diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index c499829a9..8f61197a1 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -1,1296 +1,1312 @@
 // Copyright (c) 2018 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <script/descriptor.h>
 
 #include <chainparams.h> // For Params()
 #include <config.h>
 #include <key_io.h>
 #include <pubkey.h>
 #include <script/standard.h>
 #include <span.h>
 #include <util/bip32.h>
 #include <util/spanparsing.h>
 #include <util/strencodings.h>
 #include <util/system.h>
 #include <util/vector.h>
 
 #include <memory>
 #include <string>
 
 namespace {
 
 ////////////////////////////////////////////////////////////////////////////
 // Checksum                                                               //
 ////////////////////////////////////////////////////////////////////////////
 
 // This section implements a checksum algorithm for descriptors with the
 // following properties:
 // * Mistakes in a descriptor string are measured in "symbol errors". The higher
 //   the number of symbol errors, the harder it is to detect:
 //   * An error substituting a character from 0123456789()[],'/*abcdefgh@:$%{}
 //   for
 //     another in that set always counts as 1 symbol error.
 //     * Note that hex encoded keys are covered by these characters. Xprvs and
 //       xpubs use other characters too, but already have their own checksum
 //       mechanism.
 //     * Function names like "multi()" use other characters, but mistakes in
 //       these would generally result in an unparsable descriptor.
 //   * A case error always counts as 1 symbol error.
 //   * Any other 1 character substitution error counts as 1 or 2 symbol errors.
 // * Any 1 symbol error is always detected.
 // * Any 2 or 3 symbol error in a descriptor of up to 49154 characters is always
 // detected.
 // * Any 4 symbol error in a descriptor of up to 507 characters is always
 // detected.
 // * Any 5 symbol error in a descriptor of up to 77 characters is always
 // detected.
 // * Is optimized to minimize the chance a 5 symbol error in a descriptor up to
 // 387 characters is undetected
 // * Random errors have a chance of 1 in 2**40 of being undetected.
 //
 // These properties are achieved by expanding every group of 3 (non checksum)
 // characters into 4 GF(32) symbols, over which a cyclic code is defined.
 
 /*
  * Interprets c as 8 groups of 5 bits which are the coefficients of a degree 8
  * polynomial over GF(32), multiplies that polynomial by x, computes its
  * remainder modulo a generator, and adds the constant term val.
  *
  * This generator is G(x) = x^8 + {30}x^7 + {23}x^6 + {15}x^5 + {14}x^4 +
  * {10}x^3 + {6}x^2 + {12}x + {9}. It is chosen to define an cyclic error
  * detecting code which is selected by:
  * - Starting from all BCH codes over GF(32) of degree 8 and below, which by
  * construction guarantee detecting 3 errors in windows up to 19000 symbols.
  * - Taking all those generators, and for degree 7 ones, extend them to degree 8
  * by adding all degree-1 factors.
  * - Selecting just the set of generators that guarantee detecting 4 errors in a
  * window of length 512.
  * - Selecting one of those with best worst-case behavior for 5 errors in
  * windows of length up to 512.
  *
  * The generator and the constants to implement it can be verified using this
  * Sage code: B = GF(2) # Binary field BP.<b> = B[] # Polynomials over the
  * binary field F_mod = b**5 + b**3 + 1 F.<f> = GF(32, modulus=F_mod,
  * repr='int') # GF(32) definition FP.<x> = F[] # Polynomials over GF(32) E_mod
  * = x**3 + x + F.fetch_int(8) E.<e> = F.extension(E_mod) # Extension field
  * definition alpha = e**2743 # Choice of an element in extension field for p in
  * divisors(E.order() - 1): # Verify alpha has order 32767. assert((alpha**p ==
  * 1) == (p % 32767 == 0)) G = lcm([(alpha**i).minpoly() for i in
  * [1056,1057,1058]] + [x + 1]) print(G) # Print out the generator for i in
  * [1,2,4,8,16]: # Print out {1,2,4,8,16}*(G mod x^8), packed in hex integers.
  *       v = 0
  *       for coef in reversed((F.fetch_int(i)*(G %
  * x**8)).coefficients(sparse=True)): v = v*32 + coef.integer_representation()
  *       print("0x%x" % v)
  */
 uint64_t PolyMod(uint64_t c, int val) {
     uint8_t c0 = c >> 35;
     c = ((c & 0x7ffffffff) << 5) ^ val;
     if (c0 & 1) {
         c ^= 0xf5dee51989;
     }
     if (c0 & 2) {
         c ^= 0xa9fdca3312;
     }
     if (c0 & 4) {
         c ^= 0x1bab10e32d;
     }
     if (c0 & 8) {
         c ^= 0x3706b1677a;
     }
     if (c0 & 16) {
         c ^= 0x644d626ffd;
     }
     return c;
 }
 
 std::string DescriptorChecksum(const Span<const char> &span) {
     /** A character set designed such that:
      *  - The most common 'unprotected' descriptor characters (hex, keypaths)
      * are in the first group of 32.
      *  - Case errors cause an offset that's a multiple of 32.
      *  - As many alphabetic characters are in the same group (while following
      * the above restrictions).
      *
      * If p(x) gives the position of a character c in this character set, every
      * group of 3 characters (a,b,c) is encoded as the 4 symbols (p(a) & 31,
      * p(b) & 31, p(c) & 31, (p(a) / 32) + 3 * (p(b) / 32) + 9 * (p(c) / 32).
      * This means that changes that only affect the lower 5 bits of the
      * position, or only the higher 2 bits, will just affect a single symbol.
      *
      * As a result, within-group-of-32 errors count as 1 symbol, as do
      * cross-group errors that don't affect the position within the groups.
      */
     static std::string INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}"
                                        "IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~"
                                        "ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
 
