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X.509 certificates & the PKI trust hierarchy
The same module told visually, ready to present. Speaker notes carry the full explanation.
Protocols
X.509 certificates & PKI
A certificate is a signed statement binding a public key to an identity
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Chain of trust
Leaf, intermediate, root
Signing runs root → leaf; the browser verifies leaf → root and stops at a trusted anchor
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Hostnames
What *.example.com matches
Browsers match only the SAN list, never the legacy CN field
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Revocation
CRL versus OCSP
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The fix
OCSP stapling
No extra round trip, and the CA never learns who visited
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Policing the CAs
Certificate Transparency
DigiNotar, 2011: a valid, browser-trusted certificate for google.com that Google never requested
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Both directions
Mutual TLS
Common between backend services and in zero-trust networks
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Shorter lifetimes
Short-lived certificates
A compromised key expires soon anyway, so revocation matters less
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