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arXiv · 2605.02276

Post-Quantum Cryptography Migration in Australian Real-Time Payment Infrastructure: A Monte Carlo Simulation Study of the New Payments Platform

Nazmus Salehin Sammo
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Abstract

Australia's New Payments Platform (NPP) processes 5.2 million real-time transactions per day under a 2,000 ms end-to-end SLA. With cryptographically relevant quantum computers projected for 2030-2035, financial institutions face a post-quantum cryptography (PQC) migration requirement. This paper presents a simulation study of the NIST FIPS 204 and 205 signature standards (ML-DSA, SLH-DSA/SPHINCS+) together with the NIST-selected Falcon algorithm (the forthcoming FIPS 206) in Australian payment infrastructure. Using signing latency measured with liboqs 0.14.0, we simulate 1,000 seasonally mixed days across NPP, RITS and SWIFT routes. All ML-DSA and Falcon variants achieve 100% SLA compliance, with a worst-case NPP p99 overhead of 1.57 ms (0.079% of the SLA budget). We introduce the Crypto Dilution Index (CDI), showing that PQC signing accounts for under 4% of end-to-end latency for every non-SPHINCS+ algorithm, so algorithm choice is not latency-driven. SPHINCS+ is the exception: at NPP volumes its signing time saturates a standard two-unit HSM pool, giving 0% NPP compliance, though it remains viable on the lower-rate RITS and SWIFT routes. A message-format analysis finds that SWIFT imposes no signature-size constraint. SWIFT authentication is applied out-of-band at the SWIFTNet messaging/transport layer, so neither the signature nor the verifying key travels in the Block-4 message text; every NIST PQC signature is size-compatible with SWIFT. Under a conservative harvest-now-decrypt-later scenario with a 2030 quantum arrival, roughly 9.56 billion NPP records generated between 2026 and 2029 would be retroactively exposed. We recommend ML-DSA-65 with ML-KEM-768 as the default across NPP and SWIFT, with Falcon-512 where genuinely in-band, size-constrained carriage is required.

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Nazmus Salehin Sammo. 2026-08-27. Post-Quantum Cryptography Migration in Australian Real-Time Payment Infrastructure: A Monte Carlo Simulation Study of the New Payments Platform. https://arxiv.org/abs/2605.02276

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