feat: new transcript functionality to hash elements without including in proof

barretenberg/cpp/src/barretenberg/transcript/transcript.hpp

@@ -211,7 +211,7 @@ template <typename TranscriptParams> class BaseTranscript {
      * @param label of the element sent
      * @param element_frs serialized
      */
-    void consume_prover_element_frs(const std::string& label, std::span<const Fr> element_frs)
+    void add_element_frs_to_hash_buffer(const std::string& label, std::span<const Fr> element_frs)
     {
         if (use_manifest) {
             // Add an entry to the current round of the manifest
@@ -350,11 +350,37 @@ template <typename TranscriptParams> class BaseTranscript {
         return call_get_challenges();
     }
 
+    /**
+     * @brief Adds an element to the transcript.
+     * @details Serializes the element to frs and adds it to the current_round_data buffer. Does NOT add the element to
+     * the proof.
+     *
+     * @param label Human-readable name for the challenge.
+     * @param element Element to be added.
+     */
+    template <class T> void add_to_hash_buffer(const std::string& label, const T& element)
+    {
+        DEBUG_LOG(label, element);
+
+        // TODO(Adrian): Ensure that serialization of affine elements (including point at infinity) is consistent.
+        // TODO(Adrian): Consider restricting serialization (via concepts) to types T for which sizeof(T) reliably
+        // returns the size of T in frs. (E.g. this is true for std::array but not for std::vector).
+        // convert element to field elements
+        auto element_frs = TranscriptParams::convert_to_bn254_frs(element);
+
+#ifdef LOG_INTERACTIONS
+        if constexpr (Loggable<T>) {
+            info("consumed:     ", label, ": ", element);
+        }
+#endif
+        BaseTranscript::add_element_frs_to_hash_buffer(label, element_frs);
+    }
+
     /**
      * @brief Adds a prover message to the transcript, only intended to be used by the prover.
      *
      * @details Serializes the provided object into `proof_data`, and updates the current round state in
-     * consume_prover_element_frs.
+     * add_element_frs_to_hash_buffer.
      *
      * @param label Description/name of the object being added.
      * @param element Serializable object that will be added to the transcript
@@ -379,7 +405,7 @@ template <typename TranscriptParams> class BaseTranscript {
             info("sent:     ", label, ": ", element);
         }
 #endif
-        BaseTranscript::consume_prover_element_frs(label, element_frs);
+        BaseTranscript::add_element_frs_to_hash_buffer(label, element_frs);
     }
 
     /**
@@ -397,7 +423,7 @@ template <typename TranscriptParams> class BaseTranscript {
         auto element_frs = std::span{ proof_data }.subspan(num_frs_read, element_size);
         num_frs_read += element_size;
 
-        BaseTranscript::consume_prover_element_frs(label, element_frs);
+        BaseTranscript::add_element_frs_to_hash_buffer(label, element_frs);
 
         auto element = TranscriptParams::template convert_from_bn254_frs<T>(element_frs);
         DEBUG_LOG(label, element);

barretenberg/cpp/src/barretenberg/transcript/transcript.test.cpp

@@ -144,4 +144,18 @@ TEST(NativeTranscript, TwoProversTwoFields)
         EXPECT_TRUE(received_k.is_point_at_infinity());
         EXPECT_EQ(received_k, elt_k);
     }
-}
+}
+
+/**
+ * @brief Test the add_to_hash_buffer functionality
+ *
+ */
+TEST(NativeTranscript, ConsumeElement)
+{
+    Transcript prover_transcript, verifier_transcript;
+    prover_transcript.add_to_hash_buffer("a", Fr(1));
+    verifier_transcript.add_to_hash_buffer("a", Fr(1));
+    auto prover_chal = prover_transcript.get_challenge<Fr>("alpha");
+    auto verifier_chal = verifier_transcript.get_challenge<Fr>("alpha");
+    EXPECT_EQ(prover_chal, verifier_chal);
+}