fn derive_3dh_keys>()

in src/key_exchange/tripledh.rs [453:502]

• 46 lines of code
• 1 McCabe index (conditional complexity)

fn derive_3dh_keys<D: Hash, KG: KeGroup, S: SecretKey<KG>>(
    dh: TripleDHComponents<KG, S>,
    hashed_derivation_transcript: &[u8],
) -> Result<TripleDHDerivationResult<D>, ProtocolError<S::Error>>
where
    D::Core: ProxyHash,
    <D::Core as BlockSizeUser>::BlockSize: IsLess<U256>,
    Le<<D::Core as BlockSizeUser>::BlockSize, U256>: NonZero,
{
    let mut hkdf = HkdfExtract::<D>::new(None);

    hkdf.input_ikm(
        &dh.sk1
            .diffie_hellman(dh.pk1)
            .map_err(InternalError::into_custom)?,
    );
    hkdf.input_ikm(&dh.sk2.diffie_hellman(dh.pk2)?);
    hkdf.input_ikm(
        &dh.sk3
            .diffie_hellman(dh.pk3)
            .map_err(InternalError::into_custom)?,
    );

    let (_, extracted_ikm) = hkdf.finalize();
    let handshake_secret = derive_secrets::<D>(
        &extracted_ikm,
        STR_HANDSHAKE_SECRET,
        hashed_derivation_transcript,
    )
    .map_err(ProtocolError::into_custom)?;
    let session_key = derive_secrets::<D>(
        &extracted_ikm,
        STR_SESSION_KEY,
        hashed_derivation_transcript,
    )
    .map_err(ProtocolError::into_custom)?;

    let km2 = hkdf_expand_label::<D>(&handshake_secret, STR_SERVER_MAC, b"")
        .map_err(ProtocolError::into_custom)?;
    let km3 = hkdf_expand_label::<D>(&handshake_secret, STR_CLIENT_MAC, b"")
        .map_err(ProtocolError::into_custom)?;

    Ok((
        GenericArray::clone_from_slice(&session_key),
        GenericArray::clone_from_slice(&km2),
        GenericArray::clone_from_slice(&km3),
        #[cfg(test)]
        handshake_secret,
    ))
}