With the advent of cloud technologies, there is a growing number of easy-to-use services to store files and share them with other cloud users. By providing security features, cloud service providers try to encourage users to store personal files or corporate documents on their servers. However, their server-side encryption solutions are not satisfactory when the server itself is not trusted. Although, there are several client-side solutions to provide security for cloud sharing, they are not used extensively because of usability issues in key management. In this paper, we propose TwinCloud which is an innovative solution with the goal of providing a secure system to users without compromising the usability of cloud sharing. TwinCloud achieves this by bringing a novel solution to the complex key exchange problem and by providing a simple and practical approach to store and share files by hiding all the cryptographic and key-distribution operations from users. Serving as a gateway, TwinCloud uses two or more cloud providers to store the encryption keys and encrypted files in separate clouds which ease the secure sharing without a need for trust to either of the cloud service providers with the assumption that they do not collude with each other. We implemented TwinCloud as a lightweight application and make it available as open-source. The results of our usability study show the prospect of the secure sharing solution of TwinCloud.
Yin et.al @cite_15 proposed another efficient secure data storage scheme using Elliptic Curve Cryptography (ECC) based PKI. Before using this solution, users need to authenticate to a Certificate Authority (CA) and register for a certificate. When users want to share a file with other authenticated users, the user first encrypts the data with his symmetric key and encrypts the symmetric key with the private key of his her registered certificate. After the encryption process, authenticated users can obtain the public key and decrypt the encrypted key to get the symmetric key. The symmetric key, then, will be used to decrypt the file. The main advantage of this solution is the efficiency of preferring ECC over other algorithms like RSA. Because of the small key length, this solution requires less computation and communication cost.
@cite_15
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Recently, remote user authentication schemes are implemented on elliptic curve cryptosystem (ECC) to reduce the computation loads for mobile devices. However, most remote user authentication schemes on ECC are based on public-key cryptosystem, in which the public key in the system requires the associated certificate to prove its validity. Thus, the user needs to perform additional computations to verify the certificate in these schemes. In addition, we find these schemes do not provide mutual authentication or a session key agreement between the user and the remote server. Therefore, we propose an ID-based remote mutual authentication with key agreement scheme on ECC in this paper. Based upon the ID-based concept, the proposed scheme does not require public keys for users such that the additional computations for certificates can be reduced. Moreover, the proposed scheme not only provides mutual authentication but also supports a session key agreement between the user and the server. Compared with the related works, the proposed scheme is more efficient and practical for mobile devices.