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Security Fundamentals & Crypto · Advanced

Certificate Pinning

Associating a host with an expected certificate or public key so other valid-looking certificates are rejected.

Definition

Pinning defends against fraudulent certificates from compromised or coerced CAs. It is common in mobile apps, but HTTP Public Key Pinning (HPKP) for websites was deprecated and removed from browsers due to the risk of locking users out. Pinning complicates certificate rotation and blocks TLS inspection.

Example

A banking app pins the public key of its API server and refuses connections through a corporate TLS inspection proxy.

Exam tip

Pinning breaks SSL/TLS inspection; HPKP is deprecated in favor of Certificate Transparency.

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