ssh-keygen key conversion questions

[Ben Liblit]

Using ssh-keygen from OpenSSH-2.9p1, I can perform the following key
conversions:

  - convert a commercial public key into an OpenSSH public key:

      % ssh-keygen -i -f commercial-key.pub > openssh-key.pub

  - convert a commercial private key into an OpenSSH private key,
    provided that the commercial key has no password

      % ssh-keygen -i -f commercial-key > openssh-key

  - convert an OpenSSH public key into a commercial public key:

      % ssh-keygen -e -f openssh-key.pub > commercial-key.pub
      % ssh-keygen -e -f openssh-key     > commercial-key.pub

      (these both do the same thing)

I am left with two questions.  First, the inability to convert
encrypted commercial keys into similarly encrypted OpenSSH keys is
unfortunate.  Can anyone give me the standard story on why this
doesn't work as one might hope?  Is it simply a feature that is
waiting to be implemented, or are there deeper intractable issues?

Second, there is one conversion path missing.  How does one convert an
OpenSSH private key into a commercial private key?

Thank you!