Ethereum Traditional (ETC) is at the moment being 51% attacked


On 1/5/2019, Coinbase detected a deep chain reorganization of the Ethereum Traditional blockchain that included a double spend. With a view to defend buyer funds, we instantly paused interactions with the ETC blockchain.

Up to date Jan. 7, 10:27pm PT: Subsequent to this occasion, we detected 12 further reorganizations that included double spends, totaling 219,500 ETC (~$1.1M).

We are going to proceed to observe the standing of the community and replace this text with the latest data we have now. Present ETC community standing may be discovered here.

Background Data

Web page three of Satoshi Nakamoto’s whitepaper, Bitcoin: A Peer-to-Peer Digital Money System, states the next:

“If a majority of CPU energy is managed by sincere nodes, the sincere chain will develop the quickest and outpace any competing chains.”

The “sincere[y]” of greater than half of miners is a core requirement for the safety of Bitcoin and any proof-of-work cryptocurrencies primarily based on Bitcoin. Trustworthy motion, on this context, means following the habits described within the Bitcoin white paper. That is typically described as a “safety danger” or “assault vector,” however is extra precisely described as a recognized limitation to the proof-of-work mannequin.

Failure to satisfy this requirement breaks a number of core ensures of the Bitcoin protocol, together with the irreversibility of transactions. Many different cryptocurrencies, reminiscent of Ethereum Traditional, have additionally adopted proof-of-work mining.

The perform of mining is so as to add transactions to the common, shared transaction historical past, often known as the blockchain. That is achieved by producing blocks, that are bundles of transactions, and defining the canonical historical past of transactions because the longest chain of blocks*. If a single miner has extra assets than the whole thing of the remainder of the community, this miner may choose an arbitrary earlier block from which to increase an alternate block historical past, ultimately outpacing the block historical past produced by the remainder of the community and defining a brand new canonical transaction historical past.

That is known as a “chain reorganization,” or “reorg” for brief. All reorgs have a “depth,” which is the variety of blocks that have been changed, and a “size,” which is the variety of new blocks that did the changing.

This, by itself, may find yourself being nothing greater than a minor inconvenience. In any case, the transactions all nonetheless exist, however they could have been put into a special order, maybe delaying a few of them. Nevertheless, think about a miner who additionally owns numerous cash. The miner may ship these cash to a service provider in a transaction, T, whereas additionally secretly extending an alternate block historical past. The miner’s secret blocks don't embrace T, however quite embrace a transaction that sends the identical cash utilized in T to a special tackle. Name that transaction T’. When the miner reveals this secret historical past, it should comprise T’, not T. As a result of T and T’ tried to ship the identical cash and T’ is now within the canonical historical past, which means that T is ceaselessly invalid, and the recipient of the cash despatched in transaction T by no means even acquired them within the new, now-canonical historical past. Extra data on this may be discovered here.

What we noticed

Up to date Jan. 7, 10:27pm PT.

We noticed repeated deep reorganizations of the Ethereum Traditional blockchain, most of which contained double spends. The whole worth of the double spends that we have now noticed up to now is 219,500 ETC (~$1.1M).

Timeline of occasions

  • Late on the night of Saturday 1/5, our methods alerted us to a deep reorg in ETC that contained a double spend. Our on-call engineers responded to the alert and labored to verify the report by way of the night time. We decided that we'd briefly halt ship/obtain interplay with the ETC blockchain in an effort to safeguard buyer funds.
  • This meant that prospects who tried to ship or obtain ETC on Coinbase Shopper or Professional have been unable to finish their transactions.
Prospects who tried to ship or obtain ETC on Coinbase Shopper or Professional have been unable to finish their transactions beginning early Sunday morning, Pacific Time.
  • On the morning of Sunday 1/6 we posted an replace on standing.coinbase.com stating (that) “On account of unstable community situations on the Ethereum Traditional community, we have now briefly disabled all sends and receives for ETC. Purchase and promote isn't impacted. All different methods are working usually.”
Along with in-platform notifications, we shared an replace by way of standing.coinbase.com.
  • We carried out an evaluation on Sunday afternoon/night to verify the sample and decide the important thing particulars of the double-spend assaults. Starting Sunday afternoon, we noticed eight extra incidents, all containing double spends.
  • Out of an abundance of warning, we didn't put up a weblog put up previous to authorized and technical overview. A false alarm may have inadvertently triggered market instability.
  • On Monday 1/7 morning after authorized and technical overview, we finalized our public evaluation and posted to our weblog and social media accounts.

Be aware: A full blockchain evaluation is past the scope of this text. Additional analysis into the addresses sending the double spend transactions, the historical past of sends/receives from the addresses, the block fields reminiscent of timestamp, and the next motion of miner rewards from assault blocks could make clear the menace actor or actors behind these assaults.

We noticed the next deep chain reorgs:

  • Frequent ancestor: 7245623. Depth 4 / Length 7. No double spends have been noticed on this reorg. We famous that this was a reorg of surprising depth for ETC.
  • Frequent ancestor: 7248488. Depth 5 / Length 6. No double spends have been noticed on this reorg. We famous {that a} second reorg of surprising depth was extremely suspicious, however didn't mandatory point out an assault as there was no double spend and the depth was nonetheless beneath the ETC affirmation restrict for many providers.
  • Frequent ancestor: 7249343. Depth 57 / Length 74. A transaction of worth 600 ETC in orphaned block 7249357 was double spent by a transaction in attacker block 7249361**.

We ceased interacting with the ETC blockchain upon observing this reorg. Coinbase was not the goal of this double spend and no funds have been misplaced.

Updates as of 10:27pm PT, January 7

  • Frequent ancestor: 7261497. Depth 44 / Size 54. A transaction of worth 26,000 ETC in orphaned block 7261492 was double spent by a transaction in attacker block 7261497**.
  • Frequent ancestor: 7261603. Depth 35 / Size 44. A transaction of worth 52,800 ETC in orphaned block 7261610 was double spent by a transaction in attacker block 7261614**.
  • Frequent ancestor: 7261647. Depth 8 / Length 9. No double spends have been noticed on this reorg.
  • Frequent ancestor: 7261676. Depth 37 / Length 47. A transaction of worth 52,200 ETC in orphaned block 7261684 was double spent by a transaction in attacker block 7261690**.

Subsequent Steps

The Coinbase crew is at the moment evaluating the security of re-enabling sends and receives of Ethereum Traditional and can talk to our prospects what to anticipate relating to assist for ETC. Coinbase takes safety very severely. As a part of that dedication, we monitor blockchains for exercise that could possibly be dangerous to our prospects and take immediate motion to safeguard funds. We wish to emphasize to prospects that Coinbase strives to be essentially the most trusted and most secure place to purchase, promote, or retailer cryptocurrency.

* It's truly the chain with essentially the most accrued work, quite than the chain with essentially the most blocks, that defines the canonical historical past. Usually, these chains would be the identical

** The block explorer doesn't correctly deal with reorgs and labels the transaction as confirmed. Click on on the block to see that the block is orphaned.

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Except in any other case famous, all pictures supplied herein are by Coinbase.

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