     /** The character set for the checksum itself (same as bech32). */
     static std::string CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
 
     uint64_t c = 1;
     int cls = 0;
     int clscount = 0;
     for (auto ch : span) {
         auto pos = INPUT_CHARSET.find(ch);
         if (pos == std::string::npos) {
             return "";
         }
         // Emit a symbol for the position inside the group, for every character.
         c = PolyMod(c, pos & 31);
         // Accumulate the group numbers
         cls = cls * 3 + (pos >> 5);
         if (++clscount == 3) {
             // Emit an extra symbol representing the group numbers, for every 3
             // characters.
             c = PolyMod(c, cls);
             cls = 0;
             clscount = 0;
         }
     }
     if (clscount > 0) {
         c = PolyMod(c, cls);
     }
     for (int j = 0; j < 8; ++j) {
         // Shift further to determine the checksum.
         c = PolyMod(c, 0);
     }
     // Prevent appending zeroes from not affecting the checksum.
     c ^= 1;
 
     std::string ret(8, ' ');
     for (int j = 0; j < 8; ++j) {
         ret[j] = CHECKSUM_CHARSET[(c >> (5 * (7 - j))) & 31];
     }
     return ret;
 }
 
 std::string AddChecksum(const std::string &str) {
     return str + "#" + DescriptorChecksum(MakeSpan(str));
 }
 
 ////////////////////////////////////////////////////////////////////////////
 // Internal representation                                                //
 ////////////////////////////////////////////////////////////////////////////
 
 typedef std::vector<uint32_t> KeyPath;
 
 /** Interface for public key objects in descriptors. */
 struct PubkeyProvider {
 protected:
     //! Index of this key expression in the descriptor
     //! E.g. If this PubkeyProvider is key1 in multi(2, key1, key2, key3), then
     //! m_expr_index = 0
     uint32_t m_expr_index;
 
 public:
     PubkeyProvider(uint32_t exp_index) : m_expr_index(exp_index) {}
 
     virtual ~PubkeyProvider() = default;
 
     /**
      * Derive a public key.
      * read_cache is the cache to read keys from (if not nullptr)
      * write_cache is the cache to write keys to (if not nullptr)
      * Caches are not exclusive but this is not tested. Currently we use them
      * exclusively
      */
     virtual bool GetPubKey(int pos, const SigningProvider &arg, CPubKey &key,
                            KeyOriginInfo &info,
                            const DescriptorCache *read_cache = nullptr,
-                           DescriptorCache *write_cache = nullptr) const = 0;
+                           DescriptorCache *write_cache = nullptr) = 0;
 
     /** Whether this represent multiple public keys at different positions. */
     virtual bool IsRange() const = 0;
 
     /** Get the size of the generated public key(s) in bytes (33 or 65). */
     virtual size_t GetSize() const = 0;
 
     /** Get the descriptor string form. */
     virtual std::string ToString() const = 0;
 
     /**
      * Get the descriptor string form including private data (if available in
      * arg).
      */
     virtual bool ToPrivateString(const SigningProvider &arg,
                                  std::string &out) const = 0;
 
     /** Derive a private key, if private data is available in arg. */
     virtual bool GetPrivKey(int pos, const SigningProvider &arg,
                             CKey &key) const = 0;
 };
 
 class OriginPubkeyProvider final : public PubkeyProvider {
     KeyOriginInfo m_origin;
     std::unique_ptr<PubkeyProvider> m_provider;
 
     std::string OriginString() const {
         return HexStr(std::begin(m_origin.fingerprint),
                       std::end(m_origin.fingerprint)) +
                FormatHDKeypath(m_origin.path);
     }
 
 public:
     OriginPubkeyProvider(uint32_t exp_index, KeyOriginInfo info,
                          std::unique_ptr<PubkeyProvider> provider)
         : PubkeyProvider(exp_index), m_origin(std::move(info)),
           m_provider(std::move(provider)) {}
     bool GetPubKey(int pos, const SigningProvider &arg, CPubKey &key,
                    KeyOriginInfo &info,
                    const DescriptorCache *read_cache = nullptr,
-                   DescriptorCache *write_cache = nullptr) const override {
+                   DescriptorCache *write_cache = nullptr) override {
         if (!m_provider->GetPubKey(pos, arg, key, info, read_cache,
                                    write_cache)) {
             return false;
         }
         std::copy(std::begin(m_origin.fingerprint),
                   std::end(m_origin.fingerprint), info.fingerprint);
         info.path.insert(info.path.begin(), m_origin.path.begin(),
                          m_origin.path.end());
         return true;
     }
     bool IsRange() const override { return m_provider->IsRange(); }
     size_t GetSize() const override { return m_provider->GetSize(); }
     std::string ToString() const override {
         return "[" + OriginString() + "]" + m_provider->ToString();
     }
     bool ToPrivateString(const SigningProvider &arg,
                          std::string &ret) const override {
         std::string sub;
         if (!m_provider->ToPrivateString(arg, sub)) {
             return false;
         }
         ret = "[" + OriginString() + "]" + std::move(sub);
         return true;
     }
     bool GetPrivKey(int pos, const SigningProvider &arg,
                     CKey &key) const override {
         return m_provider->GetPrivKey(pos, arg, key);
     }
 };
 
 /** An object representing a parsed constant public key in a descriptor. */
 class ConstPubkeyProvider final : public PubkeyProvider {
     CPubKey m_pubkey;
 
 public:
     ConstPubkeyProvider(uint32_t exp_index, const CPubKey &pubkey)
         : PubkeyProvider(exp_index), m_pubkey(pubkey) {}
     bool GetPubKey(int pos, const SigningProvider &arg, CPubKey &key,
                    KeyOriginInfo &info,
                    const DescriptorCache *read_cache = nullptr,
-                   DescriptorCache *write_cache = nullptr) const override {
+                   DescriptorCache *write_cache = nullptr) override {
         key = m_pubkey;
         info.path.clear();
         CKeyID keyid = m_pubkey.GetID();
         std::copy(keyid.begin(), keyid.begin() + sizeof(info.fingerprint),
                   info.fingerprint);
         return true;
     }
     bool IsRange() const override { return false; }
     size_t GetSize() const override { return m_pubkey.size(); }
     std::string ToString() const override {
         return HexStr(m_pubkey.begin(), m_pubkey.end());
     }
     bool ToPrivateString(const SigningProvider &arg,
                          std::string &ret) const override {
         CKey key;
         if (!arg.GetKey(m_pubkey.GetID(), key)) {
             return false;
         }
         ret = EncodeSecret(key);
         return true;
     }
     bool GetPrivKey(int pos, const SigningProvider &arg,
                     CKey &key) const override {
         return arg.GetKey(m_pubkey.GetID(), key);
     }
 };
 
 enum class DeriveType {
     NO,
     UNHARDENED,
     HARDENED,
 };
 
