sudo apt install xapp-sn-watcher libxapp-gtk3-module

 openssl: will use "PKCS#1", "PKCS#8", or "PEM" key format

 ssh-keygen: will use SSHv2 key format

 in short use ssh-keygen if you need to use ssh,

 use openssl otherwise (for enc, dec, verify signature, Sign something, etc...)