+ /// Gets the ECDH shared secret of our [`node secret`] and `other_key`, multiplying by `tweak` if
+ /// one is provided. Note that this tweak can be applied to `other_key` instead of our node
+ /// secret, though this is less efficient.
+ ///
+ /// [`node secret`]: Self::get_node_secret
+ fn ecdh(&self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&Scalar>) -> Result<SharedSecret, ()>;