Properly format Mifare for NDEF

[kamikazechaser]

• See https://www-sol6-de.translate.goog/tech/Mifare_Classic_-_NDEF/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp

go-pn532 NDEF formatted MCT dump:

       // WriteNDEF
	authResult, err := t.authenticateForNDEF()
	if err != nil {
		return err
	}

	if err := t.formatForNDEFWithKey(authResult.blankKey); err != nil {
		return fmt.Errorf("failed to format tag for NDEF: %w", err)
	}

	return nil

+Sector: 0
2A3E2C2F170804006263646566676869
00000000000000000000000000000000
00000000000000000000000000000000
FFFFFFFFFFFFFF078069FFFFFFFFFFFF
+Sector: 1
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 2
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 3
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 4
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 5
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 6
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 7
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 8
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 9
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 10
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 11
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 12
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 13
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 14
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF078069D3F7D3F7D3F7
+Sector: 15
00000000000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F7FF0780BCD3F7D3F7D3F7

Standard NDEF formatted MCT dump:

+Sector: 0
A2A1B5F34508040004C77A5A5C0F1490
0F0003E103E103E103E103E103E103E1
03E103E103E103E103E103E103E103E1
A0A1A2A3A4A5787788C1FFFFFFFFFFFF
+Sector: 1
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 2
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 3
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 4
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 5
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 6
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 7
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 8
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 9
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 10
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 11
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 12
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 13
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 14
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF
+Sector: 15
0300FE00000000000000000000000000
00000000000000000000000000000000
00000000000000000000000000000000
D3F7D3F7D3F77F078840FFFFFFFFFFFF

[kamikazechaser]

https://github.com/grassrootseconomics/go-pn532/blob/sohail/ethsafari-hack/mifare_extra.go

I have implemented this unsafe approach for fast bulk writing (~2 seconds for format + write, 1 second for write on blank NDEF formatted card). It would previously take me around 20 seconds and the written memory was not proper NDEF compatible. I'm using the standard NDEF format described above. Now the card is correctly picked up by iOS devices as well as mifare-classic-read-ndef libfreefare.

$ go run cmd/mifare/main.go
time=2025-08-30T15:55:02.041+03:00 level=INFO msg="writer started"
time=2025-08-30T15:55:02.041+03:00 level=INFO msg="waiting for tag to write" text=https://sarafu.network
time=2025-08-30T15:55:02.187+03:00 level=INFO msg="tag detected" type=MIFARE
time=2025-08-30T15:55:02.187+03:00 level=INFO msg="tag detection took" duration=42.464µs
time=2025-08-30T15:55:02.187+03:00 level=INFO msg="type assertion took" duration=1.397µs
time=2025-08-30T15:55:02.187+03:00 level=INFO msg="NDEF message creation took" duration=1.467µs
time=2025-08-30T15:55:04.179+03:00 level=INFO msg="NDEF formatting took" duration=1.922176017s
time=2025-08-30T15:55:04.247+03:00 level=INFO msg="writing NDEF message took" duration=67.710104ms
time=2025-08-30T15:55:04.247+03:00 level=INFO msg="writer exiting"
 

$ go run cmd/mifare/main.go
time=2025-08-30T15:56:49.686+03:00 level=INFO msg="writer started"
time=2025-08-30T15:56:49.686+03:00 level=INFO msg="waiting for tag to write" text=https://sarafu.com
time=2025-08-30T15:56:49.831+03:00 level=INFO msg="tag detected" type=MIFARE
time=2025-08-30T15:56:49.831+03:00 level=INFO msg="tag detection took" duration=54.896µs
time=2025-08-30T15:56:49.831+03:00 level=INFO msg="type assertion took" duration=1.397µs
time=2025-08-30T15:56:49.831+03:00 level=INFO msg="NDEF message creation took" duration=1.397µs
time=2025-08-30T15:56:49.918+03:00 level=INFO msg="writing NDEF message took" duration=68.009455ms
time=2025-08-30T15:56:49.918+03:00 level=INFO msg="writer exiting"

[kamikazechaser]

I noticed larger payloads that ended up touching sector 2 on wards had a serious slowdown on sector auths. Based on this well known layout we can apply some shortcuts:

	nKey = []byte{0xD3, 0xF7, 0xD3, 0xF7, 0xD3, 0xF7}
	fKey = []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}

        // ... authenticateNDEF
	switch keyType {
	case MIFAREKeyA:
		return t.AuthenticateRobust(sector, keyType, nKey)
	case MIFAREKeyB:
		return t.AuthenticateRobust(sector, keyType, fKey)
	}

I was able to cut down write time from 16 seconds to ~200ms

[wizzomafizzo]

@kamikazechaser Hey! sorry i missed this, i never got a notification. i made a new pr with your fork changes, they seem to be working well. what is the status on this?

[kamikazechaser]

@wizzomafizzo These are my final changes: https://github.com/grassrootseconomics/go-pn532/blob/sohail/ethsafari-hack/mifare_extra.go

I have written close to 1k cards this week alone with a medium size NDEF payload. Takes me an average of 13-15 min e2e (including physically moving the cards) to write 100 cards. It works on all devices and is read by all software that I have tested the cards on (libfreefare, nfctools, mct, pn532.js).

Since it is a bit hacky and i'm doing a lot of shortcuts to save me time, let me review what can go in here.