wallet: Use steady clock to calculate number of derive iterations

Author: MarcoFalke

src/wallet/wallet.cpp

@@ -565,13 +565,14 @@ bool CWallet::ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase,
                 return false;
             if (Unlock(_vMasterKey))
             {
-                int64_t nStartTime = GetTimeMillis();
+                constexpr MillisecondsDouble target{100};
+                auto start{SteadyClock::now()};
                 crypter.SetKeyFromPassphrase(strNewWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod);
-                pMasterKey.second.nDeriveIterations = static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * (100 / ((double)(GetTimeMillis() - nStartTime))));
+                pMasterKey.second.nDeriveIterations = static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * target / (SteadyClock::now() - start));
 
-                nStartTime = GetTimeMillis();
+                start = SteadyClock::now();
                 crypter.SetKeyFromPassphrase(strNewWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod);
-                pMasterKey.second.nDeriveIterations = (pMasterKey.second.nDeriveIterations + static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * 100 / ((double)(GetTimeMillis() - nStartTime)))) / 2;
+                pMasterKey.second.nDeriveIterations = (pMasterKey.second.nDeriveIterations + static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * target / (SteadyClock::now() - start))) / 2;
 
                 if (pMasterKey.second.nDeriveIterations < 25000)
                     pMasterKey.second.nDeriveIterations = 25000;
@@ -768,13 +769,14 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
     GetStrongRandBytes(kMasterKey.vchSalt);
 
     CCrypter crypter;
-    int64_t nStartTime = GetTimeMillis();
+    constexpr MillisecondsDouble target{100};
+    auto start{SteadyClock::now()};
     crypter.SetKeyFromPassphrase(strWalletPassphrase, kMasterKey.vchSalt, 25000, kMasterKey.nDerivationMethod);
-    kMasterKey.nDeriveIterations = static_cast<unsigned int>(2500000 / ((double)(GetTimeMillis() - nStartTime)));
+    kMasterKey.nDeriveIterations = static_cast<unsigned int>(25000 * target / (SteadyClock::now() - start));
 
-    nStartTime = GetTimeMillis();
+    start = SteadyClock::now();
     crypter.SetKeyFromPassphrase(strWalletPassphrase, kMasterKey.vchSalt, kMasterKey.nDeriveIterations, kMasterKey.nDerivationMethod);
-    kMasterKey.nDeriveIterations = (kMasterKey.nDeriveIterations + static_cast<unsigned int>(kMasterKey.nDeriveIterations * 100 / ((double)(GetTimeMillis() - nStartTime)))) / 2;
+    kMasterKey.nDeriveIterations = (kMasterKey.nDeriveIterations + static_cast<unsigned int>(kMasterKey.nDeriveIterations * target / (SteadyClock::now() - start))) / 2;
 
     if (kMasterKey.nDeriveIterations < 25000)
         kMasterKey.nDeriveIterations = 25000;