Banking & payments | Modelled case study
Introduce hybrid post-quantum protection at an open-banking API boundary
Where can quantum-resistant handshakes be introduced while legacy aggregators still require classical interoperability?
The modelled organisation
A recognisable problem reaches the operating agenda
This composite scenario follows the API Security Architect · Open Banking Product Owner functions. It is grounded in the cited problem context but does not identify a real customer.
Operating environment
A regulated bank operates real-time and batch payment services across internal platforms, clearing schemes, processors, HSMs, fraud controls, and external counterparties.
What is at stake
A cryptographic change must preserve authorization, settlement finality, scheme interoperability, evidence retention, and uninterrupted customer access.
Situation
The bank controls its gateway but not every client library, certificate stack, or third-party aggregator, making an all-at-once protocol cutover commercially unsafe.
Event that forces action
A new API gateway, long-lived consent data, or a regulated partner asks for a quantum-safe roadmap.
Concrete system boundary
Systems this case study puts in scope
The model is specific about the operational surfaces that must be discovered, changed, or independently checked.
open-banking API gateways
aggregator client stacks
certificate and negotiation policy
compatibility gateway telemetry
Modelled case study walkthrough
How this organisation would use QNSI
The walkthrough connects the real-world problem to a bounded QNSI contribution and an independently reviewable result.
Recognise the operating condition
The bank controls its gateway but not every client library, certificate stack, or third-party aggregator, making an all-at-once protocol cutover commercially unsafe.
Frame the decision the owners must make
Where can quantum-resistant handshakes be introduced while legacy aggregators still require classical interoperability?
Apply QNSI to the controlled boundary
Use QNSI policy tiers and conformance evidence to define native-PQC, hybrid, and exception cohorts without claiming that telemetry alone proves PQC transport.
Leave the team with a concrete result
A partner-by-partner negotiation matrix with downgrade rules, test vectors, expiry dates, and evidence gaps.
Prove the result in the organisation's environment
Each client path requires packet-level verification, performance testing, certificate-policy review, and explicit downgrade acceptance.
What useful success looks like
A decision artifact plus proof from the real environment
The model stops at a target result. It becomes an actual case study only when a customer produces and independently validates this evidence in production.
Decision artifact
A partner-by-partner negotiation matrix with downgrade rules, test vectors, expiry dates, and evidence gaps.
Independent validation boundary
Each client path requires packet-level verification, performance testing, certificate-policy review, and explicit downgrade acceptance.
Real-world problem grounding
Primary sources behind the model
These sources establish the external requirement, failure mode, or risk context used to model this case. They do not endorse HEOSSI or prove that QNSI completed the scenario.
Customer evidence status
This is modelled, not a customer claim
The organisation is a composite and the result is a target state. This page does not prove a deployment, customer outcome, certification, legal conclusion, regulator endorsement, or completed control.