Unwrap Questions - How do I do this?

I am having a problem with the current description of the unwrapKey method.
I am going to try and lay out my understanding in the hope the somebody will
tell me what I got wrong.

 

Starting Point:

 

wrapKey is in the browser

                wrapKey.type = secret

                wrapKey.extractable = false

                wrapKey.algorithm = "AES-GCM"

                wrapKey.usages[] = [unwrapKey]

 

keyData = ENCRYPTED(

'{"kty":"oct", "k":"ABCDEFGHIJKLMNOP","alg":"Magic"}'

)

 

 

First I am going to just use the normal call and attempt to unwrap the key

 

unwrapKey("jwk", keyData, wrapKey, {name:"AES-GCM"},  null, true, [encrypt,
decrypt])

 

This will fail because the browser does not implement the algorithm Magic
and through an error in step #12 of the unwrap algorithm (the import is
going to fail because of "Magic").

 

My code then says - that is fine - I have  a script version of Magic that I
have downloaded as well so I can run the algorithm in script rather than in
the browser.

 

Step #2 - Call my internal script unwrapKey function.

 

I can successfully complete steps #1-9 without any problems in the script.

 

I am now going to attempt to deal with step #10.  This says that I need to
decrypt the bytes of keyData using the value of wrapKey.  In order to do
this I could call the decrypt function, but that will fail because it does
not have the decrypt key usage.  I could export and have AES-GCM in the
script, but that fails because the key is not exportable.  I could call an
undocumented function which does the decryption operation, but that is not
documented.

 

I am not sure what my script code is supposed to be doing at this point.

 

Jim