Comment 13 for bug 238163

Okay, now things become clearer.

As explained before, you cannot expect to use a keyfile for the root file system, because the keyfile would have to be in either at some unencrypted place (/boot or initramfs) which defeats the purpose of using a keyfile. The very same reasons apply to using a keyfile for encrypting swap space from which you want to resume from. Where should the key for unencrypting the device come from?

the only "solution" to this issue is to use the "passdev" mechanism introduced with the cryptsetup in intrepid to fetch the key from some removable media.

Btw, the warning 'cryptsetup: WARNING: target luks_swap uses a key file, skipped' is perfectly valid and intended to make you aware of this issue.

For this reason, I'm converting your bug report to a support ticket, because that's what you're actually requesting. There is nothing wrong in the cryptsetup package in this point and the package is behaving exactly as I would expect it to do.