From 108cb836213818a1869714fc530a397d4c39cdd7 Mon Sep 17 00:00:00 2001
From: Daniel Lubarov <daniel@lubarov.com>
Date: Mon, 21 Nov 2022 13:24:46 -0800
Subject: [PATCH 1/3] Domain separator option

---
 plonky2/src/plonk/circuit_builder.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/plonky2/src/plonk/circuit_builder.rs b/plonky2/src/plonk/circuit_builder.rs
index 1667205f..9c899643 100644
--- a/plonky2/src/plonk/circuit_builder.rs
+++ b/plonky2/src/plonk/circuit_builder.rs
@@ -53,6 +53,11 @@ use crate::util::{log2_ceil, log2_strict, transpose, transpose_poly_values};
 pub struct CircuitBuilder<F: RichField + Extendable<D>, const D: usize> {
     pub config: CircuitConfig,
 
+    /// A domain separator, which is included in the initial Fiat-Shamir seed. This is generally not
+    /// needed, but can be used to ensure that proofs for one application are not valid for another.
+    /// Defaults to zero.
+    domain_separator: Option<F>,
+
     /// The types of gates used in this circuit.
     gates: HashSet<GateRef<F, D>>,
 
@@ -102,6 +107,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
     pub fn new(config: CircuitConfig) -> Self {
         let builder = CircuitBuilder {
             config,
+            domain_separator: None,
             gates: HashSet::new(),
             gate_instances: Vec::new(),
             public_inputs: Vec::new(),
@@ -145,6 +151,11 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         );
     }
 
+    pub fn set_domain_separator(&mut self, separator: F) {
+        assert!(self.domain_separator.is_none());
+        self.domain_separator = Some(separator);
+    }
+
     pub fn num_gates(&self) -> usize {
         self.gate_instances.len()
     }
@@ -853,6 +864,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         let circuit_digest_parts = [
             constants_sigmas_cap.flatten(),
             vec![
+                self.domain_separator.unwrap_or_default(),
                 F::from_canonical_usize(degree_bits),
                 /* Add other circuit data here */
             ],

From af1b6680e8a63c30a2f972fc8ef140e057af0e67 Mon Sep 17 00:00:00 2001
From: Daniel Lubarov <daniel@lubarov.com>
Date: Tue, 22 Nov 2022 08:02:22 -0800
Subject: [PATCH 2/3] Switch to Vec

---
 plonky2/src/plonk/circuit_builder.rs | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/plonky2/src/plonk/circuit_builder.rs b/plonky2/src/plonk/circuit_builder.rs
index 9c899643..c2c13b2c 100644
--- a/plonky2/src/plonk/circuit_builder.rs
+++ b/plonky2/src/plonk/circuit_builder.rs
@@ -40,7 +40,7 @@ use crate::plonk::circuit_data::{
     CircuitConfig, CircuitData, CommonCircuitData, ProverCircuitData, ProverOnlyCircuitData,
     VerifierCircuitData, VerifierCircuitTarget, VerifierOnlyCircuitData,
 };
-use crate::plonk::config::{GenericConfig, Hasher};
+use crate::plonk::config::{GenericConfig, GenericHashOut, Hasher};
 use crate::plonk::copy_constraint::CopyConstraint;
 use crate::plonk::permutation_argument::Forest;
 use crate::plonk::plonk_common::PlonkOracle;
@@ -56,7 +56,7 @@ pub struct CircuitBuilder<F: RichField + Extendable<D>, const D: usize> {
     /// A domain separator, which is included in the initial Fiat-Shamir seed. This is generally not
     /// needed, but can be used to ensure that proofs for one application are not valid for another.
     /// Defaults to zero.
-    domain_separator: Option<F>,
+    domain_separator: Option<Vec<F>>,
 
     /// The types of gates used in this circuit.
     gates: HashSet<GateRef<F, D>>,
@@ -151,7 +151,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         );
     }
 
-    pub fn set_domain_separator(&mut self, separator: F) {
+    pub fn set_domain_separator(&mut self, separator: Vec<F>) {
         assert!(self.domain_separator.is_none());
         self.domain_separator = Some(separator);
     }
@@ -860,11 +860,13 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
             num_partial_products(self.config.num_routed_wires, quotient_degree_factor);
 
         let constants_sigmas_cap = constants_sigmas_commitment.merkle_tree.cap.clone();
+        let domain_separator = self.domain_separator.unwrap_or_default();
+        let domain_separator_digest = C::Hasher::hash_pad(&domain_separator);
         // TODO: This should also include an encoding of gate constraints.
         let circuit_digest_parts = [
             constants_sigmas_cap.flatten(),
+            domain_separator_digest.to_vec(),
             vec![
-                self.domain_separator.unwrap_or_default(),
                 F::from_canonical_usize(degree_bits),
                 /* Add other circuit data here */
             ],

From 7ec14029c68e42b454181cf019e063e1f8669aff Mon Sep 17 00:00:00 2001
From: Daniel Lubarov <daniel@lubarov.com>
Date: Tue, 22 Nov 2022 08:04:01 -0800
Subject: [PATCH 3/3] Fix comment

---
 plonky2/src/plonk/circuit_builder.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/plonky2/src/plonk/circuit_builder.rs b/plonky2/src/plonk/circuit_builder.rs
index c2c13b2c..8bd1d994 100644
--- a/plonky2/src/plonk/circuit_builder.rs
+++ b/plonky2/src/plonk/circuit_builder.rs
@@ -55,7 +55,7 @@ pub struct CircuitBuilder<F: RichField + Extendable<D>, const D: usize> {
 
     /// A domain separator, which is included in the initial Fiat-Shamir seed. This is generally not
     /// needed, but can be used to ensure that proofs for one application are not valid for another.
-    /// Defaults to zero.
+    /// Defaults to the empty vector.
     domain_separator: Option<Vec<F>>,
 
     /// The types of gates used in this circuit.