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10

HMAC-based Key Derivation Function (HKDF) rfc5869 is what you are looking for. HMAC security proof uses the fact that the compression function of the underlying hash is itself a PRF. HKDF follows the "extract-then-expand" paradigm, where the KDF logically consists of two modules. The first stage takes the input keying material and "extracts" ...


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HKDF already has expansion on top of the MAC that it is based on. What would be the point of using a XOF for that? Why not use the XOF directly or define a different KDF? Because having two different methods for expanding the output seems troublesome to me. If you're going to use HKDF then use one of the normal SHA-3 / HMAC functions with it. Sure, that's ...


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