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maybe my question would be lost in the forum, but has somebody work with RFID tags? I know I can read them, but can I write or modify the inside data? Does anyone know where can I find more about this?
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You cannot rewrite data stored in the user memory of a passive ultrahigh-frequency (UHF) RFID tag by sending a signal from a Wi-Fi access point to the tag directly, assuming that is what you are asking.
RFID Standards: 125 Khz (low-frequency) tags are write-once/read-many, and usually only contain a small (permanent) unique identification number. 13.56 Mhz (high-frequency) tags are usually read/write, they can typically store about 1 to 2 kilbytes of data in addition to their preset (permanent) unique ID number.
In addition to a unique ID, many tags can also store further data; often, this data can be “reprogrammed”.
125 Khz (low-frequency) tags are write-once/read-many, and usually only contain a small (permanent) unique identification number.
13.56 Mhz (high-frequency) tags are usually read/write, they can typically store about 1 to 2 kilbytes of data in addition to their preset (permanent) unique ID number.
860-960 Mhz (ultra-high-frequency) tags are typically read/write and can have much larger information storage capacity (I think that 64 KB is the highest currently available for passive tags) in addition to their preset (permanent) unique ID number.
Most read/write tags can be locked to prevent further writing to specific data-blocks in the tag's internal memory, while leaving other blocks unlocked. Different tag manufacturers make their tags differently, though.
Depending on your intended application, you might have to program your own microcontroller to interface with an embedded RFID read/write module using a manufacturer-specific protocol. That's certainly a lot cheaper than buying a complete RFID read/write unit, as they can cost several thousand dollars. With a custom solution, you can build you own unit that does specifically what you want for as little as $200.
RFID Journal
RFID Toys (Book) Website
SkyTek - RFID reader manufacturing company (you can buy their products through third-party retailers & wholesalers like Mouser)
Trossen Robotics - You can buy RFID tags and readers (125 Khz & 13.56 Mhz) from here, among other things
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I did some development with Mifare Classic (ISO 14443A) cards about 7-8 years ago. You can read and write to all sectors of the card, IIRC the only data you can't change is the serial number. Back then we used a proprietary library from Philips Semiconductors. The command interface to the card was quite alike the ISO 7816-4 (used with standard Smart Cards).
I'd recomment that you look at the OpenPCD platform if you are into development.
This is also of interest regarding the cryptographic functions in some RFID cards.
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