Post-quantum key registration, depositing validators' backup keys in advance
Strawmap Hegotá (2027) · post quantum registrations
This change has validators register, in advance on the beacon chain, a key that is hard to break even with a quantum computer, alongside the signing key they use now. When the signature scheme is changed later, they prove their identity with this key.
Why it is needed
Validators on Ethereum's consensus layer attach BLS signatures to blocks and attestations. BLS relies on elliptic curve mathematics, and it is known that once a sufficiently large quantum computer exists, the private key can be derived from the public key. When that day comes, validator signatures can be forged, so the signature scheme would have to be replaced wholesale. The order is the problem. To move to a new key, you must sign a proof that "this new key is mine" with the old key, but if the old key is already broken, that proof can be forged too. So this item proposes binding a post-quantum key to the validator record now, while BLS is still safe. The registered key is not used right away and is taken out to prove identity at the actual transition point. Hash-based signatures, which are built from hash functions alone, are being studied as a candidate. The Strawmap places this registration step in the Hegotá column, but this is an estimate, not a commitment.
How it works
- The weakness of the current key Validators sign with a BLS key. As quantum computers grow, the private key can be worked out from the public key alone, so signatures can be forged.
- Backup key registration While BLS is still safe, the validator creates a post-quantum key and registers it in its own record on the beacon chain. At this point the old key's signature is still trustworthy.
- Use at the transition When the time comes to change the signature scheme, the validator proves its identity with the key registered in advance and moves to the new scheme. This avoids the risk of registering after the key has been broken.