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Remove random function #1442

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Oct 29, 2022
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Remove random function #1442

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5d058ba
Remove random function
athei Oct 19, 2022
0758443
Fix clippy
athei Oct 21, 2022
c5329c2
Merge branch 'master' into at/remove-random
athei Oct 29, 2022
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

- Remove random function from ink!.
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Suggested change
- Remove random function from ink!.
### Removed
- Remove random function ‒ [#1442](https://github.com/paritytech/ink/pull/1442)

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Could you please add some more information in a section ### How to replace random here?

My concern is that we're just removing it without providing guidance on how to substitute this functionality.

Is there no pallet out there which we could create a chain extension with?

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On ethereum contracts need to look for randomness on their own anyways. They rely on oracle contracts AFAIK. If we had some reliable way to provide randomness in the general case we wouldn't remove it. I don't think there is anything at the moment.

@burdges has some ideas but nothing readily available. So we can't really give any advice beyond "good luck bro".

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This pseudo random function was useful enough for our contract but now its removed. Any guidance on how to recreate this functionality would be appreciated.

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@forgetso forgetso Jan 12, 2023 •
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We need a random seed per block that is good enough to randomly read a value from a vector within our contract. There is no transaction involved. The operation is not high value and the seed calculated by the validators was fulfilling this purpose very well. Are the validators no longer committing this random seed to each block?

Could the current block hash be made available in ink! as a substitute?

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@burdges burdges Jan 12, 2023 •
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There are several randomness sources available in polkadot, but they won't all be available in all ink deployments, especially ink deployments on stand along chains. We'd really like deployers to understand their limitations.

A block hash based randomness is good when you're doing a Fiat-Shamir transform, but usually not so great otherwise, but if your usage is low enough value then fine. There is nothing wrong with a parachain block knowing its own block hash, because although this makes parachain execution non-deterministic relative to when the block is built, it clearly stays deterministic from the perspective of polkadot. It's fine to make the block hash available and just warn people that they should look at other randomness options if they think about using it for randomness.

BABE's VRF usage provides three slightly different randomness sources, each with their own use cases. Sassafras should add a fourth, but not too different either. ParentBlockRandomness might fit your use case.

A drand gives strong fresh randomness every 15 seconds. It's desynced from polkadot though, so one needs a "drand bridge" to sync reads from drand, without giving someone too much authority to tweak the syncing.

Advanced randomness like polkadot's candle auctions require some sort of commitment before the randomness exists, after which the chain chooses the randomness with which the commitment gets used. VRF keys held by users fit roughly into this category too, but less strictly.

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@athei athei Jan 15, 2023 •
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We need a random seed per block that is good enough to randomly read a value from a vector within our contract. There is no transaction involved. The operation is not high value and the seed calculated by the validators was fulfilling this purpose very well. Are the validators no longer committing this random seed to each block?

Could the current block hash be made available in ink! as a substitute?

We would need way for information to give some advice and to determine if using predictable randomness is actually safe. I recommend asking on stack exchange.

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I've provided more info on stack exchange.


## Version 4.0.0-alpha.3

### Breaking Changes
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2 changes: 0 additions & 2 deletions crates/engine/Cargo.toml
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Expand Up @@ -23,8 +23,6 @@ sha2 = { version = "0.10" }
sha3 = { version = "0.10" }
blake2 = { version = "0.10" }

rand = { version = "0.8" }

# ECDSA for the off-chain environment.
secp256k1 = { version = "0.24", features = ["recovery", "global-context"], optional = true }

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11 changes: 1 addition & 10 deletions crates/engine/src/exec_context.rs
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Expand Up @@ -17,9 +17,7 @@ use super::types::{
Balance,
BlockNumber,
BlockTimestamp,
Hash,
};
use rand::Rng;

/// The context of a contract execution.
#[cfg_attr(test, derive(Debug, PartialEq, Eq))]
Expand All @@ -44,21 +42,16 @@ pub struct ExecContext {
pub block_number: BlockNumber,
/// The current block timestamp.
pub block_timestamp: BlockTimestamp,
/// The randomization entropy for a block.
pub entropy: Hash,
}

impl Default for ExecContext {
fn default() -> Self {
let mut entropy: [u8; 32] = Default::default();
rand::thread_rng().fill(entropy.as_mut());
Self {
caller: None,
callee: None,
value_transferred: 0,
block_number: 0,
block_timestamp: 0,
entropy,
}
}
}
Expand Down Expand Up @@ -101,10 +94,8 @@ mod tests {
assert_eq!(exec_cont.callee(), vec![13]);

exec_cont.reset();
exec_cont.entropy = Default::default();

let mut new_exec_cont = ExecContext::new();
new_exec_cont.entropy = Default::default();
let new_exec_cont = ExecContext::new();
assert_eq!(exec_cont, new_exec_cont);
}
}
32 changes: 0 additions & 32 deletions crates/engine/src/ext.rs
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Expand Up @@ -31,10 +31,6 @@ use crate::{
BlockTimestamp,
},
};
use rand::{
Rng,
SeedableRng,
};
use scale::Encode;
use std::panic::panic_any;

