What does ed448 mitigate against vs ed25519?

The simplified answer is, larger keys that demand a far larger effort to break, in a way similar to RSA-4096 vs RSA-2048.

The predicted timelines for quantum computer advances (and the requirements for practical applications) have shrunk dramatically in the past 15 years. What used to be a no-later-than-2035 recommendation for getting off e.g. RSA-2048 in good time, is today no-later-than-2030. The admission of 256-bit curves for ECDSA/ECDH has been supplanted by 384-bit curves already years ago.

In the absolutely ground shaking event that a future application of quantum computation somehow manages to cut Ed448's equivalent security of ~224 bits in half, exploring even a small portion of a 112-bit space will still cost more electrical energy than we can possibly provide.

▲

rcxdude 2 days ago | parent [-]

The whole point is that RSA and ECDH can't be made safe against quantum computers by making the keys bigger. The speedup is exponential and so breaking a 4096-bit key is only twice as hard as a 2048-bit key. The 'cutting in keysize in half' is true in principle in general (but not in practice, as the article points out), but for some algorithms it's much worse.

	▲	daneel_w 2 days ago \| parent [-]
		Just to be clear, I'm not advocating for Ed448 for the KEX - we already have ML-KEM and SNTRUP in OpenSSH and everyone should start using those. I'm advocating for Ed448 DSA ("SSH pubkey").