Yesterday, I came across a statement by Etherealize co-founder Grant Hammer: they say, for a 51% attack on Bitcoin today, only $8 billion is needed, and when this bar drops to $ 2 billion, prepare for a real catastrophe. At first I thought, "Mmm... seriously?" I decided to Google where these numbers came from, and that's what I found out.:

✴️ #BTC #crypto

, Real cases of 51% attacks

Ethereum Classic (January 2019)

– The hacker organized a series of reorganizations of the ETC blockchain, double spending amounted to 219,500 ETC (~$1.1 million) (neptunemutual.com , CoinMarketCap).

– The Coinbase exchange stopped trading after deep "rollbacks" of the 11-block chain (WIRED).

Ethereum Classic (August 2020)

– Three more attacks on ETC, the total amount of double spending is $5.6 million (CoinMarketCap).

Bitcoin Gold (May 2018)

– The attacker rented the hashrate through NiceHash, as a result, 388,000 BTG (~$18 million) was stolen from exchanges (en.wikipedia.org ).

Bitcoin Gold (January 2020)

– A new wave of attacks on BTG with duplicates of transactions for $72,000 (en.wikipedia.org ).

Conclusion: even large Ethash and Equihash networks are vulnerable if someone is willing to invest hundreds of thousands of dollars in capacity rentals.

⚠️ Quantum computer: the next threat

– What can he do?

Bitcoin cryptography (ECDSA, SHA-256) will theoretically crack the quantum algorithms of Shor and Grover, finding the private key in hours or even minutes (ft.com ).

When should I wait?

Government projects (Google, IBM) promise "cryptographically relevant" quantum PCs by 2028-2030, and by 2035— a massive Q-computer capable of "declassifying" current algorithms (Sectigo® Official, ft.com ).

How are they prepared?

On August 13, 2024, NIST published FIPS 203-205 — the first standards for post-quantum cryptography (CRYSTALS-Dilithium, Kyber, SPHINCS+) (NIST Computer Security Resource Center).

By 2030, NIST recommends 

migrate from RSA/ECDSA to sustainable schemes, complete ban by 2035 (Sectigo® Official).

What does this mean for Bitcoin? 

we will have to introduce a soft fork with new cryptos or hybrid signatures (PoW + Post-Q) in order to preserve the privacy of addresses and incorruptibility.

, The result:

51%-attacks have already occurred on other networks and cost the attackers millions of dollars.

In theory, the threat of quantum hacking is real in 5-10 years.(I've been waiting for an announcement from Google about a quantum computer for 3 years now, but they always carry it over) 

Keep an eye not only on the price and hashrate, but also on the development of post-quantum solutions — this is the next frontier of Bitcoin security.