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Writing
Notes on payment systems, device software, transaction uncertainty, platform design, and the emerging role of AI in commerce. I write from the questions that appear in real operating conditions.
A host can approve a payment while the terminal still shows UNKNOWN. That third state is not a bug — it's the whole point.
A short field guide to the structure that carries every EMV response — tags, lengths, primitives, constructed nesting — with a live parser.
The contactless-with-CVM threshold quietly moved in most European markets during 2024. What the practical implications look like.
PCI's MPoC standard formalises PIN entry on off-the-shelf phones. The assumptions worth challenging in an integration review.
Terminal firmware breaks in patterns. Three rules would eliminate about half of the incidents I've been paged for.
The temptation is to log everything. The practical answer is more like ten fields, plus a mechanism for turning on more when you need them.
SoftPOS acceptance has passed the novelty stage. What the integration realities look like now that the certifications are stable.
Kernel updates arrive with regularity, and each one triggers a certification cycle. What actually goes wrong.
Signature-based card verification in the US is quietly winding down. The remaining edge cases are worth planning around.
Pushing firmware to a fleet is easy in a lab and hard in the field. What actually goes wrong at scale.