Its a key that lets you get in to anyone in the worlds house.
Just kidding its a file from an unbanned xbox that you inject into a banned xbox which unbans the banned xbox and people sell them so they can unban their banned jtags to host again.
A keyvault is somthing that your extract from the nand. It is used to unban your jtag. People sell them because in order to get this keyvault they need to jtag an xbox.
I belive its a file on your xbox which tells whether or not your banned. not really sure though. if you replace a banned one with a unbanned one on a Jtag it unbans it. Let me search forums real quick :blink:
Don't quote me on this but, I think of it as an Xbox's ID. You extract it from the NAND Flash of an Xbox (no matter if it's banned/unbanned doesn't matter because it can still be extracted). Unbanned preferably it is sold to someone who has a banned "JTAGed" console that can rewrite its NAND (since it can run unsigned code) and become unbanned.
And just to add, KVs never "come back" that's why the pricing is high.
the key vault contains the serial number, console id, manufacturing date, dvd key, dvd drive information on type 2 kv's and region infor too. each kv is unique.