Reading and Writing RFID Tags

17 Dec 2018

I am going to start a project soon where I want to use RFID tags to enable user authentication and individual profiles for a home automation remote controller. I haven't worked with RFID tags before, even though they are fairly ubiquitous at this point. I imagine this is old hat to most folks, but I thought I'd share my learning.

I purchased an RC522 RFID Reader/Writer module and a set of RFID tags on Amazon. The RC522 chip itself offers multiple interfaces (SPI, I2C, Serial UART), but I discovered that the board that I got was only set up for SPI. I had wanted to use I2C, but decided it wasn't worth hacking up the board. The Reader/Writer supports most of the standard Mifare card types (Mini, 1K, 4K, Ultralight, DESFire EV1, and Plus). The tags that were included were Mifare 1K.

I had a breadboard already set up with a Sparkfun ESP8266 Thing Dev and a 128x64 OLED display, so I decided to use that for testing.

I've been using the Arduino IDE to program my Thing Dev and there is an MFRC522 library available so that worked out well. Took a while adjusting the pin configurations to get the SPI and I2C to coexist nicely.

Been having fun reading stuff that I have lying around. I had a Ventra ticket from a recent trip to Chicago and it happened to be an Ultralight card.

Then I moved on to testing the write capability using the example code that is in the library.

Here's the output:

Card UID: 72 DF 5D 96

PICC type: MIFARE 1KB

Authenticating using key A...

Current data in sector:

1 7 00 00 00 00 00 00 FF 07 80 69 FF FF FF FF FF FF [ 0 0 1 ]

6 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 0 0 0 ]

5 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 0 0 0 ]

4 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 0 0 0 ]

Reading data from block 4 ...

Data in block 4:

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Authenticating again using key B...

Writing data into block 4 ...

01 02 03 04 05 06 07 08 09 0A FF 0B 0C 0D 0E 0F

Reading data from block 4 ...

Data in block 4:

01 02 03 04 05 06 07 08 09 0A FF 0B 0C 0D 0E 0F

Checking result...

Number of bytes that match = 16

Success :-)

Current data in sector:

1 7 00 00 00 00 00 00 FF 07 80 69 FF FF FF FF FF FF [ 0 0 1 ]

6 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 0 0 0 ]

5 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 0 0 0 ]

4 01 02 03 04 05 06 07 08 09 0A FF 0B 0C 0D 0E 0F [ 0 0 0 ]

*************************************************************************************

The 1K card has 16 sectors of 4 blocks and each block has 16 bytes (16x4x16 = 1024 bytes). The fourth block (sector trailer) in each sector contains the authentication keys.

In the example above I was writing Block 4 which is the first block in the second sector. You can see the authentication key in Block 7.

The factory default is 0xFFFFFFFFFFFF.

Now I need to figure out what type of data keys I want to store for my application......

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Fred27 over 7 years ago

I'm glad you're enjoying your first forays into the world of RFID and NFC. If you're doing some home automation you can probably limit your efforts to just reading the ID on the card and having a list of IDs (stored wherever is convenient) that you give access to. No need to write to tags.

Fred - another NFC implantee!
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ralphjy over 7 years ago in reply to Fred27

The implementation that I'm considering would store the personalization info on the tag rather than the controller. The controller would have generic categories like access groups (admin,user,guest,etc) and slots for user preferences. That way, the controller could just read the info rather than need to look it up (either on the device or on the network or the cloud). I'm just starting so I haven't really looked at what different NFC/RFID protocols exist besides the Mifare ones. In truth, writing the tags is more of a learning exercise although I hate wasting that extra storage .

What type of info is stored on your implanted devices? Just a unique ID?
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e14phil over 7 years ago in reply to Fred27

Hey Dave, thats a great blog, I enjoyed reading it. Nice to see the similar experiences.
Mine is the https://dangerousthings.com/shop/xnti/ Which looks like the same as yours.
the xNTI are these two standards rolled into one: 13.56MHz ISO14443A & NFC Type 2 NTAG216 chip which basically emulates a MiFareUltralight.

Other options were:
https://dangerousthings.com/product-category/x-series/

For the Hackspace they actually changed the reader to support me and a few others who have it, Ill see if I can get the name for you.
Phil
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e14phil over 7 years ago in reply to e14phil

At the Hackspace we are using:
Keypad Reader - Paxton KP75
https://www.paxton.co.uk/products.asp?id=&strStage=specification&strFamily=net2&strProduct=375-130&strGroup=group-05119&…
Bear in mind that to get the Net2 software technically you need to be an installer, Or make friends with an installer
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Fred27 over 7 years ago in reply to e14phil

Good to know that that one works. Unfortunately our work Paxton system use the P series readers which are 125kHz. No appetite to upgrade just for my benefit. I'm lucky that our infrastructure guys have turned a blind eye to my keyboard emulating LoginNFC device.

Sorry if we're dragging your discussion off on a bit of a tangent ralphjy!
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ralphjy over 7 years ago in reply to Fred27

NP, these side discussions are informative.
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gadget.iom over 7 years ago in reply to Fred27

Paxton is a good system, used and installed it for years. Their token format is proprietary, though you can get multi-format readers that will read Paxton tokens, Mifare (13.56MHz) and EM4100 (125kHz).
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gadget.iom over 7 years ago in reply to Fred27

Paxton is a good system, used and installed it for years. Their token format is proprietary, though you can get multi-format readers that will read Paxton tokens, Mifare (13.56MHz) and EM4100 (125kHz).
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