We develop a grid platform architecture based on a secure root of trust. This component provides a tamperresistant environment for grid job execution that resists attack even if the host itself is compromised. We use Trusted Computing, a security technology currently being integrated into an increasing number of mainstream PCs, for dynamic trust establishment within the grid. These elements are combined to create a novel and practical solution for the grid malicious host problem, ensuring that data integrity and confidentiality is appropriately protected for jobs that span multiple administrative domains.