Paul,
Is the key associated with SSH or SSL? If the key is available, the top half of the key will display the key length. A Hex to ASCII converted can be used to get this information. A pregenerated key in EXOS shows a value of 2048 bit as shown below which would be default.
---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----
Subject: root
Comment: "2048-bit DSA key, root, Fri Jul 24 18:21:20 2015"
P2/56wAAA4IAAAAmZGwtbW9kcHtzaWdue2RzYS1uaXN0LXNoYTF9LGRoe3BsYWlufX0AAAAE
bm9uZQAAA0QAAANAAAAAAAAACACi4wAL/xGQRKGC+ZY02NEB8FKGKDI9/FG3WsyYU/tINalT
........
If SSL is enabled, the 'show ssl' command will provide the RSA key length in the output. The 'show sshd2 user-key' command may also provide some insight.