  Cloud computing allows users to view computing in a new direction, as it uses
the existing technologies to provide better IT services at low-cost. To offer
high QOS to customers according SLA, cloud services broker or cloud service
provider uses individual cloud providers that work collaboratively to form a
federation of clouds. It is required in applications like Real-time online
interactive applications, weather research and forecasting etc., in which the
data and applications are complex and distributed. In these applications secret
data should be shared, so secure data sharing mechanism is required in
Federated clouds to reduce the risk of data intrusion, the loss of service
availability and to ensure data integrity. So In this paper we have proposed
zero knowledge data sharing scheme where Trusted Cloud Authority (TCA) will
control federated clouds for data sharing where the secret to be exchanged for
computation is encrypted and retrieved by individual cloud at the end. Our
scheme is based on the difficulty of solving the Discrete Logarithm problem
(DLOG) in a finite abelian group of large prime order which is NP-Hard. So our
proposed scheme provides data integrity in transit, data availability when one
of host providers are not available during the computation.
