trussed 0.2.0-rc.1

Modern Cryptographic Firmware
Documentation 
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use trussed_core::{
    api::{reply, request},
    types::Signature,
    Error,
};

use crate::key;
use crate::service::MechanismImpl;
use crate::store::Keystore;

impl MechanismImpl for super::HmacSha256 {
    #[inline(never)]
    fn derive_key(
        &self,
        keystore: &mut impl Keystore,
        request: &request::DeriveKey,
    ) -> Result<reply::DeriveKey, Error> {
        use hmac::{Hmac, Mac};
        type HmacSha256 = Hmac<sha2::Sha256>;

        let key_id = request.base_key;
        let key = keystore.load_key(key::Secrecy::Secret, None, &key_id)?;
        if !matches!(key.kind, key::Kind::Symmetric(..) | key::Kind::Shared(..)) {
            // We have to disable this check for compatibility with fido-authenticator, see:
            // https://github.com/solokeys/fido-authenticator/issues/21
            warn!(
                "derive_key for hmacsha256 called with invalid key kind ({:?})",
                key.kind
            );
        }
        let shared_secret = key.material;

        let mut mac =
            HmacSha256::new_from_slice(shared_secret.as_ref()).map_err(|_| Error::InternalError)?;

        if let Some(additional_data) = &request.additional_data {
            mac.update(additional_data);
        }
        let derived_key: [u8; 32] = mac.finalize().into_bytes().into();
        let key_id = keystore.store_key(
            request.attributes.persistence,
            key::Secrecy::Secret,
            key::Kind::Symmetric(32),
            &derived_key,
        )?;

        Ok(reply::DeriveKey { key: key_id })
    }

    #[inline(never)]
    fn sign(
        &self,
        keystore: &mut impl Keystore,
        request: &request::Sign,
    ) -> Result<reply::Sign, Error> {
        use hmac::{Hmac, Mac};
        use sha2::Sha256;
        type HmacSha256 = Hmac<Sha256>;

        let key_id = request.key;
        let key = keystore.load_key(key::Secrecy::Secret, None, &key_id)?;
        if !matches!(key.kind, key::Kind::Symmetric(..) | key::Kind::Shared(..)) {
            return Err(Error::WrongKeyKind);
        }
        let shared_secret = key.material;

        let mut mac =
            HmacSha256::new_from_slice(shared_secret.as_ref()).map_err(|_| Error::InternalError)?;

        mac.update(&request.message);
        let result = mac.finalize();
        let signature = Signature::try_from(&*result.into_bytes()).unwrap();

        Ok(reply::Sign { signature })
    }
}