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This is cool, but the most interesting part is the part that requires investigation, i.e., what do the compatibility tools write to the card to make it iOS-compatible? I've done some work with iOS NFC, but not enough to have experienced the undocumented quirks.

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My read of the proxmark code (https://github.com/RfidResearchGroup/proxmark3/blob/master/c...) is that the `ndefformat` formatted the tag MAD (https://www.nxp.com/docs/en/application-note/AN10787.pdf), which you'd do for NDEF, then had a single TLV TERMINATOR at the block where the NDEF message starts. Then he used NFC Tools to write on an NDEF text record (which iOS background reading would ignore) and maybe something else? After that he then used `ndefwrite` to write on a URL record. I wonder if he could have skipped the NFC Tools and written the URL record and gotten the same result. Proxmark dumps before and after using NFC Tools would be insightful.

Ya, I have no clue tbh.

This is one of those cases where I know I really should investigate further, but I'm taking this one step at a time. Perhaps digging in to the "why" will become a follow-up post

But what happens if you dump the card with the Proxmark? Surely you should be able to see some differences.

Actually, I have all the components, so I'll try this now and report back.

My quick eye-skim didn't see much, but I'll do a byte-for-byte diff. I imagine its a difference in the NDEF headers? (but even that doesn't make sense, since I wrote the headers again from the pm3)

Well it turns out I'm much worse at this than I thought, as I can't even figure out what kind of cards I have. I'm learning, though!

HN formatting is going to do bad things here..

Here's the first 6 blocks of the card after I ran through the instructions of the post, then a ndefformat-only card (that never touched an iphone).

[=] 0 | 0 | 00 56 78 BB 95 08 04 00 02 B2 1E 24 23 27 1E 1D | .Vx........$#'.. [=] | 1 | 14 01 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 | ...�.�.�.�.�.�.� [=] | 2 | 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 | .�.�.�.�.�.�.�.� [=] | 3 | A0 A1 A2 A3 A4 A5 78 77 88 C1 89 EC A9 7F 8C 2A | ......xw.......* [=] 1 | 4 | 00 00 03 12 D1 01 0E 55 04 65 77 70 72 61 74 74 | ....�..U.ewpratt [=] | 5 | 65 6E 2E 63 6F 6D FE 00 00 00 00 00 00 00 00 00 | en.com�.........

[=] 0 | 0 | 00 56 78 BB 95 08 04 00 02 B2 1E 24 23 27 1E 1D | .Vx........$#'.. [=] | 1 | 14 01 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 | ...�.�.�.�.�.�.� [=] | 2 | 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 03 E1 | .�.�.�.�.�.�.�.� [=] | 3 | A0 A1 A2 A3 A4 A5 78 77 88 C1 89 EC A9 7F 8C 2A | ......xw.......* [=] 1 | 4 | 03 00 FE 00 00 00 00 00 00 00 00 00 00 00 00 00 | ..�............. [=] | 5 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................

Here's mine:

https://www.pastery.net/tckuyc+dausye/

Ya, looks like the iPhone is tinkering with the NDEF message itself.

If my Android phone wasn't dead, I'd love to compare an iPhone's write against the Android NFC Tools app's write.

If anyone else has an iPhone, an Android phone, and a Proxmark, I'd be interested in seeing a three-way diff between them all.

EDIT: I'm going to try to cross-post to the DT forum to see if anyone has ideas.

I've got both phones next to me, what do you want me to do exactly?

Wipe the card.

Make a dump after doing "hf mf ndefformat".

Then make a dump after writing a payload from an iPhone. (since iPhone seems to want ndefformat anyways)

Then wipe again and make a dump after writing from Android.

Here you go: https://www.pastery.net/xajezk+gbkqqz+aqwygg+ukrdad/

Thank you very much!

Something's clearly up there. You can see that even IOS and Android disagree with each other on what NDEF should look like by a few bytes. Very interesting.

Yep, 89 EC A9 7F 8C 2A 00 00 on iOS versus FF FF FF FF FF FF on Android. Interesting how the number of bytes is different, I should play with them a bit.

There's lots of info about the NDEF "packet" format online.

I used this page as reference when I was putting together the "magic bytes" in the final section of the blog post: https://www.oreilly.com/library/view/beginning-nfc/978144932...

This is fantastic, thanks!

Also, one thing that might be of interest: Even after a wipe and an ndefformat, my Android-written tag can be read by my iPhone 15.

NFC tools will only read it in compatibility mode, though.

Are you sure? The NFC app for iPhone can always read tags. Its specifically getting phones without the app to read them.

Try wiping, then writing a URL from Android.

Then just tap to the iPhone and see if Safari opens or not. It shouldn't

Yes:

https://imgz.org/i9ZqL6Ax.png

I don't know if it's Vivaldi doing that, but I can't imagine they would have added NFC tag reading capability to the browser specifically.

Feel free to email me if you want, btw, as this thread is getting a bit too deep.

If a URL is written using NFCTools on iPhone, iOS will open it in the default browser without using NFCTools, or in the related app (eg Instagram) if there is one.

I find this only to be true when used on the same iPhone where NFCTools was used.

If you try to have another iPhone detect the badge, it appears not to work - unless you use NFCTools on that iPhone, too. I don't have conclusive proof but that's what the evidence seems to indicate.

Are you seeing something different?

Proxmark's "auto" command should get you most of the way to knowing. Then check if any of the "hf mf c*" commands work on it (in which case, you have a gen1a magic card)

Nice, I didn't know about auto, thanks! It turns out I have some Gen 1a "magic" cards (as in, actually in a card form factor), and some tags that seem to be Gen 3, but not magic?

There's approx 4 generations of "Magic".

Gen 1, 1a, 3 and 4 all use special commands to unlock and edit block 0.

Gen 2 treats block 0 as always being r/w. This allows Android phones to directly write to it (but also makes it possible to lock the card).

In terms of pm3 commands, "auto" tries everything. You might also want to use "lf search" or "hf search" to only try one of your antennas and not the other.

The actual Magic part isn't really important here, since my phone doesn't even care about block 0. It just makes it easier to read and wipe the card when you have the extra command set at your disposal.

This is great, thanks! Do you know of any resource to learn more about Mifare cards? Is "beginning NFC" that you linked me to a good general resource?

All my knowledge is trial & error.

I've found the people over in the DT forum are pretty helpful with the cloning and usage aspect of things: https://forum.dangerousthings.com

Additionally, Iceman's Discord people has tons of smart people: https://discord.com/invite/iceman

Thank you!

Hm, its definitely blocks 0-2. All remaining blocks after that are identical.

Going to look further at the actual data in the first 3 blocks momentarily.

I didn't intend for what I wrote to be a criticism; that's on me. I just found it funny the most interesting step was akin to "... and now you've drawn the animal", if you understand the reference.

I suspect the comment (above, at the time I wrote this), where they mention that Apple only wants partners to be usable, is the Ockham's Razor answer.

Probably some "magic key" ID.

But this is not my area of expertise. It's a cool story, though, and why I like hanging here. Considering getting a Proxmark and the NFC Tools app, just to play around.

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