Chain profile
Nexus accepts Falcon-512 signatures on mainnet as an opt-in key type for its signature chains, but its node defaults every account to ECDSA over the Brainpool P-512 curve, every holder transaction we sampled was signed that way, and its "Quantum Resistant" headline describes a classical curve.
Not by default. Nexus accounts are signature chains, and its node accepts two key types for them at the consensus level: ECDSA over the brainpoolP512t1 curve and Falcon-512, a lattice-based scheme selected by NIST for standardisation as FN-DSA. When an API call names no scheme, the node uses Brainpool. A holder can choose Falcon by passing scheme=falcon, including from the API console in the released Nexus wallet, but in our reading of the source the next call that omits the parameter switches the chain back to Brainpool, and mining and staking transactions are built without it. Of the transactions we sampled in blocks 6,906,897 to 6,911,385, up to 23 October 2026, almost all were mining and staking transactions, which the node builds with the Brainpool default; about 170 were holder transactions, and none of those carried an 897-byte Falcon key either. Older releases had a setting that kept an account on Falcon, so Falcon signature chains may exist outside that window. The homepage lists "571-bit" under "Quantum Resistant", which describes sect571r1, a classical curve, so the profile carries the "Claims unverified" flag. What Nexus does have is a design that limits harvest-now-decrypt-later exposure: each transaction reveals a key whose hash the previous one committed to, and commits to the hash of a fresh key for the next, so a public key read off the chain no longer controls anything.
Claims unverified This chain markets itself as quantum-safe, but no primary source confirms a post-quantum scheme protecting its funds. Its tier records what the evidence supports, not what the project claims. See the methodology.
Where we are making a judgement call Nexus ranks outside the seventy-five largest layer 1s and is covered on both the position and the deployment tests: it markets quantum resistance, and a post-quantum signature is accepted on its mainnet. We confirmed the chain was live on 23 October 2026, when its explorer's node reported block 6,911,365 at 06:30 UTC. The row carries the "Claims unverified" flag: the homepage lists "571-bit" under "Quantum Resistant", which describes a classical curve, every fund-protecting signature we observed was Brainpool ECDSA, and no source shows NXS behind Falcon. The flag sits on the rung the evidence supports, which is Tier 2, because Falcon is accepted on mainnet and reachable with released software. Several readings are ours, each with the Hardy Score the other reading gives, from 73.0. One: the Tier 2 placement rests on demanding tools, the API console of the released wallet, as the Solana profile's rests on a command-line tool; a reader who finds that not usable in practice would hold Nexus back, as Pearl is held back, because a chain with a post-quantum signature live on mainnet fits no rung below Shipping. Two: signature is a 7; read as an experimental option it would be a 5, giving 67.0. Three: migration is an 8, because in our reading of the source a holder who moves to Falcon is switched back by any call that omits the scheme, including staking; a 9 gives 74.5. Four: exposure is a 7; on signature chains the literal reading of the anchors would allow a 9, giving 75.0, while the rule for UTXO key-hash chains would give 4, or 70.0. Five: verification is a 2 under the flag; a 3 gives 73.5. The behaviour of the scheme parameter is our reading of Tritium Core 5.1.6, not something we ran.
ECDSA over brainpoolP512t1 by default for signature-chain transactions; Falcon-512 accepted as an opt-in key type; ECDSA over sect571r1 for the legacy UTXO layer
Falcon-512 (Falcon reference implementation, 2019), selectable per transaction through the node API's scheme parameter
Falcon, selected by NIST for standardisation as FN-DSA (FIPS 206); standard not final at the time of writing
Tier 2: Shipping. A post-quantum signature is live on mainnet and usable by ordinary holders.
A role not listed is not evidenced either way. Every scheme, and which other chains share it, is in the cryptography registry.
| No. | Dimension | Score | Weight | Contribution |
|---|---|---|---|---|
| 1 | Signature scheme | 7 | 30% | 21.0 |
| 2 | Deployment stage | 8 | 25% | 20.0 |
| 3 | NIST alignment | 8 | 15% | 12.0 |
| 4 | Migration path | 8 | 15% | 12.0 |
| 5 | Exposure | 7 | 10% | 7.0 |
| 6 | Verification | 2 | 5% | 1.0 |
| Hardy Score | 73.0 | |||
Band 7 to 9: A post-quantum signature is available on mainnet at the protocol level as a first-class account type.