Expand Down Expand Up @@ -431,34 +427,6 @@ impl Engine {
set_output(output, &fee[..])
}

/// Returns a randomized hash.
///
/// # Note
///
/// - This is the off-chain environment implementation of `random`.
/// It provides the same behavior in that it will likely yield the
/// same hash for the same subjects within the same block (or
/// execution context).
///
/// # Example
///
/// ```rust
/// let engine = ink_engine::ext::Engine::default();
/// let subject = [0u8; 32];
/// let mut output = [0u8; 32];
/// engine.random(&subject, &mut output.as_mut_slice());
/// ```
pub fn random(&self, subject: &[u8], output: &mut &mut [u8]) {
let seed = (self.exec_context.entropy, subject).encode();
let mut digest = [0u8; 32];
Engine::hash_blake2_256(&seed, &mut digest);

let mut rng = rand::rngs::StdRng::from_seed(digest);
let mut rng_bytes: [u8; 32] = Default::default();
rng.fill(&mut rng_bytes);
set_output(output, &rng_bytes[..])
}

/// Calls the chain extension method registered at `func_id` with `input`.
pub fn call_chain_extension(
&mut self,
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3 changes: 0 additions & 3 deletions crates/engine/src/types.rs
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Expand Up @@ -17,9 +17,6 @@

use derive_more::From;

/// Same type as the `DefaultEnvironment::Hash` type.
pub type Hash = [u8; 32];

/// Same type as the `DefaultEnvironment::BlockNumber` type.
pub type BlockNumber = u32;

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3 changes: 0 additions & 3 deletions crates/env/Cargo.toml
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Expand Up @@ -47,7 +47,6 @@ secp256k1 = { version = "0.24", features = ["recovery", "global-context"], optio
#
# Sadly couldn't be marked as dev-dependency.
# Never use this crate outside the off-chain environment!
rand = { version = "0.8", default-features = false, features = ["alloc"], optional = true }
scale-info = { version = "2", default-features = false, features = ["derive"], optional = true }

[features]
Expand All @@ -62,8 +61,6 @@ std = [
"scale/std",
"scale-info/std",
"secp256k1",
"rand/std",
"rand/std_rng",
"num-traits/std",
# Enables hashing crates for off-chain environment.
"sha2",
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28 changes: 0 additions & 28 deletions crates/env/src/api.rs
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Expand Up @@ -405,34 +405,6 @@ where
})
}

/// Returns a random hash seed and the block number since which it was determinable
/// by chain observers.
///
/// # Note
///
/// - The subject buffer can be used to further randomize the hash.
/// - Within the same execution returns the same random hash for the same subject.
///
/// # Errors
///
/// If the returned value cannot be properly decoded.
///
/// # Important
///
/// The returned seed should only be used to distinguish commitments made before
/// the returned block number. If the block number is too early (i.e. commitments were
/// made afterwards), then ensure no further commitments may be made and repeatedly
/// call this on later blocks until the block number returned is later than the latest
/// commitment.
pub fn random<E>(subject: &[u8]) -> Result<(E::Hash, E::BlockNumber)>
where
E: Environment,
{
<EnvInstance as OnInstance>::on_instance(|instance| {
TypedEnvBackend::random::<E>(instance, subject)
})
}

/// Appends the given message to the debug message buffer.
pub fn debug_message(message: &str) {
<EnvInstance as OnInstance>::on_instance(|instance| {
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9 changes: 0 additions & 9 deletions crates/env/src/backend.rs
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Expand Up @@ -450,15 +450,6 @@ pub trait TypedEnvBackend: EnvBackend {
where
E: Environment;

/// Returns a random hash seed.
///
/// # Note
///
/// For more details visit: [`random`][`crate::random`]
fn random<E>(&mut self, subject: &[u8]) -> Result<(E::Hash, E::BlockNumber)>
where
E: Environment;

/// Checks whether a specified account belongs to a contract.
///
/// # Note
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9 changes: 0 additions & 9 deletions crates/env/src/engine/off_chain/impls.rs
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Expand Up @@ -495,15 +495,6 @@ impl TypedEnvBackend for EnvInstance {
})
}

fn random<E>(&mut self, subject: &[u8]) -> Result<(E::Hash, E::BlockNumber)>
where
E: Environment,
{
let mut output: [u8; BUFFER_SIZE] = [0; BUFFER_SIZE];
self.engine.random(subject, &mut &mut output[..]);
scale::Decode::decode(&mut &output[..]).map_err(Into::into)
}

fn is_contract<E>(&mut self, _account: &E::AccountId) -> bool
where
E: Environment,
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12 changes: 0 additions & 12 deletions crates/env/src/engine/off_chain/test_api.rs
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Expand Up @@ -98,18 +98,6 @@ where
})
}

