Make secio almost compile for asmjs/wasm (#519)

* Use the sha2 crate in the handshake

* Return a Digest in algo_support instead of a ring ref

* Switch to ed25519-dalek for keys

* Make ring more or less optional

* Switch to ed25519_dalek for the verification

* Extract the key exchange to its own module

* Remove the ring RNG from the handshake

* Some warning fixes and forgot file

* Move key exchange to own module

* Remove usage of ring::digest

* Remove ring from handshake entirely

* Implement ECDH for WebCrypto

* Remove the libp2p-secio feature

* Fix ring being included

* Address some concerns

* Provde some panics in WebCrypto

* Prove the Hmac panic

* Prove more panics

protocols/secio/src/exchange/impl_ring.rs

@@ -0,0 +1,70 @@
+// Copyright 2018 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.
+
+//! Implementation of the key agreement process using the `ring` library.
+
+use futures::{future, prelude::*};
+use ring::agreement as ring_agreement;
+use ring::rand as ring_rand;
+use untrusted::Input as UntrustedInput;
+use {KeyAgreement, SecioError};
+
+impl Into<&'static ring_agreement::Algorithm> for KeyAgreement {
+    #[inline]
+    fn into(self) -> &'static ring_agreement::Algorithm {
+        match self {
+            KeyAgreement::EcdhP256 => &ring_agreement::ECDH_P256,
+            KeyAgreement::EcdhP384 => &ring_agreement::ECDH_P384,
+        }
+    }
+}
+
+/// Opaque private key type.
+pub type AgreementPrivateKey = ring_agreement::EphemeralPrivateKey;
+
+/// Generates a new key pair as part of the exchange.
+///
+/// Returns the opaque private key and the corresponding public key.
+pub fn generate_agreement(algorithm: KeyAgreement) -> impl Future<Item = (AgreementPrivateKey, Vec<u8>), Error = SecioError> {
+    let rng = ring_rand::SystemRandom::new();
+
+    match ring_agreement::EphemeralPrivateKey::generate(algorithm.into(), &rng) {
+        Ok(tmp_priv_key) => {
+            let mut tmp_pub_key: Vec<u8> = (0 .. tmp_priv_key.public_key_len()).map(|_| 0).collect();
+            tmp_priv_key.compute_public_key(&mut tmp_pub_key).unwrap();
+            future::ok((tmp_priv_key, tmp_pub_key))
+        },
+        Err(_) => {
+            debug!("failed to generate ECDH key");
+            future::err(SecioError::EphemeralKeyGenerationFailed)
+        },
+    }
+}
+
+/// Finish the agreement. On success, returns the shared key that both remote agreed upon.
+pub fn agree(algorithm: KeyAgreement, my_private_key: AgreementPrivateKey, other_public_key: &[u8], _out_size: usize)
+    -> impl Future<Item = Vec<u8>, Error = SecioError>
+{
+    ring_agreement::agree_ephemeral(my_private_key, algorithm.into(),
+                                    UntrustedInput::from(other_public_key),
+                                    SecioError::SecretGenerationFailed,
+                                    |key_material| Ok(key_material.to_vec()))
+        .into_future()
+}