Most major blockchains besides Bitcoin run on proof of stake, where validators vote on each block by signing it. Signature aggregation is what makes large validator sets practical. Ethereum uses BLS signatures, whose algebraic structure lets it combine tens of thousands of validator signatures every slot into a single group element. Solana, where validator votes have made up about three-quarters of all transactions, is adopting BLS aggregation too, as part of its Alpenglow upgrade.

But as useful as BLS is, it is not post-quantum — and in fact, no known post-quantum signature scheme aggregates this way. Post-quantum signatures are also 10 to 100 times larger than today’s elliptic-curve signatures, so without aggregation these…