a Possession Model:
It is used for keeping data files on unstructed storage which provide RSA based homomorphic linear authenticator for giving randomly sampling a few block of the file. Thus it may leak user data information to external parties because of their protocol which is not secure [7]. The Proof of Retrievability Model in which spot checking and error correcting code are used [8]. A skip list based mechanism which then makes the use of provable data possession with full dynamics support but the verification in protocol requires linear combination of samples blocks .Thus it does not support secure transmission of data [5].
B. The Virtual Machine Technique of Security:
In the figure1, there are user, cloud server and third party auditor as explain in the previous section. As client request the cloud server to provide service in which cloud server initially authenticate the client and then provide a virtual machine by means of Software as a service.
In Virtual Machine, RSA is used for secure communication between user and cloud server where as SHA-512 algorithm is used for data integrity but problem over here is that SHA-512 is designed only for 32 bit machine [2].
C. Short Signature Technique to Security:
It is based on computational Diffe- Hellman algorithm, elliptic curve and hipper elliptic algorithm, digital signature algorithm in which signature length is half size of DSA signature on similar level of security. The plan for making short signature is to make reliable system in which signature typed in by human or signatures are sent under low bandwidth channel but problem over here is that Diffe–Hellman algorithm shared secret at both end of communication link (key agreement) which provide only key management but not authentication where as in DSA which provide only authentication but not key management [9].
D. An Overview of Privacy Preserving Public Auditing:
In existing systems, third party auditor demanding local copy of user outsourced data. So this will increase the possibility of client files to be stolen by third party auditor. Thus the correctness of data is being put at high risk and it is not provide any assurance on data integrity, availability, threat of identity spoofing attack, information disclosure on upload / download attack, denial of service attack [1].
The goal of Privacy Preserving Public Auditing is to achieve the uniquely integrate homomorphic linear authenticator along with arbitrary masking technique. In this protocol, it uses linear combination of sampled blocks of server response which masked with arbitrary generated by server. As using arbitrary masking, the third party auditor has no longer all information which significant to make up correct group of linear equation that means the TPA does not demand local of copy user data content [1],[3],[4].
To fulfill this goal, system uses two algorithms which are as follows:
1) MAC Based Solution:
The massage authenticator code is used to authenticate the block of data in which client upload block of data where uploaded data go through MAC to cloud sever which provide secret key to third party auditing . so limitation on these solution are TPA acquire priori information of data blocks for identification , data files to be verify as secret key are fixed [1],[6].
2) HLA Based Solut
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