Consolidate keypairs in core. (#972)

* Consolidate keypairs in core.

Introduce the concept of a node's identity keypair in libp2p-core,
instead of only the public key:

  * New module: libp2p_core::identity with submodules for the currently
    supported key types. An identity::Keypair and identity::PublicKey
    support the creation and verification of signatures. The public key
    supports encoding/decoding according to the libp2p specs.

  * The secio protocol is simplified as a result of moving code to libp2p-core.

  * The noise protocol is slightly simplified by consolidating ed25519
    keypairs in libp2p-core and using x25519-dalek for DH. Furthermore,
    Ed25519 to X25519 keypair conversion is now complete and tested.

Generalise over the DH keys in the noise protocol.

Generalise over the DH keys and thus DH parameter in handshake patterns
of the Noise protocol, such that it is easy to support other DH schemes
in the future, e.g. X448.

* Address new review comments.

protocols/noise/src/protocol.rs

@@ -0,0 +1,173 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+//! Components of a Noise protocol.
+
+pub mod x25519;
+
+use crate::NoiseError;
+use rand::FromEntropy;
+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 {
+    /// Turn the protocol parameters into a session builder.
+    pub(crate) fn into_builder(self) -> snow::Builder<'static> {
+        snow::Builder::with_resolver(self.0, Box::new(Resolver))
+    }
+}
+
+/// 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.
+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>, NoiseError>;
+}
+
+/// DH keypair.
+#[derive(Clone)]
+pub struct Keypair<T: Zeroize> {
+    secret: SecretKey<T>,
+    public: PublicKey<T>
+}
+
+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
+    }
+}
+
+/// 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 the `RingResolver`
+/// for hash functions and symmetric ciphers, while using x25519-dalek
+/// for Curve25519 DH. We do not use the default resolver for any of
+/// the choices, because it comes with unwanted additional dependencies,
+/// notably rust-crypto, and to avoid being affected by changes to
+/// the defaults.
+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::X25519>::default()))
+        } else {
+            None
+        }
+    }
+
+    fn resolve_hash(&self, choice: &snow::params::HashChoice) -> Option<Box<dyn snow::types::Hash>> {
+        snow::resolvers::RingResolver.resolve_hash(choice)
+    }
+
+    fn resolve_cipher(&self, choice: &snow::params::CipherChoice) -> Option<Box<dyn snow::types::Cipher>> {
+        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 {}
+