If you use the setup wizard for Cisco ASA appliances to allow SSH access it doesn’t auto-generate a key. It will create the access-rules, but you still won’t be able to SSH to the firewall until the key is generated. The quickest way to generate the key is via the command:
“generate crypto key rsa modulus-size” [more]
Note: The modulus-size can be 512, 768, 1024, or 2048. The value of 1024 is recommended.