A Crypto-Agile Post-Quantum Architecture for Banking Systems
Josephat Kasile, Isaac Shaban, Dominick Joseph, Mariam Slim, Edward Fadhili, Daniel Makange, Allan Jada, Elina Kassabaje, Swirtbert Shija, Joshua Mushi, Angel Mmari, Mrisho Lukamba, Sarah Kamwela
Post-quantum cryptography is usually evaluated one algorithm at a time: can ML-KEM encrypt a session, can ML-DSA sign a transaction. A bank is not one application, though, but an ecosystem of customer channels, ATMs, point-of-sale terminals, USSD services, core banking systems, internal PKI and hardware security modules, and interbank messaging, each with different constraints and each currently secured by classical public-key cryptography that a cryptographically relevant quantum computer would break. This paper asks a narrower and more concrete question than whether post-quantum cryptography works: where, specifically, it belongs inside that ecosystem, and how it should be built in so the answer does not depend permanently on whichever algorithms are standardized today. It proposes a three-layer security model (communication, transaction, and long-term cryptographic infrastructure) built around a crypto-agile cryptographic-service abstraction rather than direct application-level dependence on any single algorithm, evaluates representative post-quantum mechanisms from different mathematical families (ML-KEM and HQC for key establishment; ML-DSA, SLH-DSA, and FN-DSA for signatures) against their documented security, performance, and size characteristics for different banking components, and develops a conceptual, component-differentiated migration path from classical through hybrid to crypto-agile post-quantum infrastructure. The design is literature-based and conceptual, so the paper does not build a complete banking system; it draws on finalized and draft standards, published benchmarks, and existing banking-security and crypto-agility research, and states explicitly what it does not claim. It is a companion to, and assumes without re-arguing, the case this research team's earlier paper made for why African financial institutions need to prepare for post-quantum migration now.
Post-quantum cryptography is usually evaluated one algorithm at a time: can ML-KEM encrypt a session, can ML-DSA sign a transaction. A bank is not one application, though, but an ecosystem of customer channels, ATMs, point-of-sale terminals, USSD services, core banking systems, internal PKI and hardware security modules, and interbank messaging, each with different constraints and each currently secured by classical public-key cryptography that a cryptographically relevant quantum computer would break. This paper asks a narrower and more concrete question than whether post-quantum cryptography works: where, specifically, it belongs inside that ecosystem, and how it should be built in so the answer does not depend permanently on whichever algorithms are standardized today. It proposes a three-layer security model (communication, transaction, and long-term cryptographic infrastructure) built around a crypto-agile cryptographic-service abstraction rather than direct application-level dependence on any single algorithm, evaluates representative post-quantum mechanisms from different mathematical families (ML-KEM and HQC for key establishment; ML-DSA, SLH-DSA, and FN-DSA for signatures) against their documented security, performance, and size characteristics for different banking components, and develops a conceptual, component-differentiated migration path from classical through hybrid to crypto-agile post-quantum infrastructure. The design is literature-based and conceptual, so the paper does not build a complete banking system; it draws on finalized and draft standards, published benchmarks, and existing banking-security and crypto-agility research, and states explicitly what it does not claim. It is a companion to, and assumes without re-arguing, the case this research team's earlier paper made for why African financial institutions need to prepare for post-quantum migration now.
