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Diffstat (limited to 'src/cryptonote_basic/cryptonote_basic_impl.h')
-rw-r--r-- | src/cryptonote_basic/cryptonote_basic_impl.h | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/src/cryptonote_basic/cryptonote_basic_impl.h b/src/cryptonote_basic/cryptonote_basic_impl.h index 984bee19f..53dbc47d7 100644 --- a/src/cryptonote_basic/cryptonote_basic_impl.h +++ b/src/cryptonote_basic/cryptonote_basic_impl.h @@ -112,6 +112,41 @@ namespace cryptonote { bool operator ==(const cryptonote::transaction& a, const cryptonote::transaction& b); bool operator ==(const cryptonote::block& a, const cryptonote::block& b); + + /************************************************************************/ + /* K-anonymity helper functions */ + /************************************************************************/ + + /** + * @brief Compares two hashes up to `nbits` bits in reverse byte order ("LMDB key order") + * + * The comparison essentially goes from the 31th, 30th, 29th, ..., 0th byte and compares the MSBs + * to the LSBs in each byte, up to `nbits` bits. If we use up `nbits` bits before finding a + * difference in the bits between the two hashes, we return 0. If we encounter a zero bit in `ha` + * where `hb` has a one in that bit place, then we reutrn -1. If the converse scenario happens, + * we return a 1. When `nbits` == 256 (there are 256 bits in `crypto::hash`), calling this is + * functionally identical to `BlockchainLMDB::compare_hash32`. + * + * @param ha left hash + * @param hb right hash + * @param nbits the number of bits to consider, a higher value means a finer comparison + * @return int 0 if ha == hb, -1 if ha < hb, 1 if ha > hb + */ + int compare_hash32_reversed_nbits(const crypto::hash& ha, const crypto::hash& hb, unsigned int nbits); + + /** + * @brief Make a template which matches `h` in LMDB order up to `nbits` bits, safe for k-anonymous fetching + * + * To be more technical, this function creates a hash which satifies the following property: + * For all `H_prime` s.t. `0 == compare_hash32_reversed_nbits(real_hash, H_prime, nbits)`, + * `1 > compare_hash32_reversed_nbits(real_hash, H_prime, 256)`. + * In other words, we return the "least" hash nbit-equal to `real_hash`. + * + * @param nbits The number of "MSB" bits to include in the template + * @param real_hash The original hash which contains more information than we want to disclose + * @return crypto::hash hash template that contains `nbits` bits matching real_hash and no more + */ + crypto::hash make_hash32_loose_template(unsigned int nbits, const crypto::hash& real_hash); } bool parse_hash256(const std::string &str_hash, crypto::hash& hash); |