Adds prehashed message variant of EcDSA (AztecProtocol/barretenberg#437)

* verification takes a pre-hashed message : Note: if len(hash) > 32 bytes, then bigfield will fail

* use hashed_message when generating signature

* modify acir structure and function to now use prehashed variant

* message -> hashed_message

barretenberg/cpp/src/barretenberg/dsl/acir_format/ecdsa_secp256k1.cpp

@@ -89,7 +89,7 @@ void create_ecdsa_verify_constraints(Composer& composer, const EcdsaSecp256k1Con
 
     auto new_sig = ecdsa_convert_signature(composer, input.signature);
 
-    auto message = ecdsa_vector_of_bytes_to_byte_array(composer, input.message);
+    auto message = ecdsa_vector_of_bytes_to_byte_array(composer, input.hashed_message);
     auto pub_key_x_byte_arr = ecdsa_vector_of_bytes_to_byte_array(composer, input.pub_x_indices);
     auto pub_key_y_byte_arr = ecdsa_vector_of_bytes_to_byte_array(composer, input.pub_y_indices);
 
@@ -113,16 +113,16 @@ void create_ecdsa_verify_constraints(Composer& composer, const EcdsaSecp256k1Con
         pub_key_x_byte_arr[i].assert_equal(field_ct::from_witness_index(&composer, input.pub_x_indices[i]));
         pub_key_y_byte_arr[i].assert_equal(field_ct::from_witness_index(&composer, input.pub_y_indices[i]));
     }
-    for (size_t i = 0; i < input.message.size(); ++i) {
-        message[i].assert_equal(field_ct::from_witness_index(&composer, input.message[i]));
+    for (size_t i = 0; i < input.hashed_message.size(); ++i) {
+        message[i].assert_equal(field_ct::from_witness_index(&composer, input.hashed_message[i]));
     }
 
     bool_ct signature_result =
-        stdlib::ecdsa::verify_signature_noassert<Composer,
-                                                 secp256k1_ct,
-                                                 secp256k1_ct::fq_ct,
-                                                 secp256k1_ct::bigfr_ct,
-                                                 secp256k1_ct::g1_bigfr_ct>(message, public_key, sig);
+        stdlib::ecdsa::verify_signature_prehashed_message_noassert<Composer,
+                                                                   secp256k1_ct,
+                                                                   secp256k1_ct::fq_ct,
+                                                                   secp256k1_ct::bigfr_ct,
+                                                                   secp256k1_ct::g1_bigfr_ct>(message, public_key, sig);
     bool_ct signature_result_normalized = signature_result.normalize();
     composer.assert_equal(signature_result_normalized.witness_index, input.result);
 }

barretenberg/cpp/src/barretenberg/dsl/acir_format/ecdsa_secp256k1.hpp

@@ -5,10 +5,8 @@
 namespace acir_format {
 
 struct EcdsaSecp256k1Constraint {
-    // This is just a bunch of bytes
-    // which need to be interpreted as a string
-    // Note this must be a bunch of bytes
-    std::vector<uint32_t> message;
+    // This is the byte representation of the hashed message.
+    std::vector<uint32_t> hashed_message;
 
     // This is the supposed public key which signed the
     // message, giving rise to the signature.
@@ -33,7 +31,7 @@ void create_ecdsa_verify_constraints(Composer& composer, const EcdsaSecp256k1Con
 template <typename B> inline void read(B& buf, EcdsaSecp256k1Constraint& constraint)
 {
     using serialize::read;
-    read(buf, constraint.message);
+    read(buf, constraint.hashed_message);
     read(buf, constraint.signature);
     read(buf, constraint.pub_x_indices);
     read(buf, constraint.pub_y_indices);
@@ -43,7 +41,7 @@ template <typename B> inline void read(B& buf, EcdsaSecp256k1Constraint& constra
 template <typename B> inline void write(B& buf, EcdsaSecp256k1Constraint const& constraint)
 {
     using serialize::write;
-    write(buf, constraint.message);
+    write(buf, constraint.hashed_message);
     write(buf, constraint.signature);
     write(buf, constraint.pub_x_indices);
     write(buf, constraint.pub_y_indices);

barretenberg/cpp/src/barretenberg/dsl/acir_format/ecdsa_secp256k1.test.cpp

@@ -14,6 +14,12 @@ size_t generate_ecdsa_constraint(acir_format::EcdsaSecp256k1Constraint& ecdsa_co
 {
     std::string message_string = "Instructions unclear, ask again later.";
 
