Why it matters

ECDH is TLS foundation. Understanding shapes crypto.

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The architecture

Alice: A = a*G. Bob: B = b*G.

Shared: a*B = b*A = ab*G.

ECDH exchangeAlice A = a*GpublishBob B = b*GpublishShared ab*GderivedX25519 Curve25519 modern default; contant-time + simple + fast
ECDH.
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How it works end to end

ECDHE for forward secrecy.

X25519 modern.

Post-quantum + classical hybrids emerging.