Generate a passphrase protected 4096 bit rsa keypair with a custom name

gistfile1.sh-session

Username$ ssh-keygen -b 4096 -t rsa -f ~/.ssh/demo_key
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/Username/.ssh/demo_key.
Your public key has been saved in /Users/Username/.ssh/demo_key.pub.
The key fingerprint is:
dd:6b:c9:de:d0:df:3c:74:92:97:1c:97:7b:7d:9b:fb Username@Username.local
The key's randomart image is:
+--[ RSA 4096]----+
|                 |
|                 |
|                .|
|         . .   o.|
|        S . . ..*|
|           . +o=*|
|            * oo*|
|           o o *.|
|            . ..E|
+-----------------+