Why PQC Matters

Every HTTPS connection, SSH session, and VPN tunnel you operate relies on public-key cryptography — RSA, ECDSA, Diffie-Hellman, ECDH. A sufficiently powerful quantum computer breaks all of them.

This isn’t theoretical hand-wringing. NIST has published replacement standards and set a 2035 deadline to deprecate classical algorithms.

What Breaks and Why

In 1994, mathematician Peter Shor discovered a quantum algorithm that efficiently factors large integers and computes discrete logarithms — the two hard problems that all modern public-key crypto depends on.

The short version: Shor’s algorithm turns exponentially hard problems into polynomial-time problems on a quantum computer. RSA’s security comes from “multiplying two primes is easy, factoring the product is hard.” A quantum computer makes factoring easy too.

flowchart TD
    SHOR[Shor's Algorithm] --> RSA[RSA — Broken]
    SHOR --> DH[Diffie-Hellman — Broken]
    SHOR --> ECDSA[ECDSA — Broken]
    SHOR --> ECDH[ECDH — Broken]
    SHOR --> DSA[DSA — Broken]

    GROVER[Grover's Algorithm] --> AES[AES — Weakened]
    GROVER --> SHA[SHA — Weakened]

    AES --> FIX1[Fix: Use AES-256<br/>instead of AES-128]
    SHA --> FIX2[Fix: Use SHA-384/512<br/>or double output size]

    classDef broken fill:#8e5050,stroke:#6e3030,color:#2c3e50
    classDef weakened fill:#8e7060,stroke:#6e5040,color:#2c3e50
    classDef fix fill:#6b8e6b,stroke:#4a6a4a,color:#2c3e50
    classDef algo fill:#5a8eaa,stroke:#3a6e8a,color:#2c3e50

    class SHOR,GROVER algo
    class RSA,DH,ECDSA,ECDH,DSA broken
    class AES,SHA weakened
    class FIX1,FIX2 fix

What	Status	Impact
RSA (all key sizes)	Completely broken	TLS, code signing, certificates
ECDSA / EdDSA	Completely broken	TLS, SSH, JWT, blockchain
Diffie-Hellman / ECDH	Completely broken	Key exchange in TLS, VPN, SSH
AES-128	Weakened to 64-bit	Use AES-256 instead
AES-256	Safe (128-bit quantum)	No change needed
SHA-256	Weakened to 128-bit	Still adequate for most uses

Key takeaway: All public-key cryptography is broken. Symmetric cryptography (AES, SHA) survives with larger key/output sizes.

The Harvest-Now-Decrypt-Later Threat

This is why migration is urgent today, even before large quantum computers exist.

Adversaries — nation-states in particular — are recording encrypted traffic right now. When quantum computers become available, they’ll decrypt everything they’ve stored.

flowchart LR
    A[Adversary records<br/>encrypted traffic<br/>TODAY] --> B[Stores<br/>ciphertext<br/>for years]
    B --> C[Quantum computer<br/>becomes available<br/>2030s?]
    C --> D[Decrypts all<br/>stored data]

    classDef dark fill:#5a8eaa,stroke:#3a6e8a,color:#2c3e50
    classDef broken fill:#8e5050,stroke:#6e3030,color:#2c3e50

    class A,B,C dark
    class D broken

If your data needs to stay confidential for more than 10 years (medical records, financial data, government communications, trade secrets), the threat window is already open.

The Timeline

flowchart LR
    S1[1994<br/>Shor's algorithm<br/>published] --> S2[2016<br/>NIST PQC<br/>competition<br/>launched]
    S2 --> S3[2024<br/>FIPS 203-205<br/>published]
    S3 --> S4[2025<br/>FIPS 206-207<br/>expected]
    S4 --> S5[2030<br/>Recommended<br/>migration<br/>complete]
    S5 --> S6[2035<br/>Classical crypto<br/>DEPRECATED]

    classDef past fill:#6b8e6b,stroke:#4a6a4a,color:#2c3e50
    classDef now fill:#8e6b8e,stroke:#6e4a6e,color:#2c3e50
    classDef future fill:#8e7060,stroke:#6e5040,color:#2c3e50
    classDef deadline fill:#8e5050,stroke:#6e3030,color:#2c3e50

    class S1,S2 past
    class S3,S4 now
    class S5 future
    class S6 deadline

Date	Event
1994	Shor publishes quantum factoring algorithm
2016	NIST launches Post-Quantum Cryptography standardization
Aug 2024	FIPS 203 (ML-KEM), 204 (ML-DSA), 205 (SLH-DSA) finalized
Mar 2025	HQC selected as 5th algorithm (will become FIPS 207)
2025	FIPS 206 (FN-DSA) expected
2035	NIST deprecates all quantum-vulnerable algorithms (NIST IR 8547)

What You Should Do Now

Don’t panic — quantum computers capable of breaking crypto don’t exist yet (estimated 2030s+)
Do start planning — migration takes years across large systems
Prioritize key exchange — this is where harvest-now-decrypt-later hits hardest
Use hybrid mode — run classical + PQC in parallel during transition (more on this in Migration Guide)

Next: Learn about the PQC algorithms that replace what’s breaking.

Sources: NIST PQC Project

NIST IR 8547 Transition Guidance

Last updated: 2026-02-13