Introduce interface for signing providers

CKeyStore is a rich interface that provides many features, including knowledge
of scripts and pubkeys for solving, private keys for signing, in addition to
watch-only keys and scripts, and distinguishing lack of keys from them just
being encrypted.

The signing logic in script/sign does not actually need most of these features.
Here we introduce a simpler interface (SigningProvider) which *only* provides
keys and scripts. This is actually sufficient for signing.

In addtion, we swap the dependency between keystore and script/sign
(keystore now depends on script/script with CKeyStore deriving from
SigningProvider, rather than CKeyStore being the interface that signing
relies on).

2 files changed, 33 insertions, 23 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index baa712dc2d..d22d4e161b 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -6,7 +6,6 @@
 #include <script/sign.h>
 
 #include <key.h>
-#include <keystore.h>
 #include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <script/standard.h>
@@ -15,12 +14,12 @@
 
 typedef std::vector<unsigned char> valtype;
 
-TransactionSignatureCreator::TransactionSignatureCreator(const CKeyStore* keystoreIn, const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : BaseSignatureCreator(keystoreIn), txTo(txToIn), nIn(nInIn), nHashType(nHashTypeIn), amount(amountIn), checker(txTo, nIn, amountIn) {}
+TransactionSignatureCreator::TransactionSignatureCreator(const SigningProvider* provider, const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : BaseSignatureCreator(provider), txTo(txToIn), nIn(nInIn), nHashType(nHashTypeIn), amount(amountIn), checker(txTo, nIn, amountIn) {}
 
 bool TransactionSignatureCreator::CreateSig(std::vector<unsigned char>& vchSig, const CKeyID& address, const CScript& scriptCode, SigVersion sigversion) const
 {
     CKey key;
-    if (!keystore->GetKey(address, key))
+    if (!m_provider->GetKey(address, key))
         return false;
 
     // Signing with uncompressed keys is disabled in witness scripts
@@ -91,12 +90,12 @@ static bool SignStep(const BaseSignatureCreator& creator, const CScript& scriptP
         else
         {
             CPubKey vch;
-            creator.KeyStore().GetPubKey(keyID, vch);
+            creator.Provider().GetPubKey(keyID, vch);
             ret.push_back(ToByteVector(vch));
         }
         return true;
     case TX_SCRIPTHASH:
-        if (creator.KeyStore().GetCScript(uint160(vSolutions[0]), scriptRet)) {
+        if (creator.Provider().GetCScript(uint160(vSolutions[0]), scriptRet)) {
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
@@ -112,7 +111,7 @@ static bool SignStep(const BaseSignatureCreator& creator, const CScript& scriptP
 
     case TX_WITNESS_V0_SCRIPTHASH:
         CRIPEMD160().Write(&vSolutions[0][0], vSolutions[0].size()).Finalize(h160.begin());
-        if (creator.KeyStore().GetCScript(h160, scriptRet)) {
+        if (creator.Provider().GetCScript(h160, scriptRet)) {
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
@@ -206,12 +205,12 @@ void UpdateTransaction(CMutableTransaction& tx, unsigned int nIn, const Signatur
     UpdateInput(tx.vin[nIn], data);
 }
 
-bool SignSignature(const CKeyStore &keystore, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType)
+bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType)
 {
     assert(nIn < txTo.vin.size());
 
     CTransaction txToConst(txTo);
-    TransactionSignatureCreator creator(&keystore, &txToConst, nIn, amount, nHashType);
+    TransactionSignatureCreator creator(&provider, &txToConst, nIn, amount, nHashType);
 
     SignatureData sigdata;
     bool ret = ProduceSignature(creator, fromPubKey, sigdata);
@@ -219,14 +218,14 @@ bool SignSignature(const CKeyStore &keystore, const CScript& fromPubKey, CMutabl
     return ret;
 }
 
-bool SignSignature(const CKeyStore &keystore, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType)
+bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType)
 {
     assert(nIn < txTo.vin.size());
     CTxIn& txin = txTo.vin[nIn];
     assert(txin.prevout.n < txFrom.vout.size());
     const CTxOut& txout = txFrom.vout[txin.prevout.n];
 
-    return SignSignature(keystore, txout.scriptPubKey, txTo, nIn, txout.nValue, nHashType);
+    return SignSignature(provider, txout.scriptPubKey, txTo, nIn, txout.nValue, nHashType);
 }
 
 static std::vector<valtype> CombineMultisig(const CScript& scriptPubKey, const BaseSignatureChecker& checker,
@@ -427,13 +426,13 @@ bool DummySignatureCreator::CreateSig(std::vector<unsigned char>& vchSig, const
     return true;
 }
 
