I’ve been seeing people mention in chat that they have a bunch of copies of keys for the same portal. How are they doing this? I feel like I have a hard enough time getting one copy of a key for most portals.
Before recent changes about portal key generation to own multiple keys of the same portal you had to drop the key of the aimed portal before hacking it. Then, you had chances to gain a second portal, grab the dropped key and you had two keys.
Now that portal keys are much rarest when hacking, you can gain a key even if you were already carrying the same portal key, but you’ll have to be patient and persistent.
Note that sometimes, when making a big XMP blast on an enemy resonator, a portal can drop a portal key (his key or a key of the linked portal).
EDIT January 2014 :
since a few weeks, if you already hold a portal key, you have nearly 0% of chances to get another one. To obtain a new key, drop the keys you own, then hack and you’ll probably get a new key (~80%)
Source : Link , Question Author : mmrobins , Answer Author : Cédric Julien