 /** An object representing a parsed extended public key in a descriptor. */
 class BIP32PubkeyProvider final : public PubkeyProvider {
     // Root xpub, path, and final derivation step type being used, if any
     CExtPubKey m_root_extkey;
     KeyPath m_path;
     DeriveType m_derive;
+    // Cache of the parent of the final derived pubkeys.
+    // Primarily useful for situations when no read_cache is provided
+    CExtPubKey m_cached_xpub;
 
     bool GetExtKey(const SigningProvider &arg, CExtKey &ret) const {
         CKey key;
         if (!arg.GetKey(m_root_extkey.pubkey.GetID(), key)) {
             return false;
         }
         ret.nDepth = m_root_extkey.nDepth;
         std::copy(m_root_extkey.vchFingerprint,
                   m_root_extkey.vchFingerprint + sizeof(ret.vchFingerprint),
                   ret.vchFingerprint);
         ret.nChild = m_root_extkey.nChild;
         ret.chaincode = m_root_extkey.chaincode;
         ret.key = key;
         return true;
     }
 
     // Derives the last xprv
     bool GetDerivedExtKey(const SigningProvider &arg, CExtKey &xprv) const {
         if (!GetExtKey(arg, xprv)) {
             return false;
         }
         for (auto entry : m_path) {
             xprv.Derive(xprv, entry);
         }
         return true;
     }
 
     bool IsHardened() const {
         if (m_derive == DeriveType::HARDENED) {
             return true;
         }
         for (auto entry : m_path) {
             if (entry >> 31) {
                 return true;
             }
         }
         return false;
     }
 
 public:
     BIP32PubkeyProvider(uint32_t exp_index, const CExtPubKey &extkey,
                         KeyPath path, DeriveType derive)
         : PubkeyProvider(exp_index), m_root_extkey(extkey),
           m_path(std::move(path)), m_derive(derive) {}
     bool IsRange() const override { return m_derive != DeriveType::NO; }
     size_t GetSize() const override { return 33; }
     bool GetPubKey(int pos, const SigningProvider &arg, CPubKey &key_out,
                    KeyOriginInfo &final_info_out,
                    const DescriptorCache *read_cache = nullptr,
-                   DescriptorCache *write_cache = nullptr) const override {
+                   DescriptorCache *write_cache = nullptr) override {
         // Info of parent of the to be derived pubkey
         KeyOriginInfo parent_info;
         CKeyID keyid = m_root_extkey.pubkey.GetID();
         std::copy(keyid.begin(),
                   keyid.begin() + sizeof(parent_info.fingerprint),
                   parent_info.fingerprint);
         parent_info.path = m_path;
 
         // Info of the derived key itself which is copied out upon successful
         // completion
         KeyOriginInfo final_info_out_tmp = parent_info;
         if (m_derive == DeriveType::UNHARDENED) {
             final_info_out_tmp.path.push_back((uint32_t)pos);
         }
         if (m_derive == DeriveType::HARDENED) {
             final_info_out_tmp.path.push_back(((uint32_t)pos) | 0x80000000L);
         }
 
         // Derive keys or fetch them from cache
         CExtPubKey final_extkey = m_root_extkey;
         CExtPubKey parent_extkey = m_root_extkey;
         bool der = true;
         if (read_cache) {
             if (!read_cache->GetCachedDerivedExtPubKey(m_expr_index, pos,
                                                        final_extkey)) {
                 if (m_derive == DeriveType::HARDENED) {
                     return false;
                 }
                 // Try to get the derivation parent
                 if (!read_cache->GetCachedParentExtPubKey(m_expr_index,
                                                           parent_extkey)) {
                     return false;
                 }
                 final_extkey = parent_extkey;
                 if (m_derive == DeriveType::UNHARDENED) {
                     der = parent_extkey.Derive(final_extkey, pos);
                 }
             }
+        } else if (m_cached_xpub.pubkey.IsValid() &&
+                   m_derive != DeriveType::HARDENED) {
+            parent_extkey = final_extkey = m_cached_xpub;
+            if (m_derive == DeriveType::UNHARDENED) {
+                der = parent_extkey.Derive(final_extkey, pos);
+            }
         } else if (IsHardened()) {
             CExtKey xprv;
             if (!GetDerivedExtKey(arg, xprv)) {
                 return false;
             }
             parent_extkey = xprv.Neuter();
             if (m_derive == DeriveType::UNHARDENED) {
                 der = xprv.Derive(xprv, pos);
             }
             if (m_derive == DeriveType::HARDENED) {
                 der = xprv.Derive(xprv, pos | 0x80000000UL);
             }
             final_extkey = xprv.Neuter();
         } else {
             for (auto entry : m_path) {
                 der = parent_extkey.Derive(parent_extkey, entry);
                 assert(der);
             }
             final_extkey = parent_extkey;
             if (m_derive == DeriveType::UNHARDENED) {
                 der = parent_extkey.Derive(final_extkey, pos);
             }
             assert(m_derive != DeriveType::HARDENED);
         }
         assert(der);
 
         final_info_out = final_info_out_tmp;
         key_out = final_extkey.pubkey;
 
