Read more about k-anonymity [here](https://en.wikipedia.org/wiki/K-anonymity). We implement this feature in the monero daemon for transactions
by providing a "Txid Template", which is simply a txid with all but `num_matching_bits` bits zeroed out, and the number `num_matching_bits`. We add an operation to `BlockchainLMDB` called
`get_txids_loose` which takes a txid template and returns all txids in the database (chain and mempool) that satisfy that template. Thus, a client can
ask about a specific transaction from a daemon without revealing the exact transaction they are inquiring about. The client can control the statistical
chance that other TXIDs (besides the one in question) match the txid template sent to the daemon up to a power of 2. For example, if a client sets their `num_matching_bits`
to 5, then statistically any txid has a 1/(2^5) chance to match. With `num_matching_bits`=10, there is a 1/(2^10) chance, so on and so forth.
Co-authored-by: ACK-J <60232273+ACK-J@users.noreply.github.com>
Implements view tags as proposed by @UkoeHB in MRL issue
https://github.com/monero-project/research-lab/issues/73
At tx construction, the sender adds a 1-byte view tag to each
output. The view tag is derived from the sender-receiver
shared secret. When scanning for outputs, the receiver can
check the view tag for a match, in order to reduce scanning
time. When the view tag does not match, the wallet avoids the
more expensive EC operations when deriving the output public
key using the shared secret.
It avoids dividing by 8 when deserializing a tx, which is a slow
operation, and multiplies by 8 when verifying and extracing the
amount, which is much faster as well as less frequent
If an invalid input type were to get to this, the code could
remove key images that might be present already in the chain,
which could allow a double spend, even if this is impossible
with the current code.
Reported by KeyboardWarrior.
There are quite a few variables in the code that are no longer
(or perhaps never were) in use. These were discovered by enabling
compiler warnings for unused variables and cleaning them up.
In most cases where the unused variables were the result
of a function call the call was left but the variable
assignment removed, unless it was obvious that it was
a simple getter with no side effects.
These are functions that check whether a tx is in the db, so whether
it is there or not is really not interesting, and it seems to scare
people from time to time
On startup, it checks against the difficulty checkpoints, and if any mismatch is found, recalculates all the blocks with wrong difficulties. Additionally, once a week it recalculates difficulties of blocks after the last difficulty checkpoint.
- New flag in NOTIFY_NEW_TRANSACTION to indicate stem mode
- Stem loops detected in tx_pool.cpp
- Embargo timeout for a blackhole attack during stem phase
If a db resize happened, the txpool meta cursor might be stale,
and was not being renewed when necessary.
It would cause this SEGSEGV:
in mdb_cursor_set ()
in mdb_cursor_get ()
in cryptonote::BlockchainLMDB::get_txpool_tx_blob(crypto::hash const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, cryptonote::relay_category) const ()
in cryptonote::tx_memory_pool::get_transaction(crypto::hash const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, cryptonote::relay_category) const ()
in cryptonote::t_cryptonote_protocol_handler<cryptonote::core>::handle_notify_new_fluffy_block(int, epee::misc_utils::struct_init<cryptonote::NOTIFY_NEW_FLUFFY_BLOCK::request_t>&, cryptonote::cryptonote_connection_context&) ()
