Split off System random functions into a new Randomness module

Cargo.toml

@@ -92,6 +92,7 @@ members = [
 	"srml/membership",
 	"srml/metadata",
 	"srml/offences",
+	"srml/randomness",
 	"srml/scored-pool",
 	"srml/session",
 	"srml/staking",

node-template/runtime/Cargo.toml

@@ -20,6 +20,7 @@ babe-primitives = { package = "substrate-consensus-babe-primitives", path = "../
 executive = { package = "srml-executive", path = "../../srml/executive", default_features = false }
 indices = { package = "srml-indices", path = "../../srml/indices", default_features = false }
 grandpa = { package = "srml-grandpa", path = "../../srml/grandpa", default-features = false }
+randomness = { package = "srml-randomness", path = "../../srml/randomness", default_features = false }
 system = { package = "srml-system", path = "../../srml/system", default_features = false }
 timestamp = { package = "srml-timestamp", path = "../../srml/timestamp", default_features = false }
 sudo = { package = "srml-sudo", path = "../../srml/sudo", default_features = false }
@@ -46,6 +47,7 @@ std = [
 	"grandpa/std",
 	"primitives/std",
 	"sr-primitives/std",
+	"randomness/std",
 	"system/std",
 	"timestamp/std",
 	"sudo/std",

node-template/runtime/src/lib.rs

@@ -271,6 +271,7 @@ construct_runtime!(
 		Sudo: sudo,
 		// Used for the module template in `./template.rs`
 		TemplateModule: template::{Module, Call, Storage, Event<T>},
+		Randomness: randomness::{Module, Call, Storage},
 	}
 );
 
@@ -339,7 +340,7 @@ impl_runtime_apis! {
 		}
 
 		fn random_seed() -> <Block as BlockT>::Hash {
-			System::random_seed()
+			Randomness::random_seed()
 		}
 	}
 

node/runtime/Cargo.toml

@@ -40,6 +40,7 @@ im-online = { package = "srml-im-online", path = "../../srml/im-online", default
 indices = { package = "srml-indices", path = "../../srml/indices", default-features = false }
 membership = { package = "srml-membership", path = "../../srml/membership", default-features = false }
 offences = { package = "srml-offences", path = "../../srml/offences", default-features = false }
+randomness = { package = "srml-randomness", path = "../../srml/randomness", default-features = false }
 session = { package = "srml-session", path = "../../srml/session", default-features = false, features = ["historical"] }
 staking = { package = "srml-staking", path = "../../srml/staking", default-features = false }
 srml-staking-reward-curve = { path = "../../srml/staking/reward-curve"}
@@ -77,6 +78,7 @@ std = [
 	"offchain-primitives/std",
 	"offences/std",
 	"primitives/std",
+	"randomness/std",
 	"rstd/std",
 	"rustc-hex",
 	"safe-mix/std",

node/runtime/src/lib.rs

@@ -84,8 +84,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 165,
-	impl_version: 165,
+	spec_version: 166,
+	impl_version: 166,
 	apis: RUNTIME_API_VERSIONS,
 };
 
@@ -508,6 +508,7 @@ construct_runtime!(
 		ImOnline: im_online::{Module, Call, Storage, Event<T>, ValidateUnsigned, Config<T>},
 		AuthorityDiscovery: authority_discovery::{Module, Call, Config<T>},
 		Offences: offences::{Module, Call, Storage, Event},
+		Randomness: randomness::{Module, Call, Storage},
 	}
 );
 
@@ -579,7 +580,7 @@ impl_runtime_apis! {
 		}
 
 		fn random_seed() -> <Block as BlockT>::Hash {
-			System::random_seed()
+			Randomness::random_seed()
 		}
 	}
 

srml/contracts/Cargo.toml

@@ -17,6 +17,7 @@ rstd = { package = "sr-std", path = "../../core/sr-std", default-features = fals
 sandbox = { package = "sr-sandbox", path = "../../core/sr-sandbox", default-features = false }
 support = { package = "srml-support", path = "../support", default-features = false }
 system = { package = "srml-system", path = "../system", default-features = false }
+randomness = { package = "srml-randomness", path = "../randomness", default-features = false }
 timestamp = { package = "srml-timestamp", path = "../timestamp", default-features = false }
 
 [dev-dependencies]
@@ -33,6 +34,7 @@ std = [
 	"codec/std",
 	"primitives/std",
 	"sr-primitives/std",
+	"randomness/std",
 	"runtime-io/std",
 	"rstd/std",
 	"sandbox/std",

srml/contracts/src/exec.rs

@@ -754,7 +754,7 @@ where
 	}
 
 	fn random(&self, subject: &[u8]) -> SeedOf<T> {
-		system::Module::<T>::random(subject)
+		randomness::Module::<T>::random(subject)
 	}
 
