feat(acvm)!: Add ReferenceString backend trait

acvm/Cargo.toml

@@ -28,6 +28,7 @@ k256 = { version = "0.7.2", features = [
 ] }
 indexmap = "1.7.0"
 thiserror = "1.0.21"
+async-trait = "0.1"
 
 [features]
 default = ["bn254"]

acvm/src/lib.rs

@@ -20,6 +20,9 @@ use pwg::{block::Blocks, directives::solve_directives};
 use std::collections::BTreeMap;
 use thiserror::Error;
 
+// We re-export async-trait so consumers can attach it to their impl
+pub use async_trait::async_trait;
+
 // re-export acir
 pub use acir;
 pub use acir::FieldElement;
@@ -92,7 +95,26 @@ fn first_missing_assignment(
     })
 }
 
-pub trait Backend: SmartContract + ProofSystemCompiler + PartialWitnessGenerator + Default {}
+pub trait Backend:
+    SmartContract + ProofSystemCompiler + PartialWitnessGenerator + ReferenceString + Default
+{
+}
+
+#[async_trait]
+pub trait ReferenceString {
+    /// The Error type returned by failed function calls in the ReferenceString trait.
+    type Error: std::error::Error; // fully-qualified named because thiserror is `use`d at the top of the crate
+
+    /// Provides the reference string that is needed by other traits
+    async fn get_reference_string(&self, circuit: &Circuit) -> Result<Vec<u8>, Self::Error>;
+
+    /// Validates a (likely cached) reference string against a circuit
+    fn is_reference_string_valid(
+        &self,
+        reference_string: &[u8],
+        circuit: &Circuit,
+    ) -> Result<bool, Self::Error>;
+}
 
 /// This component will generate the backend specific output for
 /// each OPCODE.
@@ -201,7 +223,11 @@ pub trait SmartContract {
     // TODO: Allow a backend to support multiple smart contract platforms
 
     /// Returns an Ethereum smart contract to verify proofs against a given verification key.
-    fn eth_contract_from_vk(&self, verification_key: &[u8]) -> Result<String, Self::Error>;
+    fn eth_contract_from_vk(
+        &self,
+        reference_string: &[u8],
+        verification_key: &[u8],
+    ) -> Result<String, Self::Error>;
 }
 
 pub trait ProofSystemCompiler {
@@ -222,13 +248,18 @@ pub trait ProofSystemCompiler {
 
     /// Generates a proving and verification key given the circuit description
     /// These keys can then be used to construct a proof and for its verification
-    fn preprocess(&self, circuit: &Circuit) -> Result<(Vec<u8>, Vec<u8>), Self::Error>;
+    fn preprocess(
+        &self,
+        reference_string: &[u8],
+        circuit: &Circuit,
+    ) -> Result<(Vec<u8>, Vec<u8>), Self::Error>;
 
     /// Creates a Proof given the circuit description, the initial witness values, and the proving key
     /// It is important to note that the intermediate witnesses for black box functions will not generated
     /// This is the responsibility of the proof system.
     fn prove_with_pk(
         &self,
+        reference_string: &[u8],
         circuit: &Circuit,
         witness_values: BTreeMap<Witness, FieldElement>,
         proving_key: &[u8],
@@ -237,6 +268,7 @@ pub trait ProofSystemCompiler {
     /// Verifies a Proof, given the circuit description, the circuit's public inputs, and the verification key
     fn verify_with_vk(
         &self,
+        reference_string: &[u8],
         proof: &[u8],
         public_inputs: BTreeMap<Witness, FieldElement>,
         circuit: &Circuit,