decrypting help please:
 

Hi guys do you need an Apple Developers Account to decrypt an ios?
I am trying to decrypt ios 4.0 for 3g iphone but this is all i get when i run the .dmg in vfdecrypt.exe on windows 7.

must specify one of -k or -p
incorrect arguments.
usage: vfdecrypt -i in-file [-p password] [-k key] -o out-file

Here are the commands i've tried in vfdecrypt:

vfdecrypt.exe -i 018-5536-600.dmg -0 rootfs.dmg -k 0da2d3316d5ee7cd1858e4035e451387cd8156e97535fb0902 8859e68e5b7b39a6649552

and

vfdecrypt.exe -i C:\Users\Jimbo\Desktop\iPhone1,2_4.0_8A293_Restore \018-5536-600.dmg -o decrypted_fs.dmg -k 0da2d3316d5ee7cd1858e4035e451387cd8156e97535fb0902 8859e68e5b7b39a6649552

My files are in a folder on my desktop name iPhone1,2_4.0_8A293_Restore.
Thanks for any help just trying to learn something new.