+        // We rely on the consumer to check that m_derive isn't HARDENED as
+        // above But we can't have already cached something in case we read
+        // something from the cache and parent_extkey isn't actually the parent.
+        if (!m_cached_xpub.pubkey.IsValid()) {
+            m_cached_xpub = parent_extkey;
+        }
+
         if (write_cache) {
             // Only cache parent if there is any unhardened derivation
             if (m_derive != DeriveType::HARDENED) {
                 write_cache->CacheParentExtPubKey(m_expr_index, parent_extkey);
             } else if (final_info_out.path.size() > 0) {
                 write_cache->CacheDerivedExtPubKey(m_expr_index, pos,
                                                    final_extkey);
             }
         }
 
         return true;
     }
     std::string ToString() const override {
         std::string ret =
             EncodeExtPubKey(m_root_extkey) + FormatHDKeypath(m_path);
         if (IsRange()) {
             ret += "/*";
             if (m_derive == DeriveType::HARDENED) {
                 ret += '\'';
             }
         }
         return ret;
     }
     bool ToPrivateString(const SigningProvider &arg,
                          std::string &out) const override {
         CExtKey key;
         if (!GetExtKey(arg, key)) {
             return false;
         }
         out = EncodeExtKey(key) + FormatHDKeypath(m_path);
         if (IsRange()) {
             out += "/*";
             if (m_derive == DeriveType::HARDENED) {
                 out += '\'';
             }
         }
         return true;
     }
     bool GetPrivKey(int pos, const SigningProvider &arg,
                     CKey &key) const override {
         CExtKey extkey;
         if (!GetDerivedExtKey(arg, extkey)) {
             return false;
         }
         if (m_derive == DeriveType::UNHARDENED) {
             extkey.Derive(extkey, pos);
         }
         if (m_derive == DeriveType::HARDENED) {
             extkey.Derive(extkey, pos | 0x80000000UL);
         }
         key = extkey.key;
         return true;
     }
 };
 
 /** Base class for all Descriptor implementations. */
 class DescriptorImpl : public Descriptor {
     //! Public key arguments for this descriptor (size 1 for PK, PKH; any size
     //! for Multisig).
     const std::vector<std::unique_ptr<PubkeyProvider>> m_pubkey_args;
     //! The sub-descriptor argument (nullptr for everything but SH).
     //! In doc/descriptors.m this is referred to as SCRIPT expressions
     //! sh(SCRIPT), and distinct from KEY expressions and ADDR expressions.
     const std::unique_ptr<DescriptorImpl> m_subdescriptor_arg;
     //! The string name of the descriptor function.
     const std::string m_name;
 
 protected:
     //! Return a serialization of anything except pubkey and script arguments,
     //! to be prepended to those.
     virtual std::string ToStringExtra() const { return ""; }
 
     /**
      * A helper function to construct the scripts for this descriptor.
      *
      *  This function is invoked once for every CScript produced by evaluating
      *  m_subdescriptor_arg, or just once in case m_subdescriptor_arg is
      nullptr.
 
      *  @param pubkeys The evaluations of the m_pubkey_args field.
      *  @param script The evaluation of m_subdescriptor_arg (or nullptr when
      m_subdescriptor_arg is nullptr).
      *  @param out A FlatSigningProvider to put scripts or public keys in that
      are necessary to the solver.
      *             The script arguments to this function are automatically
      added, as is the origin info of the provided pubkeys.
      *  @return A vector with scriptPubKeys for this descriptor.
      */
     virtual std::vector<CScript>
     MakeScripts(const std::vector<CPubKey> &pubkeys, const CScript *script,
                 FlatSigningProvider &out) const = 0;
 
 public:
     DescriptorImpl(std::vector<std::unique_ptr<PubkeyProvider>> pubkeys,
                    std::unique_ptr<DescriptorImpl> script,
                    const std::string &name)
         : m_pubkey_args(std::move(pubkeys)),
           m_subdescriptor_arg(std::move(script)), m_name(name) {}
 
     bool IsSolvable() const override {
         if (m_subdescriptor_arg) {
             if (!m_subdescriptor_arg->IsSolvable()) {
                 return false;
             }
         }
         return true;
     }
 
     bool IsRange() const final {
         for (const auto &pubkey : m_pubkey_args) {
             if (pubkey->IsRange()) {
                 return true;
             }
         }
         if (m_subdescriptor_arg) {
             if (m_subdescriptor_arg->IsRange()) {
                 return true;
             }
         }
         return false;
     }
 
     bool ToStringHelper(const SigningProvider *arg, std::string &out,
                         bool priv) const {
         std::string extra = ToStringExtra();
         size_t pos = extra.size() > 0 ? 1 : 0;
         std::string ret = m_name + "(" + extra;
         for (const auto &pubkey : m_pubkey_args) {
             if (pos++) {
                 ret += ",";
             }
             std::string tmp;
             if (priv) {
                 if (!pubkey->ToPrivateString(*arg, tmp)) {
                     return false;
                 }
             } else {
                 tmp = pubkey->ToString();
             }
             ret += std::move(tmp);
         }
         if (m_subdescriptor_arg) {
             if (pos++) {
                 ret += ",";
             }
             std::string tmp;
             if (!m_subdescriptor_arg->ToStringHelper(arg, tmp, priv)) {
                 return false;
             }
             ret += std::move(tmp);
         }
         out = std::move(ret) + ")";
         return true;
     }
 
     std::string ToString() const final {
         std::string ret;
         ToStringHelper(nullptr, ret, false);
         return AddChecksum(ret);
     }
 
     bool ToPrivateString(const SigningProvider &arg,
                          std::string &out) const override final {
         bool ret = ToStringHelper(&arg, out, true);
         out = AddChecksum(out);
         return ret;
     }
 
     bool ExpandHelper(int pos, const SigningProvider &arg,
                       const DescriptorCache *read_cache,
                       std::vector<CScript> &output_scripts,
                       FlatSigningProvider &out,
                       DescriptorCache *write_cache) const {
         std::vector<std::pair<CPubKey, KeyOriginInfo>> entries;
         entries.reserve(m_pubkey_args.size());
 
