PTLE: Physical Time-Lock and Key Generation from Astrophysical Observations — Quantum-Entropy Multi-Purpose Cryptography from Millisecond Pulsar X-Ray Observations

We introduce the PTLE framework (Physical Time-Lock and key-generation from Astrophysical Observations), a family of cryptographic constructions that derive key material from physical observations whose security rests on quantum mechanics and relativistic causality rather than any mathematical hardness assumption. PTLE fills a gap left by all existing timed-release encryption approaches: it provides a quantum-entropy key source with a physically-enforced time-lock, global reach via orbital deployment, and no trusted third party — none of which are simultaneously achievable by QKD, verifiable delay functions, or trusted-timestamp services. The primary construction, PTLE-Quantum, derives key material from individual X-ray photon arrivals recorded by an orbital instrument observing a private millisecond pulsar set at a designated epoch T. A 30-minute observation of 7 pulsars with a NICER-class instrument yields approximately 2,000–17,255 bits of quantum entropy — sufficient to simultaneously derive a 256-bit session key, authentication key, one-time pad material, and a physical ratchet seed from a single observation event. No mathematical hardness assumption is required: Shor's algorithm and Grover's algorithm have no attack surface against a key derivation step rooted in physical observation. The ground-deployable variant, PTLE-v1, derives keys from stochastic pulsar timing residuals using radio telescopes, providing a physically-enforced causal time-lock and epoch binding. PTLE-v2-Hybrid combines physical epoch binding with a 256-bit cryptographic seed for full IND-CPA security without real-time observatory access. We provide formal security definitions and a precise threat model, prove the epoch binding property, and prove entropy bounds for the quantum photon construction. Working proofs of concept are demonstrated using real NASA NICER X-ray photon data for PSR J0437-4715 (17,255 bits quantum entropy measured) and real NANOGrav 15-year wideband data (0.19 μs verification residual, 5 μs tolerance). Extended architectures include multi-domain k-of-n threshold constructions, epoch hierarchies for selective temporal disclosure, per-message and per-chunk key rotation, and hemisphere-independent global deployment. Applications include harvest-now-decrypt-later immunity, sovereign communications, intelligence declassification, and treaty-bound disclosure. This work is the subject of Australian provisional patents AU2026903450, AU2026903588, and AU2026905145 (OceanSparx Pty Ltd).