Bitcoin is staring down a quantum computing threat that could expose more than a third of its total supply. Google projects that encryption risks from quantum computers could materialize as early as 2029 — a timeline that puts the crypto industry on notice. The warning lands as the network's security model faces its most fundamental challenge since inception.
The 35% exposure
Roughly 35% of all Bitcoin ever mined sits in addresses whose public keys are already visible on the blockchain. That includes coins from early miners, old transactions, and reused addresses. A sufficiently powerful quantum computer could derive the private key from a public key, giving an attacker full control over those funds. The figure is not hypothetical — it's a count of coins in addresses that lack the protection of a hashed public key.
Google's 2029 projection
Google's internal research points to quantum computers breaking widely used public-key cryptography by 2029. That's sooner than many in the crypto space had assumed. The company's timeline is based on advances in error correction and qubit count, not on a single breakthrough. For Bitcoin, the clock is ticking: the network relies on the Elliptic Curve Digital Signature Algorithm, which is vulnerable to Shor's algorithm — a quantum algorithm that can factor large numbers and compute discrete logarithms efficiently.
What the industry faces
Bitcoin's design assumes that classical computers cannot reverse the one-way function of a public key. Quantum computers change that equation. The threat is not immediate — no existing quantum machine can run Shor's algorithm at the scale needed to break a Bitcoin key. But the trajectory is clear. The 2029 projection means the window for upgrading the network is narrow. A soft fork to introduce quantum-resistant signatures would require broad consensus among miners, developers, and node operators. That process takes years.
The timing isn't great. Bitcoin is still recovering from the market turbulence of early 2026, and the community is already debating other protocol changes. Adding a quantum-proof upgrade to the list could stretch resources and political capital thin.
For now, the threat is theoretical. But the 35% figure is a concrete number — and 2029 is a concrete year. The industry has a deadline, whether it likes it or not.
