text: 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.
  @cite_15: Cloud computing is set of resources and services offered through the Internet. Cloud services are delivered from data centres located throughout the world. Cloud computing facilitates its consumers by providing virtual resources via internet. The rapid growth in field of "cloud computing" also increases severe security concerns. Security has remained a constant issue for Open Systems and internet, when we are talking about security, cloud really suffers. Lack of security is the only hurdle in wide adoption of cloud computing. Cloud computing is surrounded by many security issues like securing data and examining the utilization of cloud by the cloud computing vendors. This paper proposes a scheme to securely store and access of data via internet. We have used ECC based PKI for certificate procedure because the use of ECC significantly reduces the computation cost, message size and transmission overhead over RSA based PKI as 160-bit key size in ECC provides comparable security with 1024-bit key in RSA. We have designed Secured Cloud Storage Framework (SCSF). In this framework, users not only can securely store and access data in cloud but also can share data with multiple users through the unsecure internet in a secured way. This scheme can ensure the security and privacy of the data in the cloud.
summary: 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.