         // Construct temporary data in `entries` and `subscripts`, to avoid
         // producing output in case of failure.
         for (const auto &p : m_pubkey_args) {
             entries.emplace_back();
             if (!p->GetPubKey(pos, arg, entries.back().first,
                               entries.back().second, read_cache, write_cache)) {
                 return false;
             }
         }
         std::vector<CScript> subscripts;
         if (m_subdescriptor_arg) {
             FlatSigningProvider subprovider;
             if (!m_subdescriptor_arg->ExpandHelper(pos, arg, read_cache,
                                                    subscripts, subprovider,
                                                    write_cache)) {
                 return false;
             }
             out = Merge(out, subprovider);
         }
 
         std::vector<CPubKey> pubkeys;
         pubkeys.reserve(entries.size());
         for (auto &entry : entries) {
             pubkeys.push_back(entry.first);
             out.origins.emplace(
                 entry.first.GetID(),
                 std::make_pair<CPubKey, KeyOriginInfo>(
                     CPubKey(entry.first), std::move(entry.second)));
         }
         if (m_subdescriptor_arg) {
             for (const auto &subscript : subscripts) {
                 out.scripts.emplace(CScriptID(subscript), subscript);
                 std::vector<CScript> addscripts =
                     MakeScripts(pubkeys, &subscript, out);
                 for (auto &addscript : addscripts) {
                     output_scripts.push_back(std::move(addscript));
                 }
             }
         } else {
             output_scripts = MakeScripts(pubkeys, nullptr, out);
         }
         return true;
     }
 
     bool Expand(int pos, const SigningProvider &provider,
                 std::vector<CScript> &output_scripts, FlatSigningProvider &out,
                 DescriptorCache *write_cache = nullptr) const final {
         return ExpandHelper(pos, provider, nullptr, output_scripts, out,
                             write_cache);
     }
 
     bool ExpandFromCache(int pos, const DescriptorCache &read_cache,
                          std::vector<CScript> &output_scripts,
                          FlatSigningProvider &out) const final {
         return ExpandHelper(pos, DUMMY_SIGNING_PROVIDER, &read_cache,
                             output_scripts, out, nullptr);
     }
 
     void ExpandPrivate(int pos, const SigningProvider &provider,
                        FlatSigningProvider &out) const final {
         for (const auto &p : m_pubkey_args) {
             CKey key;
             if (!p->GetPrivKey(pos, provider, key)) {
                 continue;
             }
             out.keys.emplace(key.GetPubKey().GetID(), key);
         }
         if (m_subdescriptor_arg) {
             FlatSigningProvider subprovider;
             m_subdescriptor_arg->ExpandPrivate(pos, provider, subprovider);
             out = Merge(out, subprovider);
         }
     }
 };
 
 /** A parsed addr(A) descriptor. */
 class AddressDescriptor final : public DescriptorImpl {
     const CTxDestination m_destination;
 
 protected:
     std::string ToStringExtra() const override {
         return EncodeDestination(m_destination, GetConfig());
     }
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &,
                                      const CScript *,
                                      FlatSigningProvider &) const override {
         return Vector(GetScriptForDestination(m_destination));
     }
 
 public:
     AddressDescriptor(CTxDestination destination)
         : DescriptorImpl({}, {}, "addr"),
           m_destination(std::move(destination)) {}
     bool IsSolvable() const final { return false; }
 };
 
 /** A parsed raw(H) descriptor. */
 class RawDescriptor final : public DescriptorImpl {
     const CScript m_script;
 
 protected:
     std::string ToStringExtra() const override {
         return HexStr(m_script.begin(), m_script.end());
     }
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &,
                                      const CScript *,
                                      FlatSigningProvider &) const override {
         return Vector(m_script);
     }
 
 public:
     RawDescriptor(CScript script)
         : DescriptorImpl({}, {}, "raw"), m_script(std::move(script)) {}
     bool IsSolvable() const final { return false; }
 };
 
 /** A parsed pk(P) descriptor. */
 class PKDescriptor final : public DescriptorImpl {
 protected:
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &keys,
                                      const CScript *,
                                      FlatSigningProvider &) const override {
         return Vector(GetScriptForRawPubKey(keys[0]));
     }
 
 public:
     PKDescriptor(std::unique_ptr<PubkeyProvider> prov)
         : DescriptorImpl(Vector(std::move(prov)), {}, "pk") {}
 };
 
 /** A parsed pkh(P) descriptor. */
 class PKHDescriptor final : public DescriptorImpl {
 protected:
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &keys,
                                      const CScript *,
                                      FlatSigningProvider &out) const override {
         CKeyID id = keys[0].GetID();
         out.pubkeys.emplace(id, keys[0]);
         return Vector(GetScriptForDestination(PKHash(id)));
     }
 
 public:
     PKHDescriptor(std::unique_ptr<PubkeyProvider> prov)
         : DescriptorImpl(Vector(std::move(prov)), {}, "pkh") {}
 };
 
 /** A parsed combo(P) descriptor. */
 class ComboDescriptor final : public DescriptorImpl {
 protected:
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &keys,
                                      const CScript *,
                                      FlatSigningProvider &out) const override {
         std::vector<CScript> ret;
         CKeyID id = keys[0].GetID();
         out.pubkeys.emplace(id, keys[0]);
         // P2PK
         ret.emplace_back(GetScriptForRawPubKey(keys[0]));
         // P2PKH
         ret.emplace_back(GetScriptForDestination(PKHash(id)));
         return ret;
     }
 
 public:
     ComboDescriptor(std::unique_ptr<PubkeyProvider> prov)
         : DescriptorImpl(Vector(std::move(prov)), {}, "combo") {}
 };
 
 /** A parsed multi(...) descriptor. */
 class MultisigDescriptor final : public DescriptorImpl {
     const int m_threshold;
     const bool m_sorted;
 
 protected:
     std::string ToStringExtra() const override {
         return strprintf("%i", m_threshold);
     }
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &keys,
                                      const CScript *,
                                      FlatSigningProvider &) const override {
         if (m_sorted) {
             std::vector<CPubKey> sorted_keys(keys);
             std::sort(sorted_keys.begin(), sorted_keys.end());
             return Vector(GetScriptForMultisig(m_threshold, sorted_keys));
         }
         return Vector(GetScriptForMultisig(m_threshold, keys));
     }
 
 public:
     MultisigDescriptor(int threshold,
                        std::vector<std::unique_ptr<PubkeyProvider>> providers,
                        bool sorted = false)
         : DescriptorImpl(std::move(providers), {},
                          sorted ? "sortedmulti" : "multi"),
           m_threshold(threshold), m_sorted(sorted) {}
 };
 
