In recent days Cloud computing is a rising technique which offers data sharing with more efficient, effective and economical approaches between group members. To create an authentic and anonymous data sharing, IDentity based Ring Signature (ID-RS) is one of the promising technique between the groups. Ring signature scheme permits the manager or data owner to authenticate into the system in anonymous manner. In conventional Public Key Infrastructure (PKI) data sharing scheme contains certificate authentication process, which is a bottleneck because of its high cost. To avoid this problem, we proposed Cost Optimized Identity based Ring Signature with forward secrecy (COIRS) scheme. This scheme helps to remove the traditional certificate verification process. Only once the user needs to be verified by the manager giving his public details. The cost and time required for this process is comparatively less than traditional public key infrastructure. If the secret key holder has been compromised, all early generated signatures remains valid (Forward Secrecy). This paper discuss about how to optimize the time and cost when sharing the files to the cloud. We provide a protection from collision attack, which means revoked users will not get the original documents. In general better efficiency and secrecy can be provided for group sharing by applying above approache
