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15.3 Commercial and Organizational Pract... > 15.3.1 Amazon Web Services (AWS) - Pg. 406

406 CHAPTER 15 Data Security in Cloud Computing Authorized user with reference to bucket: ­ ­ ­ ­ TPA should still be able to handle them in a fast yet cost-effective fashion. This property could essentially enable the scalability of a public audit- ing service even under a storage cloud with a large number of data owners. To achieve these goals, strong cryptographic tools would be employed. For example, we can use the technique called POR [38] to audit data availability and integrity in the cloud. However, it could be hard to achieve all these goals simul- taneously using existing cryptographic tools. In most cases, we may still have to rely on the cloud service provider to audit data. read: can list the file names, size, modified date write: can upload, delete files read access control policy(ACP): can check ACL of a bucket write ACP: can update ACL. Authorized user with reference to object: ­ ­ ­ ­ read: can download the file write: can replace or delete file read ACP: can list ACL of the file write ACP: can modify ACL of the file. 15.3. COMMERCIAL AND ORGANIZATIONAL PRACTICES Although there is still no standardized draft avail- able for data security in cloud computing (up to the time when this book was prepared), com- mercial parties and organizations in the commu- nity do provide various proposals. This section will give a brief overview of the security mech- anisms adopted by the cloud computing ser- vice providers to ensure customer security and privacy. S3 defines four types of users who may be granted access permission: ­ ­ ­ ­ Owner (account holder) Amazon S3 users (by adding amazon.com e-mail address) Authenticated User (sharing globally with all S3 users) Non-authenticated users 15.3.1. Amazon Web Services (AWS) Amazon offers its cloud computing services using Amazon Web Services (AWS) [58], which pro- vides a collection of remote computing services, including Amazon S3, EC2, Virtual Private Cloud (VPC), etc. AWS provides a suit of data security solutions at various levels of the system stack. Amazon S3 provides both bucket- and object- level access control. By default, only authorized access is allowed by the bucket and/or object cre- ator (data owner). Access control lists (ACLs) at the bucket/object level are used to grant user access, which is authenticated via the user's sig- nature with his/her private key. Bucket and object level ACLs are independent. For example, an object will not inherit the ACLs from its bucket automatically. S3 provides the following types of ACLs: In Amazon EC2, security protection is pro- vided at multiple levels such as hypervisor, oper- ating system, virtual machine instance, and API. For hypervisor, EC2 uses a highly customized ver- sion of the Xen hypervisor and provides four separate privilege modes for CPU. The host OS executes in the most privileged mode, the guest OS runs in a lesser-privileged mode, and applications are in the least privileged mode. Host OS can only be accessed by administra- tors of AWS. Customers have full access to their guest OS and can configure multifactor authen- tication. AWS does not have any access privi- lege to customer instances and their guest OS. Different instances running on the same phys- ical machine are isolated from each other via the Xen hypervisor. "Calls to launch and termi- nate instances, change firewall parameters, and perform other functions are all signed by the customer's Amazon Secret Access Key" [61]. Without access to the customer's Secret Access Key, Amazon EC2 API calls cannot be made. In addition, API calls themselves can be encrypted, using SSL, to protect confidentiality. In addition,