Public key infrastructure (PKI) is presently deployed in most grid implementations. Existing PKI-based grid systems make extensive use of public key certificates, both long-term and short-term, in order to support various grid security services, such as single sign-on, mutual authentication and delegation. Orthogonally, the emergence of identity-based cryptography (IBC), which is certificate-free, makes possible more lightweight, simpler public key management techniques than that of conventional certificate-based PKI. In this chapter, the authors study how properties of IBC can be used to design alternative grid security infrastructures which support grid security services in a more clean and natural way.