Many research efforts are being undertaken to improve shared resources security between Virtual Organizations (VO) in a grid environment, but user security is threatened as organizations in VO keep changing dynamically. VO access should be established only through trust relationships between VO and local users. Generally, there is no trust relationship between classical organization and VO or external members. Access to VO resources by organizations users is only when they possess a Certifying Authority (CA) provided certificate. Additional computing overheads increasing computational overheads are a disadvantage of using public-key for authentication. This paper proposes a novel authentication mechanism through the use of a public key concept being generated from the local Community Authorization Service (CAS) and not CA for increased speed. The proposed architecture accesses resources with dynamically generated keys and a token instead of signing in with credentials for every access by users. Simulation results prove that VO performance improves with the proposed mechanism. © 2014 Elsevier B.V., All rights reserved.