Grid and the Grid Security Infrastructure

21st century scientific applications require fast access to large quantities of data and commensurately fast computational resources. Both resources and data are often distributed in a widearea network with components administered locally and independently. Computations may involve hundreds of processes that must be able to acquire resources dynamically and communicate efficiently. In this paper, the security requirements of largescale distributed (Grid) computing is analyzed and a security policy and the Grid Security Infrastructure (GSI) are explained.