// Copyright 2019 Parity Technologies (UK) Ltd.
//
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// copy of this software and associated documentation files (the "Software"),
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//
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//! Components of a Noise protocol.

pub(crate) mod x25519;
pub(crate) mod x25519_spec;
use crate::Error;
use libp2p_identity as identity;
use rand::SeedableRng;
use zeroize::Zeroize;

/// The parameters of a Noise protocol, consisting of a choice
/// for a handshake pattern as well as DH, cipher and hash functions.
#[derive(Clone)]
pub struct ProtocolParams(snow::params::NoiseParams);

impl ProtocolParams {
    pub(crate) fn into_builder<'b, C>(
        self,
        prologue: &'b [u8],
        private_key: &'b SecretKey<C>,
        remote_public_key: Option<&'b PublicKey<C>>,
    ) -> snow::Builder<'b>
    where
        C: Zeroize + AsRef<[u8]> + Protocol<C>,
    {
        let mut builder = snow::Builder::with_resolver(self.0, Box::new(Resolver))
            .prologue(prologue.as_ref())
            .local_private_key(private_key.as_ref());

        if let Some(remote_public_key) = remote_public_key {
            builder = builder.remote_public_key(remote_public_key.as_ref());
        }

        builder
    }
}

/// Type tag for the IK handshake pattern.
#[derive(Debug, Clone)]
pub enum IK {}

/// Type tag for the IX handshake pattern.
#[derive(Debug, Clone)]
pub enum IX {}

/// Type tag for the XX handshake pattern.
#[derive(Debug, Clone)]
pub enum XX {}

/// A Noise protocol over DH keys of type `C`. The choice of `C` determines the
/// protocol parameters for each handshake pattern.
#[deprecated(
    note = "This type will be made private in the future. Use `libp2p_noise::Config::new` instead to use the noise protocol."
)]
pub trait Protocol<C> {
    /// The protocol parameters for the IK handshake pattern.
    fn params_ik() -> ProtocolParams;
    /// The protocol parameters for the IX handshake pattern.
    fn params_ix() -> ProtocolParams;
    /// The protocol parameters for the XX handshake pattern.
    fn params_xx() -> ProtocolParams;

    /// Construct a DH public key from a byte slice.
    fn public_from_bytes(s: &[u8]) -> Result<PublicKey<C>, Error>;

    /// Determines whether the authenticity of the given DH static public key
    /// and public identity key is linked, i.e. that proof of ownership of a
    /// secret key for the static DH public key implies that the key is
    /// authentic w.r.t. the given public identity key.
    ///
    /// The trivial case is when the keys are byte for byte identical.
    #[allow(unused_variables)]
    #[deprecated]
    fn linked(id_pk: &identity::PublicKey, dh_pk: &PublicKey<C>) -> bool {
        false
    }

    /// Verifies that a given static DH public key is authentic w.r.t. a
    /// given public identity key in the context of an optional signature.
    ///
    /// The given static DH public key is assumed to already be authentic
    /// in the sense that possession of a corresponding secret key has been
    /// established, as is the case at the end of a Noise handshake involving
    /// static DH keys.
    ///
    /// If the public keys are [`linked`](Protocol::linked), verification succeeds
    /// without a signature, otherwise a signature over the static DH public key
    /// must be given and is verified with the public identity key, establishing
    /// the authenticity of the static DH public key w.r.t. the public identity key.

    fn verify(id_pk: &identity::PublicKey, dh_pk: &PublicKey<C>, sig: &Option<Vec<u8>>) -> bool
    where
        C: AsRef<[u8]>,
    {
        Self::linked(id_pk, dh_pk)
            || sig
                .as_ref()
                .map_or(false, |s| id_pk.verify(dh_pk.as_ref(), s))
    }

    fn sign(id_keys: &identity::Keypair, dh_pk: &PublicKey<C>) -> Result<Vec<u8>, Error>
    where
        C: AsRef<[u8]>,
    {
        Ok(id_keys.sign(dh_pk.as_ref())?)
    }
}

/// DH keypair.
#[derive(Clone)]
pub struct Keypair<T: Zeroize> {
    secret: SecretKey<T>,
    public: PublicKey<T>,
}

/// A DH keypair that is authentic w.r.t. a [`identity::PublicKey`].
#[derive(Clone)]
pub struct AuthenticKeypair<T: Zeroize> {
    pub(crate) keypair: Keypair<T>,
    pub(crate) identity: KeypairIdentity,
}

impl<T: Zeroize> AuthenticKeypair<T> {
    /// Returns the public DH key of this keypair.
    pub fn public_dh_key(&self) -> &PublicKey<T> {
        &self.keypair.public
    }

    /// Extract the public [`KeypairIdentity`] from this `AuthenticKeypair`,
    /// dropping the DH `Keypair`.
    #[deprecated(
        since = "0.40.0",
        note = "This function was only used internally and will be removed in the future unless more usecases come up."
    )]
    pub fn into_identity(self) -> KeypairIdentity {
        self.identity
    }
}

/// The associated public identity of a DH keypair.
#[derive(Clone)]
pub struct KeypairIdentity {
    /// The public identity key.
    pub public: identity::PublicKey,
    /// The signature over the public DH key.
    pub signature: Option<Vec<u8>>,
}

impl<T: Zeroize> Keypair<T> {
    /// The public key of the DH keypair.
    pub fn public(&self) -> &PublicKey<T> {
        &self.public
    }

