  Today, cloud computing is an emerging way of computing in computer science.
Cloud computing is a set of resources and services that are offered by the
network or internet. Cloud computing extends various computing techniques like
grid computing, distributed computing. Today cloud computing is used in both
industrial field and academic field. Cloud facilitates its users by providing
virtual resources via internet. As the field of cloud computing is spreading
the new techniques are developing. This increase in cloud computing environment
also increases security challenges for cloud developers. Users of cloud save
their data in the cloud hence the lack of security in cloud can lose the users
trust. In this paper we will discuss some of the cloud security issues in
various aspects like multi-tenancy, elasticity, availability etc. The paper
also discuss existing security techniques and approaches for a secure cloud.
This paper will enable researchers and professionals to know about different
security threats and models and tools proposed.
