The Liquid Network said Sunday that purported white-hat hackers withdrew about 4,000 bitcoin, worth about $320 million, from the federation wallet that backs L-BTC. Bridge nodes were disabled, and the sidechain was paused. Other issued assets, including USDT, DePix and RWAs, were unaffected, the official account said on X.

The Liquid Network is a federated sidechain of Bitcoin, founded by Adam Back’s Blockstream. The Liquid chain issues a variety of assets such as LBTC, which it backs with BTC on the Bitcoin main chain, held in a large multisig of 15 corporate and known members. 11 of the 15 members need to sign a valid multi-signature transaction to move coins from the treasury. Before the hack, the treasury held over 4200 BTC; after the hack, Blockstream’s proof of reserves page reports a little over 207 BTC left. 

The hackers withdrew 4,019.4 BTC from the reserve address in a peg-out transaction using the SideSwap Peg-out Authorization Key. SideWap is a bridge exchange and a member of the Liquid Federation. While details on the mechanism of the hack are not confirmed yet, it appears an inflation bug on the LBTC side chain was exploited by the hackers to create over 4,000 LBTC that did not exist before, and cash them out for on-chain bitcoin from the federation. Because the transaction appeared as valid, given the consensus bug, the federation members’ HSM security servers signed the BTC withdrawal transaction, worth roughly 320 million at the time. 

The hacker moved the funds to an address ending in 6gyqjlte, from which they quickly signed a new transaction with a message on the OP_RETURN arbitrary data field saying “we are whitehats. contact us on chain.” Those coins were still at that address at the time of writing.

A small mainnet transaction to the hacker address followed by an OP_RETURN saying “Please contact [email protected]”, presumably from a Blockstream public address, though that remains unconfirmed. A later OP_RETURN spend from the hacker address carried “Please contact us on Signal @m671aw.70.” Because this transaction includes an input from the address holding the 4000 BTC hacked, the message must come from the hacker.

In response to the breach, exchanges were told to pause L-BTC deposits and withdrawals. Bridge nodes on the Liquid Network have been paused, limiting access to the side chain, which continues to produce blocks. 

JAN3 CEO Samson Mow said Aqua’s Liquid features were affected and that on-chain bitcoin still worked. Other wallets in the industry that use the Liquid Network are expected to be affected. Users holding LBTC now effectively have their savings at risk, since the underlying BTC is currently not redeemable. Given the private nature of the Liquid chain, user onchain analytics are scarce and not much public information is known about how much LBTC is held by retail users versus corporations of Blockstream itself. Nevertheless, should the funds not be returned, it would be a heavy blow to the Liquid Network’s user base.

Users of LBTC don’t have many options but to wait for conversations with the hackers to resolve. Given the size of the hack, it would be difficult for the hackers to get away with stealing all that bitcoin, though perhaps not impossible. What may happen is that the hackers ask for a finder’s fee and return the majority of the funds.