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Diffie-Hellman key exchange
The same module told visually, ready to present. Speaker notes carry the full explanation.
Public-key
Diffie-Hellman key exchange
Agree on a secret over a public channel without ever sending it
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Worked example
p = 23, g = 5
An eavesdropper sees 23, 5, 8 and 19, and must solve a discrete log
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Into a usable key
From shared secret to AES key
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No authentication
The man in the middle
TLS signs the handshake with a certificate key; Signal verifies identity keys
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Advanced · parameter injection
Rewrite g, skip the maths
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On curves
ECDH and X25519
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Advanced · small subgroups
Confined to {1, 22}
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Advanced · discrete logs
Brute force versus baby-step giant-step
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Forward secrecy
Ephemeral keys protect the past
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