    /// The secret key of the DH keypair.
    pub fn secret(&self) -> &SecretKey<T> {
        &self.secret
    }

    /// Turn this DH keypair into a [`AuthenticKeypair`], i.e. a DH keypair that
    /// is authentic w.r.t. the given identity keypair, by signing the DH public key.
    pub fn into_authentic(self, id_keys: &identity::Keypair) -> Result<AuthenticKeypair<T>, Error>
    where
        T: AsRef<[u8]>,
        T: Protocol<T>,
    {
        let sig = T::sign(id_keys, &self.public)?;

        let identity = KeypairIdentity {
            public: id_keys.public(),
            signature: Some(sig),
        };

        Ok(AuthenticKeypair {
            keypair: self,
            identity,
        })
    }
}

/// DH secret key.
#[derive(Clone)]
pub struct SecretKey<T: Zeroize>(T);

impl<T: Zeroize> Drop for SecretKey<T> {
    fn drop(&mut self) {
        self.0.zeroize()
    }
}

impl<T: AsRef<[u8]> + Zeroize> AsRef<[u8]> for SecretKey<T> {
    fn as_ref(&self) -> &[u8] {
        self.0.as_ref()
    }
}

/// DH public key.
#[derive(Clone)]
pub struct PublicKey<T>(T);

impl<T: AsRef<[u8]>> PartialEq for PublicKey<T> {
    fn eq(&self, other: &PublicKey<T>) -> bool {
        self.as_ref() == other.as_ref()
    }
}

impl<T: AsRef<[u8]>> Eq for PublicKey<T> {}

impl<T: AsRef<[u8]>> AsRef<[u8]> for PublicKey<T> {
    fn as_ref(&self) -> &[u8] {
        self.0.as_ref()
    }
}

/// Custom `snow::CryptoResolver` which delegates to either the
/// `RingResolver` on native or the `DefaultResolver` on wasm
/// for hash functions and symmetric ciphers, while using x25519-dalek
/// for Curve25519 DH.
struct Resolver;

impl snow::resolvers::CryptoResolver for Resolver {
    fn resolve_rng(&self) -> Option<Box<dyn snow::types::Random>> {
        Some(Box::new(Rng(rand::rngs::StdRng::from_entropy())))
    }

    fn resolve_dh(&self, choice: &snow::params::DHChoice) -> Option<Box<dyn snow::types::Dh>> {
        if let snow::params::DHChoice::Curve25519 = choice {
            Some(Box::new(Keypair::<x25519_spec::X25519Spec>::default()))
        } else {
            None
        }
    }

    fn resolve_hash(
        &self,
        choice: &snow::params::HashChoice,
    ) -> Option<Box<dyn snow::types::Hash>> {
        #[cfg(target_arch = "wasm32")]
        {
            snow::resolvers::DefaultResolver.resolve_hash(choice)
        }
        #[cfg(not(target_arch = "wasm32"))]
        {
            snow::resolvers::RingResolver.resolve_hash(choice)
        }
    }

    fn resolve_cipher(
        &self,
        choice: &snow::params::CipherChoice,
    ) -> Option<Box<dyn snow::types::Cipher>> {
        #[cfg(target_arch = "wasm32")]
        {
            snow::resolvers::DefaultResolver.resolve_cipher(choice)
        }
        #[cfg(not(target_arch = "wasm32"))]
        {
            snow::resolvers::RingResolver.resolve_cipher(choice)
        }
    }
}

/// Wrapper around a CSPRNG to implement `snow::Random` trait for.
struct Rng(rand::rngs::StdRng);

impl rand::RngCore for Rng {
    fn next_u32(&mut self) -> u32 {
        self.0.next_u32()
    }

    fn next_u64(&mut self) -> u64 {
        self.0.next_u64()
    }

    fn fill_bytes(&mut self, dest: &mut [u8]) {
        self.0.fill_bytes(dest)
    }

    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand::Error> {
        self.0.try_fill_bytes(dest)
    }
}

impl rand::CryptoRng for Rng {}

impl snow::types::Random for Rng {}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::X25519Spec;
    use once_cell::sync::Lazy;

    #[test]
    fn handshake_hashes_disagree_if_prologue_differs() {
        let alice = xx_builder(b"alice prologue").build_initiator().unwrap();
        let bob = xx_builder(b"bob prologue").build_responder().unwrap();

        let alice_handshake_hash = alice.get_handshake_hash();
        let bob_handshake_hash = bob.get_handshake_hash();

        assert_ne!(alice_handshake_hash, bob_handshake_hash)
    }

    #[test]
    fn handshake_hashes_agree_if_prologue_is_the_same() {
        let alice = xx_builder(b"shared knowledge").build_initiator().unwrap();
        let bob = xx_builder(b"shared knowledge").build_responder().unwrap();

        let alice_handshake_hash = alice.get_handshake_hash();
        let bob_handshake_hash = bob.get_handshake_hash();

        assert_eq!(alice_handshake_hash, bob_handshake_hash)
    }

    fn xx_builder(prologue: &'static [u8]) -> snow::Builder<'static> {
        X25519Spec::params_xx().into_builder(prologue, TEST_KEY.secret(), None)
    }

    // Hack to work around borrow-checker.
    static TEST_KEY: Lazy<Keypair<X25519Spec>> = Lazy::new(Keypair::<X25519Spec>::new);
}