Why it matters

DH enables TLS + Signal + others. Understanding shapes crypto.

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The architecture

Alice: A = g^a. Bob: B = g^b.

Shared: A^b = B^a = g^ab.

Classic DH modular; ECDH on elliptic curves.

DH exchangeAlice A = g^apublishBob B = g^bpublishShared g^abderivedTLS 1.3 uses ECDHE (ephemeral) for forward secrecy
DH.
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How it works end to end

Diffie + Hellman 1976.

ECDH modern.

DHE for forward secrecy.

Curve25519 preferred group.