hkdf: impl kdf::Kdf for GenericHkdfExtract#173
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Due to the `&self` requirement in the `Kdf` trait, this seems like the only existing type that a `Kdf` impl makes sense for, since `derive_key` needs to be able to input IKM. The "salt" parameter of `Kdf::derive_key` has been mapped to the HKDF `info` parameter, as what HKDF calls the "salt" (the non-secret value that goes into the extract step) has already been (potentially) configured via `&self`, whereas the "info" parameter (the non-secret value that goes into the expand step) is the one we can actually configure through this API.
tarcieri
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Jan 14, 2026
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| #[cfg(feature = "kdf")] | ||
| impl<H: HmacImpl> Kdf for GenericHkdfExtract<H> { | ||
| fn derive_key(&self, secret: &[u8], info: &[u8], out: &mut [u8]) -> kdf::Result<()> { |
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@newpavlov per your point on RustCrypto/traits#1879 it does seem like the non-secret argument to derive_key is a better fit for HKDF info and maybe we can consider renaming it in the trait.
For now I have used the info name in the impl.
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I can't tell if being able to input IKM before invoking |
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@tarcieri |
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Due to the
&selfrequirement in theKdftrait, this seems like the only existing type that aKdfimpl makes sense for, sincederive_keyneeds to be able to input IKM.The "salt" parameter of
Kdf::derive_keyhas been mapped to the HKDFinfoparameter, as what HKDF calls the "salt" (the non-secret value that goes into the extract step) has already been (potentially) configured via&self, whereas the "info" parameter (the non-secret value that goes into the expand step) is the one we can actually configure through this API.