feat: Connect the public inputs but not the proof in ivc recursion constraints

barretenberg/cpp/src/barretenberg/dsl/acir_format/acir_format.cpp

@@ -513,22 +513,19 @@ MegaCircuitBuilder create_kernel_circuit(AcirFormat& constraint_system,
     // Create stdlib representations of each {proof, vkey} pair to be recursively verified
     ivc.instantiate_stdlib_verification_queue(circuit, stdlib_verification_keys);
 
-    // Connect the proof/public_input witness indices from each constraint to the corresponding proof witnesses in the
-    // internal verification queue. This ensures that the witnesses utlized in constraints generated based on acir are
-    // properly connected to the constraints generated herein via the ivc scheme (e.g. recursive verifications).
+    // Connect the public_input witnesses in each constraint to the corresponding public input witnesses in the internal
+    // verification queue. This ensures that the witnesses utlized in constraints generated based on acir are properly
+    // connected to the constraints generated herein via the ivc scheme (e.g. recursive verifications).
     for (auto [constraint, queue_entry] :
          zip_view(constraint_system.ivc_recursion_constraints, ivc.stdlib_verification_queue)) {
 
-        // Reconstruct complete proof indices from acir constraint data (in which proof is
-        // stripped of public inputs)
-        std::vector<uint32_t> complete_proof_indices =
-            ProofSurgeon::create_indices_for_reconstructed_proof(constraint.proof, constraint.public_inputs);
-        ASSERT(complete_proof_indices.size() == queue_entry.proof.size());
+        // Get the witness indices for the public inputs contained within the proof in the verification queue
+        std::vector<uint32_t> public_input_indices = ProofSurgeon::get_public_inputs_witness_indices_from_proof(
+            queue_entry.proof, constraint.public_inputs.size());
 
-        // Assert equality between the proof indices from the constraint data and those of the
-        // internal proof
-        for (auto [proof_value, proof_idx] : zip_view(queue_entry.proof, complete_proof_indices)) {
-            circuit.assert_equal(proof_value.get_witness_index(), proof_idx);
+        // Assert equality between the internal public input witness indices and those in the acir constraint
+        for (auto [witness_idx, constraint_witness_idx] : zip_view(public_input_indices, constraint.public_inputs)) {
+            circuit.assert_equal(witness_idx, constraint_witness_idx);
         }
     }
 

barretenberg/cpp/src/barretenberg/dsl/acir_format/ivc_recursion_constraint.test.cpp

@@ -57,7 +57,7 @@ class IvcRecursionConstraintTest : public ::testing::Test {
     {
         // Assemble simple vectors of witnesses for vkey and proof
         std::vector<FF> key_witnesses = input.honk_verification_key->to_field_elements();
-        std::vector<FF> proof_witnesses = input.proof;
+        std::vector<FF> proof_witnesses = input.proof; // proof contains the public inputs at this stage
 
         // Construct witness indices for each component in the constraint; populate the witness array
         auto [key_indices, proof_indices, public_inputs_indices] =
@@ -68,7 +68,7 @@ class IvcRecursionConstraintTest : public ::testing::Test {
 
         return RecursionConstraint{
             .key = key_indices,
-            .proof = proof_indices,
+            .proof = {}, // the proof witness indices are not needed in an ivc recursion constraint
             .public_inputs = public_inputs_indices,
             .key_hash = 0, // not used
             .proof_type = proof_type,

barretenberg/cpp/src/barretenberg/dsl/acir_format/proof_surgeon.hpp

@@ -2,6 +2,7 @@
 #include "barretenberg/common/map.hpp"
 #include "barretenberg/common/serialize.hpp"
 #include "barretenberg/ecc/curves/bn254/fr.hpp"
+#include "barretenberg/honk/proof_system/types/proof.hpp"
 #include "barretenberg/plonk_honk_shared/types/aggregation_object_type.hpp"
 #include "barretenberg/serialize/msgpack.hpp"
 #include <barretenberg/common/container.hpp>
@@ -103,6 +104,28 @@ class ProofSurgeon {
         return public_input_witnesses;
     }
 
+    /**
+     * @brief Get the witness indices for a given number of public inputs contained within a stdlib proof
+     *
+     * @param proof A bberg style stdlib proof (contains public inputs)
+     * @param num_public_inputs The number of public input witness indices to get from the proof
+     * @return std::vector<bb::fr> The corresponding public input witness indices
+     */
+    static std::vector<uint32_t> get_public_inputs_witness_indices_from_proof(
+        const bb::StdlibProof<bb::MegaCircuitBuilder>& proof, const size_t num_public_inputs_to_extract)
+    {
+        std::vector<uint32_t> public_input_witness_indices;
+        public_input_witness_indices.reserve(num_public_inputs_to_extract);
+
+        const size_t start = HONK_RECURSION_PUBLIC_INPUT_OFFSET;
+        const size_t end = start + num_public_inputs_to_extract;
+        for (size_t i = start; i < end; ++i) {
+            public_input_witness_indices.push_back(proof[i].get_witness_index());
+        }
+
+        return public_input_witness_indices;
+    }
+
     struct RecursionWitnessData {
         std::vector<uint32_t> key_indices;
         std::vector<uint32_t> proof_indices;