Does it mean Merkle’s authentication tree is still used today?
It is. In fact, the Merkle tree is a fundamental part of blockchain.
True, and merkle trees are just about everywhere, but more interestingly it's part of SLH-DSA (the NIST standardization of SPHINCS+), a quantum-secure signature scheme. And it's not just any old merkle tree, it's a continued evolution of the original Lamport signature scheme discussed in the article.
Current signature schemes can use as few as 32 bytes per key and 64 bytes per signature [RFC8032], but post-quantum replacements are much larger. [...] a new form of X.509 certificate that integrates logging with certificate issuance [...] This achieves the following: Log entries do not scale with public key and signature sizes. Entries replace public keys with hashes and do not contain signatures
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True, and merkle trees are just about everywhere, but more interestingly it's part of SLH-DSA (the NIST standardization of SPHINCS+), a quantum-secure signature scheme. And it's not just any old merkle tree, it's a continued evolution of the original Lamport signature scheme discussed in the article.
And maybe soon in even more places :) Merkle Tree Certificates (https://datatracker.ietf.org/doc/draft-ietf-plants-merkle-tr...) seems to be in order to "make space" for quantum-secure signatures if I understand it correctly: