We present the design and formal analysis of a remote attestation protocol and accompanying security architecture that generate evidence of trustworthy execution for legacy software. For formal guarantees of measurement ordering and cryptographic evidence strength, we leverage the Copland language and Copland Virtual Machine execution semantics. For isolation of attestation mechanisms we design a layered attestation architecture that leverages the seL4 microkernel. The formal properties of the protocol and architecture together serve to discharge assumptions made by an existing higher-level model-finding tool to characterize all ways an active adversary can corrupt a target and go undetected. As a proof of concept, we instantiate this analysis framework with a specific Copland protocol and security architecture to measure a legacy flight planning application. By leveraging components that are amenable to formal analysis, we demonstrate a principled way to design an attestation protocol and argue for its end-to-end correctness.