If you are planning on installing a new Cisco ASA 5515-X, or any other ASA from their 55X5-X line of ASAs, running 8.6 or above, you might run into a situation where you cannot SSH into the ASA or access ASDM.
Start off by verifying if you have activated the 3DES license. If not, grab the 3DES license key from cisco product license registration. Once Cisco emails you the activation key, console into your ASA and type 'activation-key ' under the global configuration mode. This will allow SSH version 2 on the ASA. You can verify this by doing a 'show version' on the ASA and checking the status next to 'VPN-3DES-AES'.
Next, create a username and password like you would.
username admin password cisco encrypted privilege 15
Then allow SSH on the inside and/or outside on all/specific subnets. Configure SSH version 2.
ssh 10.0.10.0 255.255.255.0 inside
ssh timeout 5
ssh version 2
And finally allow LOCAL authentication.
aaa authentication ssh console LOCAL
Next, you need to add an ssl encryption standard to the ASA. Most browsers and SSH/Telnet clients will reject the cipher that is present on the ASA by default.