Mesh-Routed Deferred Settlement: A Proof-of-Concept Architecture for Offline Digital Payments
Keywords:
Deferred settlement, Hybrid encryption, Idempotency, Offline payments, Optimistic concurrency controlAbstract
Digital payment systems such as India’s Unified Payments Interface (UPI) require continuous connectivity at the moment of payment, an assumption that fails in basements, remote regions, and during network outages. This study describes a proof-of-concept implementation of Mesh-Routed Deferred Settlement, focusing on offline payment creation, hop-by-hop message relay, and deferred backend settlement after connectivity is restored. Three threats in this setting are addressed: loss of confidentiality and integrity through intermediate carriers, mitigated by hybrid RSA-OAEP and AES-256-GCM encryption; duplicate settlement caused by concurrent uploads, prevented through an atomic idempotency claim based on the SHA-256 hash of the ciphertext; and replay of captured packets, mitigated by a bounded freshness window and per-payment nonces. Settlement runs in one atomic transaction with optimistic concurrency control and a database uniqueness constraint as a backstop. A Spring Boot backend with a software-simulated mesh reproduces the full packet lifecycle, and automated tests cover encryption correctness, tamper rejection, and exactly-once settlement under concurrent delivery. The central limitation of deferred settlement is that, because the backend cannot verify the payer’s balance during offline transit, multiple offline payments may collectively exceed the available funds.
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