How to make a NFC Tag read only?

Question

I have an NTAG213 NFC sticker. I was wondering how I can make this sticker read only. If later I switch to a NTAG215, how could I make that tag read only. What is the process involved in actually making different types of stickers read only. When I say read only, I mean the NFC's records cannot ever be modified but devices can still read the records without authentication.

I had a read of https://answers.launchpad.net/nfcpy/+question/242606 and tried to implement it's solution

import nfc
from time import sleep
from nfc.clf import RemoteTarget
import ndef

clf = nfc.ContactlessFrontend('usb')

while True:
    target = clf.sense(RemoteTarget('106A'), RemoteTarget('106B'), RemoteTarget('212F'))
    if target is None:
        sleep(1)
        continue

    serial = target.sdd_res.hex()
    tag = nfc.tag.activate(clf, target)

    if not tag.ndef:
        print("No NDEF records found!")
        continue
    
    for record in tag.ndef.records:
        print("Found record: " + str(record))

    record = ndef.UriRecord("https://www.example.com")
    tag.ndef.records = [record]
    # Code is fine until it gets to these tag indexes
    tag[15] = tag[15] | 0x0F
    tag[10] = 0xFF
    tag[11] = 0xFF

I get the error:

  File "test.py", line 26, in <module>
    tag[15] = tag[15] | 0x0F
TypeError: 'NTAG213' object does not support indexing

Answer 1

Looking that the Python library it has a simple method to make readonly using lock bytes or via password.

https://nfcpy.readthedocs.io/en/stable-0.10/modules/tag.html#nfc.tag.tt2_nxp.NTAG21x

Just call the protect method on the tag object with or without password (without password uses the lock bytes and is permanent read-only).

So the library has got programmed in it the right memory addresses and bits to flip for various cards including all the NTAG21x cards.