It identifies the requirements for a vTPM, including those related to migration between hardware platforms.It introduces a vTPM architecture that meets these requirements, including extensions to the standard TPM command set and a protocol for secure vTPM migration.It describes our implementation of this vTPM architecture on Xen, including support for remoteintegrity attestation of the complete system: boot loader, hypervisor, vTPMsubsystem, operating systems, and applications.It discusses four alternative schemes for certifying a vTPM’s security credentials, including the trade-offs involved in choosing between them.It demonstrates that our vTPM facility works by running an existing TPM application inside Xen virtual machines.