Remote attestation is the activity of making a claim about properties of a target by supplying evidence to an appraiser over a net- work. We identify ve central principles to guide development of attes- tation systems. We argue that (i) attestation must be able to deliver temporally fresh evidence; (ii) comprehensive information about the tar- get should be accessible; (iii) the target, or its owner, should be able to constrain disclosure of information about the target; (iv) attestation claims should have explicit semantics to allow decisions to be derived from several claims; and (v) the underlying attestation mechanism must be trustworthy. We illustrate how to acquire evidence from a running system, and how to transport it via protocols to remote appraisers. We propose an architecture for attestation guided by these principles. Virtualized platforms, which are increasingly well supported on stock hardware, provide a natural basis for our attestation architecture.