Post-quantum cryptography

The cryptographic algorithms that secure today's digital communications — RSA, ECC, Diffie-Hellman — rely on the computational difficulty of certain mathematical problems, such as integer factorisation and discrete logarithms. A sufficiently powerful quantum computer running Shor's algorithm would solve these problems in polynomial time, rendering the current public-key infrastructure obsolete.

The threat to ATM communications

ATM systems depend on cryptographic protocols for secure ground-ground coordination, air-ground data links (CPDLC, ADS-C), SWIM node authentication, and key management processes. A quantum-capable adversary could:

• Harvest now, decrypt later (HNDL) — intercept and store encrypted communications today, to decrypt them once a quantum computer is available
• Break PKI trust models — forge digital signatures and impersonate trusted entities in the ATM network
• Compromise key distribution centres — undermine the cryptographic foundations of secure communication between ANSPs, airlines, and service providers

NIST-standardised PQC algorithms

The US National Institute of Standards and Technology (NIST) has conducted a multi-year process to select and standardise post-quantum cryptographic algorithms. The selected algorithms fall into two categories:

• CRYSTALS-Kyber — a lattice-based key encapsulation mechanism (KEM) for secure key exchange. Primary choice for general encryption.
• CRYSTALS-Dilithium — a lattice-based digital signature scheme, selected as the primary standard for authentication.
• FALCON — a lattice-based signature scheme optimised for compact signatures, suited to bandwidth-constrained environments.
• Sphincs+ — a stateless hash-based signature scheme providing a conservative security fallback not reliant on lattice assumptions.

PQC in the ATM context

In JANUS, these algorithms are evaluated against the specific requirements of ATM/UTM communication service classes — ground-ground coordination links, aircraft communication links, SWIM nodes, and CNS/ATM payloads. The evaluation considers:

• Theoretical security requirements and latency constraints for each service class
• Hybrid deployment strategies combining classical and PQC algorithms for transitional periods
• Key management concepts including algorithm agility and key rollover strategies
• Alignment with regulatory frameworks from ICAO, EUROCAE WG-72, and EASA

The output is a phased PQC migration roadmap (Deliverable D7.1), defining transition timelines, dependency maps, and implementation milestones aligned with the aviation upgrade cycle.