NDEF | Read and Write NDEF Messages

A NdefMessage is made up of multiple NdefRecord items and you msg has 1 record

so this should do it (not tested)

You need to read the datasheet for the tag.

Section 8.5.7 and allows you with the AUTH0 field to set the first page at which the password is used from.

Thus the first part of the Tag can be readable and later pages can be read/write protected. As long as the tag is big enough to store Ndef message at the beginning of the Tag and your private data at the end of the Tag without using overlapping pages you can achieve free to read and password protected data.

You can also set the AUTHLIM to set the maximum number of negative password verification attempts so that it is not possible to brute force the password.

To configure these features you need to write to the appropriate memory pages using the low level NfcA transceive commands detailed in the datasheet.

The biggest problem you have with password protection is if you freely hand out an App that uses the password as it is trivial to reverse engineer the password from the JVM byte code that uses it.

You don't really need to know the different Tags are identified but having a good understanding of how the different levels of protocols and standards fit together is key, this is where this diagram from wikipedia is good.

You don't seem to be doing any foreground detection, really manifest entries are only used to start your App via NFC if not already running.

If your App is running you should use one of the 2 foreground detection API's, the old an not so reliable enableForegroundDispatch or the newer and better enableReaderMode

Here is an example of how use the better enableReaderMode

You can use both of these in conjunction with Manifest filters to handle NFC when your App is and is not running when the NFC Tag is presented.

Also note that your Manifest filter won't trigger for the NdefFormatable of your write method, your Manifest filter need to filter for ACTION_TECH_DISCOVERED and android.nfc.tech.NdefFormatable. See Here for details

The first byte is the length of the characters of the language string

So this should work (my dart is not that good)

If you intend to see what's the decorator @app.route() does, the answer lies in Python flask source code. I'm using flask 1.1.2 (the newest stable version currently is 2.0.0), and here is what it's defined in the file app.py, putting aside the many comments:

So the normal pattern for NFC in Android is:-

1)When you App is not running an you want it started when a certain type of NFC Tag is presented to the device then you put your intent-filters in the manifest. Your App then gets started and passed an Intent that you need to process in your onCreate method using getIntent()

2a)Your App is already running in the foreground then you use enableForegroundDispatch, giving it a pending Intent on what you want to be notified about, this is then processed in onNewIntent when your App is restarted (paused and resumed) to receive the Intent.

onNewIntent won't get invoked by any manifest entry.

or

2b)Your App is already running in the foreground then you use enableReaderMode which is a better replacement for enableForegroundDispatch, you then process the Tag in onTagDiscovered which is in a separate thread.

How to process the Intent received via pattern 1 and 2a is the same, just they need to be called from the correct path in the code that matches the method that triggered the Intent i.e in onCreate or in onNewIntent

Check out Empty NFC Tag read and write Android Application. Mobile own message returning while scanning Empty Tag but Application not working? for an example of how to use Manifest and enableForeGroundDispatch

The are also plenty examples of using enableReaderMode on Stackoverflow as well.

To handle unformatted Ndef Tags change your "nfc_tech_filter.xml" file to the one below:-

You need to encrypt with the private key and then decrypt with the public key

There are two problems with this code.

1)You have created a "stream of bytes" of the ndef message but the SimpleMFRC522 package expects a Unicode String and encodes it to convert it to a "stream of bytes", so basically as it is already a "stream of bytes" it cannot be double encoded.

2)The Mifare S50 chip is a Mifare Classic family chip and these are a proprietary format and don't conform to the NFC Forum Standards and thus don't have a Standards defined way to store Ndef data on them (You need to do more than write a raw set of bytes to the memory to chip for it to be recognised as the data being the Ndef format of data).

For NFC standard compliant/compatible chips there are a number of defined types of how the Ndef data is stored on each type.

While NXP has defined a proprietary way to store Ndef data on a Mifare Classic chip, but the "SimpleMFRC522" is very simple indeed and does not have the code to write the Standard Ndef messages never mind the non standard proprietary methods.

I also note that while the iPhone hardware can read Mifare Classic cards at the low level, I'm not sure it has implemented the Ndef data format on top as well. I do know that some Android phones don't support the proprietary Mifare Classic Hardware at all.

I suggest you read https://www.nxp.com/docs/en/application-note/AN1305.pdf as this is the proprietary format definition on how to store NDEF data on these cards

Unfortunately the RC522 is very old and has limited capabilities and thus is not well supported by more capable Python NFC modules.

You might be better off with https://github.com/ondryaso/pi-rc522 as that at least allows you to write raw bytes.