Research On Leakage-resilient Attribute-based Encryption Mechanisms

In attribute-based encryption(ABE), an access structure is typically composed of a linear secret sharing scheme(LSSS) such as a Boolean formula or an access tree. In this paper, the access structure encoded is in minimal sets, which means there is a smallest monotonic span program with the same access structure. The two leakage-resilient attribute-based encryption schemes presented here are ciphertext-policy ABE(LR-CP-ABE) and key-policy ABE(LR-KP-ABE), both of which can tolerate partial leakage of private key and master key. By using the encoding mechanism mentioned in this paper, short ciphertext in LR-CP-ABE and short key in LR-KP-ABE can be obtained. Additionally, these schemes possess higher decryption efficiency and the decryption cost does not depend on the depth of access structures. Given that the proposed schemes are tolerant of both master key leakage and continual leakage, therefore there are many master keys for universal set Σ and private keys for attribute set S. A refresh algorithm is employed to prevent the leakage of a(master) key beyond the allowable leakage bound. It is proved that the schemes are adaptively leakage-resilient secure standard model under the static hypothesis of Composite Order bilinear groups.The arrival of public key cryptography has symbolized the formation of modern cryptography. Its development has undergone the stages of Public Key Infrastructure(PKI), Identity Based Encryption(IBE), and Attribute Based Encryption(ABE), and has been widely used in the practical application. Therefore, it has important theoretical and practical significance to study the security problem of public key encryption scheme under different leakage attacks. The emphasis of this thesis lies in designing a new leakage-resilient attribute-based encryption scheme in the public key encryption system and analyzing its security.Traditionally, in attribute-based encryption(ABE), an access structure is constructed from a linear secret sharing scheme(LSSS), a boolean formula or an access tree. In this work, we encode the access structure as their minimal sets, which is equivalent to the existence of a smallest monotonic span program for the characteristic function of the same access structure. We present two leakage-resilient attribute-based encryption schemes, ciphertext-policy ABE(LR-CP-ABE) and key-policy ABE(LR-KP-ABE), that can tolerate private key and master key to be partially leaked. By using our encoding mechanism, we obtain short ciphertext in LR-CP-ABE and short key in LR-KP-ABE. Also, our schemes have higher decryption efficiency in that the decryption cost is independent to the depth of access structures. Meanwhile, our proposed schemes provide the tolerance of both master key leakage and continual leakage in the sense that there are many master keys for universal set Σ and many private keys per attribute set S. We explicitly employ a refresh algorithm to update a(master) key while the leakage information will beyond the allowable leakage bound. The schemes are proven to be adaptively leakage-resilient secure in the standard model under the static assumptions in composite order bilinear groups.