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Match Monero 0.17.2.3 decoy selection algo

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j-berman 2021-09-03 19:04:17 -07:00 committed by Lee *!* Clagett
parent 73fd14a53f
commit a9794d39b8
2 changed files with 22 additions and 7 deletions
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27
src/util/gamma_picker.cpp
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@ -40,6 +40,8 @@ namespace lws
constexpr const double gamma_shape = 19.28;
constexpr const double gamma_scale = 1 / double(1.61);
constexpr const std::size_t blocks_in_a_year = (86400 * 365) / DIFFICULTY_TARGET_V2;
constexpr const std::size_t defaut_unlock_time = CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE * DIFFICULTY_TARGET_V2;
constexpr const std::size_t recent_spend_window = 50 * DIFFICULTY_TARGET_V2;
}
gamma_picker::gamma_picker(std::vector<uint64_t> rct_offsets)
@ -49,7 +51,7 @@ namespace lws
gamma_picker::gamma_picker(std::vector<std::uint64_t> offsets_in, double shape, double scale)
: rct_offsets(std::move(offsets_in)),
gamma(shape, scale),
outputs_per_second(0)
seconds_per_output(0)
{
if (!rct_offsets.empty())
{
@ -59,8 +61,11 @@ namespace lws
const std::size_t outputs_to_consider = rct_offsets.back() - initial;
static_assert(0 < DIFFICULTY_TARGET_V2, "block target time cannot be zero");
// match wallet2's integer truncation implementation to avoid creating distinct anonymity puddles
// this assumes constant target over the whole rct range
outputs_per_second = outputs_to_consider / double(DIFFICULTY_TARGET_V2 * blocks_to_consider);
seconds_per_output = DIFFICULTY_TARGET_V2 * blocks_to_consider / outputs_to_consider;
if (seconds_per_output == 0)
seconds_per_output = double(DIFFICULTY_TARGET_V2 * blocks_to_consider) / outputs_to_consider;
}
}
@ -84,17 +89,27 @@ namespace lws
static_assert(std::is_empty<crypto::random_device>(), "random_device is no longer cheap to construct");
static constexpr const crypto::random_device engine{};
const auto end = offsets().end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE;
const uint64_t num_rct_outputs = spendable_upper_bound();
for (unsigned tries = 0; tries < 100; ++tries)
{
std::uint64_t output_index = std::exp(gamma(engine)) * outputs_per_second;
if (offsets().back() <= output_index)
double output_age_in_seconds = std::exp(gamma(engine));
// match wallet2 implementation to avoid creating distinct anonymity pools
// shift output back by unlock time to apply distribution from chain tip
if (output_age_in_seconds > defaut_unlock_time)
output_age_in_seconds -= defaut_unlock_time;
else
output_age_in_seconds = crypto::rand_idx(recent_spend_window);
std::uint64_t output_index = output_age_in_seconds / seconds_per_output;
if (num_rct_outputs <= output_index)
continue; // gamma selected older than blockchain height (rare)
output_index = offsets().back() - 1 - output_index;
output_index = num_rct_outputs - 1 - output_index;
const auto selection = std::lower_bound(offsets().begin(), end, output_index);
if (selection == end)
continue; // gamma selected within locked/non-spendable range (rare)
throw std::runtime_error{"Unable to select random output - output not found"};
const std::uint64_t first_rct = offsets().begin() == selection ? 0 : *(selection - 1);
const std::uint64_t n_rct = *selection - first_rct;

2
src/util/gamma_picker.h
View file

@ -36,7 +36,7 @@ namespace lws
{
std::vector<uint64_t> rct_offsets;
std::gamma_distribution<double> gamma;
double outputs_per_second;
double seconds_per_output;
gamma_picker(const gamma_picker&) = default; // force explicit usage of `clone()` to copy.
public: