Source Count: 0 | Weighted Score: 0 | Source Confidence: [1/5] | Primary Tier: 1–2 | Last Updated: March 10, 2026
Keywords: quantum cryptography, quantum key distribution, QKD, post-quantum cryptography, RSA, Shor's algorithm, lattice-based cryptography, BB84, quantum internet, NIST PQC, cryptographic agility, harvest now decrypt later
Category Tags: future technology, cryptography, quantum, security, computing
Cross-References: S_1_04 — Quantum Computing · ZA_2_01 — Quantum Mechanics · V_1_01 — Information Theory · S_1_06 — Internet

QUICK SUMMARY

Quantum cryptography and post-quantum cryptography address the existential threat that quantum computers pose to current encryption. The threat: large-scale quantum computers running Shor's algorithm (Peter Shor, 1994) can efficiently factor large integers and compute discrete logarithms — breaking the mathematical foundations of RSA, Diffie-Hellman, and Elliptic Curve Cryptography (ECC), which secure virtually all current internet communications (HTTPS, TLS, VPNs, digital signatures, banking). A sufficiently powerful quantum computer (estimated at ~4,000+ error-corrected logical qubits for 2048-bit RSA) would break these systems in hours rather than the billions of years required classically. Current quantum computing status: as of 2024, the largest quantum processors (~1,100+ physical qubits, IBM "Condor") are far from the millions of physical qubits needed to implement error-corrected Shor's algorithm on cryptographically relevant key sizes; estimates for timeline range from 10 to 30+ years, but the "harvest now, decrypt later" threat — adversaries collecting encrypted communications today to decrypt when quantum computers are available — makes the transition urgent. Quantum Key Distribution (QKD): the BB84 protocol (Bennett & Brassard, 1984) uses quantum mechanics (the no-cloning theorem, measurement disturbance) to guarantee secure key exchange — any eavesdropping attempt physically perturbs the quantum states and is detectable; QKD has been commercially deployed (ID Quantique, Toshiba) and demonstrated over satellite links (China's Micius satellite, 2017, key distribution over 1,200 km); however, QKD requires dedicated physical infrastructure (optical fiber or line-of-sight), is expensive, and cannot protect stored data or authenticate users. Post-quantum cryptography (PQC): NIST finalized its first PQC standards in August 2024 — CRYSTALS-Kyber (lattice-based key encapsulation) and CRYSTALS-Dilithium, FALCON, and SPHINCS+ (digital signature schemes) — designed to be secure against both classical and quantum computers while running on existing hardware; migration to PQC across global infrastructure is a massive, multi-year undertaking requiring cryptographic agility.

1. VERIFIED CLAIMS (Tier 1 — Peer-Reviewed / Scholarly Consensus)

1.1 Shor's Algorithm Threat

• Shor's algorithm is mathematically proven to efficiently break RSA, DH, and ECC on a sufficiently large quantum computer — this is not a theoretical speculation but a mathematical certainty; the only uncertainty is when quantum computers powerful enough to execute it will exist; the threat is universally acknowledged by cryptographic and national security communities (NSA, NIST, GCHQ)

1.2 NIST PQC Standards

• NIST's PQC standardization process (begun 2016, finalized 2024) produced algorithms based on mathematical problems believed to be resistant to both classical and quantum attack — primarily lattice-based problems (Learning With Errors) and hash-based signatures; these algorithms have undergone extensive public cryptanalysis over 8+ years; migration to PQC is recommended by NIST, NSA, and CISA for all federal and critical infrastructure systems

2. CREDIBLE CLAIMS (Tier 2 — Academic / Debated but Supported)

2.1 QKD Practicality

• QKD is information-theoretically secure (proven by physics, not mathematical assumptions) — but practical QKD systems have implementation vulnerabilities (side-channel attacks on detectors, Trojan horse attacks on sources) that weaken their theoretical guarantees; furthermore, QKD addresses only key distribution (not authentication, data-at-rest encryption, or digital signatures) and requires expensive dedicated infrastructure; many cryptographers argue that PQC on existing networks provides better security-per-dollar for most applications (Bernstein & Lange, 2017)