 	fn now(&self) -> &T::Moment {

srml/randomness/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "srml-randomness"
+version = "2.0.0"
+authors = ["Parity Technologies <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+safe-mix = { version = "1.0", default-features = false}
+codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false, features = ["derive"] }
+sr-primitives = { path = "../../core/sr-primitives", default-features = false }
+support = { package = "srml-support", path = "../support", default-features = false }
+system = { package = "srml-system", path = "../system", default-features = false }
+rstd = { package = "sr-std", path = "../../core/sr-std", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"safe-mix/std",
+	"system/std",
+	"codec/std",
+	"support/std",
+	"sr-primitives/std",
+	"rstd/std",
+]

srml/randomness/src/lib.rs

@@ -0,0 +1,145 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! # Randomness Module
+//!
+//! The Randomness module provides a [`random`](./struct.Module.html#method.random) function that
+//! generates low-influence random values based on the block hashes from the previous 81 blocks.
+//!
+//! ## Public Functions
+//!
+//! See the [`Module`](./struct.Module.html) struct for details of publicly available functions.
+//!
+//! ## Usage
+//!
+//! ### Prerequisites
+//!
+//! Import the Randomness module and derive your module's configuration trait from the system trait.
+//!
+//! ### Example - Get random seed for the current block
+//!
+//! ```
+//! use support::{decl_module, dispatch::Result};
+//!
+//! trait Trait: system::Trait {}
+//!
+//! decl_module! {
+//! 	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+//! 		pub fn random_module_example(origin) -> Result {
+//! 			let _random_seed = <srml_random::Module<T>>::random_seed();
+//! 			Ok(())
+//! 		}
+//! 	}
+//! }
+//! # fn main() { }
+//! ```
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use rstd::prelude::*;
+use sr_primitives::traits::Hash;
+use support::{decl_module, decl_storage};
+use safe_mix::TripletMix;
+use codec::Encode;
+use system::Trait;
+
+decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		fn on_initialize() {
+			let parent_hash = <system::Module<T>>::parent_hash();
+
+			<RandomMaterial<T>>::mutate(|&mut(ref mut index, ref mut values)| if values.len() < 81 {
+				values.push(parent_hash)
+			} else {
+				values[*index as usize] = parent_hash;
+				*index = (*index + 1) % 81;
+			});
+		}
+	}
+}
+
+decl_storage! {
+	trait Store for Module<T: Trait> as System {
+		/// Series of block headers from the last 81 blocks that acts as random seed material. This is arranged as a
+		/// ring buffer with the `i8` prefix being the index into the `Vec` of the oldest hash.
+		RandomMaterial get(random_material): (i8, Vec<T::Hash>);
+	}
+}
+
+impl<T: Trait> Module<T> {
+	/// Get the basic random seed.
+	///
+	/// In general you won't want to use this, but rather `Self::random` which
+	/// allows you to give a subject for the random result and whose value will
+	/// be independently low-influence random from any other such seeds.
+	pub fn random_seed() -> T::Hash {
+		Self::random(&[][..])
+	}
+
+	/// Get a low-influence "random" value.
+	///
+	/// Being a deterministic block chain, real randomness is difficult to come
+	/// by. This gives you something that approximates it. `subject` is a
+	/// context identifier and allows you to get a different result to other
+	/// callers of this function; use it like `random(&b"my context"[..])`.
+	///
+	/// This is initially implemented through a low-influence "triplet mix"
+	/// convolution of previous block hash values. In the future it will be
+	/// generated from a secure verifiable random function (VRF).
+	///
+	/// ### Security Notes
+	///
+	/// This randomness uses a low-influence function, drawing upon the block
+	/// hashes from the previous 81 blocks. Its result for any given subject
+	/// will be known in advance by the block producer of this block (and,
+	/// indeed, anyone who knows the block's `parent_hash`). However, it is
+	/// mostly impossible for the producer of this block *alone* to influence
+	/// the value of this hash. A sizable minority of dishonest and coordinating
+	/// block producers would be required in order to affect this value. If that
+	/// is an insufficient security guarantee then two things can be used to
+	/// improve this randomness:
+	///
+	/// - Name, in advance, the block number whose random value will be used;
+	///   ensure your module retains a buffer of previous random values for its
+	///   subject and then index into these in order to obviate the ability of
+	///   your user to look up the parent hash and choose when to transact based
+	///   upon it.
+	/// - Require your user to first commit to an additional value by first
+	///   posting its hash. Require them to reveal the value to determine the
+	///   final result, hashing it with the output of this random function. This
+	///   reduces the ability of a cabal of block producers from conspiring
+	///   against individuals.
+	///
+	/// WARNING: Hashing the result of this function will remove any
+	/// low-influence properties it has and mean that all bits of the resulting
+	/// value are entirely manipulatable by the author of the parent block, who
+	/// can determine the value of `parent_hash`.
+	pub fn random(subject: &[u8]) -> T::Hash {
+		let (index, hash_series) = <RandomMaterial<T>>::get();
+		if hash_series.len() > 0 {
+			// Always the case after block 1 is initialised.
+			hash_series.iter()
+				.cycle()
+				.skip(index as usize)
+				.take(81)
+				.enumerate()
+				.map(|(i, h)| (i as i8, subject, h).using_encoded(T::Hashing::hash))
+				.triplet_mix()
+		} else {
+			T::Hash::default()
+		}
+	}
+}