+    // hash the message since the dsl ecdsa gadget uses the prehashed message
+    // NOTE: If the hash being used outputs more than 32 bytes, then big-field will panic
+    std::vector<uint8_t> message_buffer;
+    std::copy(message_string.begin(), message_string.end(), std::back_inserter(message_buffer));
+    auto hashed_message = sha256::sha256(message_buffer);
+
     crypto::ecdsa::key_pair<curve::fr, curve::g1> account;
     account.private_key = curve::fr::random_element();
     account.public_key = curve::g1::one * account.private_key;
@@ -29,9 +35,9 @@ size_t generate_ecdsa_constraint(acir_format::EcdsaSecp256k1Constraint& ecdsa_co
     std::vector<uint32_t> pub_y_indices_in;
     std::vector<uint32_t> signature_in;
     size_t offset = 1;
-    for (size_t i = 0; i < message_string.size(); ++i) {
+    for (size_t i = 0; i < hashed_message.size(); ++i) {
         message_in.emplace_back(i + offset);
-        const auto byte = static_cast<uint8_t>(message_string[i]);
+        const auto byte = static_cast<uint8_t>(hashed_message[i]);
         witness_values.emplace_back(byte);
     }
     offset += message_in.size();
@@ -63,7 +69,7 @@ size_t generate_ecdsa_constraint(acir_format::EcdsaSecp256k1Constraint& ecdsa_co
     witness_values.emplace_back(1);
 
     ecdsa_constraint = acir_format::EcdsaSecp256k1Constraint{
-        .message = message_in,
+        .hashed_message = message_in,
         .pub_x_indices = pub_x_indices_in,
         .pub_y_indices = pub_y_indices_in,
         .result = result_in,

barretenberg/cpp/src/barretenberg/stdlib/encryption/ecdsa/ecdsa.hpp

@@ -24,6 +24,10 @@ template <typename Composer, typename Curve, typename Fq, typename Fr, typename
 bool_t<Composer> verify_signature_noassert(const stdlib::byte_array<Composer>& message,
                                            const G1& public_key,
                                            const signature<Composer>& sig);
+template <typename Composer, typename Curve, typename Fq, typename Fr, typename G1>
+bool_t<Composer> verify_signature_prehashed_message_noassert(const stdlib::byte_array<Composer>& hashed_message,
+                                                             const G1& public_key,
+                                                             const signature<Composer>& sig);
 
 template <typename Composer>
 static signature<Composer> from_witness(Composer* ctx, const crypto::ecdsa::signature& input)

barretenberg/cpp/src/barretenberg/stdlib/encryption/ecdsa/ecdsa_impl.hpp

@@ -117,20 +117,17 @@ bool_t<Composer> verify_signature(const stdlib::byte_array<Composer>& message,
  * @tparam Fq
  * @tparam Fr
  * @tparam G1
- * @param message
+ * @param hashed_message
  * @param public_key
  * @param sig
  * @return bool_t<Composer>
  */
 template <typename Composer, typename Curve, typename Fq, typename Fr, typename G1>
-bool_t<Composer> verify_signature_noassert(const stdlib::byte_array<Composer>& message,
-                                           const G1& public_key,
-                                           const signature<Composer>& sig)
+bool_t<Composer> verify_signature_prehashed_message_noassert(const stdlib::byte_array<Composer>& hashed_message,
+                                                             const G1& public_key,
+                                                             const signature<Composer>& sig)
 {
-    Composer* ctx = message.get_context() ? message.get_context() : public_key.x.context;
-
-    stdlib::byte_array<Composer> hashed_message =
-        static_cast<stdlib::byte_array<Composer>>(stdlib::sha256<Composer>(message));
+    Composer* ctx = hashed_message.get_context() ? hashed_message.get_context() : public_key.x.context;
 
     Fr z(hashed_message);
     z.assert_is_in_field();
@@ -186,6 +183,30 @@ bool_t<Composer> verify_signature_noassert(const stdlib::byte_array<Composer>& m
     return output;
 }
 
+/**
+ * @brief Verify ECDSA signature. Returns 0 if signature fails (i.e. does not produce unsatisfiable constraints)
+ *
+ * @tparam Composer
+ * @tparam Curve
+ * @tparam Fq
+ * @tparam Fr
+ * @tparam G1
+ * @param message
+ * @param public_key
+ * @param sig
+ * @return bool_t<Composer>
+ */
+template <typename Composer, typename Curve, typename Fq, typename Fr, typename G1>
+bool_t<Composer> verify_signature_noassert(const stdlib::byte_array<Composer>& message,
+                                           const G1& public_key,
+                                           const signature<Composer>& sig)
+{
+    stdlib::byte_array<Composer> hashed_message =
+        static_cast<stdlib::byte_array<Composer>>(stdlib::sha256<Composer>(message));
+
+    return verify_signature_prehashed_message_noassert<Composer, Curve, Fq, Fr, G1>(hashed_message, public_key, sig);
+}
+
 } // namespace ecdsa
 } // namespace stdlib
 } // namespace proof_system::plonk