2.2 Harvest Now, Decrypt Later

• Intelligence agencies and adversaries are plausibly collecting encrypted communications now in anticipation of future quantum decryption capability — this is widely assumed in the security community and has driven urgency in PQC migration; the actual scope of such collection is classified, but the strategic logic is sound for long-lived secrets (diplomatic cables, military plans, trade secrets with multi-decade relevance)

3. SPECULATIVE CLAIMS (Tier 3 — Possible but Unverified)

3.1 Quantum Internet

• A global quantum internet — connecting quantum computers and enabling distributed quantum computing, unconditionally secure communication, and quantum sensor networks — is a long-term research goal; quantum repeaters (needed to extend QKD beyond ~100 km fiber distance) have been demonstrated in laboratories but not deployed at scale; China's 2,000 km Beijing-Shanghai quantum backbone (2017, using trusted relay nodes — not end-to-end quantum) is the most ambitious implementation; a true quantum internet likely requires quantum memory and entanglement distribution technologies that remain immature

4. DUBIOUS CLAIMS (Tier 4 — No Credible Source / Contradicted by Evidence)

4.1 Quantum Computers Already Breaking Encryption

• DEBUNKED Claims that quantum computers have already broken or can currently break RSA/ECC encryption are false — the largest numbers factored by quantum computers (as of 2024) are tiny (tens of bits vs. the 2048+ bits used in practice); current quantum processors lack the scale and error correction needed by orders of magnitude; while the future threat is real, current quantum computers pose zero threat to deployed cryptographic systems

Counter-Arguments

• The timeline for cryptographically relevant quantum computers is highly uncertain — pessimistic estimates suggest 30+ years or never (if error correction scaling proves impractical); overly urgent migration may impose unnecessary costs and risks (PQC algorithms have larger key sizes and computational overhead, and may themselves prove vulnerable to future cryptanalysis)
• PQC algorithms, while extensively vetted, are based on mathematical hardness assumptions that could be broken by new classical or quantum algorithms — lattice-based cryptography has not been studied for as long as RSA; NIST's process is rigorous but not a guarantee of permanent security
• QKD advocates argue that information-theoretic security (guaranteed by physics) is fundamentally superior to computational security (guaranteed by mathematical assumptions that could be overturned); QKD critics argue this theoretical advantage is undermined by practical implementation challenges

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BIBLIOGRAPHY

• Shor, P.W. "Algorithms for Quantum Computation: Discrete Logarithms and Factoring." In Proc. 35th Annual Symposium on Foundations of Computer Science (1994): 124–134. DOI: 10.1109/sfcs.1994.365700
• Bennett, C. H. & Brassard, G. "Quantum Cryptography." In Proc. IEEE International Conference on Computers, Systems and Signal Processing (1984): 175–179.
• NIST. Post-Quantum Cryptography: FIPS 203, 204, 205. National Institute of Standards and Technology (2024).
• Bernstein, D. J. & Lange, T. "Post-Quantum Cryptography." Nature 549 (2017): 188–194. DOI: 10.1038/nature23461.
• Liao, S.-K. et al. "Satellite-to-Ground Quantum Key Distribution." Nature 549 (2017): 43–47.
• Mosca, M. "Cybersecurity in an Era with Quantum Computers." IEEE Security & Privacy 16 (2018): 50–57. DOI: 10.1109/msp.2018.3761723
• Alagic, G. et al. Status Report on the Third Round of the NIST Post-Quantum Cryptography Standardization Process. NIST (2022). DOI: 10.30837/rt.2022.3.210.05
• Gisin, N. et al. "Quantum Cryptography." Reviews of Modern Physics 74 (2002): 145–195. DOI: 10.1103/revmodphys.74.145
• Pirandola, S. et al. "Advances in Quantum Cryptography." Advances in Optics and Photonics 12 (2020): 1012–1236.
• NSA. Announcing Suite B Cryptography Replacement. NSA Cybersecurity Advisory (2022).
• Wehner, S. et al. "Quantum Internet: A Vision for the Road Ahead." Science 362 (2018): eaam9288.

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Last Updated: March 10, 2026