diff --git a/src/script/sign.h b/src/script/sign.h
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -49,6 +49,19 @@
     bool GetPubKey(const CKeyID &address, CPubKey &pubkey) const;
 };
 
+struct FlatSigningProvider final : public SigningProvider {
+    std::map<CScriptID, CScript> scripts;
+    std::map<CKeyID, CPubKey> pubkeys;
+    std::map<CKeyID, CKey> keys;
+
+    bool GetCScript(const CScriptID &scriptid, CScript &script) const override;
+    bool GetPubKey(const CKeyID &keyid, CPubKey &pubkey) const override;
+    bool GetKey(const CKeyID &keyid, CKey &key) const override;
+};
+
+FlatSigningProvider Merge(const FlatSigningProvider &a,
+                          const FlatSigningProvider &b);
+
 /** Interface for signature creators. */
 class BaseSignatureCreator {
 public:
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -428,6 +428,17 @@
         return true;
     }
 };
+
+template <typename M, typename K, typename V>
+bool LookupHelper(const M &map, const K &key, V &value) {
+    auto it = map.find(key);
+    if (it != map.end()) {
+        value = it->second;
+        return true;
+    }
+    return false;
+}
+
 } // namespace
 
 const BaseSignatureCreator &DUMMY_SIGNATURE_CREATOR = DummySignatureCreator();
@@ -554,3 +565,27 @@
                                           CPubKey &pubkey) const {
     return m_provider->GetPubKey(address, pubkey);
 }
+
+bool FlatSigningProvider::GetCScript(const CScriptID &scriptid,
+                                     CScript &script) const {
+    return LookupHelper(scripts, scriptid, script);
+}
+bool FlatSigningProvider::GetPubKey(const CKeyID &keyid,
+                                    CPubKey &pubkey) const {
+    return LookupHelper(pubkeys, keyid, pubkey);
+}
+bool FlatSigningProvider::GetKey(const CKeyID &keyid, CKey &key) const {
+    return LookupHelper(keys, keyid, key);
+}
+
+FlatSigningProvider Merge(const FlatSigningProvider &a,
+                          const FlatSigningProvider &b) {
+    FlatSigningProvider ret;
+    ret.scripts = a.scripts;
+    ret.scripts.insert(b.scripts.begin(), b.scripts.end());
+    ret.pubkeys = a.pubkeys;
+    ret.pubkeys.insert(b.pubkeys.begin(), b.pubkeys.end());
+    ret.keys = a.keys;
+    ret.keys.insert(b.keys.begin(), b.keys.end());
+    return ret;
+}