vTPM

vTPM, or virtual Trusted Platform Module, is a virtualization-enabled implementation of a TPM that provides the functionality of a hardware TPM to virtual machines. A vTPM allows a VM to perform cryptographic operations, store keys securely, and use TPM-based attestation and sealing without requiring a dedicated physical TPM per VM. In typical deployments, the hypervisor or host provides the vTPM, and each VM receives its own vTPM instance, which may be backed by a hardware TPM, a software emulator, or a combination of both.

In operation, a vTPM presents the TPM interface to the guest OS (for TPM 1.2 or 2.0 commands) while translating those requests to the host’s TPM resources or to a software emulation layer. The vTPM maintains its own non-volatile and volatile state, including PCR values, keys, and platform measurements. This state can be preserved with the VM, migrated with the VM, or backed by a separate trust boundary. Endorsement keys and attestation keys are managed to support remote attestation and binding of VM measurements to trust statements.

Security and use cases: vTPMs enable secure boot or measured boot for virtual machines, protect disk encryption keys, and support remote attestation in cloud or multi-tenant environments. They facilitate VM migration and lifecycle management while maintaining TPM-based trust. Risks include reliance on the host for isolation and potential exposure of vTPM state if not properly protected; robust isolation, careful key management, and trusted boot paths are essential.

Standards and implementations: vTPMs are aligned with the Trusted Computing Group TPM 1.2/2.0 standards. Implementations appear in various hypervisors, such as KVM/QEMU (often using software TPM emulators like swtpm), VMware, and Hyper-V, each integrating a virtual TPM device into the virtual machine environment.