Am Mittwoch, dem 06.01.2021 um 23:30 -0800 schrieb Eric Biggers: > On Mon, Jan 04, 2021 at 10:49:13PM +0100, Stephan Müller wrote: > > RFC5869 specifies an extract and expand two-step key derivation > > function. The HKDF implementation is provided as a service function that > > operates on a caller-provided HMAC cipher handle. > > HMAC isn't a "cipher". > > > The extract function is invoked via the crypto_hkdf_setkey call. > > Any reason not to call this crypto_hkdf_extract(), to match the > specification?
I named it to match the other KDF implementation. But you are right, I will name it accordingly. > > > 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. > > > > > The expand function is invoked via the crypto_hkdf_generate and can be > > invoked multiple times. This function allows the caller to provide a > > context for the key derivation operation. As specified in RFC5869, it is > > optional. In case such context is not provided, the caller must provide > > NULL / 0 for the info / info_nvec parameters. > > Any reason not to call this crypto_hkdf_expand() to match the specification? I will update the function name. Thanks Stephan > > - Eric
