  The cloud model allows many enterprises able to outsource computing resources
at an affordable price without having to commit the expense upfront. Although
the cloud providers are responsible for the security of the cloud, there are
still many security concerns due to inherently complex model the cloud
providers operate on (e.g.,multi-tenancy). In addition, the enterprises whose
services have migrated into the cloud have a preference for their own
cybersecurity situation awareness capability on top of the security mechanisms
provided by the cloud providers. In this way, the enterprises can monitor the
performance of the security offerings of the cloud and have a choice to decide
and select potential response strategies more appropriate to the enterprise in
the presence of the attack where the defense provided by the cloud doesn't work
for them. However, some response strategies, such as Moving Target Defense
(MTD) techniques shown to be effective to secure cloud, cannot be deployed by
the enterprise themselves. In this paper, we propose a framework that enables
better collaboration between enterprises and cloud providers. Our proposed
framework, which offers more in-depth security analysis based on the set of
most advanced security metrics, allows the security experts of the enterprise
to obtain better situational awareness in the cloud. With better and more
effective situation awareness of cloud security, our framework can support
better decision making and further allows to deploy more appropriate threat
responses to protect the outsourced resources. We also propose a secure
protocol which can facilitate more secure communication between the enterprises
and cloud provider. Using our proposed secure protocol, which is based on
authentication and key exchange mechanism, the enterprises can send a secure
request to the cloud provider to perform a selected defensive strategy.
