From 437f70a70bcf58fef564034575c4fc1aa4cbf6b4 Mon Sep 17 00:00:00 2001
From: Aayush Rajasekaran <arajasek94@gmail.com>
Date: Fri, 25 Aug 2023 13:13:24 -0400
Subject: [PATCH] feat: FVM no longer draws randomness for you (#1378)

---
 Cargo.lock                        |  1 +
 runtime/Cargo.toml                |  1 +
 runtime/src/runtime/fvm.rs        | 23 +++++++++--
 runtime/src/runtime/randomness.rs | 63 +++++++++++++++++++++++++++++++
 4 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 7827e88d65..bd0aa4894a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1749,6 +1749,7 @@ name = "fil_actors_runtime"
 version = "12.0.0"
 dependencies = [
  "anyhow",
+ "base64 0.21.3",
  "blake2b_simd",
  "byteorder",
  "castaway",
diff --git a/runtime/Cargo.toml b/runtime/Cargo.toml
index 2edb7badbe..cb0ec0f765 100644
--- a/runtime/Cargo.toml
+++ b/runtime/Cargo.toml
@@ -44,6 +44,7 @@ blake2b_simd = { workspace = true, optional = true }
 hex = { workspace = true, optional = true }
 pretty_env_logger = { workspace = true, optional = true }
 rand = { workspace = true, optional = true }
+base64 = "0.21.2"
 
 [dependencies.libsecp256k1]
 workspace = true
diff --git a/runtime/src/runtime/fvm.rs b/runtime/src/runtime/fvm.rs
index 9b67b407ad..47ca30f61d 100644
--- a/runtime/src/runtime/fvm.rs
+++ b/runtime/src/runtime/fvm.rs
@@ -36,6 +36,7 @@ use std::cell::RefCell;
 
 use crate::runtime::actor_blockstore::ActorBlockstore;
 use crate::runtime::builtins::Type;
+use crate::runtime::randomness::draw_randomness;
 use crate::runtime::{
     ActorCode, ConsensusFault, DomainSeparationTag, MessageInfo, Policy, Primitives, RuntimePolicy,
     Verifier,
@@ -231,14 +232,21 @@ where
         rand_epoch: ChainEpoch,
         entropy: &[u8],
     ) -> Result<[u8; RANDOMNESS_LENGTH], ActorError> {
-        fvm::rand::get_chain_randomness(personalization as i64, rand_epoch, entropy).map_err(|e| {
+        let digest = fvm::rand::get_chain_randomness(rand_epoch).map_err(|e| {
             match e {
                 ErrorNumber::LimitExceeded => {
                     actor_error!(illegal_argument; "randomness lookback exceeded: {}", e)
                 }
                 e => actor_error!(assertion_failed; "get chain randomness failed with an unexpected error: {}", e),
             }
-        })
+        })?;
+        Ok(draw_randomness(
+            fvm::crypto::hash_blake2b,
+            &digest,
+            personalization,
+            rand_epoch,
+            entropy,
+        ))
     }
 
     fn get_randomness_from_beacon(
@@ -247,14 +255,21 @@ where
         rand_epoch: ChainEpoch,
         entropy: &[u8],
     ) -> Result<[u8; RANDOMNESS_LENGTH], ActorError> {
-        fvm::rand::get_beacon_randomness(personalization as i64, rand_epoch, entropy).map_err(|e| {
+        let digest = fvm::rand::get_beacon_randomness(rand_epoch).map_err(|e| {
             match e {
                 ErrorNumber::LimitExceeded => {
                     actor_error!(illegal_argument; "randomness lookback exceeded: {}", e)
                 }
                 e => actor_error!(assertion_failed; "get beacon randomness failed with an unexpected error: {}", e),
             }
-        })
+        })?;
+        Ok(draw_randomness(
+            fvm::crypto::hash_blake2b,
+            &digest,
+            personalization,
+            rand_epoch,
+            entropy,
+        ))
     }
 
     fn get_state_root(&self) -> Result<Cid, ActorError> {
diff --git a/runtime/src/runtime/randomness.rs b/runtime/src/runtime/randomness.rs
index b303c68e77..bb7d05d848 100644
--- a/runtime/src/runtime/randomness.rs
+++ b/runtime/src/runtime/randomness.rs
@@ -1,6 +1,8 @@
 // Copyright 2019-2022 ChainSafe Systems
 // SPDX-License-Identifier: Apache-2.0, MIT
 
+use fvm_shared::clock::ChainEpoch;
+use fvm_shared::randomness::RANDOMNESS_LENGTH;
 use num_derive::FromPrimitive;
 use serde_repr::*;
 
@@ -19,3 +21,64 @@ pub enum DomainSeparationTag {
     PoStChainCommit = 9,
     EvmPrevRandao = 10,
 }
+
+#[allow(unused)]
+pub fn draw_randomness(
+    hasher: impl FnOnce(&[u8]) -> [u8; 32],
+    rbase: &[u8; RANDOMNESS_LENGTH],
+    pers: DomainSeparationTag,
+    round: ChainEpoch,
+    entropy: &[u8],
+) -> [u8; RANDOMNESS_LENGTH] {
+    let mut data = Vec::with_capacity(RANDOMNESS_LENGTH + 8 + 8 + entropy.len());
+
+    // Append the personalization value
+    let i64_bytes = (pers as i64).to_be_bytes();
+    data.extend_from_slice(&i64_bytes);
+
+    // Append the randomness
+    data.extend_from_slice(rbase);
+
+    // Append the round
+    let i64_bytes = round.to_be_bytes();
+    data.extend_from_slice(&i64_bytes);
+
+    // Append the entropy
+    data.extend_from_slice(entropy);
+
+    hasher(&data)
+    //
+    // fvm::crypto::hash_blake2b(&data)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::runtime::randomness::draw_randomness;
+    use crate::runtime::DomainSeparationTag;
+    use crate::test_utils::blake2b_256;
+    use base64::Engine;
+
+    #[test]
+    fn draw_randomness_test() {
+        let expected_randomness = base64::engine::general_purpose::STANDARD
+            .decode("3MCqcLHKZ+pil4MqTS9wjsd+yPvTuTrq8PkGjEo3tYQ=")
+            .unwrap();
+
+        let digest = base64::engine::general_purpose::STANDARD
+            .decode("GOobxkrhS1hiFA1EYUKZM3xsyVfy5Xy3bQ0gLPnecYs=")
+            .unwrap();
+
+        let entropy = base64::engine::general_purpose::STANDARD.decode("RACZyzQ=").unwrap();
+
+        assert_eq!(
+            expected_randomness,
+            draw_randomness(
+                blake2b_256,
+                <&[u8; 32]>::try_from(digest.as_slice()).unwrap(),
+                DomainSeparationTag::SealRandomness,
+                2797727,
+                entropy.as_slice(),
+            )
+        );
+    }
+}