 /** A parsed sh(...) descriptor. */
 class SHDescriptor final : public DescriptorImpl {
 protected:
     std::vector<CScript> MakeScripts(const std::vector<CPubKey> &,
                                      const CScript *script,
                                      FlatSigningProvider &) const override {
         return Vector(GetScriptForDestination(ScriptHash(*script)));
     }
 
 public:
     SHDescriptor(std::unique_ptr<DescriptorImpl> desc)
         : DescriptorImpl({}, std::move(desc), "sh") {}
 };
 
 ////////////////////////////////////////////////////////////////////////////
 // Parser                                                                 //
 ////////////////////////////////////////////////////////////////////////////
 
 enum class ParseScriptContext {
     TOP,
     P2SH,
 };
 
 /**
  * Parse a key path, being passed a split list of elements (the first element is
  * ignored).
  */
 NODISCARD bool ParseKeyPath(const std::vector<Span<const char>> &split,
                             KeyPath &out, std::string &error) {
     for (size_t i = 1; i < split.size(); ++i) {
         Span<const char> elem = split[i];
         bool hardened = false;
         if (elem.size() > 0 &&
             (elem[elem.size() - 1] == '\'' || elem[elem.size() - 1] == 'h')) {
             elem = elem.first(elem.size() - 1);
             hardened = true;
         }
         uint32_t p;
         if (!ParseUInt32(std::string(elem.begin(), elem.end()), &p)) {
             error = strprintf("Key path value '%s' is not a valid uint32",
                               std::string(elem.begin(), elem.end()).c_str());
             return false;
         } else if (p > 0x7FFFFFFFUL) {
             error = strprintf("Key path value %u is out of range", p);
             return false;
         }
         out.push_back(p | (uint32_t(hardened) << 31));
     }
     return true;
 }
 
 /** Parse a public key that excludes origin information. */
 std::unique_ptr<PubkeyProvider> ParsePubkeyInner(uint32_t key_exp_index,
                                                  const Span<const char> &sp,
                                                  FlatSigningProvider &out,
                                                  std::string &error) {
     using namespace spanparsing;
 
     auto split = Split(sp, '/');
     std::string str(split[0].begin(), split[0].end());
     if (str.size() == 0) {
         error = "No key provided";
         return nullptr;
     }
     if (split.size() == 1) {
         if (IsHex(str)) {
             std::vector<uint8_t> data = ParseHex(str);
             CPubKey pubkey(data);
             if (pubkey.IsFullyValid()) {
                 return std::make_unique<ConstPubkeyProvider>(key_exp_index,
                                                              pubkey);
             }
             error = strprintf("Pubkey '%s' is invalid", str);
             return nullptr;
         }
         CKey key = DecodeSecret(str);
         if (key.IsValid()) {
             CPubKey pubkey = key.GetPubKey();
             out.keys.emplace(pubkey.GetID(), key);
             return std::make_unique<ConstPubkeyProvider>(key_exp_index, pubkey);
         }
     }
     CExtKey extkey = DecodeExtKey(str);
     CExtPubKey extpubkey = DecodeExtPubKey(str);
     if (!extkey.key.IsValid() && !extpubkey.pubkey.IsValid()) {
         error = strprintf("key '%s' is not valid", str);
         return nullptr;
     }
     KeyPath path;
     DeriveType type = DeriveType::NO;
     if (split.back() == MakeSpan("*").first(1)) {
         split.pop_back();
         type = DeriveType::UNHARDENED;
     } else if (split.back() == MakeSpan("*'").first(2) ||
                split.back() == MakeSpan("*h").first(2)) {
         split.pop_back();
         type = DeriveType::HARDENED;
     }
     if (!ParseKeyPath(split, path, error)) {
         return nullptr;
     }
     if (extkey.key.IsValid()) {
         extpubkey = extkey.Neuter();
         out.keys.emplace(extpubkey.pubkey.GetID(), extkey.key);
     }
     return std::make_unique<BIP32PubkeyProvider>(key_exp_index, extpubkey,
                                                  std::move(path), type);
 }
 
 /** Parse a public key including origin information (if enabled). */
 std::unique_ptr<PubkeyProvider> ParsePubkey(uint32_t key_exp_index,
                                             const Span<const char> &sp,
                                             FlatSigningProvider &out,
                                             std::string &error) {
     using namespace spanparsing;
 
     auto origin_split = Split(sp, ']');
     if (origin_split.size() > 2) {
         error = "Multiple ']' characters found for a single pubkey";
         return nullptr;
     }
     if (origin_split.size() == 1) {
         return ParsePubkeyInner(key_exp_index, origin_split[0], out, error);
     }
     if (origin_split[0].size() < 1 || origin_split[0][0] != '[') {
         error = strprintf("Key origin start '[ character expected but not "
                           "found, got '%c' instead",
                           origin_split[0][0]);
         return nullptr;
     }
     auto slash_split = Split(origin_split[0].subspan(1), '/');
     if (slash_split[0].size() != 8) {
         error = strprintf("Fingerprint is not 4 bytes (%u characters instead "
                           "of 8 characters)",
                           slash_split[0].size());
         return nullptr;
     }
     std::string fpr_hex =
         std::string(slash_split[0].begin(), slash_split[0].end());
     if (!IsHex(fpr_hex)) {
         error = strprintf("Fingerprint '%s' is not hex", fpr_hex);
         return nullptr;
     }
     auto fpr_bytes = ParseHex(fpr_hex);
     KeyOriginInfo info;
     static_assert(sizeof(info.fingerprint) == 4, "Fingerprint must be 4 bytes");
     assert(fpr_bytes.size() == 4);
     std::copy(fpr_bytes.begin(), fpr_bytes.end(), info.fingerprint);
     if (!ParseKeyPath(slash_split, info.path, error)) {
         return nullptr;
     }
     auto provider =
         ParsePubkeyInner(key_exp_index, origin_split[1], out, error);
     if (!provider) {
         return nullptr;
     }
     return std::make_unique<OriginPubkeyProvider>(
         key_exp_index, std::move(info), std::move(provider));
 }
 
