One of the world’s largest exchanges, Binance, was hacked. According to an official statement, about $41 million worth Bitcoin [7,000 BTC] was lost in this hack. According to CZ, the hackers were careful and patient in executing the hack, which let them get access and details to multiple user accounts. All the Bitcoins gathered from these accounts were sent out in one transaction.
A very small percentage of the Twitter community suggested that CZ could reorg [chain reorganization] the Bitcoin network to recover those stolen BTCs. Jeremy Rubin tweeted,
@cz_binance if you reveal your private keys for the hacked coins (or a subset of them) you can decentralized-ly at zero cost to you, coordinate a reorg to undo the theft.
— Jeremy Rubin (@JeremyRubin) May 8, 2019
A few hours later, in a previously scheduled AMA, CZ addressed this tweet and said that he would consider doing a reorg. Subsequently, most people in the community objected to a reorg. Subsequently, CZ tweeted that he would not be going forward with the reorg idea.
What is a ‘Reorg?’
According to Bitcoin forums, “A blockchain reorganize (or reorg) happens when one chain becomes longer than the one you are currently working on. All of the blocks in the old chain that are not in the new one become orphan blocks, and their generations are invalidated. Transactions that use the newly invalid generated coins also become invalid.”
In this hypothetical scenario, CZ/Binance would incentivize gathered miners/mining pool by paying them BTCs to reorg the chain, i.e, manually create a second chain and invalidate the chain which recorded transactions of the hackers.
A Brief History of Bitcoin’s reorgs
There are have been other instances in Bitcoin’s history where reorgs have reared their heads,
- August 15, 2010: Value Overflow/Integer Overflow Bug caused the software to think that the transaction contained only a small amount of BTC, while in reality the outputs together had thousands of times more than the 21 million that should ever exist. A new version of the Bitcoin software had to be published, the blockchain was forked, and a new, valid chain overtook the old one at block 74691 – 53 blocks after the original fork.
- March 11, 2013: When Bitcoin upgraded from version 0.7 to 0.8, it caused the chain to split into two and the chain went on until 25 blocks. The reorg was spotted and reverted back. This is considered as the biggest reorg in Bitcoin history.
- August 2016: Reorg was suggested by many in the community when Bitfinex suffered a hack of 120,000 BTC. However, the reorg suggestion failed.
Can Binance execute a successful reorg?
The reorg to recover the stolen or hacked funds gets more expensive as more blocks are mined after the hack. Moreover, the reorg also depends on the incentives the miners need to receive, which in turn, depends on the mining reward. Additionally, the security model of Bitcoin rests on economic incentives which prevent miners from working on large reorgs. Further, these economic incentives tend to cease when the possibility of gain is much higher than the usual miner rewards, and if this was possible,
- it would require massive hashrate to execute a reorg.
- it would put a dent on/in Bitcoin “decentralized” network.
Due to these reasons, the community opposed the reorg of the Bitcoin network and it is the same reason why the community is set against reorg for Binance’s loss of 7,000 BTCs. Also, organizing a cumulative hash power of 51% or higher is easier said than done. Jimmy Song, a well-known Bitcoin developer, put out a thread on Twitter detailing how expensive and tedious a reorg would be.
1/ Back of the envelope math for doing a 58 block reorg (current confirmations for the tx that took money from binance):
Minimal cost: 58 * 12.5 btc = 725 BTC (assumes every miner would get roughly the same tx fees in the new chain and that 100% of miners go with this scheme)
— Jimmy Song (송재준) (@jimmysong) May 8, 2019
Assuming that CZ would be able to gather the hashrate required for the reorg, he would still need to make sure that every miner is informed and coordinated to know which “new” block to build on, which otherwise, would risk eruption of many chains. According to Song, it would take CZ/Binance 24 hours or 144 blocks to arrange for the hash power. Others were more pessimistic, with some even suggesting that reorging is only theoretically possible and under the present circumstances, it would take more than at least 75% of the hash power to even begin the reorg.
The hacked transaction was witnessed in block 575,012, whereas at press time, the ongoing block was 575,114, i.e., a difference of 102 blocks.
Even if he managed the above, the reorg would also face a challenge as the hackers could sweeten the deal for miners and thus, prevent the reorg from happening. Plus, it wouldn’t be economic for CZ.
The bottom line is, even if the reorg took place successfully, the idea of a “decentralized and immutable network” would be lost forever. Additionally, every exchange could undergo a reorg, if hacked, which would also destroy the chances of Bitcoin becoming a “store of value.”
Crypto Community Reacts
People from all around the crypto community, from Peter Wuille and Vitalik Buterin to Mike Novogratz, voiced their opinion on CZ’s idea to reorg the Bitcoin network. Most of the people in the community were outraged by the idea of a reorg. However, CZ clarified in subsequent tweets that reorg was an outlandish idea and that the exchange would not consider it.
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