//! Mid-level cryptographic operations used in the onion service protocol.

use tor_llcrypto::d::Sha3_256;

use tor_llcrypto::util::ct::CtByteArray;

use digest::Digest;

/// The length of the MAC returned by [`hs_mac`].

pub const HS_MAC_LEN: usize = 32;

/// Compute the lightweight MAC function used in the onion service protocol.

///

/// (See rend-spec-v3 section 0.3 `MAC`.)

///

/// This is not a great MAC; KMAC wasn't defined at the time that the HSv3

/// design was written. Please don't use this MAC in new protocols.

    // rend-spec-v3 says: "Instantiate H with SHA3-256... Instantiate MAC(key=k,

    // message=m) with H(k_len | k | m), where k_len is htonll(len(k))."

/// Reference to a slice of bytes usable to compute the [`hs_mac`] function.

#[derive(Copy, Clone, derive_more::From)]

pub struct HsMacKey<'a>(&'a [u8]);

impl<'a> tor_llcrypto::traits::ShortMac<HS_MAC_LEN> for HsMacKey<'a> {

        use subtle::ConstantTimeEq;

}

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    #![allow(clippy::string_slice)] // See arti#2571

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use hex_literal::hex;

    /// Helper: just call Sha3_256 and return the result as a CtByteArray.

    fn d(s: &[u8]) -> CtByteArray<32> {

        let a: [u8; 32] = Sha3_256::digest(s).into();

        a.into()

    }

    #[test]

    fn mac_from_definition() {

        assert_eq!(hs_mac(b"", b""), d(&[0; 8]));

        assert_eq!(

            hs_mac(b"hello", b"world"),

            d(b"\0\0\0\0\0\0\0\x05helloworld")

        );

        assert_eq!(

            hs_mac(b"helloworl", b"d"),

            d(b"\0\0\0\0\0\0\0\x09helloworld")

        );

    }

    #[test]

    fn mac_testvec() {

        // From C Tor; originally generated in Python.

        let msg = b"i am in a library somewhere using my computer";

        let key = b"i'm from the past talking to the future.";

        assert_eq!(

            hs_mac(key, msg).as_ref(),

            &hex!("753fba6d87d49497238a512a3772dd291e55f7d1cd332c9fb5c967c7a10a13ca")

        );

    }

}