Can a Blockchain Reorg Reverse Your Crypto Transaction? What Ravencoin Users Should Know

A blockchain transaction can show as confirmed and still disappear later if the network undergoes a sufficiently deep reorganization. Ravencoin users are facing exactly that possibility after a consensus exploit left several days of the blockchain potentially reversible. Ravencoin warned that transactions confirmed after block 4,487,775 should currently be considered at risk. Mining pools 2Miners and RavenMiner are building a competing chain that excludes the exploited branch beginning at block 4,487,776. If that chain becomes dominant, Ravencoin said the resulting reorganization could span approximately three days. For users, the important question is no longer simply how the vulnerability worked. It is what happens to a payment, deposit or withdrawal that already appeared to be confirmed. Can a blockchain reorg reverse a transaction?Yes. A blockchain reorganization, usually shortened to a “reorg,” happens when nodes replace part of their current blockchain history with a competing chain that the network ultimately accepts as canonical. Short reorgs can happen naturally on proof-of-work networks when miners temporarily produce competing blocks. A deep reorg is much more disruptive because multiple blocks, and potentially hours or days of transactions, can be removed from the accepted chain. In Ravencoin's case, the proposed recovery chain starts immediately before the first known invalid block on Aug. 7. If it overtakes the exploited branch, blocks that users previously saw as confirmed could become orphaned. (Source: Medium) That does not mean coins literally disappear. Instead, the blockchain's accepted transaction history changes. What happens to transactions after a reorg?An orphaned transaction has several possible outcomes. The simplest outcome is that the transaction returns to the network's mempool, where it waits to be included in another block. A miner could then confirm the same payment on the new chain, making the disruption largely temporary. But this is not guaranteed. Ravencoin specifically warned that some affected transactions may return to mempools and be mined again while others may not. A transaction could also conflict with another transaction on the replacement chain. This is one reason deep reorgs create double-spend risks: something that appeared settled on one version of blockchain history may no longer be settled once another version becomes authoritative. Users should therefore avoid assuming that an old transaction will simply reappear automatically. Why are exchanges suspending Ravencoin deposits and withdrawals?Deep reorgs are particularly dangerous for exchanges because exchanges often credit customer accounts after waiting for a predefined number of blockchain confirmations. Suppose a user deposits RVN, waits for the exchange to credit the deposit and then trades or withdraws another asset. If the original RVN deposit later disappears because of a reorg, the exchange may have already allowed value to leave its platform despite no longer possessing the corresponding RVN. This is why confirmation requirements exist in the first place.