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hkdf: impl kdf::Kdf for GenericHkdfExtract #173

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Merged
tarcieri merged 1 commit into from
Jan 15, 2026
Merged

hkdf: impl kdf::Kdf for GenericHkdfExtract #173

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7 changes: 7 additions & 0 deletions Cargo.lock
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3 changes: 3 additions & 0 deletions hkdf/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,9 @@ rust-version = "1.85"
[dependencies]
hmac = "0.13.0-rc.3"

# optional dependencies
kdf = { version = "0.1.0-pre.1", optional = true }

[dev-dependencies]
blobby = "0.4"
hex-literal = "1"
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13 changes: 13 additions & 0 deletions hkdf/src/lib.rs
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Expand Up @@ -20,6 +20,9 @@ pub use errors::{InvalidLength, InvalidPrkLength};
pub use hmac;
pub use hmac_impl::HmacImpl;

#[cfg(feature = "kdf")]
pub use kdf::{self, Kdf};

/// [`GenericHkdfExtract`] variant which uses [`Hmac`] for the underlying HMAC implementation.
pub type HkdfExtract<H> = GenericHkdfExtract<Hmac<H>>;
/// [`GenericHkdf`] variant which uses [`Hmac`] for the underlying HMAC implementation.
Expand Down Expand Up @@ -62,6 +65,16 @@ impl<H: HmacImpl> GenericHkdfExtract<H> {
}
}

#[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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@tarcieri tarcieri Jan 14, 2026

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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.

let mut extract = self.clone();
extract.input_ikm(secret);
let (_, hkdf) = extract.finalize();
hkdf.expand(info, out).map_err(|_| kdf::Error)
}
}

/// Structure representing the HKDF, capable of HKDF-Expand and HKDF-Extract operations.
/// Recommendations for the correct usage of the parameters can be found in the
/// [crate root](index.html#usage).
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