Research On Public-Key Cryptographic Schemes In Cloud Computing

Cloud computing is a novel computing model.It offers flexible computing resources and pay-to-use services.Under such infrastructure,users are not restrained by time and locations.They can access resources according to their needs and pay for the costs as negotiated.However,security has become the bottleneck of cloud computing in recent years.To cope with,researchers have carried out studies from various aspects.Since cloud computing relies on public channel to transmit data,it suffers from cyber attacks.Public-Key Cryptographic Algorithms(PKCA)is a promising technology to achieve secure data transmission in public channel.PKCA produces a pair of public and private keys for each user.Generally,the public key is publicly known by everyone,and is used for encryption and verification.Meanwhile,private key is secretely kept by each user,and is used for decryption and signing.The introduction of NP hard problem paves the way of PKCA and offers rigorous mathematical supports.With developments of cloud computing,more demonds emerge in the design of PKCA.Take cloud storage and blockchain as examples,four security requirements of data are involved: hash projection,integrity,confidentiality and reliability.Recently,blockchain is widely adopted as trust layer in cloud computing.It relies on hash function to take effect.Recent studies reveal some efficient ways to break the known hash functions.Meanwhile,it also reveals the misuses of anonymity and discentralization of blockchain.Therefore,it calls for a secure design of Public-Key Hash Function(PKHF)for building robust blockchain.What's more,cloud storage offers convienent data outsourcing services but suffers from integrity,confidentiality and reliability threats against the associated data.To cope with,we carry out following researches:1.Research on Public-Key Chameleon Hash Function(PKCHF)to gurantee secure hash projection for cloud data.We propose three novel designs of PKCHF,namely: threshold,homomorphic and policy-driven chameleon hash functions.Our threshold version allows generating redactable hash securely under distributed environment.This allows us to build a redactable and secure blockchain where illegal block contents can be re-written.Moreover,the other two PKCHFs can achieve efficient and autonomous deduplication respectively for cloud storage.This helps decrease the cost of running cloud storage.As guaranteed by our theoretical and experimental evaluations,our proposals are provably secure and efficient.2.Research on public-key based data auditing scheme to guarantee integrity for cloud data.We propose a versatile tag-based auditing scheme.Our novel design allows multiple set of metadata to be integrated into a single set.Thus,metadata is minimized to save storage cost.The evidence suggests that our proposal is secure and as practical as peer works.3.Research on public-key based encrypted deduplication scheme to guarantee confidentiality for cloud data.We propose a dual-level deduplication scheme for encrypted data.Our design allows deduplication to take place at both file level and block level under encryption.This maximizes the savings for storage and bandwidth between server and user.According to analysis,our proposal is provably secure and efficient for large file.4.Research on public-key based signature scheme to gurantee authenticility of cloud data.We propose a redactable-and-linkable ring signature.It achieves anonymity for user meanwhile enabling redactable blockchain,which re-writes any illegal block contents if needed.According to analysis,our proposed scheme is provably secure and much efficient than other works.Based on above,we study four PKCAs to achieve hash projection,integrity,confidentiality and reliability requirements for cloud data.Our proposals help improve security and efficiency for blockchain and cloud storage in cloud computing environment.