Ethereum Classic

Is Ethereum Classic quantum-safe?

Where we are making a judgement call Two judgement calls carry this profile. The first is the tier. The ECIP process is open to anyone and a draft is a legitimate route in, and in July 2026 an ECIP editor said the ML-DSA precompile would anchor a dedicated post-quantum number range once submitted, so a reader could count it as the formal proposal the Tier 4 floor asks for, which would raise the deployment score from 1 to 2 and the Hardy Score from 13.0 to 15.5. We do not, because the floor asks for work documented by people with authority over the chain, and the author, GravityLab LLC, has none; the pull request has not been formally submitted, and the editor said the number will be assigned only then; and the editor has also pointed the work upstream. The precompile would also serve contract wallets without touching the chain's own transaction signatures. The second is exposure. The inheritance rule applies, but there is no published measurement of the shared pre-2016 history to inherit, so the score rests on the address model alone. A measurement of Ethereum Classic, or of the shared history, could lower it.

At a glance

Cryptography in use

• Account signatures ECDSA on secp256k1 Mainnet, default Source code or release
• Contract level ML-DSA ML-DSA-65 Proposed An EVM verification precompile for contract wallets, in an unsubmitted draft ECIP by an outside author, GravityLab LLC. Not assigned a number or merged. Specification or proposal

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. July 2016 shipped

   Ethereum Classic continues the original chain at the DAO fork, block 1,920,000, sharing all of Ethereum's history and every key revealed in it up to that point. source

2. 26 January 2026 proposed

   An outside author opens a work-in-progress ECIP pull request and discussion for an ML-DSA-65 (FIPS 204) verification precompile, with a Core-Geth implementation in progress. source

3. 3 February 2026 shipped

   ECIP editor Chris Mercer replies that upstream adoption is the more effective path for the work, citing Ethereum Classic's constrained resources. source

4. 16 July 2026 shipped

   ECIP editor Chris Mercer removes the number 1122 from the draft's title, as it belongs to the Olympia suite, and says a dedicated 1140s range makes sense for post-quantum proposals, with the ML-DSA precompile as its anchor and the number to be assigned at formal submission. source

5. No date published proposed

   No numbered ECIP, roadmap or timeline for post-quantum signatures on Ethereum Classic exists. source

If holders never migrate

No stated policy

No ECIP or statement from Ethereum Classic's maintainers addresses accounts that never move to post-quantum keys. The draft precompile leaves existing accounts unchanged.

As of 22 October 2026. source 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.

Ethereum Classic is the original Ethereum chain continued past the DAO fork of July 2016, so it shares Ethereum's history up to block 1,920,000. Under the v1.8 inheritance rule, published measurements of that shared history apply here, but none exists: Deloitte's finding that over 65% of Ether sits in addresses that have sent a transaction was measured on Ethereum's state after the split and does not transfer to the shared history. The structural picture is still clear. Every account that signed before the split has its key public on both chains, and because the two chains share an address and key format, a holder who has signed on Ethereum since with the same key has exposed the matching ETC address too. No measurement specific to Ethereum Classic has been published.

Questions

Sources

1. Core-Geth crypto package (crypto/crypto.go) Ethereum Classic (GitHub) · primary · checked 22 October 2026
2. ECIP (draft): Quantum-resistance for Ethereum Classic, ML-DSA verification precompile Ethereum Classic ECIPs (GitHub) · primary · checked 22 October 2026
3. Quantum-resistance for Ethereum Classic: ML-DSA verification precompile (discussion) Ethereum Classic (GitHub) · primary · checked 22 October 2026
4. Core-Geth ML-DSA-65 precompile work in progress Ethereum Classic (GitHub) · primary · checked 22 October 2026
5. Ethereum Classic Improvement Proposals Ethereum Classic (GitHub) · primary · checked 22 October 2026
6. Quantum risk to the Ethereum blockchain Deloitte · primary · checked 22 October 2026

@misc{hardyindex_ethereum_classic_2026,
  author       = {{The Hardy Index}},
  title        = {Ethereum Classic: quantum readiness assessment},
  year         = {2026},
  howpublished = {\url{https://hardyindex.com/chains/ethereum-classic}},
  note         = {Hardy Score 13.0 of 100, Tier 5: Exposed. Methodology v1.8},
  urldate      = {2026-11-13}
}