Mixnet integration (#1346)

See #1345, <https://github.com/paritytech/substrate/pull/14207>.

This adds all the necessary mixnet components, and puts them together in
the "kitchen-sink" node/runtime. The components added are:

- A pallet (`frame/mixnet`). This is responsible for determining the
current mixnet session and phase, and the mixnodes to use in each
session. It provides a function that validators can call to register a
mixnode for the next session. The logic of this pallet is very similar
to that of the `im-online` pallet.
- A service (`client/mixnet`). This implements the core mixnet logic,
building on the `mixnet` crate. The service communicates with other
nodes using notifications sent over the "mixnet" protocol.
- An RPC interface. This currently only supports sending transactions
over the mixnet.

---------

Co-authored-by: David Emett <dave@sp4m.net>
Co-authored-by: Javier Viola <javier@parity.io>

substrate/client/cli/src/params/mixnet_params.rs

@@ -0,0 +1,67 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use clap::Args;
+use sp_core::H256;
+use std::str::FromStr;
+
+fn parse_kx_secret(s: &str) -> Result<sc_mixnet::KxSecret, String> {
+	H256::from_str(s).map(H256::to_fixed_bytes).map_err(|err| err.to_string())
+}
+
+/// Parameters used to create the mixnet configuration.
+#[derive(Debug, Clone, Args)]
+pub struct MixnetParams {
+	/// Enable the mixnet service.
+	///
+	/// This will make the mixnet RPC methods available. If the node is running as a validator, it
+	/// will also attempt to register and operate as a mixnode.
+	#[arg(long)]
+	pub mixnet: bool,
+
+	/// The mixnet key-exchange secret to use in session 0.
+	///
+	/// Should be 64 hex characters, giving a 32-byte secret.
+	///
+	/// WARNING: Secrets provided as command-line arguments are easily exposed. Use of this option
+	/// should be limited to development and testing.
+	#[arg(long, value_name = "SECRET", value_parser = parse_kx_secret)]
+	pub mixnet_session_0_kx_secret: Option<sc_mixnet::KxSecret>,
+}
+
+impl MixnetParams {
+	/// Returns the mixnet configuration, or `None` if the mixnet is disabled.
+	pub fn config(&self, is_authority: bool) -> Option<sc_mixnet::Config> {
+		self.mixnet.then(|| {
+			let mut config = sc_mixnet::Config {
+				core: sc_mixnet::CoreConfig {
+					session_0_kx_secret: self.mixnet_session_0_kx_secret,
+					..Default::default()
+				},
+				..Default::default()
+			};
+			if !is_authority {
+				// Only authorities can be mixnodes; don't attempt to register
+				config.substrate.register = false;
+				// Only mixnodes need to allow connections from non-mixnodes
+				config.substrate.num_gateway_slots = 0;
+			}
+			config
+		})
+	}
+}

substrate/client/cli/src/params/mod.rs

@@ -19,6 +19,7 @@ mod database_params;
 mod import_params;
 mod keystore_params;
 mod message_params;
+mod mixnet_params;
 mod network_params;
 mod node_key_params;
 mod offchain_worker_params;
@@ -39,9 +40,10 @@ use sp_runtime::{
 use std::{fmt::Debug, str::FromStr};
 
 pub use crate::params::{
-	database_params::*, import_params::*, keystore_params::*, message_params::*, network_params::*,
-	node_key_params::*, offchain_worker_params::*, prometheus_params::*, pruning_params::*,
-	runtime_params::*, shared_params::*, telemetry_params::*, transaction_pool_params::*,
+	database_params::*, import_params::*, keystore_params::*, message_params::*, mixnet_params::*,
+	network_params::*, node_key_params::*, offchain_worker_params::*, prometheus_params::*,
+	pruning_params::*, runtime_params::*, shared_params::*, telemetry_params::*,
+	transaction_pool_params::*,
 };
 
 /// Parse Ss58AddressFormat