-bool IsSolvable(const CKeyStore& store, const CScript& script)
+bool IsSolvable(const SigningProvider& provider, const CScript& script)
 {
     // This check is to make sure that the script we created can actually be solved for and signed by us
     // if we were to have the private keys. This is just to make sure that the script is valid and that,
     // if found in a transaction, we would still accept and relay that transaction. In particular,
     // it will reject witness outputs that require signing with an uncompressed public key.
-    DummySignatureCreator creator(&store);
+    DummySignatureCreator creator(&provider);
     SignatureData sigs;
     // Make sure that STANDARD_SCRIPT_VERIFY_FLAGS includes SCRIPT_VERIFY_WITNESS_PUBKEYTYPE, the most
     // important property this function is designed to test for.
diff --git a/src/script/sign.h b/src/script/sign.h
index 2c749521cd..c301f0544f 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -8,21 +8,32 @@
 
 #include <script/interpreter.h>
 
+class CKey;
 class CKeyID;
-class CKeyStore;
 class CScript;
+class CScriptID;
 class CTransaction;
 
 struct CMutableTransaction;
 
+/** An interface to be implemented by keystores that support signing. */
+class SigningProvider
+{
+public:
+    virtual ~SigningProvider() {}
+    virtual bool GetCScript(const CScriptID &scriptid, CScript& script) const =0;
+    virtual bool GetPubKey(const CKeyID &address, CPubKey& pubkey) const =0;
+    virtual bool GetKey(const CKeyID &address, CKey& key) const =0;
+};
+
 /** Virtual base class for signature creators. */
 class BaseSignatureCreator {
 protected:
-    const CKeyStore* keystore;
+    const SigningProvider* m_provider;
 
 public:
-    explicit BaseSignatureCreator(const CKeyStore* keystoreIn) : keystore(keystoreIn) {}
-    const CKeyStore& KeyStore() const { return *keystore; };
+    explicit BaseSignatureCreator(const SigningProvider* provider) : m_provider(provider) {}
+    const SigningProvider& Provider() const { return *m_provider; }
     virtual ~BaseSignatureCreator() {}
     virtual const BaseSignatureChecker& Checker() const =0;
 
@@ -39,7 +50,7 @@ class TransactionSignatureCreator : public BaseSignatureCreator {
     const TransactionSignatureChecker checker;
 
 public:
-    TransactionSignatureCreator(const CKeyStore* keystoreIn, const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn=SIGHASH_ALL);
+    TransactionSignatureCreator(const SigningProvider* provider, const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn=SIGHASH_ALL);
     const BaseSignatureChecker& Checker() const override { return checker; }
     bool CreateSig(std::vector<unsigned char>& vchSig, const CKeyID& keyid, const CScript& scriptCode, SigVersion sigversion) const override;
 };
@@ -48,13 +59,13 @@ class MutableTransactionSignatureCreator : public TransactionSignatureCreator {
     CTransaction tx;
 
 public:
-    MutableTransactionSignatureCreator(const CKeyStore* keystoreIn, const CMutableTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : TransactionSignatureCreator(keystoreIn, &tx, nInIn, amountIn, nHashTypeIn), tx(*txToIn) {}
+    MutableTransactionSignatureCreator(const SigningProvider* provider, const CMutableTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : TransactionSignatureCreator(provider, &tx, nInIn, amountIn, nHashTypeIn), tx(*txToIn) {}
 };
 
 /** A signature creator that just produces 72-byte empty signatures. */
 class DummySignatureCreator : public BaseSignatureCreator {
 public:
-    explicit DummySignatureCreator(const CKeyStore* keystoreIn) : BaseSignatureCreator(keystoreIn) {}
+    explicit DummySignatureCreator(const SigningProvider* provider) : BaseSignatureCreator(provider) {}
     const BaseSignatureChecker& Checker() const override;
     bool CreateSig(std::vector<unsigned char>& vchSig, const CKeyID& keyid, const CScript& scriptCode, SigVersion sigversion) const override;
 };
@@ -71,8 +82,8 @@ struct SignatureData {
 bool ProduceSignature(const BaseSignatureCreator& creator, const CScript& scriptPubKey, SignatureData& sigdata);
 
 /** Produce a script signature for a transaction. */
-bool SignSignature(const CKeyStore &keystore, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType);
-bool SignSignature(const CKeyStore& keystore, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType);
+bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType);
+bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType);
 
 /** Combine two script signatures using a generic signature checker, intelligently, possibly with OP_0 placeholders. */
 SignatureData CombineSignatures(const CScript& scriptPubKey, const BaseSignatureChecker& checker, const SignatureData& scriptSig1, const SignatureData& scriptSig2);
@@ -84,8 +95,8 @@ void UpdateInput(CTxIn& input, const SignatureData& data);
 
 /* Check whether we know how to sign for an output like this, assuming we
  * have all private keys. While this function does not need private keys, the passed
- * keystore is used to look up public keys and redeemscripts by hash.
+ * provider is used to look up public keys and redeemscripts by hash.
  * Solvability is unrelated to whether we consider this output to be ours. */
-bool IsSolvable(const CKeyStore& store, const CScript& script);
+bool IsSolvable(const SigningProvider& provider, const CScript& script);
 
 #endif // BITCOIN_SCRIPT_SIGN_H