Abstract: One embodiment relates to a method for enabling an entity to delegate calculation of a bilinear pairing value e(A,B) between two values A and B to a calculation server. The entity may select public elements P1 and P2 and secret elements S1 and S2, two of the elements from among P1, P2, S1, and S2 being selected to be equal to A and B, generate elements R1=vS1, R2=uS2, T1=uP1+S1, T2=vP2=S2, where u and v are random numbers, and transmit R1, R2, T1, and T2 to the calculation server. The server may calculate (a1)y=e(T1,T2)[e(R1,P2)e(P1,R2)]?1, and (a2)z=e(D1,D2), y and z designating two integers equal to 1 or to an integer c, D1 and D2 designating two public elements from among A and B or from among R1 and R2 and transmit a1 and a2 to the entity. The entity may obtain the value e(A,B) from a1 or a2.

Abstract: One embodiment relates to a method of updating, by an electronic device of a first user of a tree of data files and/or folders of the first user stored in a storage server configured to implement a re-encryption mechanism, this tree comprising at least one target folder that the first user has authorized a second user to access by providing the storage server with a re-encryption key for this target folder from the first user to the second user.

Abstract: One embodiment relates to a method of updating, by an electronic device of a first user of a tree of data files and/or folders of the first user stored in a storage server configured to implement a re-encryption mechanism, this tree comprising at least one target folder that the first user has authorized a second user to access by providing the storage server with a re-encryption key for this target folder from the first user to the second user.

Abstract: One embodiment relates to a method for enabling an entity to delegate calculation of a bilinear pairing value e(A,B) between two values A and B to a calculation server. The entity may select public elements P1 and P2 and secret elements S1 and S2, two of the elements from among P1, P2, S1, and S2 being selected to be equal to A and B, generate elements R1=vS1, R2=uS2, T1=uP1+S1, T2=vP2=S2, where u and v are random numbers, and transmit R1, R2, T1, and T2 to the calculation server. The server may calculate (a1)y=e(T1,T2)[e(R1,P2)e(P1,R2)]?1, and (a2)z=e(D1,D2), y and z designating two integers equal to 1 or to an integer c, D1 and D2 designating two public elements from among A and B or from among R1 and R2 and transmit a1 and a2 to the entity. The entity may obtain the value e(A,B) from a1 or a2.