2.1. Data Storage On Cloud

Cloud storage (Figure 2) is a model of networked enterprise storage where data is stored in virtualized pools of storage which are generally hosted by third parties. Hosting companies operate large data centers, and people who require their data to be hosted buy or lease storage capacity from them. The data center operators, in the background, virtualize the resources according to the requirements of the customer and expose them as storage pools, which the customers can themselves use to store files or data objects. Physically, the resource may span across multiple servers and multiple locations. The safety of the files depends upon the hosting companies, and on the applications that leverage the cloud storage.

Figure 2. Cloud Storage

• When data is distributed it is stored at more locations increasing the risk of unauthorised physical access to the data. For example, in cloud based architecture, data is replicated and moved frequently so the risk of unauthorised data recovery increases dramatically. (e.g. disposal of old equipment, reuse of drives, reallocation of storage space). The manner that data is replicated depends on the service level a customer chooses and on the service provided. Different cloud vendors offer different service levels. Risk of unauthorized access to data can be mitigated through the use of encryption, which can be applied to data as part of the storage service or by on-premises equipment that encrypts data prior to uploading it to the cloud.
• The number of people with access to the data who could be compromised (i.e. bribed, or coerced) increases dramatically. A single company might have a small team of administrators, network engineers and technicians, but a cloud storage company will have many customers and thousands of servers and therefore a much larger team of technical staff with physical and electronic access to almost all of the data at the entire facility or perhaps the entire company. Encryption keys that are kept by the service user, as opposed to the service provider limit the access to data by service provider employees.
• It increases the number of networks over which the data travels. Instead of just a Local Area Network (LAN) or Storage Area Network (SAN), data stored on a cloud requires a WAN (wide area network) to connect them both.
• By sharing storage and networks with many other users/customers it is possible for other customers to access the data, sometimes because of erroneous actions, faulty equipment, a bug and sometimes because of criminal intent. This risk applies to all types of storage and not only cloud storage. The risk of having data read during transmission can be mitigated through encryption technology. Encryption in transit protects data as it is being transmitted to and from the cloud service. Encryption at rest protects data that is stored at the service provider. Encrypting data in an on-premises cloud service on-ramp system can provide both kinds of encryption protection.

A cloud provider provides two cloud-based services: storage and content delivery. A content provider utilizes these two services to store and distribute her content to multiple subscribers. The content provider and subscribers can access content via a cloud-based application service, which reads and manages the content stored in the storage service via cloud storage APIs. The application service is an application deployed in the cloud by the content provider or a third party. The content provider can use multiple cloud-based services from different cloud service providers to host her application service, content storage service, and content delivery service. The problem is identified in the systems with a Minimum distributed peer-to- peer systems. To achieve an MDT objective for a group of client requires judicious use of client uplink and downlink capacities, which are typically highly asymmetric as offered to their clients and download speeds that are significantly larger than upload speeds. In this paper we investigate the potential benefit from the on- demand deployment of cloud resources to upload capacity, we propose the use of Bit Torrent in receiving the entire content[6]. The major aspects of Content distribution are,

• Integrity and Authenticity: Safeguarding the accuracy and typically completeness of data and processing methods. Unauthorized single entities cannot change data; adversaries cannot substitute a forged document for a requested one.
• Availability and Persistence: Ensuring that authorized users have access to data and associated assets when required. For a content distribution system this often means always. This property entails stability in the presence of failure or changing node populations.
• Performance: The time required for performing the operations allowed by the system, typically publication, searching and retrieval of documents.

A BitTorrent client is a computer program that manages downloads and uploads using the Bit Torrent protocol. Bit Torrent is for distributing large amounts of data over the Internet. Bit Torrent is one of the most common protocols for transferring large files and it has been estimated that networks collectively have accounted for roughly 43% to 70% of all Internet Traffic[2]. The Bit Torrent protocol can be used to reduce the server and network impact of distributing large files. Rather than downloading a file from a single source server, the Bit Torrent protocol allows users to join a file of hosts to download and upload from each other simultaneously.

Broadcast Encryption (BE) schemes enable the sender of a message to specify a subset of the registered (the target set or privileged set), who will be able to decrypt the ciphertext sent to all users via a broadcast channel. The complement of the target set (in the set of the registered users) is called the revoked set[3]. To accomplish user revocation when sending a message, a BE generally generates three parts: the ID Header, that is a bit-string that unambiguously identifies the target set/revoked set; the Key Header, that encapsulates a session key for the privileged users; and the Message Body, that contains the payload encrypted under the session key.

Broadcast encryption is the cryptographic problem of delivering encrypted content (e.g. TV programs or data on DVDs) over a broadcast channel in such a way that only qualified users can decrypt the content. The challenge arises from the requirement that the set of qualified users can change in each broadcast emission, and therefore revocation of individual users or user groups should be possible using broadcast transmissions, only, and without affecting any remaining users. 26

Figure 3. Digital Signature

Figure 4. Group Signature

A Group Signature scheme GS = (GKg, GSig, GVf, Open) consists of four polynomial-time algorithms:

• The randomized group key generation algorithm GKg takes input 1k , 1n , where k ∈N is the security parameter and n ∈ N is the group size (ie. the number of members of the group), and returns a tuple (gpk, gmsk, gsk), where gpk is the group public key, gmsk is the group manager's secret key, and gsk is an n-vector of keys with gsk[i] being a secret signing key for player i ∈ [n].
• The randomized group signing algorithm GSig takes as input a secret signing key gsk[i] and a message m to return a signature of m under gsk[i] (i ∈ [n]).
• The deterministic group signature verification algorithm GVf takes as input the group public key gpk, a message m, and a candidate signature σ for m to return either 1 or 0.
• The deterministic opening algorithm Open takes as input the group manager secret key gmsk, a message m, and a signature σ of m to return an identity i or the symbol ⊥to indicate failure. Figure 3 shows the Digital Signature and Figure 4 shows Group Signature.

The overarching goal of this setting is to get minimizing the maximum time of bulk synchronous content distribution where it takes any client in a set to download content of the required file. In the paper, the authors have developed a formulation of Bit Torrent to split the content over the file, through the cloud resources. In future work the authors would use another content distribution algorithm by implementing RSA algorithm along with dynamic broadcast encryption algorithm to provide security in the cloud.