 /** Parse a script in a particular context. */
 std::unique_ptr<DescriptorImpl> ParseScript(uint32_t key_exp_index,
                                             Span<const char> &sp,
                                             ParseScriptContext ctx,
                                             FlatSigningProvider &out,
                                             std::string &error) {
     using namespace spanparsing;
 
     auto expr = Expr(sp);
     bool sorted_multi = false;
     if (Func("pk", expr)) {
         auto pubkey = ParsePubkey(key_exp_index, expr, out, error);
         if (!pubkey) {
             return nullptr;
         }
         return std::make_unique<PKDescriptor>(std::move(pubkey));
     }
     if (Func("pkh", expr)) {
         auto pubkey = ParsePubkey(key_exp_index, expr, out, error);
         if (!pubkey) {
             return nullptr;
         }
         return std::make_unique<PKHDescriptor>(std::move(pubkey));
     }
     if (ctx == ParseScriptContext::TOP && Func("combo", expr)) {
         auto pubkey = ParsePubkey(key_exp_index, expr, out, error);
         if (!pubkey) {
             return nullptr;
         }
         return std::make_unique<ComboDescriptor>(std::move(pubkey));
     } else if (ctx != ParseScriptContext::TOP && Func("combo", expr)) {
         error = "Cannot have combo in non-top level";
         return nullptr;
     }
     if ((sorted_multi = Func("sortedmulti", expr)) || Func("multi", expr)) {
         auto threshold = Expr(expr);
         uint32_t thres;
         std::vector<std::unique_ptr<PubkeyProvider>> providers;
         if (!ParseUInt32(std::string(threshold.begin(), threshold.end()),
                          &thres)) {
             error = strprintf(
                 "Multi threshold '%s' is not valid",
                 std::string(threshold.begin(), threshold.end()).c_str());
             return nullptr;
         }
         size_t script_size = 0;
         while (expr.size()) {
             if (!Const(",", expr)) {
                 error = strprintf("Multi: expected ',', got '%c'", expr[0]);
                 return nullptr;
             }
             auto arg = Expr(expr);
             auto pk = ParsePubkey(key_exp_index, arg, out, error);
             if (!pk) {
                 return nullptr;
             }
             script_size += pk->GetSize() + 1;
             providers.emplace_back(std::move(pk));
             key_exp_index++;
         }
         if (providers.size() < 1 || providers.size() > 16) {
             error = strprintf("Cannot have %u keys in multisig; must have "
                               "between 1 and 16 keys, inclusive",
                               providers.size());
             return nullptr;
         } else if (thres < 1) {
             error = strprintf(
                 "Multisig threshold cannot be %d, must be at least 1", thres);
             return nullptr;
         } else if (thres > providers.size()) {
             error =
                 strprintf("Multisig threshold cannot be larger than the number "
                           "of keys; threshold is %d but only %u keys specified",
                           thres, providers.size());
             return nullptr;
         }
         if (ctx == ParseScriptContext::TOP) {
             if (providers.size() > 3) {
                 error = strprintf("Cannot have %u pubkeys in bare multisig; "
                                   "only at most 3 pubkeys",
                                   providers.size());
                 return nullptr;
             }
         }
         if (ctx == ParseScriptContext::P2SH) {
             if (script_size + 3 > MAX_SCRIPT_ELEMENT_SIZE) {
                 error = strprintf("P2SH script is too large, %d bytes is "
                                   "larger than %d bytes",
                                   script_size + 3, MAX_SCRIPT_ELEMENT_SIZE);
                 return nullptr;
             }
         }
         return std::make_unique<MultisigDescriptor>(thres, std::move(providers),
                                                     sorted_multi);
     }
     if (ctx == ParseScriptContext::TOP && Func("sh", expr)) {
         auto desc = ParseScript(key_exp_index, expr, ParseScriptContext::P2SH,
                                 out, error);
         if (!desc || expr.size()) {
             return nullptr;
         }
         return std::make_unique<SHDescriptor>(std::move(desc));
     } else if (ctx != ParseScriptContext::TOP && Func("sh", expr)) {
         error = "Cannot have sh in non-top level";
         return nullptr;
     }
     if (ctx == ParseScriptContext::TOP && Func("addr", expr)) {
         CTxDestination dest =
             DecodeDestination(std::string(expr.begin(), expr.end()), Params());
         if (!IsValidDestination(dest)) {
             error = "Address is not valid";
             return nullptr;
         }
         return std::make_unique<AddressDescriptor>(std::move(dest));
     }
     if (ctx == ParseScriptContext::TOP && Func("raw", expr)) {
         std::string str(expr.begin(), expr.end());
         if (!IsHex(str)) {
             error = "Raw script is not hex";
             return nullptr;
         }
         auto bytes = ParseHex(str);
         return std::make_unique<RawDescriptor>(
             CScript(bytes.begin(), bytes.end()));
     }
     if (ctx == ParseScriptContext::P2SH) {
         error = "A function is needed within P2SH";
         return nullptr;
     }
     error = strprintf("%s is not a valid descriptor function",
                       std::string(expr.begin(), expr.end()));
     return nullptr;
 }
 
 std::unique_ptr<PubkeyProvider> InferPubkey(const CPubKey &pubkey,
                                             ParseScriptContext,
                                             const SigningProvider &provider) {
     std::unique_ptr<PubkeyProvider> key_provider =
         std::make_unique<ConstPubkeyProvider>(0, pubkey);
     KeyOriginInfo info;
     if (provider.GetKeyOrigin(pubkey.GetID(), info)) {
         return std::make_unique<OriginPubkeyProvider>(0, std::move(info),
                                                       std::move(key_provider));
     }
     return key_provider;
 }
 
