention is intended to cover all such substitutions, modifications and variations falling within the broad scope. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An outsourced decryption method based on cloud environment data protection with revocable user attributes, characterized in that: The cryptographic algorithm comprises: Initialization algorithm Setup(λ), encryption algorithm Encrypt(PP,M,S1), key generation algorithm KeyGen(MSK,PP,(A,ρ)), outsourced decryption algorithm Decrypt out (CT,SK out ), attribute revocation algorithm 2. According to claim 1, the outsourced decryption method based on cloud environment data protection revocable user attributes is characterized in that: The initialization algorithm Setup(λ): Input security parameter λ, select composite order group G with order N=p1p2p3, where p1, p2, p3 are three completely different prime numbers, randomly selected H1:G→Z N , let U be the user set and S be the attribute set, where the attribute is represented by the attribute name att i and attribute value s i Composition, select MSK = α as the system master key, and then output the public parameters The key generation center generates a random number u for each registered user ε ,for Assumptions Is att i User collection of attributes, Is att i The number of users of the attribute, The key generation center sends the attribute user set to the cloud server, and the cloud server calculates The specific algorithm is as follows: The cloud server calculates the polynomial function based on the attribute user set Finally, the coefficient calculated by Composition and attributes att i Related in Equal to 3. According to claim 1, the outsourced decryption method based on cloud environment data protection revocable user attributes is characterized in that: The encryption algorithm Encrypt(PP,M,S1): The encryption algorithm is executed by the data owner (DO), and the plaintext M and the attribute set S1 used for encryption are input. Randomly select s,t1,…,t l ∈Z N , calculate C = Me (g, g) αs ,C0=g s , The data owner will ciphertext Upload to the cloud server, The cloud server binds each attribute in the newly uploaded ciphertext CT in 4. According to claim 1, the outsourced decryption method based on cloud environment data protection revocable user attributes is characterized in that: The key generation algorithm KeyGen(MSK,PP,(A,ρ)): The key generation center executes the algorithm to distribute keys to data accessors, inputs the public parameter PP, the linear secret sharing scheme LSSS matrix (A, ρ) and the master key MSK = α, and lets S2 be the attribute set composed of the attributes related to the private key SK, and A is composed of the attributes belonging to Z N The n×m matrix is ​​composed of elements of A, ρ represents the mapping function of a certain attribute to a row of matrix A, let i∈{1,…n}, use A i Let ρ(i) represent the attributes associated with this row by mapping ρ, and randomly select ω,r1,…,r n ,y1…y n ∈Z N and a random vector make i∈{1,…,n},α i Yes A i The secret value of the attribute corresponding to the row is calculated: The key generation center sends the private key SK={(A,ρ),u ε ,k0,k i,1 ,k i,2 ,k i,3 ,k i,4 } i∈{1,…,n} Sent to the data accessor.

5. According to claim 1, the outsourcing decryption method based on cloud environment data protection revocable user attributes is characterized in that: The outsourced decryption algorithm Decrypt out (CT,SK out ): When the proxy server receives the partial key of the data access user When retrieving properties related to ciphertext, the proxy server will perform the following operations: After the proxy server retrieves the requested ciphertext CT, it will ε and attribute att in S2 i Corresponding Substitution If one of the calculation results is not equal to 1, it means that the user's attributes are revoked and the calculation is terminated directly. Otherwise, continue to execute the following algorithm: 1) If the attribute set S1 of the ciphertext satisfies the access structure (A, ρ), then partially decrypt the ciphertext, let ξ = (1, 0, ..., 0), is the attribute correspondence matrix in the S2 set, and calculates is a vector The value corresponding to the attribute in , where s i ∈S2 where s i =ρ(i); 2) The proxy server sends D to the data access user, Decrypt(C,D,SK): The data access user executes the decryption algorithm, inserts k0 into D, and calculates 6. The outsourced decryption method based on cloud environment data protection revocable user attributes according to claim 1 is characterized in that: The attribute revocation algorithm When a user in the attribute user collection needs to be updated, the key authorization center will update the attribute user collection To the cloud server, the cloud server Recalculate polynomial function By calculating the coefficients above Constructs a property-related In the future, if the user is not revoked, the cloud server will use the newly calculated Re-encrypt the relevant ciphertext.

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