Design And Analysis Of Functional Encryption

Functional Encryption?FE?is a novel paradigm that extends the notion of traditional public key encryption.It covers a range of public key encryption systems such as identity-based encryption?IBE?,inner product encryption?IPE?and attribute-based encryption?ABE?.Because of its flexibility,scalability,and the ability to achieve fine-grained access control over encrypted data,function encryption has a wide range of application in cloud storage and has become one of the hot research topics in current public key cryptosystem.This thesis focuses on the study of specific function encryption schemes from the perspective of security and efficiency,and has achieved the following results.1.We studied the issue of security reduction and security loss in the construction of fully secure IBE scheme.The classical dual system paradigm requires?46??q₁+q₂?transition steps,hence results in?46??q₁+q₂?loss for security reduction,where q₁,q₂ is the number of key queries in phase 1 and phase 2 respectively.We presented an IBE scheme with tighter security reduction in prime order bilinear groups by using delayed parameters and dual pairing vector space.The security loss of our scheme is slashed to?46??q₁?from?46??q₁+q₂?.Our scheme is fully secure,and the security is based upon the standard decisional linear?DLin?and three-party Diffie-Hellman assumption.2.Decentralized attribute-based encryption is a special form of multi authority ABE systems.It does not require any central authority?CA?,which makes system more scalable.There is no requirement for any global coordination other than the creation of an initial set of common reference parameters and different attribute authorities?AA?need not even be aware of each other.We proposed a more efficient decentralized ABE in prime-order groups by using extended dual system groups.Our proposed scheme is fully secure under the standard6)6)-Lin assumption in random oracle model and can support any monotone access structures.Compared with existing fully secure decentralized ABE systems,our construction has shorter ciphertexts and secret keys.Moreover,fast decryption is achieved in our system,in which ciphertexts can be decrypted with a constant number of bilinear pairings.3.We introduced a new multi-authority ciphertext policy attribute-based encryption?MA-CP-ABE?system.Our system possesses multiple CA and AA,which can avoid the performance bottleneck incurred by relying on a single central authority.Any party can become a CA by creating a public key.The CA issue identity-related keys to users and AA issue attribute-related keys to users.The authorities can function entirely independently,and the corruption of some authorities will not affect the operation of uncorrupted authorities,which makes our system more robust.Moreover,we presented two concrete instantiations that will be proved fully secure in the standard model.By using attribute aggregation,the first scheme constructed in composite-order bilinear group and can work for any monotone access structure achieves constant size ciphertext for AND-gate policy in prime-order bilinear group.The second one.4.In order to resist side channel attacks,leakage resilient cryptography is proposed and becomes an important research direction.It seeks to build more excellent security models allow that cryptographic scheme remains secure even when some information about secret key is leaked.We presented a modular framework for designing leakage-resilient FE schemes based on extended predicate encoding.We introduced the formalized definition of leakage-resilient predicate encodings and showed a generic construction of fully secure leakage-resilient FE schemes for a large class of predicates.We can instantiate our framework in prime order bilinear groups to obtain concrete schemes.The proposed schemes can resist the continual memory leakage attack and allow leakage on both master key and secret keys.