Excerpt from Quantum Quarterly: Deconstructing how much of Bitcoin's supply is vulnerable to quantum attacks, and the practical operational challenges involved in mitigating this exposure.

As of block 950,000, 6.9 million BTC are cryptographically exposed—equivalent to 34.45% of the circulating supply. This total should not be interpreted as the number of bitcoins potentially lost in a quantum event. Actual risk depends on whether holders can respond, whether relevant entities remain operationally active, whether balances are large enough to justify attack costs, and how quickly funds can be migrated. When these dimensions are factored in, the risk landscape is narrower, more concentrated, and skewed toward dormant holdings.

6.9 million BTC: Raw Exposed Supply

34.45%: Raw Exposure Share

3.33 million BTC: Active & ≥1 BTC Exposed

2.28 million BTC: Dormant & Identity Unknown, ≥1 BTC Exposed

Exposure Breakdown

View | Exposed BTC | Supply Share | Raw Exposure Share | Group Count | UTXO Count | Migration Estimate

Total Raw Exposure | 6,900,573 | 34.45% | 100.00% | 16,047,454 | 102,347,011 | ~140.99 days

Active, ≥1 BTC, 5-year threshold | 3,331,639 | 16.63% | 48.28% | 46,163 | 4,906,508 | ~9.37 days

Never spent + inactive, ≥1 BTC | 3,413,767 | 17.04% | 49.47% | 113,627 | 2,669,847 | ~5.29 days

Never spent + inactive, ≥1 BTC, exclude known entities, retain Satoshi’s coins | 2,277,978 | 11.37% | 33.01% | 73,658 | 1,096,018 | ~2.56 days

Same criteria, ≥10 BTC | 2,187,481 | 10.92% | 31.70% | 39,897 | 365,830 | ~23.33 hours

Same criteria, ≥100 BTC | 351,654 | 1.76% | 5.10% | 675 | 33,573 | ~2.17 hours

Migration estimates are useful for comparing relative scale but should not be construed as predictions of real-world coordination difficulty, fee pressure, or user behavior.

Bitcoin Quantum Exposure Brief – Block 950,000, Page 1

Core Analysis

1. The total exposure figure overstates actual theft risk.

The raw view shows 6,900,573 BTC in an exposed state, intentionally treating "exposure" as a cryptographic condition: namely, that the public key has already been revealed on-chain. Starting from this premise is valid, but it does not equate to economic loss risk. A functioning exchange wallet, a multisig operated by an institution, a dormant early address, and a discarded private key may all be cryptographically exposed, yet their ability to migrate differs drastically.

2. Exposure among active and known entities is less concerning than the raw numbers suggest.

The “active, ≥1 BTC” filter covers 3,331,639 BTC—48.28% of total exposed supply. This is a substantial amount of Bitcoin, but it is concentrated in just 46,163 groups, not scattered across millions of unmanaged holders. The largest visible segment of active exposure currently stems from exchanges, brokers, custodial multisigs, stablecoin infrastructure, and mining-related wallets—all operational entities likely to monitor quantum developments closely, coordinate wallet rotation, and complete migration before any feasible attack window opens.

This does not imply the exposure is negligible. It carries coordination and execution risks. But it fundamentally differs from private key loss risk: under credible threat scenarios, actively held and custodied balances are typically the first to move.

3. In the long term, the core issue lies in dormant, non-responsive exposure.

After excluding active entities and narrowing the view to balances ≥1 BTC that have never been spent or are inactive, exposed supply stands at 3,413,767 BTC. After further removing known operating entities while retaining coins attributed to Satoshi, the remaining exposed supply drops to 2,277,978 BTC—distributed across 73,658 groups and 1,096,018 UTXOs.

These 2.28 million BTC represent the cleanest approximation within this dataset of the “harder-to-mitigate exposure surface”: early holders, inactive self-custody, reused old addresses, dormant P2PK outputs, and coins possibly lost or otherwise unresponsive. This is where quantum risk is most entrenched in practice.

4. The economics of a quantum attack further narrows the target set.

A capable quantum attacker still faces operational costs, limited computational capacity, opportunity cost, transaction fees, and execution risk. Thus, rational targets are unlikely to be every exposed public key, but rather the highest-value exposed balances.

Introducing balance thresholds reveals how rapidly the attack surface contracts. After excluding known entities and focusing only on dormant or never-spent balances, the ≥10 BTC view still includes 2,187,481 BTC—but only 39,897 groups and 365,830 UTXOs. At ≥100 BTC, the target set shrinks to 351,654 BTC, confined to just 675 groups and 33,573 UTXOs.

Bitcoin Quantum Exposure Brief – Block 950,000, Page 2

Script Type & Threshold Observations

Filter Criteria: Show only never-spent + inactive balances; exclude known operational entities; retain Satoshi’s coins unless excluded by balance threshold.

Script Type | ≥1 BTC | ≥10 BTC | ≥100 BTC | Observation

P2PK | 1,715,778 BTC | 1,715,539 BTC | 10,246 BTC | Dominates dormant exposure at lower thresholds because early P2PK outputs are inherently exposed and mostly inactive.

P2PKH | 408,789 BTC | 356,368 BTC | 273,865 BTC | Becomes dominant in the ≥100 BTC view after exclusion of 50 BTC outputs from the Satoshi era.

P2SH | 43,444 BTC | 34,225 BTC | 21,113 BTC | Drops significantly after excluding known entities; remaining dormant script hash exposures are relatively small.

P2WPKH | 8,696 BTC | 5,271 BTC | 2,194 BTC | Very low share in non-entity dormant views, consistent with modern wallet usage patterns and higher activity levels.

P2WSH | 2,938 BTC | 2,886 BTC | 2,750 BTC | Very small after excluding known entities; the broader P2WSH exposure likely belongs to active institutional wallets.

P2TR | 98,327 BTC | 73,193 BTC | 41,486 BTC | Always exposed at the key level, but high-value, dormant, non-entity portions remain limited.

Due to rounding in the dashboard at the script type level, displayed totals may differ by several BTC from key metric sums.

Important Note on Thresholds

The apparent crossover—from P2PK dominating at ≥10 BTC to P2PKH dominating at ≥100 BTC—should not be interpreted as P2PK risk vanishing. This is largely an artifact of the filtering mechanism: in this dataset, P2PK outputs attributed to Satoshi each correspond to exactly 50 BTC, so they are included at ≥10 BTC but excluded when the balance threshold exceeds 50 BTC. It is precisely this exclusion that causes P2PK exposure to plummet from approximately 1.716 million BTC to about 10,000 BTC in the ≥100 BTC view.

Conclusion

The most compelling interpretation of the snapshot at block 950,000 is that while Bitcoin’s cryptographic exposure surface is large, its practical exposure surface is far narrower. Known active entities account for a significant portion of exposed supply, but they are also the most likely to execute rapid migration. More persistent risks reside in dormant, unresponsive, and potentially lost coins. Once known entities and low-value targets are filtered out, the economically attractive target set becomes extremely small: only 675 groups containing 351,654 BTC at the ≥100 BTC threshold. Therefore, quantum exposure should best be understood as a problem concentrated on dormant coins—not as a uniformly distributed risk across all exposed Bitcoin.

Data Source: Snapshot from the Bitcoin Quantum Exposure Dashboard at block 950,000. This analysis assumes the methodology detailed in a separate PDF provided to editors.

This article is featured in the latest print edition of Bitcoin Magazine’s Quantum Issue. We present it here in advance as a preview of the full issue.

Author: Wicked, Translated by DeepTide TechFlow