Abstract: Cloud computingrelies on sharing of resources to achieve coherence and economies of scale. Cloud resources are shared & owned by multiple users. Security of shared data in multi owner manner is an important and critical aspect due to frequent change of membership. To provide anonymous sharing of data between cloud users group signature & broadcast encryption techniques are used. To provide secure access to accounts one time password technique is used. Security of shared data in multi owner manner is increased by providing authentication at multiple levels. To handle the failure of group admin due to large user requests, it supports to increasing the number of backup group admin, which also improves reliability & scalability.

Keywords: Cloud computing, dynamic groups, reliability, scalability