merge bitcoin#15024: Allow specific private keys to be derived from descriptor

src/script/descriptor.cpp

@@ -166,6 +166,9 @@ struct PubkeyProvider
 
     /** 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
@@ -197,6 +200,10 @@ public:
         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. */
@@ -224,6 +231,10 @@ public:
         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 {
@@ -268,14 +279,9 @@ public:
     {
         if (key) {
             if (IsHardened()) {
-                CExtKey extkey;
-                if (!GetExtKey(arg, extkey)) return false;
-                for (auto entry : m_path) {
-                    extkey.Derive(extkey, entry);
-                }
-                if (m_derive == DeriveType::UNHARDENED) extkey.Derive(extkey, pos);
-                if (m_derive == DeriveType::HARDENED) extkey.Derive(extkey, pos | 0x80000000UL);
-                *key = extkey.Neuter().pubkey;
+                CKey priv_key;
+                if (!GetPrivKey(pos, arg, priv_key)) return false;
+                *key = priv_key.GetPubKey();
             } else {
                 // TODO: optimize by caching
                 CExtPubKey extkey = m_extkey;
@@ -314,6 +320,18 @@ public:
         }
         return true;
     }
+    bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const override
+    {
+        CExtKey extkey;
+        if (!GetExtKey(arg, extkey)) return false;
+        for (auto entry : m_path) {
+            extkey.Derive(extkey, entry);
+        }
+        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. */
@@ -468,6 +486,20 @@ public:
         Span<const unsigned char> span = MakeSpan(cache);
         return ExpandHelper(pos, DUMMY_SIGNING_PROVIDER, &span, output_scripts, out, nullptr) && span.size() == 0;
     }
+
+    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);
+        }
+    }
 };
 
 /** Construct a vector with one element, which is moved into it. */

src/script/descriptor.h

@@ -63,6 +63,14 @@ struct Descriptor {
      * @param[out] out: Scripts and public keys necessary for solving the expanded scriptPubKeys (may be equal to `provider`).
      */
     virtual bool ExpandFromCache(int pos, const std::vector<unsigned char>& cache, std::vector<CScript>& output_scripts, FlatSigningProvider& out) const = 0;
+
+    /** Expand the private key for a descriptor at a specified position, if possible.
+     *
+     * pos: the position at which to expand the descriptor. If IsRange() is false, this is ignored.
+     * provider: the provider to query for the private keys.
+     * out: any private keys available for the specified pos will be placed here.
+     */
+    virtual void ExpandPrivate(int pos, const SigningProvider& provider, FlatSigningProvider& out) const = 0;
 };
 
 /** Parse a `descriptor` string. Included private keys are put in `out`.

src/wallet/rpcdump.cpp

@@ -1258,8 +1258,7 @@ static UniValue ProcessImportDescriptor(ImportData& import_data, std::map<CKeyID
 
     const UniValue& priv_keys = data.exists("keys") ? data["keys"].get_array() : UniValue();
 
-    // Expand all descriptors to get public keys and scripts.
-    // TODO: get private keys from descriptors too
+    // Expand all descriptors to get public keys and scripts, and private keys if available.
     for (int i = range_start; i <= range_end; ++i) {
         FlatSigningProvider out_keys;
         std::vector<CScript> scripts_temp;
@@ -1273,7 +1272,10 @@ static UniValue ProcessImportDescriptor(ImportData& import_data, std::map<CKeyID
             import_data.import_scripts.emplace(x.second);
         }
 
+        parsed_desc->ExpandPrivate(i, keys, out_keys);
+
         std::copy(out_keys.pubkeys.begin(), out_keys.pubkeys.end(), std::inserter(pubkey_map, pubkey_map.end()));
+        std::copy(out_keys.keys.begin(), out_keys.keys.end(), std::inserter(privkey_map, privkey_map.end()));
         import_data.key_origins.insert(out_keys.origins.begin(), out_keys.origins.end());
     }
 

test/functional/wallet_importmulti.py

@@ -448,13 +448,12 @@ class ImportMultiTest(BitcoinTestFramework):
                               error_code=-8,
                               error_message='Descriptor is ranged, please specify the range')
 
-        # Test importing of a ranged descriptor without keys
+        # Test importing of a ranged descriptor with xpriv
         self.log.info("Should import the ranged descriptor with specified range as solvable")
         self.test_importmulti({"desc": descsum_create(desc),
                                "timestamp": "now",
                                "range": 1},
-                              success=True,
-                              warnings=["Some private keys are missing, outputs will be considered watchonly. If this is intentional, specify the watchonly flag."])
+                              success=True)
 
         self.test_importmulti({"desc": descsum_create(desc), "timestamp": "now", "range": -1},
                               success=False, error_code=-8, error_message='End of range is too high')
@@ -471,6 +470,23 @@ class ImportMultiTest(BitcoinTestFramework):
         self.test_importmulti({"desc": descsum_create(desc), "timestamp": "now", "range": [0, 1000001]},
                               success=False, error_code=-8, error_message='Range is too large')
 
+        # Test importing a descriptor containing a WIF private key
+        wif_priv = "cTT3BvHnd51YJf8fkdr2XvZTQRRUZruWhRvRyQY1raVFg5Lvam2A"
+        address = "ySWABbcNKyHUgBb1ffhpuETuis9jsdR3aq"
+        desc = "sh(pkh(" + wif_priv + "))"
+        self.log.info("Should import a descriptor with a WIF private key as spendable")
+        self.test_importmulti({"desc": descsum_create(desc),
+                               "timestamp": "now"},
+                              success=True)
+        test_address(self.nodes[1],
+                     address,
+                     solvable=True,
+                     ismine=True)
+
+        # dump the private key to ensure it matches what was imported
+        privkey = self.nodes[1].dumpprivkey(address)
+        assert_equal(privkey, wif_priv)
+
         # Test importing of a P2PKH address via descriptor
         key = get_key(self.nodes[0])
         self.log.info("Should import a p2pkh address from descriptor")