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fix decoy selection off-by-1

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Justin Berman 2023-04-22 17:35:59 -07:00 committed by GitHub
parent 153a153460
commit 8b93274c43
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 11 additions and 3 deletions
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14
src/util/gamma_picker.cpp
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@ -68,14 +68,21 @@ namespace lws
bool gamma_picker::is_valid() const noexcept
{
return CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE < rct_offsets.size();
static_assert(CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE > 0);
return CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE - 1 < rct_offsets.size();
}
std::uint64_t gamma_picker::spendable_upper_bound() const noexcept
{
if (!is_valid())
return 0;
return *(rct_offsets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE - 1);
return *(rct_offsets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE);
/* Assume block indexes: [0, 1, ..., n-2, n-1]
where n is the number of blocks in the chain
A user can spend an output starting in block index n - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE
The total number of spendable outputs is the cumulative count stored at that block
rct_offsets.end() points to index n
Therefore we need to return index rct_offets.end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE */
}
std::uint64_t gamma_picker::operator()()
@ -85,7 +92,8 @@ 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;
static_assert(CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE > 0);
const auto end = offsets().end() - CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE + 1;
const uint64_t num_rct_outputs = spendable_upper_bound();
for (unsigned tries = 0; tries < 100; ++tries)