{"id":1173,"date":"2026-10-22T09:35:54","date_gmt":"2026-10-22T07:35:54","guid":{"rendered":"https:\/\/hadamard.com\/c\/bitcoin-addresses-vulnerable-quantum-computers\/"},"modified":"2026-10-22T09:35:54","modified_gmt":"2026-10-22T07:35:54","slug":"bitcoin-addresses-vulnerable-quantum-computers","status":"publish","type":"post","link":"https:\/\/hadamard.com\/c\/bitcoin-addresses-vulnerable-quantum-computers\/","title":{"rendered":"Which Bitcoin Addresses Are Vulnerable to Quantum Computers?"},"content":{"rendered":"

A Bitcoin address is vulnerable to a future quantum computer when its public key is visible on-chain. That covers P2PK outputs, Taproot (bc1p) outputs, and any hashed address that has already spent and still holds coins. Hashed addresses (starting with 1, 3 or bc1q) that have never spent show only a hash, so their public key is not exposed while the coins sit still.<\/p>\n

This guide explains which Bitcoin addresses are vulnerable to quantum computers and why. It covers how many coins are affected, how far away the hardware is, and what Bitcoin developers have proposed. It reflects the state of research and proposals as of October 2026.<\/p>\n

The short answer: quantum attacks target exposed public keys, not the blockchain<\/h2>\n

Bitcoin uses two kinds of cryptography. Mining and the chain’s history rely on hash functions such as SHA-256. Ownership relies on elliptic-curve signatures (ECDSA and Schnorr over secp256k1). A large, fault-tolerant quantum computer running Shor’s algorithm could derive a private key from a public key. It cannot meaningfully reverse a hash.<\/p>\n

Europol made the same distinction in an October 7 warning reported by CoinDesk<\/a>. It said the hash functions behind mining and chain history are far more resistant to quantum attacks than wallet signatures. It also said that keys already exposed cannot be made safe after the fact. For more on why hashing holds up, see our explainer on whether quantum computers can break SHA-256<\/a>.<\/p>\n

So the practical question is simple: is the public key that controls your coins visible to anyone reading the blockchain?<\/p>\n

Which Bitcoin addresses are vulnerable to quantum computers? A risk ranking<\/h2>\n

Exposure depends on the output type and on whether the address has spent before. Based on 24\/7 Wall St.’s September 2026 breakdown<\/a> and CoinDesk’s reporting, the picture looks like this:<\/p>\n\n\n\n\n\n\n\n\n
Output type<\/th>\nTypical prefix<\/th>\nPublic key on-chain?<\/th>\nQuantum exposure at rest<\/th>\n<\/tr>\n<\/thead>\n
P2PK (pay-to-public-key)<\/td>\nNo standard address format<\/td>\nYes, in the locking script from the start<\/td>\nAlways exposed<\/td>\n<\/tr>\n
Taproot (P2TR)<\/td>\nbc1p<\/td>\nYes, by design (key-path spend)<\/td>\nExposed<\/td>\n<\/tr>\n
P2PKH, P2WPKH, P2SH, P2WSH that have already spent and still hold funds<\/td>\n1, bc1q, 3<\/td>\nYes, revealed at first spend and visible permanently<\/td>\nExposed<\/td>\n<\/tr>\n
P2PKH, P2WPKH, P2SH, P2WSH that have never spent<\/td>\n1, bc1q, 3<\/td>\nNo, only a hash<\/td>\nNot exposed until spent<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

P2PK outputs date largely from Bitcoin’s earliest years, which is why they dominate discussions of early-miner and Satoshi-era coins. Taproot is the less obvious case. It is a modern format, but its key-path spend places a public key directly in the output, so a bc1p address is exposed from the moment it receives funds.<\/p>\n

Address reuse is the most common way modern users create exposure. Spending from a hashed address reveals its public key. Any coins later sent to, or left on, that address are protected only by that now-public key. EU financial watchdogs warned on September 24<\/a> that older and reused addresses are especially vulnerable.<\/p>\n

How many BTC have exposed public keys?<\/h3>\n

Estimates range from about 6.0 to 6.9 million BTC, depending on who is counting and how:<\/p>\n