Well, this is a weird one. I set up a Broadcom BCM43142 wireless network connection using the linux driver I downloaded from the Broadcom.com web site. Some time ago I disabled Secure Boot to change the boot order such that the computer boots from the optical drive before the hard disk. I thought I was done with installing operating systems, at least for now, so I decided to re-enable Secure Boot. After that, the wifi would not connect. When I disabled Secure Boot, the wifi showed the available networks and connected again. Weird.

Note Secure Boot is not the same as legacy boot. I have never enabled legacy boot at all. Everything that has been installed has been with UEFI only (if that makes sense).

I'm using Fedora 23. Please let me know if there you need further information or have suggestions. I appreciate all your help.

Did you inspect your dmesg?

UEFI is still not standard.

On one of my systems when you select a different mode it automatically changes other settings and disables the ability to change some settings. I get the feeling the bios either only allows it under one setting or it automatically changes it when you select another.

You might try Ubuntu LTS to see if it changes how it works.

I asked about dmesg because I do not know how secureboot works. I consider it is possible the self built wireless module was rejected as not trusted.

Your question is good and hopefully will be answered. I didn't mean to step all over your suggestion.

I ran the command:
In the dmesg output, I got about a million copies of the line:
When I googled the error message above, I found an answer in an Ubuntu forum that suggested:
But when I tried to install linux-firmware-nonfree, it said "No package linux-firmware-nonfree available.". I suspect this package exists in an Ubuntu repository, but not in the Fedora repositories, at least not the ones I have installed.

How do I fix this error?

After further nosing around, I found this error in my broadcom installation script output when I tried to install with secure boot enabled.
modprobe: ERROR: could not insert 'wl': Required key not available

According to some other posts, this appears to have something to do with secure boot and the broadcom wireless module not being signed (whatever that means).

Is there any way to sign this 'wl' module or otherwise provide a key?

Bump