الفهرس 
Cloud Computing Overview……………………………………Only 14 pages are availabe for public view
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Abstract
Cloud computing is widely used by many users, so any one must be authenticated before accessing any service into the cloud. In this thesis, a two-factor authentication scheme is proposed to authenticate users in cloud computing. The first factor uses the traditional user name and password, while the second factor uses one time password, which is valid for only one login session or transaction. This authentication scheme can resist practical attacks, easy for users, doesn’t have strong constrains, and doesn’t require specific extra hardware. After authenticating the user to access the cloud, users can use cloud storage service to store important files and access it anytime and anywhere easily. An efficient two-stage cryptography scheme is proposed to encrypt files before sending into the cloud. Plaintext can be divided into two parts. In each part, half of characters must be encrypted. Each one is encrypted using a unique key which is generated using logistic chaos model theory. This scheme achieves less complexity and reduces the execution time of encryption and decryption.