wallet: Make encryption derivation clock mockable
What the developer wrote
Authored by David Gumberg
wallet: Make encryption derivation clock mockable
Adds a special case where if the elapsed time during measurement of DKF
performance is 0, the default derive iterations are used so that
behavior is stable for testing and benchmarks.
What changed, and why it matters
This is a small Bitcoin Core wallet change that makes the encryption key-stretching benchmark use a mockable clock during testing. If the measured time is zero (likely because a test fakes the clock), it falls back to a fixed default number of iterations instead of trying to divide by zero or produce unstable results. It is a test-stability improvement, not a fix for an active security vulnerability.
No urgent action. Treat as normal code-quality/testability patch. Review that DEFAULT_DERIVE_ITERATIONS remains strong enough for production use and that the mockable clock cannot be accidentally enabled in production builds.
Security signals we found
Division-by-zero guard added in key-derivation iteration calibration
Clock source changed from SteadyClock to mockable NodeClock
Behavior explicitly scoped to test/benchmark environment via comment
Evidence from the diff
The commit replaces SteadyClock with NodeClock in the wallet encryption derivation benchmark loop and adds a special case: if elapsed_time <= 0s, it sets master_key.nDeriveIterations to CMasterKey::DEFAULT_DERIVE_ITERATIONS and breaks. NodeClock is mockable in tests, so a mocked clock can return identical start/end times, yielding zero elapsed time. Without this guard, the subsequent division target_iterations = nDeriveIterations * target_time / elapsed_time would divide by zero. The change prevents undefined behavior / floating/integer division issues under mocked time and makes benchmarks deterministic.
Changed components
src/wallet/wallet.cppCMasterKey encryption derivation benchmarkNodeClock / SteadyClock time measurementInspect captured patch +8 / −2
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 782667cc..dae37e05 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -584,9 +584,15 @@ static bool EncryptMasterKey(const SecureString& wallet_passphrase, const CKeyin
// Get the weighted average of iterations we can do in 100ms over 2 runs.
for (int i = 0; i < 2; i++){
- auto start_time{SteadyClock::now()};
+ auto start_time{NodeClock::now()};
crypter.SetKeyFromPassphrase(wallet_passphrase, master_key.vchSalt, master_key.nDeriveIterations, master_key.nDerivationMethod);
- auto elapsed_time{SteadyClock::now() - start_time};
+ auto elapsed_time{NodeClock::now() - start_time};
+
+ if (elapsed_time <= 0s) {
+ // We are probably in a test with a mocked clock.
+ master_key.nDeriveIterations = CMasterKey::DEFAULT_DERIVE_ITERATIONS;
+ break;
+ }
// target_iterations : elapsed_iterations :: target_time : elapsed_time
unsigned int target_iterations = master_key.nDeriveIterations * target_time / elapsed_time;
Why this scored 18/100
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