 std::unique_ptr<DescriptorImpl> InferScript(const CScript &script,
                                             ParseScriptContext ctx,
                                             const SigningProvider &provider) {
     std::vector<std::vector<uint8_t>> data;
     txnouttype txntype = Solver(script, data);
 
     if (txntype == TX_PUBKEY) {
         CPubKey pubkey(data[0].begin(), data[0].end());
         if (pubkey.IsValid()) {
             return std::make_unique<PKDescriptor>(
                 InferPubkey(pubkey, ctx, provider));
         }
     }
     if (txntype == TX_PUBKEYHASH) {
         uint160 hash(data[0]);
         CKeyID keyid(hash);
         CPubKey pubkey;
         if (provider.GetPubKey(keyid, pubkey)) {
             return std::make_unique<PKHDescriptor>(
                 InferPubkey(pubkey, ctx, provider));
         }
     }
     if (txntype == TX_MULTISIG) {
         std::vector<std::unique_ptr<PubkeyProvider>> providers;
         for (size_t i = 1; i + 1 < data.size(); ++i) {
             CPubKey pubkey(data[i].begin(), data[i].end());
             providers.push_back(InferPubkey(pubkey, ctx, provider));
         }
         return std::make_unique<MultisigDescriptor>((int)data[0][0],
                                                     std::move(providers));
     }
     if (txntype == TX_SCRIPTHASH && ctx == ParseScriptContext::TOP) {
         uint160 hash(data[0]);
         CScriptID scriptid(hash);
         CScript subscript;
         if (provider.GetCScript(scriptid, subscript)) {
             auto sub =
                 InferScript(subscript, ParseScriptContext::P2SH, provider);
             if (sub) {
                 return std::make_unique<SHDescriptor>(std::move(sub));
             }
         }
     }
 
     CTxDestination dest;
     if (ExtractDestination(script, dest)) {
         if (GetScriptForDestination(dest) == script) {
             return std::make_unique<AddressDescriptor>(std::move(dest));
         }
     }
 
     return std::make_unique<RawDescriptor>(script);
 }
 
 } // namespace
 
 /**
  * Check a descriptor checksum, and update desc to be the checksum-less part.
  */
 bool CheckChecksum(Span<const char> &sp, bool require_checksum,
                    std::string &error, std::string *out_checksum = nullptr) {
     using namespace spanparsing;
 
     auto check_split = Split(sp, '#');
     if (check_split.size() > 2) {
         error = "Multiple '#' symbols";
         return false;
     }
     if (check_split.size() == 1 && require_checksum) {
         error = "Missing checksum";
         return false;
     }
     if (check_split.size() == 2) {
         if (check_split[1].size() != 8) {
             error =
                 strprintf("Expected 8 character checksum, not %u characters",
                           check_split[1].size());
             return false;
         }
     }
     auto checksum = DescriptorChecksum(check_split[0]);
     if (checksum.empty()) {
         error = "Invalid characters in payload";
         return false;
     }
     if (check_split.size() == 2) {
         if (!std::equal(checksum.begin(), checksum.end(),
                         check_split[1].begin())) {
             error = strprintf(
                 "Provided checksum '%s' does not match computed checksum '%s'",
                 std::string(check_split[1].begin(), check_split[1].end()),
                 checksum);
             return false;
         }
     }
     if (out_checksum) {
         *out_checksum = std::move(checksum);
     }
     sp = check_split[0];
     return true;
 }
 
 std::unique_ptr<Descriptor> Parse(const std::string &descriptor,
                                   FlatSigningProvider &out, std::string &error,
                                   bool require_checksum) {
     Span<const char> sp(descriptor.data(), descriptor.size());
     if (!CheckChecksum(sp, require_checksum, error)) {
         return nullptr;
     }
     auto ret = ParseScript(0, sp, ParseScriptContext::TOP, out, error);
     if (sp.size() == 0 && ret) {
         return std::unique_ptr<Descriptor>(std::move(ret));
     }
     return nullptr;
 }
 
 std::string GetDescriptorChecksum(const std::string &descriptor) {
     std::string ret;
     std::string error;
     Span<const char> sp(descriptor.data(), descriptor.size());
     if (!CheckChecksum(sp, false, error, &ret)) {
         return "";
     }
     return ret;
 }
 
 std::unique_ptr<Descriptor> InferDescriptor(const CScript &script,
                                             const SigningProvider &provider) {
     return InferScript(script, ParseScriptContext::TOP, provider);
 }
 
 void DescriptorCache::CacheParentExtPubKey(uint32_t key_exp_pos,
                                            const CExtPubKey &xpub) {
     m_parent_xpubs[key_exp_pos] = xpub;
 }
 
 void DescriptorCache::CacheDerivedExtPubKey(uint32_t key_exp_pos,
                                             uint32_t der_index,
                                             const CExtPubKey &xpub) {
     auto &xpubs = m_derived_xpubs[key_exp_pos];
     xpubs[der_index] = xpub;
 }
 
 bool DescriptorCache::GetCachedParentExtPubKey(uint32_t key_exp_pos,
                                                CExtPubKey &xpub) const {
     const auto &it = m_parent_xpubs.find(key_exp_pos);
     if (it == m_parent_xpubs.end()) {
         return false;
     }
     xpub = it->second;
     return true;
 }
 
 bool DescriptorCache::GetCachedDerivedExtPubKey(uint32_t key_exp_pos,
                                                 uint32_t der_index,
                                                 CExtPubKey &xpub) const {
     const auto &key_exp_it = m_derived_xpubs.find(key_exp_pos);
     if (key_exp_it == m_derived_xpubs.end()) {
         return false;
     }
     const auto &der_it = key_exp_it->second.find(der_index);
     if (der_it == key_exp_it->second.end()) {
         return false;
     }
     xpub = der_it->second;
     return true;
 }
 
 const ExtPubKeyMap DescriptorCache::GetCachedParentExtPubKeys() const {
     return m_parent_xpubs;
 }
 
 const std::unordered_map<uint32_t, ExtPubKeyMap>
 DescriptorCache::GetCachedDerivedExtPubKeys() const {
     return m_derived_xpubs;
 }