On Thu, Jan 07, 2021 at 08:53:15AM +0100, Stephan Mueller wrote: > > > > > RFC5869 > > > allows two optional parameters to be provided to the extract operation: > > > the salt and additional information. Both are to be provided with the > > > seed parameter where the salt is the first entry of the seed parameter > > > and all subsequent entries are handled as additional information. If > > > the caller intends to invoke the HKDF without salt, it has to provide a > > > NULL/0 entry as first entry in seed. > > > > Where does "additional information" for extract come from? RFC 5869 has: > > > > HKDF-Extract(salt, IKM) -> PRK > > > > Inputs: > > salt optional salt value (a non-secret random value); > > if not provided, it is set to a string of HashLen > > zeros. > > IKM input keying material > > > > There's no "additional information". > > I used the terminology from SP800-108. I will update the description > accordingly. For HKDF, it would be better to stick to the terminology used in RFC 5869 (https://tools.ietf.org/html/rfc5869), as generally that's what people are most familiar with for HKDF. It also matches the HKDF paper (https://eprint.iacr.org/2010/264.pdf) more closely. - Eric
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