How can RFID/NFC tags not be cloned when they are passive technology?
Your question assumes 2 things:
- That RFID tags cannot be cloned
- And they are passive, not active.
Both points are incorrect:
- RFID tags can be cloned. Tags which do not make use of password-protection or over-the-air (OTA) encryption can have their data banks copied into new tags.
- RFID tags (at least Class 1 Generation 2 tags, aka UHF RFID tags) are computationally active, not passive. Their "passive" nature refers to their not needing an attached power source.
RFID tags (at least "Class 1 Generation 2" tags) are transponders and they're powered by the very RF wave sent to query them.
The majority of RFID tags are not encrypted or have any secrets - they act like a barcode does and merely repeat the same information every time they're queried, in which case they can very easily be cloned.
However the Class 1 Gen 2 tags (at least) support features like passwords (the scanner includes a password in the RF signal sent to query the tags) and over-the-air encryption, though this is not a mandatory feature and not every Class 1 Gen 2 chip supports it.
Research has been done into the security of RFID, here is one such recent paper: http://www.cs.fsu.edu/~burmeste/410.pdfThe security of EPC Gen2 compliant RFID protocols.