The data provider for the digital asset market Coinmetrics published a report entitled “Do not trust, verify: Bitcoin Private Example”, which analyzed the anonymous cryptocurrency resulting from the merger of Bitcoin and ZClassic blockchains and created to restore activity in the ZClassic community.
While the announced issue of Bitcoin Private is limited to 21 million coins, like Bitcoin, Coinmetrics managed to find out that additional “2.04m additional units were covertly minted during the import of the Bitcoin UTXOs and sent to the BTCP shielded pool” . Because of these actions, the real BTCP emission limit has increased to 22.6 million coins.
According to Coinmetrics, the additional issue of BTCP has become a violation of the provisions outlined in the white paper cryptocurrency and in the announcement on Bitcointalk, according to which 21 million coins can be issued to the maximum, and the possibility of their premine is excluded.
Coinmetrics analysts drew attention to the problem when they detected discrepancies between the data on the number of BTCP coins in circulation, obtained by their node, at 20.841 million (excluding coins in the hidden pool) and the declared volume of 20.607 million.
Having this information, the authors of the report made several assumptions:
- Our node is not on the correct chain – someone is somehow feeding our node garbage
- There’s a bug in the gettxoutsetinfo code
- The mining reward changed since the publication of the whitepaper making our original estimate wrong
- Zk-snarks have been broken and someone is minting BTCP in the shielded pool
- There was a hidden premine
As analysts explain, in the process of implementing the fork and importing unspent transaction outputs into the Bitcoin Private network, “special blocks” were issued, which contained 400 additional outputs for 50 units of cryptocurrency each. A total of 102 such blocks were detected, which in total gives 2,040,000 BTCP above the stated emission limit.
According to Coinmetrics, the coins thus mined were sent to protected addresses on April 29, 2018, and about 300,000 BTCP were issued from July 11 to August 18. According to the authors of the report, the sale of these coins on the market could bring developers from $ 1 million to $ 3 million. The remaining 1.74 million BTCP, moved to protected addresses, still remain there.
It is curious that only 15% of the available coins were “activated” in the BTCP network, Coinmetrics note. Thus, a significant proportion of BTCPs in circulation today may fall on the part of the premine that was liquidated by the organizers. According to analysts, in the fork process, 3.12 million BTCP were requested by the holders of the original cryptocurrency. Accordingly, 300,000 BTCPs issued by developers over and above the established limit amount to 9.5% of all Bitcoin Private coins in circulation. “For every 10 BTCPs in wallets, 0.95 BTCPs received during the Premine are accounted for,” the publication says.
The implementation of this kind of scam was made possible due to the intricate process of the fork based on the blockchain of the two cryptocurrencies, which, in fact, forced users to exert excessive trust in the developers.
The process of auditing Bitcoin Private fork really involved community members who were provided with the necessary tools and files. They were able to verify that “each of these files displayed the contents of the imported blocks”, but did not have the opportunity to learn about the presence of additional transaction outputs.