EXERCISE 3 — Why post-quantum now, and the whole course in one sentence
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WHY POST-QUANTUM CRYPTO IS BEING DEPLOYED NOW (not when quantum computers exist):
  - The threat is "HARVEST NOW, DECRYPT LATER" (Chapter 3). An attacker can
    record today's encrypted TLS traffic and simply store it.
  - Today's key exchange ((EC)DHE) relies on math (discrete log) that a
    sufficiently powerful quantum computer could break in the future.
  - When such a computer arrives, the attacker can go back and break the
    key exchange of the OLD recorded sessions, recovering the session keys
    and decrypting traffic that was captured years earlier.
  - Therefore the data sent TODAY is only safe if it's ALREADY protected by
    quantum-resistant key exchange. Waiting until quantum computers exist is
    too late for any traffic recorded in the meantime.
  - Note forward secrecy alone does NOT save you here: ephemeral DH protects
    against a stolen long-term KEY, but a quantum break attacks the key
    EXCHANGE itself, recovering the ephemeral secret from the recorded
    handshake. So browsers/servers are rolling out HYBRID classical +
    post-quantum key exchange now, before the threat materializes.
  - This is the clearest case of TLS evolving AHEAD of the threat.

THE WHOLE COURSE IN ONE SENTENCE (with chapter labels):

  "HTTPS uses ASYMMETRIC CRYPTOGRAPHY [Ch.2-3] and a CA-ISSUED [Ch.5],
   TRANSPARENCY-LOGGED [Ch.12] CERTIFICATE [Ch.4] to AUTHENTICATE THE
   SERVER [Ch.1 authentication, Ch.6 handshake] and AGREE -- WITH FORWARD
   SECRECY [Ch.3] -- ON A SYMMETRIC KEY [Ch.2], which then protects every
   byte with CONFIDENTIALITY and INTEGRITY [Ch.1 guarantees, Ch.2 AEAD]."

  Term -> chapter map:
    asymmetric cryptography ...... Ch.2 (primitives), Ch.3 (key exchange)
    CA-issued .................... Ch.5 (chain of trust)
    transparency-logged .......... Ch.12 (Certificate Transparency)
    certificate .................. Ch.4 (X.509)
    authenticate the server ...... Ch.1 (guarantee), Ch.6 (handshake proof)
    forward secrecy .............. Ch.3 (ephemeral DH), Ch.7 (mandatory in 1.3)
    symmetric key ................ Ch.2 (symmetric/AEAD)
    confidentiality + integrity .. Ch.1 (guarantees), Ch.2 (AEAD)
    [supporting: Ch.7 TLS 1.3, Ch.8 cipher suites, Ch.9 getting a cert,
     Ch.10 server config, Ch.11 attacks & defences]

  Every term unpacks into a chapter you've worked through -- that's the
  whole course compressed into one line.