Implement T-Money balance parsing

[justuswilhelm]

I've written a small plugin for Metroflip that lets you read the balance off a T-Money card. I've tested it with my T-Money card bought in 2018 in Seoul, Korea.

I wasn't sure whether adding my code to metroflip_scene_detect_scan_callback is a good pattern. Metroflip might recognize other cards as T-Money that support the same Iso14443_4a protocol. Let me know if there's a better way.

The ISO7816 and KSX6924 reading mechanism is inspired by metrodroid.

[luu176]

Hi @justuswilhelm,

Thanks for your contribution! Wondering how we're going to implement this as mifare classic runs on that same protocol, it would probablt be best to check iso 14a at the very bottom of the else if loop. to make sure no other cards detect as T-Money. It would also be good for you to find something unique about T-Money cards, so if someone scans a regular 14a card that isn;t supported it also doesnt get detected as T-Money.

[justuswilhelm]

Thank you for your feedback. I'll take a look at this and find out if there's a way I can use the Mifare part for this somehow. I'll get back some time this month, so please wait.

[justuswilhelm]

Hi @justuswilhelm,

Thanks for your contribution! Wondering how we're going to implement this as mifare classic runs on that same protocol, it would probablt be best to check iso 14a at the very bottom of the else if loop. to make sure no other cards detect as T-Money. It would also be good for you to find something unique about T-Money cards, so if someone scans a regular 14a card that isn;t supported it also doesnt get detected as T-Money.

Hi, I haven't had time to look into this further this month, unfortunately. For the first solution, putting the check at the bottom, I can implement this. On the other hand, to check "unique" properties of the T-Money card would possibly require creating a Poller instance during the general card detection loop.

Do you have any suggestions for how to implement this?

[luu176]

Hi, I am currently working on a detection scheme for knowing what type of card it is based on the ATR (Answer To Reset). This value is unique to each public transport, so if you can find the ATR for T-Money or maybe I can ask around, and then I will implement.

[luu176]

I found this ATR:

3B 88 80 01 04 02 00 20 00 71 C1 40 DF

can you verify the bytes in that payload that DO match the ATR in your card please?

[luu176]

Can you read the card in the main nfc application in flipper and go to more>Info then scroll all the way down to historical bytes and it write that in here

[justuswilhelm]

Here's everything from the Flipper Zero dump in the .nfc file:

Filetype: Flipper NFC device
Version: 4
# Device type can be ISO14443-3A, ISO14443-3B, ISO14443-4A, ISO14443-4B, ISO15693-3, FeliCa, NTAG/Ultralight, Mifare Classic, Mifare Plus, Mifare DESFire, SLIX, ST25TB, NTAG4xx, Type 4 Tag, EMV
Device type: ISO14443-4A
# UID is common for all formats
UID: XX XX XX XX
# ISO14443-3A specific data
ATQA: 00 04
SAK: 20
# ISO14443-4A specific data
T0: 78
TA(1): 80
TB(1): B0
TC(1): 02
T1...Tk: 04 09 22 02

[luu176]

thanks, i've added your ATR, then I will fix your PR and merge

[justuswilhelm]

Thank you!