Falcon-512 is a protocol-level key type for Nexus signature chains: Transaction::Verify in Tritium Core 5.1.6 checks a FALCON or BRAINPOOL signature by the transaction's key type, with no activation gate, and FLKey generates keys at Falcon degree 512. It is opt-in. ExtractScheme returns BRAINPOOL when no scheme parameter is given, and no holder transaction in our mainnet sample used Falcon. source
Placement in the band The bottom of the band rather than an 8: Falcon is a consensus-level account key type, which is what this band describes, but it is reachable only through a per-call API parameter, the code reverts to Brainpool when the parameter is left out, and we found no Falcon-signed transaction on mainnet. Read as an experimental option on those grounds, it would be a 5.
Band 8: Tier 2: Shipping.
Tier 2: Shipping. A Falcon-512 signature is accepted on mainnet for signature-chain transactions, and a holder can select it with released software, without anyone's permission: the stable Nexus wallet, v3.1.5 with installers for Windows, macOS and Linux, bundles Core 5.1.4 and an API console that accepts scheme=falcon. Brainpool ECDSA remains the default. source
Band 6 to 8: The scheme is NIST-selected but the standard is not yet final, or a NIST-approved scheme is named but not yet deployed.
Falcon was selected by NIST for standardisation as FN-DSA in FIPS 206, which was not final at the time of writing. Nexus vendors the Falcon project's 2017 to 2019 reference implementation at degree 512, whose sampler table matches the version fixed in September 2019, and the consensus code accepts it on mainnet today. It is not the FN-DSA standard, which had not been published. source
Placement in the band The top of the band rather than a 7: the scheme is the NIST selection and is accepted by mainnet consensus now, not merely named for later. It cannot reach 9 because FN-DSA was not final at the time of writing.
Band 6 to 8: A credible published plan exists with a mechanism identified, but key parts are unbuilt or undated.
The mechanism exists: every Nexus transaction names the key type of the next one, so a holder can move a signature chain to Falcon in place, keeping the account, with the documented scheme parameter. Keeping it there is the gap. In our reading of create.cpp, a transaction built without the parameter sets the next key type back to Brainpool, mining and stake blocks are built that way, and the wallet exposes the parameter only through its API console. source
Placement in the band An 8 rather than the 9 that holders being able to move today would otherwise earn: a holder can switch, but the released software switches them back on any call that omits the parameter, including staking, so a migrated account does not stay migrated without care at every step. It is above a 7 because the rotation mechanism is built into every transaction rather than proposed.
Band 6 to 8: Addresses are key hashes and exposure is limited to spent outputs, keeping a meaningful share of supply unexposed.
Each signature-chain transaction reveals the public key whose SK256 hash the previous transaction committed to as its next hash, and commits in turn to the hash of a fresh key derived from the holder's credentials. Consensus rejects a transaction whose key does not match that commitment, so a Brainpool key read off the chain has already been retired and the key that controls the funds stays hidden. The pre-2019 legacy UTXO layer, whose transactions blocks still carry, uses Bitcoin-style key-hash addresses with ECDSA over sect571r1. source
Placement in the band A 7 rather than an 8 or a 9: on signature chains a revealed key protects nothing, which would read as the band above, but the legacy UTXO cohort keeps Bitcoin's address model and no measurement of its size or exposure has been published. It is above a 6 because the signature chains, where Tritium-era balances sit, never leave a controlling key exposed.
Band 0 to 2: No post-quantum component exists, or the claims rest on marketing.
A post-quantum component exists and is open source under the MIT licence: the vendored Falcon-512 code and the consensus path that verifies it. We found no outside review or audit of it, and no holder transaction using it in our mainnet sample. The project's headline claim, "571-bit" listed under "Quantum Resistant" on its homepage, matches the default curve of the node's elliptic-curve key, sect571r1, which Shor's algorithm breaks. source
Placement in the band The top of the band rather than a 0 or 1: a real post-quantum component is open source and accepted by consensus, where a chain flagged with no such component sits at 0. Not a 3, because nothing outside the project has verified the component and the headline quantum-resistance claim rests on marketing about a classical curve.
The deployment dimension is not a separate judgement. It is Tier 2 expressed as a number. See the tier mapping.
