Offline Payments over LoRa Mesh Networks with Asymmetric Compute Placement

Hundreds of millions of people live outside mobile broadband coverage, mostly in rural areas [GSMA 2024]. There, cash remains the only payment instrument, and existing offline schemes either shift double-spending risk to the merchant or require costly secure hardware. We present Trama™ Pagos, a payment architecture for no-signal areas built on a very low-cost LoRa mesh. Its core idea is to reframe the problem: instead of an offline payment between two disconnected parties, we build a relayed online payment. The order is signed on the payer's device, crosses the mesh in seconds and reaches a connected settlement authority, which returns a receipt that can be verified without internet access. We apply Asymmetric Compute Placement (ACP): only the minimal message (on the order of a hundred bytes) travels over the air, while authorization logic, the ledger and the single internet uplink are concentrated at the gateway. For the residual case in which the gateway itself loses connectivity, we propose bounded-exposure provisional authorization: the issuer's worst-case loss is limited by construction to the sum of pre-provisioned per-user allowances. We describe the threat model, the targeted security properties (authenticity, non-repudiation, replay resistance, idempotency and bounded exposure) and a field deployment in Colombia. In that deployment, a signed order reaches the ledger in about 4–5 s. Replayed and tampered orders were rejected in live tests. Double-entry accounting stayed balanced against an external witness. An airtime model estimates a capacity of about 150 users per radio channel.