Enabling comparable data access control for lightweight mobile devices in clouds
View Patent ↗A new efficient framework based on a Constant-size Ciphertext Policy Comparative Attribute-Based Encryption (CCP-CABE) approach. CCP-CABE assists lightweight mobile devices and storing privacy-sensitive sensitive data into cloudbased storage by offloading major cryptography-computation overhead into the cloud without exposing data content to the cloud. CCP-CABE extends existing attribute-based data access control solutions by incorporating comparable attributes to incorporate more flexible security access control policies. CCP-CABE generates constant-size ciphertext regardless of the number of involved attributes, which is suitable for mobile devices considering their limited communication and storage capacities.
1. A method for encrypting data in a computer based processing system using a trust authority with a public key PK and a master key MK, the method comprising:
sending a request for a partially encrypted header {tilde over (H)} to the trust authority with a specified access control policy Ps;
receiving a partially encrypted header computed by the trust authority, wherein the partially encrypted header {tilde over (H)} is based on the public key PK, the master key MK, and the specified access control policy Ps;
encrypting data using the partially encrypted header {tilde over (H)};
wherein the data is encrypted according to the following algorithm:
Encrypt(Ĥ)→(H, K s ): Given the partially encrypted header, the algorithm produces the session key K s and ciphertext H={ S , C, E S , E S , Ê S , Ê S } to cloud storage; and
further wherein each part of H is generated as follows:
1) randomly choosing two secrets s 1 , s 2 ∈ n ,
2) computing the main secret s=s 1 +s 2 ∈ n and deriving
C=sW∈ ,
3) producing the session key K s =e(G, W) αs and using K s to encrypt the data,
4) computing E S =s 1 T and E S =s 2 T, and
5) computing each of Ê S =s 1 {right arrow over (ψ)} S T·s 1 W=s 1 {right arrow over (ψ)} S λW·s 1 W=s 1 (λ{right arrow over (ψ)} S +1)W and Ê S =s 2 S T·s 2 W=s 2 S λW·s 2 W=s 2 (λ S +1)W.
2. The method of claim 1 , wherein the step of encrypting the data comprises generating the session key K s and the ciphertext H using the partially encrypted header {tilde over (H)}.
3. The method of claim 1 , wherein the computer based processing system is a cloud storage system.
4. The method of claim 1 , wherein the size of any key and any ciphertext overhead remains constant without regard to a number of attributes.
5. The method of claim 1 , wherein the algorithm term
H={ S , C, E S , E S , Ê S , Ê S } represents ciphertext H being generated as a function of:
C, the product of the main secret s (the sum of two random secrets s 1 and s 2 ) and generator W, which are elements of set ;
E S , the product of secret 1 (s 1 ) and T=λW∈ , the product of λ and generator W, elements of set ;
E S , the product of secret 2 (s 2 ) and T=λW∈ , the product of λ and generator W, elements of set ;
Ê S the function of secret 1 (s 1 ), λ (an element of the master key), {right arrow over (ψ)} S (the first part of the partially decrypted header) and generator W; and
Ê S , the function of secret 2 (s 2 ), λ (an element of the master key), S (the second part of the partially decrypted header) and generator W.
6. A method of decrypting data, wherein the method comprises:
storing the data in a computer based processing system, wherein the data includes an encrypted header H and encrypted target data;
receiving a request for access to the data, wherein the request includes a user identity;
partially decrypting an encrypted header H when the user is entitled to access the data based on the user's public key PKLU, privilege LU and access control policy Ps;
sending the partially decrypted header {tilde over (H)} to the user;
wherein partially decrypting the header H is performed according to the following algorithm:
DecDelegate(H, PK u , u , S )→Ĥ: Given the user's public key PK u and privilege u along with the access control policy s , the algorithm outputs {right arrow over (ψ)} S and S when [ν i,j , ν i,k ]∩[ν i,a , ν i,b ]≠Ø for all A i ∈ :
({right arrow over (ψ)} U )=({right arrow over (ψ)} U ) w U , s =({right arrow over (π)} Π 1≤i≤m {right arrow over (w)} i,a ) Π 1≤i≤m ( w i,(a,k) ) ={right arrow over (ψ)} S (mod n )
( Ū )=( Ū ) w s ,Ū =( Π 1≤i≤m i,b ) Π 1≤i≤m ( w i,(j,b) ) = s (mod n );
where {right arrow over (w)} U , s =Π 1≤i≤m ( w i,(a,k) ) and w S ,Ū =Π 1≤i≤m ( w i,(j,b) );
and further wherein the algorithm outputs {tilde over (H)}={H,{right arrow over (ψ)} U −{right arrow over (ψ)} S , Ū − S } as the partially decrypted header.
7. The method of claim 6 , further comprising:
retrieving a session key K s ; Decrypt( , Ĥ)→K S : Given the delegation key and header Ĥ, the algorithm performs the following computation:
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8. The method of claim 7 , further comprising decrypting data utilizing the session key K s .
9. The method of claim 8 , wherein the processing system comprises a cloud storage system.
10. The method of claim 6 , wherein the access control policy Ps is revealed at an attribute domain level.
11. The method of claim 6 , wherein encryption of the header H and the partially decrypting of the encrypted header H are performed over each of a plurality of attribute domains in a batch-processing manner.
12. The method of claim 6 , wherein the algorithm terms
({right arrow over (ψ)} U )=({right arrow over (ψ)} U ) w U , s =({right arrow over (π)} Π 1≤i≤m {right arrow over (w)} i,a ) Π 1≤i≤m ( w i,(a,k) ) ={right arrow over (ψ)} S (mod n );
( Ū )=( Ū ) w S ,Ū =( Π 1≤i≤m i,b ) Π 1≤i≤m ( w i,(j,b) ) = s (mod n ); and
{tilde over (H)}={H,{right arrow over (ψ)} U −{right arrow over (ψ)} S , Ū − S }only if [ν i,j , ν i,k ]∩[ν i,a , ν i,b ]≠Ø for all A i ∈
represent the first and second parts of the partially decrypted header {right arrow over (ψ)} S and S , respectively, as outputted when the user's attribute range (A i ) on the i-th attribute of the attribute set [ν i,a , ν i,b ] matches the access control policy's attribute range on attribute A i [ν i,j , ν i,k ]; and
wherein the partially decrypted header is outputted as a function of encrypted header H, the difference beween the first part of the public key {right arrow over (ψ)} U and partially decrypted header {right arrow over (ψ)} S and the difference between the second part of the public key Ū and the second part of the partially decrypted header S .