Berkeley Transport Protocol (BTP): A Post-Quantum Application Substrate with Witness-Anchored Identity

This whitepaper accompanies the BTP v0.7.0 reference implementation at https://git.securityops.co/cristiancmoises/btp. The normative protocol specification (SPEC.md and the family of SPEC-*.md addenda) is the load-bearing artefact; this paper summarises and contextualises those specifications. Status of the protocol: pre-1.0. The remaining v1.0 gates are operational, not implementation; see §10 of the paper for the complete list. The conformance test suite is included in v0.7.0 (29 normative test vectors); the reference implementation passes 29/29 MUST-level vectors. The author retains the BTP trademark per TRADEMARK.md in the source repository. The text of this whitepaper is CC-BY 4.0; the reference implementation is Apache-2.0.