Education
Shor's algorithm for CISOs (no math degree required)
You do not need quantum physics to understand the business risk: Shor's algorithm breaks the public-key math your TLS, VPNs, and code signing depend on today.
The one-sentence version
A sufficiently large quantum computer running Shor's algorithm can factor the large numbers and solve the discrete logarithm problems that make RSA, Diffie-Hellman, and elliptic-curve cryptography secure today.
What breaks vs what mostly survives
| Category | Examples | Quantum impact |
|---|---|---|
| Public-key encryption & key exchange | RSA, ECDH | Broken by Shor's |
| Digital signatures | RSA-PSS, ECDSA | Broken by Shor's |
| Symmetric encryption | AES-256 | Weakened by Grover's — use larger keys |
| Hash functions | SHA-256, SHA-3 | Grover's reduces effective strength — generally manageable |
NIST's PQC overview focuses migration on public-key systems. See our Grover's algorithm explainer for symmetric crypto guidance.
How Shor's works (conceptually)
- Pick a random number related to the target composite (N).
- Find the period of a modular exponentiation function — classically hard, quantum-friendly.
- Use number theory to recover factors from the period.
The IBM Quantum Shor's tutorial shows code; PennyLane's period-finding demo illustrates the core idea interactively.
What CISOs should do
- Watch the embedded minutephysics video and read PostQuantum.com's Shor's article.
- Inventory quantum-vulnerable algorithms on external TLS and critical dependencies.
- Begin hybrid PQC pilots aligned to NIST IR 8547.
Quantum-vulnerable does not mean broken today — but harvest-now-decrypt-later means long-lived secrets need action now.
Continue on the Q-Day hub: What is Q-Day? guide
References & further reading
Authoritative primary sources cited in this article. Summaries are our own — follow links for full context.
Last verified 2026-06-21
- How Quantum Computers Break Encryption | Shor's Algorithm Explainedminutephysics (YouTube) · 2019Accessible explainer on Shor's algorithm, period-finding, and why RSA breaks on a large quantum computer.
- Shor's Algorithm: A Quantum Threat to Modern CryptographyPostQuantum.com · 2024Written explainer for security professionals — RSA, ECC, Shor's steps, and PQC migration strategies.
- What Is Post-Quantum Cryptography?NIST · 2024Official overview of NIST's PQC project, finalized standards, and the harvest-now-decrypt-later threat model.
- Shor's algorithm — IBM Quantum DocumentationIBM Quantum · 2024Code-based tutorial on Shor's algorithm and resource requirements for breaking RSA.
- Period finding: A problem at the heart of quantum computingPennyLane · 2024Interactive demo explaining period-finding — the core of Shor's algorithm.
See your exposure with evidence
Run a live PQC inventory scan, export a CBOM, and verify signed reports independently.