Ssh new key identification

[PerkelSimon]

hi,

I try to upgrade my key for ssh in putty, I generate Ed25519 key but it seems that I can not use that kind of authentification with putty /open wrt, possible?

[vgaetera]

[SOLVED] Dropbear and ed25519 keys - Resolved in 21.02

That is correct. New features usually don't end up in already branched releases, only bug fixes. You'll have to wait for a 20.xx release for that

[PerkelSimon]

ok so still not working, so, better to keep rsa or ssh-1 (rsa) ?
thanks

[vgaetera]

https://www.openssh.com/releasenotes.html#2.5.1p1

RSA1 is used by the SSH 1 protocol only,
RSA and DSA keys are used by the SSH 2 protocol implementation.

RSA1 is legacy/obsolete, so use RSA.

[PerkelSimon]

usualy I would take RSA 4096 but Can I take an higher number?, 5096?

[vgaetera]

http://www.openssh.com/releasenotes.html#8.0

• ssh-keygen(1): Increase the default RSA key size to 3072 bits,
  following NIST Special Publication 800-57's guidance for a
  128-bit equivalent symmetric security level.

I.e. 3072-bit RSA is the current default for OpenSSH that is considered safe enough by its developers.
I think that 4096-bit RSA should be more than enough for the time being in most cases.