Use 71 byte signature for DUMMY_SIGNATURE_CREATOR

Changes DUMMY_SIGNATURE_CREATOR to create 71 byte dummy signatures.

Update comments to reflect this change

Author: achow101

src/script/sign.cpp

@@ -423,16 +423,16 @@ class DummySignatureCreator final : public BaseSignatureCreator {
     bool CreateSig(const SigningProvider& provider, std::vector<unsigned char>& vchSig, const CKeyID& keyid, const CScript& scriptCode, SigVersion sigversion) const override
     {
         // Create a dummy signature that is a valid DER-encoding
-        vchSig.assign(72, '\000');
+        vchSig.assign(71, '\000');
         vchSig[0] = 0x30;
-        vchSig[1] = 69;
+        vchSig[1] = 68;
         vchSig[2] = 0x02;
-        vchSig[3] = 33;
+        vchSig[3] = 32;
         vchSig[4] = 0x01;
-        vchSig[4 + 33] = 0x02;
-        vchSig[5 + 33] = 32;
-        vchSig[6 + 33] = 0x01;
-        vchSig[6 + 33 + 32] = SIGHASH_ALL;
+        vchSig[4 + 32] = 0x02;
+        vchSig[5 + 32] = 32;
+        vchSig[6 + 32] = 0x01;
+        vchSig[6 + 32 + 32] = SIGHASH_ALL;
         return true;
     }
 };

src/wallet/wallet.cpp

@@ -1540,7 +1540,7 @@ int64_t CWalletTx::GetTxTime() const
     return n ? n : nTimeReceived;
 }
 
-// Helper for producing a max-sized low-S signature (eg 72 bytes)
+// Helper for producing a max-sized low-S low-R signature (eg 71 bytes)
 bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout) const
 {
     // Fill in dummy signatures for fee calculation.
@@ -1556,7 +1556,7 @@ bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout) const
     return true;
 }
 
-// Helper for producing a bunch of max-sized low-S signatures (eg 72 bytes)
+// Helper for producing a bunch of max-sized low-S low-R signatures (eg 71 bytes)
 bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts) const
 {
     // Fill in dummy signatures for fee calculation.

src/wallet/wallet.h

@@ -1308,7 +1308,7 @@ class WalletRescanReserver
 };
 
 // Calculate the size of the transaction assuming all signatures are max size
-// Use DummySignatureCreator, which inserts 72 byte signatures everywhere.
+// Use DummySignatureCreator, which inserts 71 byte signatures everywhere.
 // NOTE: this requires that all inputs must be in mapWallet (eg the tx should
 // be IsAllFromMe).
 int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet);