A host validation system runs on a portable storage device, and protects data stored thereon from unauthorized access by host computers. The system identifies a host to which the portable device is coupled, for example by using the host's TPM. This can further comprise identifying the host's current configuration. The system uses the identification and configuration information to verify whether the host is approved to access data stored on the portable device. The system provides the host a level of data access responsive to this verification. This can involve denying all data access to the host, or providing at least some access to data stored on the portable device, for example based on a stored access policy specifying levels of access to provide to specific hosts with specific configurations.