simplewallet: plug a timing leak

As reported by Tramèr et al, timing of refresh requests can be used
to see whether a password was requested (and thus at least one output
received) since this will induce a delay in subsequent calls.
To avoid this, we schedule calls at a given time instead of sleeping
for a set time (which would make delays additive).
To further avoid a scheduled call being during the time in which a
password is prompted, the actual scheduled time is now randomized.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/simplewallet/simplewallet.h b/src/simplewallet/simplewallet.h
index e8f96ad54..75bd893d5 100644
--- a/src/simplewallet/simplewallet.h
+++ b/src/simplewallet/simplewallet.h
@@ -448,10 +448,12 @@ namespace cryptonote
     std::atomic<bool> m_locked;
     std::atomic<bool> m_in_command;
 
+    template<uint64_t mini, uint64_t maxi> struct get_random_interval { public: uint64_t operator()() const { return crypto::rand_range(mini, maxi); } };
+
     epee::math_helper::once_a_time_seconds<1> m_inactivity_checker;
-    epee::math_helper::once_a_time_seconds<90> m_refresh_checker;
-    epee::math_helper::once_a_time_seconds<90> m_mms_checker;
-    epee::math_helper::once_a_time_seconds<90> m_rpc_payment_checker;
+    epee::math_helper::once_a_time_seconds_range<get_random_interval<80 * 1000000, 100 * 1000000>> m_refresh_checker;
+    epee::math_helper::once_a_time_seconds_range<get_random_interval<90 * 1000000, 110 * 1000000>> m_mms_checker;
+    epee::math_helper::once_a_time_seconds_range<get_random_interval<90 * 1000000, 115 * 1000000>> m_rpc_payment_checker;
     
     std::atomic<bool> m_need_payment;
     boost::posix_time::ptime m_last_rpc_payment_mining_time;