Right now $key is Crypt_RSA but it could be Crypt_DSA, too, when that is implemented, and  I don't know if phpdoc lets you do stuff like `@var Crypt_RSA or Crypt_DSA`. And there's not an interface that they're sharing either so we couldn't reference the interface name. And even if we did make them an interface on maybe the php5 only branch...  it's an interface that's only really useful in the context of Net_SSH2. If you're using Crypt_RSA, stand-alone, it's just extra bloat idk.