Yes, it is. ed25519 depends upon discrete log for its security, which Shor’s algorithm can (theoretically, of course, not like it’s ever been done) efficiently solve.
The post-quantum algorithms are in active research right now. I don’t blame anyone for avoiding those at least until we’ve quantum computers big enough to solve baby toy elliptic curves.
Elliptic curve was invented to replace encryption vulnerable to quantum computers. As far as I know, highly parallel prime sieves such as shors algorithm do not break elliptic curve cryptography in the way it risks doing for asymmetric prime key cryptography.
It would be highly dependent on implementation and how keys are chosen, but elliptic curve cryptography is widely regarded as resistant to brute force attacks by quantum computers.
Yes, though OpenSSH has already switched to a quantum resistant algorithm for key exchange (Streamlined NTRU Prime, combined with x25519 in case SNTRUPrime turns out to be weak), and that’s the stuff that needs to be switched as soon as possible to preserve forward secrecy. Authentication keys are less urgent.
A surprising amount of services (including Azure last I tried) can only handle RSA keys, so after trying ecdsa only for a while I ended up adding a RSA key again.
With that said - it’s 2023, in almost all cases you should have your keys in a hardware module nowadays, in which case you’d use a different command for keygeneration.
Easiest and most affordable is probably a security key like the Nitrokey or the https://www.yubico.com/. I personally don’t like the company behind yubikey much, but if you want something small you can always leave in the device that’s pretty much your only option.
For “cheaper, but a bit more effort” would be just getting a smartcard blank, a card reader (if you’re not lucky enough to have a notebook or computer with one built in), and then either write your own applet, or use one of the available opensource ones, and upload it to the card. A variant of that would be the Fidesmo card, where you get a card and their applet.
Or you just use the TPM you may have in your system - though you’ll need to be careful with that: Typically one reason for using a hardware token is to make sure keys can’t get extracted, while TPMs often do allow key extraction. Software to make that work would be opencryptoki.
Generally you’d use PKCS#11 to have the various components talk to each other. On your average Linux pretty much everything but GnuPG place nice. with PKCS#11. Typically you end up with pcscd to interface with the smartcard (the above USB tokens are technically also just USB smartcards), OpenSC as layer to provide PKCS#11 on top, and software (like OpenSSH) then talks to that.
All of that should be available as packages in any Linux distribution nowadays - and typically will also provide p11-kit configured to use a proxy library to make multiple token sources easily available, and avoid blocking on concurrent access.
ssh-add supports adding keys from pkcs#11 providers to the SSH agent (search pkcs11 in ssh-add manpage), with some distribution (like RedHat) also carrying patches allowing you to only select individual tokens for adding.
If you’re also using GnuPG it gets more complicated - you pretty much have two options: Stick with PKCS#11, in which case you’d replace GPGs own smartcard agent with gnupg-pkcs11-scd, or you use GPGs own card implementation, in which case you can forget pretty much everything I wrote above, and just follow the security key manual for setting up a GPG card, enable SSH agent support in the GPG agent, and just use that for SSH authentication.
Actually it is the same story with TLS 1.3 and TLS 1.2. A bunch of sites still doesn’t support TLS 1.3 (e. g. arstechnica.com, startpage.com) and some of them only support TLS 1.2 with RSA (e. g. startpage.com).
You can try this yourself in Firefox by disabling ciphers (search for security.ssl3 in about:config) or by setting the minimum TLS version to 1.3 (security.tls.version.min = 4 in about:config).
Strange enough TLS 1.3 still doesn’t support signed ed25519 certificates :| P‐256, NIST P‐384 or NIST P‐521 curves are known to be “backdoored” or having deliberately chosen mathematical weakness. I’m not an expert and just a noob security/selfhoster enthusiast but I don’t want to depend on curves made by NSA or other spy agencies !
I also wondering if the EU isn’t going to implement something similar with all their new spying laws currently discussed…
Probably a good idea to look for a different client, call me tinfoil but I wouldn’t want to touch a very old mechanism that is supported/pushed by a very recognisable 3 letter agency
But all the enterprise infrastructure that everything you own runs on has, which means you have, which means changes to the base libraries like this are super important for adoption
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