Qtum

Is Qtum quantum-safe?

Where we are making a judgement call Two judgement calls, and one fact a reader should have. First, exposure scores 4 on the key-hash address model, as Litecoin and Dogecoin do, although staking reveals keys on a scale those chains do not have: every block signature exposes the staker's key, and qtum.info reports a stake weight of about 20.5 million QTUM against a supply of about 106.1 million. Not all of that has produced a block, and nobody has measured how much has. A reader who takes staking to mean that most active coins have revealed a key would score 3, lowering the Hardy Score from 10.5 to 9.5. Second, migration scores 2 on Qtum's record of hard forks, one of which added a new signature type. A reader who weighs that record at nothing without a quantum plan would score 1, taking 1.5 points off. Qtum's Account Abstraction Layer earns nothing here: it connects UTXOs to the EVM's account model and does not let a holder rotate to a new kind of key. Third, the fact: Qtum's Decentralised Governance Protocol lets admin and governor keys, voting in an on-chain contract, change the minimum gas price, block gas limit, block size and gas schedule without a fork. The DGP contract template sets its first admin key to whoever calls it first, and we found no published list of who holds those keys. They govern fees and block parameters, not minting or signatures, and change no score here. Whatever its name suggests, nothing we found in Qtum's own material markets the chain as quantum-safe, so the claims-unverified flag does not apply.

At a glance

Cryptography in use

• Account signatures ECDSA on secp256k1 Mainnet, default Spends of pay-to-public-key-hash and pay-to-public-key outputs, inherited from Bitcoin Core. Source code or release
• Account signatures Schnorr signatures on secp256k1 Mainnet, opt-in BIP-340 Schnorr for Taproot outputs, which the node verifies on every block; added in the v22.0 hard fork. Source code or release
• Validator consensus ECDSA on secp256k1 Mainnet, mandatory Each proof-of-stake block carries an ECDSA signature by the block key, which the node accepts either in compact (recoverable) form or as a standard DER signature. The block key is also published in the coinstake transaction's second output, as a pay-to-public-key output or a non-spendable OP_RETURN push, and under offline staking the block is signed by the staker's key with a delegator's signed proof of delegation. Source code or release

A role not listed is not evidenced either way. Every scheme, and which other chains share it, is in the cryptography registry.

Score breakdown

How it compares

Roadmap

1. 6 September 2017 shipped

   Qtum's genesis block is mined, starting a ledger of its own. Qtum took Bitcoin Core's code, not Bitcoin's transaction history, so no Bitcoin output exists on Qtum. source

2. 31 July 2022 shipped

   The v22.0 hard fork activates at block 2,080,512, adding Taproot, Schnorr signatures and Tapscript. A new signature type on secp256k1, not post-quantum work, but evidence that Qtum can change how coins are signed. source

3. 15 February 2025 shipped

   The v27.1 hard fork activates at block 4,590,000, moving Qtum to Bitcoin Core 27.1 and the Cancun EVM. source

4. 12 January 2026 shipped

   The v29.1 hard fork activates at block 5,483,000, moving Qtum to Bitcoin Core 29.1 and the Pectra EVM. It does not change the signature scheme. source

5. No published position proposed

   No Qtum Improvement Proposal, roadmap item or research programme on post-quantum signatures was found in the qips repository, the node repository or on qtum.org at the time of writing. source

If holders never migrate

No stated policy

Qtum has published no policy on coins that stay behind ECDSA or Schnorr keys, including staking coins whose keys block signatures have already revealed.

As of 22 October 2026. Published beside the score, not in it. Every chain's stance is compared on the commitments page.

Exposure

Exposure measures how much of the chain's value already sits behind a public key that an attacker can record today and break later. This is the part of the threat that a future upgrade cannot undo.

Qtum began its own ledger with a genesis block dated 6 September 2017, so it shares no transaction history with Bitcoin and the exposure inheritance rule does not apply. Within that ledger it follows Bitcoin's UTXO model: a standard address is a key hash, and the key is revealed when an output is spent, so address reuse and ordinary spending erode the protection. Proof of stake adds a Qtum-specific exposure. Every block carries an ECDSA signature by the staker's key, and the key itself is published in the coinstake transaction's second output. A coinstake transaction must either return the stake to the same script or pay it to a pay-to-public-key output, so a coin that has staked a block has its key on-chain while it goes on staking. Under offline staking, the delegator's signed proof of delegation is checked against the delegator's address in the same way. The explorer qtum.info reports a network stake weight of about 20.5 million QTUM against a supply of about 106.1 million, but how much of that has produced a block, and so revealed its key, has not been measured. The score therefore reflects the address model rather than a measured figure.

Questions

Sources

1. Qtum Core node software Qtum (GitHub) · primary · checked 22 October 2026
2. Qtum proof-of-stake checks (src/pos.cpp) Qtum (GitHub) · primary · checked 22 October 2026
3. Qtum block validation (src/validation.cpp) Qtum (GitHub) · primary · checked 22 October 2026
4. Qtum chain parameters (src/kernel/chainparams.cpp) Qtum (GitHub) · primary · checked 22 October 2026
5. Qtum Core v22.0 release notes Qtum (GitHub) · primary · checked 22 October 2026
6. Qtum Core v27.1 release notes Qtum (GitHub) · primary · checked 22 October 2026
7. Qtum Core v29.1 release notes Qtum (GitHub) · primary · checked 22 October 2026
8. Qtum Improvement Proposals (issues) Qtum (GitHub) · primary · checked 22 October 2026
9. Decentralised Governance Protocol contract template (dgp-template.sol.js) Qtum (GitHub) · primary · checked 22 October 2026
10. Qtum Technology Qtum Foundation · primary · checked 22 October 2026
11. qtum.info network information API qtum.info explorer · secondary · checked 22 October 2026

@misc{hardyindex_qtum_2026,
  author       = {{The Hardy Index}},
  title        = {Qtum: quantum readiness assessment},
  year         = {2026},
  howpublished = {\url{https://hardyindex.com/chains/qtum}},
  note         = {Hardy Score 10.5 of 100, Tier 5: Exposed. Methodology v1.8},
  urldate      = {2026-11-13}
}