wallet: include a suggested number of confirmations based on amount

This is based on how much an attacking miner stands to lose in block
rewardy by mining a private chain which double spends a payment.
This is not foolproof, since mining is based on luck, and breaks
down as the attacking miner nears 50% of the network hash rate,
and the estimation is based on a constant block reward.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/simplewallet/simplewallet.cpp b/src/simplewallet/simplewallet.cpp
index 24c42a597..a64936e4f 100644
--- a/src/simplewallet/simplewallet.cpp
+++ b/src/simplewallet/simplewallet.cpp
@@ -7408,8 +7408,12 @@ bool simple_wallet::show_transfer(const std::vector<std::string> &args)
       if (pd.m_unlock_time < CRYPTONOTE_MAX_BLOCK_NUMBER)
       {
         uint64_t bh = std::max(pd.m_unlock_time, pd.m_block_height + CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE);
+        uint64_t last_block_reward = m_wallet->get_last_block_reward();
+        uint64_t suggested_threshold = last_block_reward ? (pd.m_amount + last_block_reward - 1) / last_block_reward : 0;
         if (bh >= last_block_height)
           success_msg_writer() << "Locked: " << (bh - last_block_height) << " blocks to unlock";
+        else if (suggested_threshold > 0)
+          success_msg_writer() << std::to_string(last_block_height - bh) << " confirmations (" << suggested_threshold << " suggested threshold)";
         else
           success_msg_writer() << std::to_string(last_block_height - bh) << " confirmations";
       }