This paper is the third member of a three-paper series on post-quantum cryptography for African financial institutions, alongside Post-Quantum Migration Readiness for African Finance (Paper 1) and A Crypto-Agile Post-Quantum Architecture for Banking (Paper 2). Paper 1 asks whether and how African financial institutions should begin migrating to post-quantum cryptography; Paper 2 asks where post-quantum cryptography belongs inside a bank's own systems. This paper asks what the research team studied, built, and tested to reach the positions Paper 1 and Paper 2 take, and what mathematics and mechanics sit underneath them. It is written as a technical narrative rather than a formal specification. The account starts with the quantum-mechanical foundations of the work (qubits, superposition, entanglement, the gate model of computation) and the phase-estimation and Hamiltonian-simulation ideas that go beyond the team's own circuits. It then covers the mathematics of the quantum threat, with Shor's and Grover's algorithms worked against concrete RSA-2048 and secp256k1 parameters, and the mathematics of the post-quantum replacements: Module-LWE, Module-SIS, and the ML-KEM and ML-DSA constructions built on them. It also explains why NIST has standardized SLH-DSA and is standardizing HQC and FN-DSA alongside them. From there the document turns to the hybrid cryptography mechanism that Paper 2's architecture assumes, a zero-knowledge compliance layer built on STARKs rather than discrete-logarithm proofs, and the team's own validation of quantum circuits on real IBM quantum hardware, reported with the job identifiers and measured data those runs produced. It does not duplicate either paper. It documents the research and experimentation underneath both, at a technical depth that neither paper's narrative form carries. The series follows a zero-fabrication discipline, and this paper does too. Every mathematical claim traces to a cited primary source or to one of two companion technical documents produced during this research (a mathematical-foundations reference and a STARK-integration architecture report), and every experimental claim traces to a specific, named quantum-hardware job. Nothing is presented as executed that was not run. The one area with no hands-on execution, Google's quantum-computing platform, is covered from published literature only and is marked as such.
The impressively fast development of quantum computing is a serious threat to classical public-key cryptography, and algorithms such as Shor's and Grover's will render RSA and elliptic curve systems essentially useless as soon as a cryptanalytically relevant quantum computer becomes available. Although it is still some way off before such machines are available, the harvest-now-encrypt-later threat highlights the need for proactive defense. In response, the National Institute of Standards and Technology (NIST) published the first post-quantum cryptography standards in 2024, including ML-KEM (Kyber) for key establishment, ML-DSA (Dilithium) for digital signatures and SLH-DSA (SPHINCS+) as a stateless hash-based alternative. This paper is a summary of the evolving post-quantum landscape, starting with the standards and their underlying security and then moving on to migration policies such as CNSA 2.0 and CISA, NSA and NIST guidance. It also looks at integration patterns for important protocols such as TLS, IPsec, SSH, and code signing. A performance, interoperability and overhead evaluation methodology is presented with results showing that hybrid deployment and crypto-agile architectures make PQC adoption a viable option. The paper concludes by providing a governance-oriented roadmap, where inventory, prioritization and pilot deployments are identified as near-term actions, with open questions remaining on performance optimization, implementation security and algorithm resilience over time.
Abstract—The advent of fault-tolerant Cryptanalytically Relevant Quantum Computers (CRQCs) presents an existential threat to modern information security. Shor's polynomial-time quantum algorithm renders widely deployed public-key cryptographic primitives—including RSA, Diffie-Hellman (DH), and Elliptic Curve Cryptography (ECDH/ECDSA)—completely vulnerable to private key derivation. Furthermore, 'Harvest Now, Decrypt Later' (HNDL) adversarial campaigns actively intercept and store encrypted enterprise telemetry today, anticipating future quantum decryption capabilities. In response, the National Institute of Standards and Technology (NIST) finalized its primary Post-Quantum Cryptography (PQC) standards in FIPS 203 (ML-KEM), FIPS 204 (ML-DSA), and FIPS 205 (SLH-DSA). However, transitioning complex enterprise IT ecosystems to quantum-resistant primitives introduces severe architectural and computational disruptions: public key and signature sizes increase by several orders of magnitude, cryptographic handshake latencies escalate, network packets experience Maximum Transmission Unit (MTU) fragmentation, and legacy Hardware Security Modules (HSMs) lack microarchitectural support for lattice-based polynomial arithmetic. This paper provides an exhaustive, mathematically grounded technical survey and architectural roadmap for enterprise PQC migration. We formalize the Module Learning with Errors (M-LWE) and Module Short Integer Solution (M-SIS) hardness foundations, evaluate hybrid classical/post-quantum cryptographic transition models across standard transport protocols (TLS 1.3, IKEv2/IPsec, SSH), and formulate an enterprise Crypto-Agility Maturity Model. Furthermore, we construct an empirical enterprise testbed measuring throughput, connection establishment latency, memory footprints, and packet fragmentation across legacy and quantum-resistant suites. Our results show that while ML-KEM-768 achieves microsecond-level encapsulation, its 1,088-byte ciphertext expands TLS ClientHello payloads into multiple TCP segments under constrained networks. Finally, we establish open research directions in post-quantum identity federations, stateful hash signature tracking, and hardware-accelerated polynomial arithmetic. Index Terms—Post-Quantum Cryptography (PQC), FIPS 203 (ML-KEM), FIPS 204 (ML-DSA), Crypto-Agility, TLS 1.3, Lattice-Based Cryptography, Harvest Now Decrypt Later, Hardware Security Modules (HSM), Enterprise Migration.
