Add a noop tx for account circuit. (#1808)

src/aztec/rollup/proofs/account/compute_circuit_data.hpp

@@ -8,14 +8,49 @@ namespace rollup {
 namespace proofs {
 namespace account {
 
+using namespace plonk::stdlib::merkle_tree;
+
+/**
+ * @brief Create an account noop transaction that sets the members in account_tx to be random/zero values.
+ * Note that the noop account tx satisfies the circuit logic, and hence can be used to create "dummy" account proofs
+ * that pass verification.
+ *
+ * @warning This must not be used in any production code!
+ */
+inline account_tx noop_tx()
+{
+    grumpkin::fr priv_key = grumpkin::fr::random_element();
+    grumpkin::g1::affine_element pub_key = grumpkin::g1::one * priv_key;
+
+    grumpkin::fr new_priv_key = grumpkin::fr::random_element();
+    grumpkin::g1::affine_element new_pub_key = grumpkin::g1::one * new_priv_key;
+
+    auto gibberish_path = fr_hash_path(DATA_TREE_DEPTH, std::make_pair(fr::random_element(), fr::random_element()));
+
+    account_tx tx = {};
+    tx.merkle_root = fr::random_element();
+    tx.account_public_key = pub_key;
+    tx.new_account_public_key = pub_key;
+    tx.new_signing_pub_key_1 = new_pub_key;
+    tx.new_signing_pub_key_2 = new_pub_key;
+    tx.alias_hash = (uint256_t(fr::random_element()) & 0xffffffff);
+    tx.create = true;
+    tx.migrate = false;
+    tx.account_note_index = 0;
+    tx.signing_pub_key = pub_key;
+    tx.account_note_path = gibberish_path;
+    tx.sign({ priv_key, pub_key });
+    return tx;
+}
+
 using circuit_data = proofs::circuit_data;
 
 inline circuit_data get_circuit_data(std::shared_ptr<waffle::ReferenceStringFactory> const& srs, bool mock = false)
 {
     std::cerr << "Getting account circuit data..." << std::endl;
 
     auto build_circuit = [&](Composer& composer) {
-        account_tx tx;
+        account_tx tx(noop_tx());
         tx.account_note_path.resize(DATA_TREE_DEPTH);
         account_circuit(composer, tx);
     };