The 9 chains Nexus sits among, out of 80 rated. The last column is the gap in Hardy points from Nexus.
| Rank | Chain | Tier | Hardy | vs NXS |
|---|---|---|---|---|
| 7 | Abelian | 1: Native | 84.0 | +11.0 |
| 8 | NEAR Protocol | 2: Shipping | 80.0 | +7.0 |
| 9 | Algorand | 2: Shipping | 77.0 | +4.0 |
| 10 | Nervos CKB | 2: Shipping | 76.0 | +3.0 |
| 11 | Nexus this chain | 2: Shipping | 73.0 | |
| 12 | Bitcoin Cash | 2: Shipping | 62.0 | -11.0 |
| 13 | Solana | 2: Shipping | 53.0 | -20.0 |
| 14 | XRP Ledger | 3: Committed | 43.0 | -30.0 |
| 15 | Sui | 3: Committed | 42.0 | -31.0 |
Tritium Core 5.1.6 is released. Its consensus code accepts Falcon-512 and Brainpool P-512 signatures on signature chains, and its API defaults to Brainpool when no scheme is named. The release notes describe security, scaling and denial-of-service work and no change to signature schemes. source
No stated policy
Nexus has published no plan to make Falcon the default key type, to retire Brainpool signature chains, or to deal with legacy UTXO outputs that never move.
As of 23 October 2026. Published beside the score, not in it. Every chain's stance is compared on the commitments page.
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.
Nexus balances sit in accounts owned by signature chains, and a signature chain uses a new key for every transaction. Each transaction reveals the public key whose hash the previous transaction committed to, signs with it, and commits to the hash of the next key, which the node derives from the holder's username, password and PIN. A quantum adversary who recorded every Nexus public key would therefore hold only retired keys: the key that controls a balance is never on-chain until the moment it is used. That is a real limit on harvest-now-decrypt-later exposure, and it holds for Brainpool chains as well as Falcon ones. It does not cover the window in which a signed transaction is waiting to confirm, which the project's own site puts at about 500 milliseconds, and it does not cover the legacy UTXO layer from before the Tritium upgrade, whose transactions blocks still accept and which uses Bitcoin-style key-hash addresses with ECDSA over sect571r1. No measurement of how much supply remains in legacy outputs has been published.
What this rating means for you
Nexus has post-quantum signatures live on mainnet, but they are not the default, so holders have to opt in. That makes this one of the few chains where you can act today rather than wait.
Editorial guidance from the Hardy Index.
We will email you the day this rating moves, with the changelog note that explains why. Nothing else, and nothing in between.
Not by default. The node defaults signature-chain accounts to ECDSA over the Brainpool P-512 curve, which Shor's algorithm breaks. Falcon-512, a post-quantum scheme, is accepted on mainnet as an opt-in key type, but no holder transaction in our recent mainnet sample used it.
With released software, yes, if you are comfortable with an API console: the stable Nexus wallet bundles one, and its documented scheme parameter accepts falcon; the consensus code verifies Falcon-512 signatures with no activation gate. In our reading of the source, though, the next transaction built without that parameter switches the account back to Brainpool, and mining and staking transactions are built without it.
Because of how signature chains rotate keys. Every transaction reveals a key that the previous transaction committed to by hash, and commits to the hash of a fresh key for the next one. A public key visible on the chain has therefore already been used up, and the key controlling the balance stays hidden until it signs. The score stops short of the top band because the older legacy UTXO layer keeps Bitcoin's address model and its exposure has not been measured.
We found no sign of it. The node source we read contains Falcon-512, Brainpool P-512 ECDSA and sect571r1 ECDSA, and no Lamport implementation. The project's own documentation names Falcon and Brainpool for signature chains.
Because its headline quantum-resistance claim does not describe what protects funds. The homepage lists "571-bit" under "Quantum Resistant", a figure that matches sect571r1, a classical elliptic curve. Every holder transaction we sampled was signed with Brainpool ECDSA, and we found no NXS behind Falcon. The flag says the claim is not confirmed; the tier records what is deployed, which is an opt-in Falcon path.
A rating is only true as of the day an editor last reviewed it, so both forms below carry that date and the methodology version, with the date its cited sources were last checked. If you are quoting the score, quote those too.
The Hardy Index (2026). Nexus: quantum readiness assessment. Hardy Score 73.0 of 100, Tier 2: Shipping. Methodology v1.8. Last reviewed 23 October 2026; sources checked 13 November 2026. https://hardyindex.com/chains/nexus
@misc{hardyindex_nexus_2026,
author = {{The Hardy Index}},
title = {Nexus: quantum readiness assessment},
year = {2026},
howpublished = {\url{https://hardyindex.com/chains/nexus}},
note = {Hardy Score 73.0 of 100, Tier 2: Shipping. Methodology v1.8},
urldate = {2026-11-13}
} The whole dataset is reusable under the terms on the about page. A machine-readable version of this page is at /chains/nexus.md.
This is a security-readiness assessment, not investment advice.