Implicitly know about P2WPKH redeemscripts

Make CKeyStore automatically known about the redeemscripts necessary for P2SH-P2WPKH
(and due to the extra checks in IsMine, also P2WPKH) spending.

1 files changed, 33 insertions, 2 deletions

diff --git a/src/keystore.cpp b/src/keystore.cpp
index cbcc6d7ca9..487784b0bf 100644
--- a/src/keystore.cpp
+++ b/src/keystore.cpp
@@ -11,6 +11,31 @@ bool CKeyStore::AddKey(const CKey &key) {
     return AddKeyPubKey(key, key.GetPubKey());
 }
 
+void CBasicKeyStore::ImplicitlyLearnRelatedKeyScripts(const CPubKey& pubkey)
+{
+    AssertLockHeld(cs_KeyStore);
+    CKeyID key_id = pubkey.GetID();
+    // We must actually know about this key already.
+    assert(HaveKey(key_id) || mapWatchKeys.count(key_id));
+    // This adds the redeemscripts necessary to detect P2WPKH and P2SH-P2WPKH
+    // outputs. Technically P2WPKH outputs don't have a redeemscript to be
+    // spent. However, our current IsMine logic requires the corresponding
+    // P2SH-P2WPKH redeemscript to be present in the wallet in order to accept
+    // payment even to P2WPKH outputs.
+    // Also note that having superfluous scripts in the keystore never hurts.
+    // They're only used to guide recursion in signing and IsMine logic - if
+    // a script is present but we can't do anything with it, it has no effect.
+    // "Implicitly" refers to fact that scripts are derived automatically from
+    // existing keys, and are present in memory, even without being explicitly
+    // loaded (e.g. from a file).
+    if (pubkey.IsCompressed()) {
+        CScript script = GetScriptForDestination(WitnessV0KeyHash(key_id));
+        // This does not use AddCScript, as it may be overridden.
+        CScriptID id(script);
+        mapScripts[id] = std::move(script);
+    }
+}
+
 bool CBasicKeyStore::GetPubKey(const CKeyID &address, CPubKey &vchPubKeyOut) const
 {
     CKey key;
@@ -31,6 +56,7 @@ bool CBasicKeyStore::AddKeyPubKey(const CKey& key, const CPubKey &pubkey)
 {
     LOCK(cs_KeyStore);
     mapKeys[pubkey.GetID()] = key;
+    ImplicitlyLearnRelatedKeyScripts(pubkey);
     return true;
 }
 
@@ -110,8 +136,10 @@ bool CBasicKeyStore::AddWatchOnly(const CScript &dest)
     LOCK(cs_KeyStore);
     setWatchOnly.insert(dest);
     CPubKey pubKey;
-    if (ExtractPubKey(dest, pubKey))
+    if (ExtractPubKey(dest, pubKey)) {
         mapWatchKeys[pubKey.GetID()] = pubKey;
+        ImplicitlyLearnRelatedKeyScripts(pubKey);
+    }
     return true;
 }
 
@@ -120,8 +148,11 @@ bool CBasicKeyStore::RemoveWatchOnly(const CScript &dest)
     LOCK(cs_KeyStore);
     setWatchOnly.erase(dest);
     CPubKey pubKey;
-    if (ExtractPubKey(dest, pubKey))
+    if (ExtractPubKey(dest, pubKey)) {
         mapWatchKeys.erase(pubKey.GetID());
+    }
+    // Related CScripts are not removed; having superfluous scripts around is
+    // harmless (see comment in ImplicitlyLearnRelatedKeyScripts).
     return true;
 }