Secure Offline Digital Euro Payments: Cryptographic Execution Control Without Surveillance

Abstract Relay-Resistant Offline Payments Without Tracking: Execution-Time Cryptographic Authorization for Secure CBDC Systems Offline digital payments today face a fundamental security trade-off. Systems either rely on proximity assumptions and device-based heuristics — which are vulnerable to relay attacks — or they depend on persistent identity tracking and online verification to prevent fraud. Both approaches introduce structural weaknesses. This paper presents a novel architecture for secure offline payments that replaces proximity-based and identity-tracking controls with deterministic, fail-closed cryptographic execution authorization. The system introduces Algorithmic Logic Fingerprints (ALF) as execution predicates embedded at the transaction finality boundary. Instead of trusting physical proximity or backend monitoring, payment execution is conditioned on cryptographically validated authorization logic that binds transaction constraints, usage limits, and contextual validity directly to the execution event. The architecture enables: Relay-resistant offline transactions Fraud prevention without continuous connectivity Privacy preservation without persistent identity tracking Deterministic fail-closed execution control We demonstrate that this model achieves three properties traditionally viewed as mutually incompatible: Strong offline security User privacy protection Fraud and double-spend prevention By enforcing authorization at irreversible transaction finality rather than relying on post-transaction monitoring, the proposed system addresses core vulnerabilities in EMV contactless payments and establishes a structural foundation for secure offline Central Bank Digital Currency (CBDC) deployments. Offline payments do not require surveillance to be secure.They require execution-time cryptographic enforcement. Keywords: offline payments, relay attacks, algorithmic logic fingerprints, virtual identities, CBDC, trusted execution environments, privacy-preserving fraud prevention