On December 10, 2024, Google announced the launch of its latest quantum computing chip — Willow.
The chip has 105 quantum bits (qubit) and has achieved best-in-class performance in quantum error correction and random circuit sampling.
Technical breakthroughs of the Willow chip
The Willow chip performed excellently in RCS benchmarks, completing a standard computation in under 5 minutes, whereas this computation would take more than 10²⁵ years to complete on the fastest supercomputers.
Hartmut Neven, head of quantum artificial intelligence at Google, pointed out that this timeframe exceeds the known time scales of physics, far surpassing the age of the universe.
Google CEO Sundar Pichai stated that Willow is an important step for the tech giant in creating a 'useful quantum computer' and is expected to have practical applications in areas such as drug discovery, fusion energy, and battery design.
The potential threat of quantum computing to Bitcoin
As quantum computing technology advances, concerns within the community about its potential threat to Bitcoin security have resurfaced.
Bitcoin relies on elliptic curve cryptography (ECDSA) and the SHA-256 hash algorithm to ensure network security.
In theory, quantum computing could use Shor's algorithm to break ECDSA and thus obtain private keys; breaking SHA-256 would require Grover's algorithm, which needs hundreds of millions of quantum bits.
Bitcoin entrepreneur Ben Sigman pointed out that breaking ECDSA requires millions of physical quantum bits, and the requirements for breaking SHA-256 are even higher, indicating that current quantum computing technology does not pose a direct threat to Bitcoin.
Satoshi Nakamoto's Bitcoin design and responses to quantum computing
The design of Bitcoin is adaptive, capable of addressing potential computational threats.
Sigman explained that if a quantum computer could compute SHA-256 faster than the current global mining hash power (750 exahash), assuming it could mine one block per minute, it would mine 6,300 Bitcoins in just 33 hours.
Subsequently, the mining difficulty would adjust back to the 10-minute target, reducing the mining efficiency of quantum computers.
Google's former senior product manager Kevin Rose also pointed out that breaking Bitcoin's encryption algorithm requires a quantum computer with about 13 million quantum bits, while the number of quantum bits in the Willow chip is far from sufficient.
The future of quantum computing and the security of Bitcoin
Avalanche founder Emin Gün Sirer further explained that while the progress in quantum computing is astounding, it does not currently threaten the security of crypto assets. Quantum computing will make some operations (like factoring) easier, but others (like reversing one-way hash functions) remain equally difficult. Additionally, the attack window for quantum computers is relatively small, complicating the work of quantum attackers.
However, Sirer also warned that there is a more pressing issue regarding the 1.1 million Bitcoins that Satoshi Nakamoto is estimated to hold. The Bitcoins mined early by Nakamoto used a very old payment-to-public-key (P2PK) format, which could expose the public key and give attackers time to exploit it.
Therefore, as the threat of quantum computing increases, the Bitcoin community may need to consider freezing Satoshi Nakamoto's coins, or more broadly, providing a sunset date to freeze all coins in P2PK UTXOs.
Conclusion
Satoshi Nakamoto foresaw this problem and proposed a solution. He believed that if SHA-256 were broken, a new start could be made through a consensus 'honest blockchain', locking in its state and continuing with a new hash function.
This flexible design allows Bitcoin to adapt to potential technological challenges that may arise in the future.