Large-scale quantum computers threaten the public-key cryptography that protects enterprise data, communications, and digital identity. Shor's algorithm solves integer factorization and discrete logarithms in polynomial time, which would break RSA, Diffie-Hellman, and elliptic-curve schemes once a cryptographically relevant quantum computer exists. The danger is not only future. Adversaries can record encrypted traffic today and decrypt it later, a tactic known as harvest-now-decrypt-later. In August 2024 the U.S. National Institute of Standards and Technology published its first post-quantum standards: FIPS 203 (ML-KEM, derived from CRYSTALS-Kyber), FIPS 204 (ML-DSA, from CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, from SPHINCS+). This paper presents a practical migration framework for enterprises. It reviews the quantum threat and Mosca's inequality for timing the transition, summarizes the new standards with their key and signature sizes, and proposes a five-phase roadmap built on crypto-agility: discovery and inventory, risk prioritization, agility engineering, hybrid deployment, and validation. Performance trade-offs are analyzed using documented parameter sizes and illustrative TLS handshake figures. ML-KEM-768 carries a 1,184-byte public key against 64 bytes for an elliptic-curve key, while SPHINCS+ signatures can exceed 17 kilobytes. The work does not report a real deployment. It consolidates published parameters and field guidance into an actionable plan, and it highlights open challenges in certificate sizing, hardware support, and long-lived embedded systems.
Large-scale quantum computers threaten the public-key cryptography that protects enterprise data, communications, and digital identity. Shor's algorithm solves integer factorization and discrete logarithms in polynomial time, which would break RSA, Diffie-Hellman, and elliptic-curve schemes once a cryptographically relevant quantum computer exists. The danger is not only future. Adversaries can record encrypted traffic today and decrypt it later, a tactic known as harvest-now-decrypt-later. In August 2024 the U.S. National Institute of Standards and Technology published its first post-quantum standards: FIPS 203 (ML-KEM, derived from CRYSTALS-Kyber), FIPS 204 (ML-DSA, from CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, from SPHINCS+). This paper presents a practical migration framework for enterprises. It reviews the quantum threat and Mosca's inequality for timing the transition, summarizes the new standards with their key and signature sizes, and proposes a five-phase roadmap built on crypto-agility: discovery and inventory, risk prioritization, agility engineering, hybrid deployment, and validation. Performance trade-offs are analyzed using documented parameter sizes and illustrative TLS handshake figures. ML-KEM-768 carries a 1,184-byte public key against 64 bytes for an elliptic-curve key, while SPHINCS+ signatures can exceed 17 kilobytes. The work does not report a real deployment. It consolidates published parameters and field guidance into an actionable plan, and it highlights open challenges in certificate sizing, hardware support, and long-lived embedded systems.
Quantum computing poses an existential threat to classical public-key cryptography, particularly RSA and elliptic-curve systems, which form the backbone of secure communication, authentication, and digital trust. Once scalable quantum computers emerge, algorithms such as Shor’s will be capable of breaking these schemes, jeopardizing confidentiality and integrity across the internet and enterprise systems. Post-quantum cryptography (PQC) offers a viable defense, providing quantum-resistant algorithms that can be implemented on today’s hardware and protocols. Recent standardization milestones—including NIST’s approval of ML-KEM (Kyber) for key establishment, ML-DSA (Dilithium) and SLH-DSA (SPHINCS+) for signatures, and the selection of HQC as a complementary KEM—mark a turning point for practical adoption. This paper surveys the quantum threat model, algorithm families, performance trade-offs, and integration patterns such as hybrid modes and crypto-agile architectures. It further outlines a phased migration roadmap for enterprises, emphasizing harvest-now-decrypt-later risks and compliance imperatives. By bridging technical, operational, and policy perspectives, the study provides actionable guidance to prepare organizations for a secure and quantum-resilient future.