On-chain data reveals that 35.4 percent of Bitcoin's total supply resides in addresses where the public key is already visible on the blockchain—an exposure vector that becomes a real threat once quantum computing reaches sufficient computational scale.
Bitcoin's security backbone is elliptic curve cryptography (ECC). Shor's algorithm, executable on a sufficiently powerful quantum computer, can derive a private key from a known public key. Traditional Pay-to-Public-Key-Hash (P2PKH) addresses expose the public key immediately upon receipt, making them vulnerable the moment funds are moved.
Newer address types change the equation. SegWit addresses (P2WPKH and P2TR) withhold the public key until a transaction is broadcast—buying time in a post-quantum scenario. Funds locked in these formats remain secure from this specific attack vector until spent.
Today's quantum computers cannot execute Shor's algorithm effectively against Bitcoin's 256-bit elliptic curves. The threat is theoretical but not distant. Cryptographers are actively developing post-quantum cryptography (PQC) solutions, and the security community is modeling migration timelines.
For holders in legacy address formats, the fix is straightforward: sweep holdings into SegWit addresses now. This migration shifts the attack surface and materially improves long-term security posture without requiring protocol changes.
The 35.4 percent figure underscores the scale of on-chain migration required if quantum computing advances faster than expected. Blockchain researchers are treating this as a long-horizon design problem, not an immediate emergency—but one that demands attention before it becomes an emergency.
