The problem is that by default ssh-keygen loves to generate an easy to crack 2048 bit key (RSA).  Supposedly having a larger keysize helps such as 4096 or 8096 but it is thought to be useless still against Quantum computing.

How can I check my existing keysize and type?

ssh-keygen -lf /path/to/your/id_rsa.pub

The output will be something like below followed by the hash.  The first number is the key size and the second part will be the type eg RSA, SHA256 etc..

2048 RSA

How can I create an ssh key?

-t = the type of key

-b = the key size (you probably shouldn't use that many 9s!)

ssh-keygen -t ed25519 -b 9999999999999

How can I see what types of keys my ssh version supports?

Don't use dsa it is weak and now deprecated in the latest ssh versions and many recommend ed25519 (EdDSA)

ssh-keygen -t
option requires an argument -- t
usage: ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1]


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