diff options
| -rw-r--r-- | src/wallet/wallet2.cpp | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/wallet/wallet2.cpp b/src/wallet/wallet2.cpp index 133db6c2a..6bff04797 100644 --- a/src/wallet/wallet2.cpp +++ b/src/wallet/wallet2.cpp @@ -144,6 +144,9 @@ using namespace cryptonote; #define IGNORE_LONG_PAYMENT_ID_FROM_BLOCK_VERSION 12 +#define DEFAULT_UNLOCK_TIME (CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE * DIFFICULTY_TARGET_V2) +#define RECENT_SPEND_WINDOW (50 * DIFFICULTY_TARGET_V2) + static const std::string MULTISIG_SIGNATURE_MAGIC = "SigMultisigPkV1"; static const std::string MULTISIG_EXTRA_INFO_MAGIC = "MultisigxV1"; @@ -1028,6 +1031,34 @@ uint64_t gamma_picker::pick() { double x = gamma(engine); x = exp(x); + + if (x > DEFAULT_UNLOCK_TIME) + { + // We are trying to select an output from the chain that appeared 'x' seconds before the + // current chain tip, where 'x' is selected from the gamma distribution recommended in Miller et al. + // (https://arxiv.org/pdf/1704.04299/). + // Our method is to get the average time delta between outputs in the recent past, estimate the number of + // outputs 'n' that would have appeared between 'chain_tip - x' and 'chain_tip', select the real output at + // 'current_num_outputs - n', then randomly select an output from the block where that output appears. + // Source code to paper: https://github.com/maltemoeser/moneropaper + // + // Due to the 'default spendable age' mechanic in Monero, 'current_num_outputs' only contains + // currently *unlocked* outputs, which means the earliest output that can be selected is not at the chain tip! + // Therefore, we must offset 'x' so it matches up with the timing of the outputs being considered. We do + // this by saying if 'x` equals the expected age of the first unlocked output (compared to the current + // chain tip - i.e. DEFAULT_UNLOCK_TIME), then select the first unlocked output. + x -= DEFAULT_UNLOCK_TIME; + } + else + { + // If the spent time suggested by the gamma is less than the unlock time, that means the gamma is suggesting an output + // that is no longer feasible to be spent (possible since the gamma was constructed when consensus rules did not enforce the + // lock time). The assumption made in this code is that an output expected spent quicker than the unlock time would likely + // be spent within RECENT_SPEND_WINDOW after allowed. So it returns an output that falls between 0 and the RECENT_SPEND_WINDOW. + // The RECENT_SPEND_WINDOW was determined with empirical analysis of observed data. + x = crypto::rand_idx(static_cast<uint64_t>(RECENT_SPEND_WINDOW)); + } + uint64_t output_index = x / average_output_time; if (output_index >= num_rct_outputs) return std::numeric_limits<uint64_t>::max(); // bad pick |