← writing · free 🪂
Published on Medium, 2018-05-28 · medium/@HusamABBOUD
A 51% attack is usually discussed as a ghost story. On Ethereum Classic in 2018, it was a business plan — and the numbers closed.
Proof-of-work security has a price, and the price is public. A chain is safe when the cost of a majority of its hashrate exceeds what an attacker can extract. For Bitcoin that cost is a sovereign budget. For Ethereum Classic in May 2018, it was a rental invoice.
ETC ran the same Ethash algorithm as Ethereum, at roughly 3% of Ethereum’s hashrate. Every Ethereum miner was, by definition, latent ETC attack capacity. And marketplaces like NiceHash would rent it by the hour — no warehouse, no hardware, no commitment.
| Input | Value (May 2018) |
|---|---|
| ETC network hashrate | ≈ 8.8 TH/s |
| Cost to rent a matching hashrate, per hour | ≈ US$ 3,800 |
| Hours needed for a deep reorganization | 1–4 |
| Double-spend capacity per pass (exchange limits) | US$ 1–10 M |
Rent the hashrate. Deposit ETC on an exchange. Sell it, withdraw, then publish your longer private chain — the deposit never happened, and you hold both the ETC and the proceeds. Cost of the attempt: a few thousand dollars an hour. Upside: seven figures. The asymmetry was the article.
Security is not a property of the ledger. It is a price, quoted hourly, and for ETC the price was wrong.
1) Rentable hashrate turns 51% attacks from capital expenditure into operating expense. 2) Chains that share an algorithm with a much larger sibling inherit that sibling’s idle capacity as a standing threat. 3) Exchange confirmation policies — not consensus — were the real security parameter, and they were set as if attacks were fiction.
In January 2019 Ethereum Classic was 51%-attacked. Deep reorganizations, roughly US$ 1.1 M double-spent, confirmed by Coinbase. The playbook was the one described eight months earlier. I take no pleasure in the accuracy — the point was that the math was public, and anyone could read it.
original: medium.com/@HusamABBOUD · …8fa0430a7c25