AID of PICC is 00 00 00. And then key#0 is the masterkey. There is a masterkey for PICC and another masterkey for an application.
In Wikipedia, the DES keying options are termed as:
keying option 1 or 3TDEA when k1 != k2 != k3 this is the strongest
keying option 2 or 2TDEA when k1 != k2 but k3 = k1
keying option 3 where k1 = k2 = k3
In Mifare, wither DES or 3DES, these keys is 16 bytes in length. The difference is that in DES the first half is mirror copy of 2nd half. These are Keying options in DES terminology.