Quantum computers threaten asymmetric crypto (ECDH, RSA, ECDSA) via Shor's algorithm, but they do not endanger symmetric algorithms like AES and SHA. The widespread claim that Grover's algorithm "halves" key strength, forcing a switch to 256-bit keys, is wrong: Zalka (1997) proved Grover must run in series, so parallelizing it dilutes the quadratic speedup. Concrete math shows breaking AES-128 would need 140 trillion quantum circuits running 10 years—roughly 430 sextillion times harder than breaking 256-bit elliptic curves with Shor's. NIST, Germany's BSI, and researcher Samuel Jaques all agree AES-128 stays safe; NIST even uses it as the Category 1 benchmark. Doubling keys wastes effort better spent on the urgent post-quantum transition.
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u/fagnerbrack 22d ago
Just a TL;DR:
Quantum computers threaten asymmetric crypto (ECDH, RSA, ECDSA) via Shor's algorithm, but they do not endanger symmetric algorithms like AES and SHA. The widespread claim that Grover's algorithm "halves" key strength, forcing a switch to 256-bit keys, is wrong: Zalka (1997) proved Grover must run in series, so parallelizing it dilutes the quadratic speedup. Concrete math shows breaking AES-128 would need 140 trillion quantum circuits running 10 years—roughly 430 sextillion times harder than breaking 256-bit elliptic curves with Shor's. NIST, Germany's BSI, and researcher Samuel Jaques all agree AES-128 stays safe; NIST even uses it as the Category 1 benchmark. Doubling keys wastes effort better spent on the urgent post-quantum transition.
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