In the grid security infrastructure (GSI), the authentication is based on traditional public key infrastructure (PKI). Grid user is in a heavily loaded point both in computation and in communication. This results in a limit for the user on the number of resource contributing sites it can use. Being certificate-free and non-interactive, identity-based cryptography (IBC) aligns well with demands of grid computing. In this paper, we first propose the identity-based architecture for grid(IBAG). Unlike the former work, IBAG is absolutely certificate-free. In addition to this, the identity-based encryption and signature schemes for IBAG are presented. Based on the encryption and signature schemes, the identity-based authentication protocol is proposed. Compared with the SAP (SSL Authentication Protocol) in the GSI, the protocol achieves better performance, specially the more lightweight user side. This contributes to the larger grid scalability.