HKDF (RFC 5869)

1. Extract-then-expand paradigm

   Overview of HKDF components.

2. HKDF-Extract

   Deriving a pseudorandom key from input keying material and salt.

3. HKDF-Expand

   Expanding PRK into output keying material with info.

4. Salt, info and context

   Roles of salt and info in applications.

5. Applications

   Using HKDF in protocols such as TLS 1.3.

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