Upgrading to MacOS Sierra will break your SSH keys and lock you out of your own servers.
Quincy Larson
49843

I always thought that nowadays, it was common practice to generate SSH keys with “-t rsa”, which will generate a 2048-bits key by default. (I believe ssh-keygen without any argument would generate a 2048-bits RSA key anyway.) In fact, I have often seen recommended using:

ssh-keygen -t rsa -b 4096

So, perhaps you moving away from 1024-bits keys were overdue.