desc spkm: Add functions to retrieve specific private keys

src/wallet/scriptpubkeyman.cpp

@@ -11,6 +11,7 @@
 #include <script/sign.h>
 #include <script/solver.h>
 #include <util/bip32.h>
+#include <util/check.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/time.h>
@@ -2143,6 +2144,36 @@ std::map<CKeyID, CKey> DescriptorScriptPubKeyMan::GetKeys() const
     return m_map_keys;
 }
 
+bool DescriptorScriptPubKeyMan::HasPrivKey(const CKeyID& keyid) const
+{
+    AssertLockHeld(cs_desc_man);
+    return m_map_keys.contains(keyid) || m_map_crypted_keys.contains(keyid);
+}
+
+std::optional<CKey> DescriptorScriptPubKeyMan::GetKey(const CKeyID& keyid) const
+{
+    AssertLockHeld(cs_desc_man);
+    if (m_storage.HasEncryptionKeys() && !m_storage.IsLocked()) {
+        const auto& it = m_map_crypted_keys.find(keyid);
+        if (it == m_map_crypted_keys.end()) {
+            return std::nullopt;
+        }
+        const std::vector<unsigned char>& crypted_secret = it->second.second;
+        CKey key;
+        if (!Assume(m_storage.WithEncryptionKey([&](const CKeyingMaterial& encryption_key) {
+            return DecryptKey(encryption_key, crypted_secret, it->second.first, key);
+        }))) {
+            return std::nullopt;
+        }
+        return key;
+    }
+    const auto& it = m_map_keys.find(keyid);
+    if (it == m_map_keys.end()) {
+        return std::nullopt;
+    }
+    return it->second;
+}
+
 bool DescriptorScriptPubKeyMan::TopUp(unsigned int size)
 {
     WalletBatch batch(m_storage.GetDatabase());

src/wallet/scriptpubkeyman.h

@@ -633,6 +633,9 @@ public:
     bool SetupDescriptorGeneration(WalletBatch& batch, const CExtKey& master_key, OutputType addr_type, bool internal);
 
     bool HavePrivateKeys() const override;
+    bool HasPrivKey(const CKeyID& keyid) const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
+    //! Retrieve the particular key if it is available. Returns nullopt if the key is not in the wallet, or if the wallet is locked.
+    std::optional<CKey> GetKey(const CKeyID& keyid) const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
 
     std::optional<int64_t> GetOldestKeyPoolTime() const override;
     unsigned int GetKeyPoolSize() const override;