I had a couple of issues running the script first off as I didn't have "Crypt::Rijndael" perl module installed (info on installing perl modules here). Once this was installed it worked fine.
Once you are on that page locate the IV & Key for kernelcache.release.n90 as below, you will need them in a minute:
- <YOUR KERNEL> = kernelcache.release.n90 we extracted from IPSW earlier.
- -v = Verbose
- -o = Output file, I use the same file name and append .lzss as it is easy to see it's lzss for decompressing.
- -k = Key from wiki
- -iv = IV from wiki