BIP-110 REPLAY ATTACK LOADED — BLAKE2B FORK TARGETS SEPT 1, OPT-IN PROTECTION LEAVES WALLETS EXPOSED

What a replay attack is, in one paragraph. When a chain splits, the same UTXOs exist on both networks. The owner controls corresponding coins on each chain with the same private key. If both networks accept the same transaction signature format, a signed transaction on Chain A is cryptographically valid on Chain B too. Another party can copy the transaction from A and broadcast it on B. Nobody stole the private key, nobody broke the crypto. The user created one authorization, and two chains recognized it. Coins move on both chains simultaneously.

The Sept 1 plan. Per Bitcoin.com’s coverage and Bitcoin Knots Discord discussions cited in the reporting: the fork would introduce a new sighash type valid on the RDTS minority chain but invalid under Bitcoin Core. That’s the mechanism. But it is opt-in — users have to deliberately use the new sighash via supporting wallet software or hardware-signing firmware. Ordinary transactions that don’t use the new sighash remain replayable across both chains. Automatic two-way protection is not on the design.

Mempool.space is already watching it happen on the stalled chain. Mononaut, Mempool.space developer, on X: “The overwhelming majority of these [BIP-110 minority chain] blocks are just replaying days-old transactions from the main chain.” The stalled BIP-110 chain sits at block 961,636 and is currently populated primarily by replayed transactions from the dominant Bitcoin chain, with no owner-consent. The BLAKE2b fork would formalize and accelerate this pattern with a chain that mines faster.

Why the protection is opt-in. Luke Dashjr, asked Aug 18 about replay protection for the proposed hard fork: “Replay protection was Spamcoin’s responsibility since it’s the airdrop altcoin.” His framing treats the BIP-110 minority network as Bitcoin and the ~97.5%-hashrate dominant chain as the breakaway that must protect itself. That framing controls the fork’s design decision. Mempolitics does not adopt or oppose it here — we report it because it is the reason the September 1 fork will not carry automatic replay protection and operators need to know exactly that.

The operator action list. For Bitcoin holders in the 12-day window before September 1:
1) Know your wallet. Does your wallet software or hardware signer implement the new sighash if you want to opt into the RDTS side? If you don’t care about RDTS, does your wallet let you sign in a way that’s explicitly Bitcoin-Core-only?
2) Know your exchange. Every custodial exchange will make its own fork policy: some will support the RDTS coin, some will ignore it, some will suspend deposits/withdrawals during the fork window. Coinbase, Kraken, and Bitfinex historically post public fork policies. Check yours.
3) Know your sighash. If you plan on-chain transactions in the September 1 window, understand which chain your signature is valid on. Ambiguous signatures = potential replay.
4) Splitting coins is possible but manual. A Bitcoin transaction containing data RDTS rejects creates an output on the dominant chain only. The reverse is possible under the proposed new sighash. Neither is automatic.
5) Not your keys, not your coins applies with double force in a contentious-fork window. Self-custody operators have full control over their sighash and their signing rules. Custodial holders are downstream of whatever their exchange decides.

The Technologist read. The protocol is doing what the protocol does: the network with hashrate, weight of work, longest chain, and economic recognition holds. BIP-110 peaked at 2.53% signaling. The minority chain stalled 8 hours after activation. That’s the market of security answering the design question. The BLAKE2b fork is a rhetorical restart that changes the PoW algorithm to bring in different miners. It doesn’t change the economic recognition question, and it doesn’t change the fact that from Sept 1 forward there will be two chains reading the same historical UTXO set until users manually split. The replay attack risk is the price of that design choice. Operators who know the primitive know what to do. The primitive still wins.