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In a traditional ciphertext-policy attribute-based encryption (CP-ABE) scheme, an access structure, also refereed to as ciphertext-policy, is sent along with a ciphertext explicitly, and anyone who obtains a ciphertext can know the access structure associated with the ciphertext. In certain applications, access structures contain sensitive information and must be protected from everyone except the users whose private key attributes satisfy the access structures.In this paper, we first propose a new model for CP-ABE with partially hidden access structures. In our model, each attribute consists of two parts: an attribute name and its value; if the private key attributes of a user do not satisfy the access structure associated with a ciphertext, the specific attribute values of the access structure are hidden, while other information about the access structure is public.Based on the CP-ABE scheme proposed by Lewko et al. [14] recently, we then present an efficient construction of CP-ABE with partially hidden access structures. Compared to previous works in this field, our construction is more flexible and expressive and is proven fully secure in the standard model.

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Different from the traditional public key encryption, searchable public key encryption allows a data owner to encrypt his data under a user's public key in such a way that the user can generate search token keys using her secret key and then query an encryption storage server. On receiving such a search token key, the server filters all or related stored encryptions and returns matched ones as response.Searchable pubic key encryption has many promising applications. Unfortunately, existing schemes either only support simple query predicates, such as equality queries and conjunctive queries, or have a superpolynomial blowup in ciphertext size and search token key size.In this paper, based on the key-policy attribute-based encryption scheme proposed by Lewko et al. recently, we present a new construction of searchable public key encryption. Compared to previous works in this field, our construction is much more expressive and efficient and is proven secure in the standard model.

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Abstract. Certificateless Public Key Cryptography (CL-PKC) has very appealing features, namely it does not require any public key certification (cf. traditional Public Key Cryptography) nor having key escrow problem (cf. Identity-Based Cryptography). However, it does suffer to the Denialof-Decryption (DoD) Attack called by Liu and Au [1], as its nature is similar to the well known Denial-of-Service (DoS) Attack. Based on CL-PKC, they introduced a new paradigm called Self-Generated-Certificate Public Key Cryptography (SGC-PKC) that captured the DoD Attack and proposed a first scheme derived from a novel application of Water's Identity-Based Encryption scheme. In this paper, we propose a new SGC-PKE scheme that does not depend on the bilinear pairings, which make it be more efficient and more short public keys than Liu and Au's scheme. More importantly, our scheme reaches Girault's trusted level 3 (cf. Girault's trusted level 2 of Liu and Au's scheme), the same level as is enjoyed in a traditional PKI.