Discourage unsigned / uncommitted annexes

src/policy/policy.h

@@ -113,7 +113,8 @@ static constexpr unsigned int STANDARD_SCRIPT_VERIFY_FLAGS{MANDATORY_SCRIPT_VERI
                                                              SCRIPT_VERIFY_CONST_SCRIPTCODE |
                                                              SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_TAPROOT_VERSION |
                                                              SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS |
-                                                             SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE};
+                                                             SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE |
+                                                             SCRIPT_VERIFY_DISCOURAGE_UNSIGNED_ANNEX};
 
 /** For convenience, standard but not mandatory verify flags. */
 static constexpr unsigned int STANDARD_NOT_MANDATORY_VERIFY_FLAGS{STANDARD_SCRIPT_VERIFY_FLAGS & ~MANDATORY_SCRIPT_VERIFY_FLAGS};

src/script/interpreter.cpp

@@ -1694,6 +1694,7 @@ bool GenericTransactionSignatureChecker<T>::CheckSchnorrSignature(Span<const uns
         return set_error(serror, SCRIPT_ERR_SCHNORR_SIG_HASHTYPE);
     }
     if (!VerifySchnorrSignature(sig, pubkey, sighash)) return set_error(serror, SCRIPT_ERR_SCHNORR_SIG);
+    execdata.m_annex_unsigned = false;
     return true;
 }
 
@@ -1788,6 +1789,7 @@ template class GenericTransactionSignatureChecker<CMutableTransaction>;
 static bool ExecuteWitnessScript(const Span<const valtype>& stack_span, const CScript& exec_script, unsigned int flags, SigVersion sigversion, const BaseSignatureChecker& checker, ScriptExecutionData& execdata, ScriptError* serror)
 {
     std::vector<valtype> stack{stack_span.begin(), stack_span.end()};
+    execdata.m_annex_unsigned = execdata.m_annex_present;
 
     if (sigversion == SigVersion::TAPSCRIPT) {
         // OP_SUCCESSx processing overrides everything, including stack element size limits
@@ -1819,6 +1821,11 @@ static bool ExecuteWitnessScript(const Span<const valtype>& stack_span, const CS
     // Run the script interpreter.
     if (!EvalScript(stack, exec_script, flags, checker, sigversion, execdata, serror)) return false;
 
+    // Discourage unsigned annexes
+    if (execdata.m_annex_unsigned && (flags & SCRIPT_VERIFY_DISCOURAGE_UNSIGNED_ANNEX)) {
+        return set_error(serror, SCRIPT_ERR_DISCOURAGE_UNSIGNED_ANNEX);
+    }
+
     // Scripts inside witness implicitly require cleanstack behaviour
     if (stack.size() != 1) return set_error(serror, SCRIPT_ERR_CLEANSTACK);
     if (!CastToBool(stack.back())) return set_error(serror, SCRIPT_ERR_EVAL_FALSE);

src/script/interpreter.h

@@ -143,6 +143,10 @@ enum : uint32_t {
     // Making unknown public key versions (in BIP 342 scripts) non-standard
     SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE = (1U << 20),
 
+    // Making unsigned annexes non-standard
+    //
+    SCRIPT_VERIFY_DISCOURAGE_UNSIGNED_ANNEX = (1U << 21),
+
     // Constants to point to the highest flag in use. Add new flags above this line.
     //
     SCRIPT_VERIFY_END_MARKER
@@ -213,6 +217,8 @@ struct ScriptExecutionData
     bool m_annex_present;
     //! Hash of the annex data.
     uint256 m_annex_hash;
+    //! Whether an unsigned annex is present.
+    bool m_annex_unsigned = false;
 
     //! Whether m_validation_weight_left is initialized.
     bool m_validation_weight_left_init = false;

src/script/script_error.cpp

@@ -79,6 +79,8 @@ std::string ScriptErrorString(const ScriptError serror)
             return "OP_SUCCESSx reserved for soft-fork upgrades";
         case SCRIPT_ERR_DISCOURAGE_UPGRADABLE_PUBKEYTYPE:
             return "Public key version reserved for soft-fork upgrades";
+        case SCRIPT_ERR_DISCOURAGE_UNSIGNED_ANNEX:
+            return "Unsigned annex";
         case SCRIPT_ERR_PUBKEYTYPE:
             return "Public key is neither compressed or uncompressed";
         case SCRIPT_ERR_CLEANSTACK:

src/script/script_error.h

@@ -59,6 +59,7 @@ typedef enum ScriptError_t
     SCRIPT_ERR_DISCOURAGE_UPGRADABLE_TAPROOT_VERSION,
     SCRIPT_ERR_DISCOURAGE_OP_SUCCESS,
     SCRIPT_ERR_DISCOURAGE_UPGRADABLE_PUBKEYTYPE,
+    SCRIPT_ERR_DISCOURAGE_UNSIGNED_ANNEX,
 
     /* segregated witness */
     SCRIPT_ERR_WITNESS_PROGRAM_WRONG_LENGTH,

src/test/transaction_tests.cpp

@@ -67,6 +67,7 @@ static std::map<std::string, unsigned int> mapFlagNames = {
     {std::string("CONST_SCRIPTCODE"), (unsigned int)SCRIPT_VERIFY_CONST_SCRIPTCODE},
     {std::string("TAPROOT"), (unsigned int)SCRIPT_VERIFY_TAPROOT},
     {std::string("DISCOURAGE_UPGRADABLE_PUBKEYTYPE"), (unsigned int)SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE},
+    {std::string("DISCOURAGE_UNSIGNED_ANNEX"), (unsigned int)SCRIPT_VERIFY_DISCOURAGE_UNSIGNED_ANNEX},
     {std::string("DISCOURAGE_OP_SUCCESS"), (unsigned int)SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS},
     {std::string("DISCOURAGE_UPGRADABLE_TAPROOT_VERSION"), (unsigned int)SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_TAPROOT_VERSION},
 };