/// Set the entropy hash of the current block.
///
/// # Note
///
/// This allows to control what [`random`][`crate::random`] returns.
pub fn set_block_entropy<T>(_entropy: T::Hash) -> Result<()>
where
T: Environment,
{
unimplemented!("off-chain environment does not yet support `set_block_entropy`");
}

/// Returns the contents of the past performed environmental debug messages in order.
pub fn recorded_debug_messages() -> RecordedDebugMessages {
<EnvInstance as OnInstance>::on_instance(|instance| {
Expand Down
23 changes: 0 additions & 23 deletions crates/env/src/engine/on_chain/ext.rs
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Expand Up @@ -347,13 +347,6 @@ mod sys {

pub fn seal_terminate(beneficiary_ptr: Ptr32<[u8]>) -> !;

pub fn seal_random(
subject_ptr: Ptr32<[u8]>,
subject_len: u32,
output_ptr: Ptr32Mut<[u8]>,
output_len_ptr: Ptr32Mut<u32>,
);

pub fn seal_call(
flags: u32,
callee_ptr: Ptr32<[u8]>,
Expand Down Expand Up @@ -675,22 +668,6 @@ pub fn weight_to_fee(gas: u64, output: &mut &mut [u8]) {
extract_from_slice(output, output_len as usize);
}

#[inline(always)]
pub fn random(subject: &[u8], output: &mut &mut [u8]) {
let mut output_len = output.len() as u32;
{
unsafe {
sys::seal_random(
Ptr32::from_slice(subject),
subject.len() as u32,
Ptr32Mut::from_slice(output),
Ptr32Mut::from_ref(&mut output_len),
)
};
}
extract_from_slice(output, output_len as usize);
}

#[cfg(feature = "ink-debug")]
/// Call `seal_debug_message` with the supplied UTF-8 encoded message.
///
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11 changes: 0 additions & 11 deletions crates/env/src/engine/on_chain/impls.rs
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Expand Up @@ -523,17 +523,6 @@ impl TypedEnvBackend for EnvInstance {
<E::Balance as FromLittleEndian>::from_le_bytes(result)
}

fn random<E>(&mut self, subject: &[u8]) -> Result<(E::Hash, E::BlockNumber)>
where
E: Environment,
{
let mut scope = self.scoped_buffer();
let enc_subject = scope.take_bytes(subject);
let output = &mut scope.take_rest();
ext::random(enc_subject, output);
scale::Decode::decode(&mut &output[..]).map_err(Into::into)
}

fn is_contract<E>(&mut self, account_id: &E::AccountId) -> bool
where
E: Environment,
Expand Down
34 changes: 0 additions & 34 deletions crates/ink/src/env_access.rs
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Expand Up @@ -666,40 +666,6 @@ where
ink_env::transfer::<E>(destination, value)
}

/// Returns a random hash seed.
///
/// # Example
///
/// ```
/// # #[ink::contract]
/// # pub mod my_contract {
/// # #[ink(storage)]
/// # pub struct MyContract { }
/// #
/// # impl MyContract {
/// # #[ink(constructor)]
/// # pub fn new() -> Self {
/// # Self {}
/// # }
/// #
/// #[ink(message)]
/// pub fn random_bool(&self) -> bool {
/// let additional_randomness = b"seed";
/// let (hash, _block_number) = self.env().random(additional_randomness);
/// hash.as_ref()[0] != 0
/// }
/// #
/// # }
/// # }
/// ```
///
/// # Note
///
/// For more details visit: [`ink_env::random`]
pub fn random(self, subject: &[u8]) -> (E::Hash, E::BlockNumber) {
ink_env::random::<E>(subject).expect("couldn't decode randomized hash")
}

/// Computes the hash of the given bytes using the cryptographic hash `H`.
///
/// # Example
Expand Down
2 changes: 0 additions & 2 deletions crates/ink/tests/ui/contract/pass/env-access.rs
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Expand Up @@ -13,7 +13,6 @@ mod contract {
let _ = Self::env().caller();
let _ = Self::env().gas_left();
let _ = Self::env().minimum_balance();
let _ = Self::env().random(&[]);
let _ = Self::env().transferred_value();
let _ = Self::env().weight_to_fee(0);
Self {}
Expand All @@ -28,7 +27,6 @@ mod contract {
let _ = self.env().caller();
let _ = self.env().gas_left();
let _ = self.env().minimum_balance();
let _ = self.env().random(&[]);
let _ = self.env().transferred_value();
let _ = self.env().weight_to_fee(0);
}
Expand Down