Post-Quantum Cryptography: The Migration That Needs No Qubits
Post-quantum cryptography (PQC) replaces RSA and elliptic-curve schemes with algorithms — now NIST-standardized as ML-KEM (FIPS 203) and ML-DSA (FIPS 204) — that run on ordinary classical hardware but resist known quantum attacks. Migration matters now because encrypted traffic recorded today can be decrypted later once a large quantum computer exists. This is the one quantum-driven action most engineering teams should take this year, and it requires zero quantum hardware.
Why migrate before any quantum computer can attack?
The previous chapter, quantum cryptanalysis, established the threat: Shor's algorithm breaks RSA and elliptic curves, but only on a large fault-tolerant machine that does not exist and is not close. So why act now? Because of harvest now, decrypt later: an adversary can record your encrypted traffic today — passively, cheaply, undetectably — store it, and decrypt it years from now when the hardware arrives. Encryption in transit protects a secret only for as long as the cipher stays unbroken, and the recording happens now.
This reframes the timeline question. The relevant deadline is not "when does a cryptographically relevant quantum computer arrive?" but "when does it arrive, minus how long my data must stay secret, minus how long my migration takes?" That subtraction — often called Mosca's inequality — is worked as arithmetic below, and for many kinds of data the answer is already negative.
Post-quantum cryptography is the fix: new public-key algorithms built on math problems for which no efficient quantum algorithm is known — running entirely on the classical hardware you already own. No qubits, no cryogenics, no vendor lock-in to a quantum roadmap. It is, without hype, the most concrete quantum-motivated engineering task of this decade.
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