Simultaneous RFID Tag Reader Hookup Guide

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Contributors: Nate
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Examples 6, 7, 8 - Passwords

The Example6-Read Passwords example will display the Access and Kill passwords of a given tag. The Access password allows a user to lock a tag, preventing modification of various parts of the memory (EPC, User, etc). The Kill password is needed to disable a tag. Both passwords are 0x00000000 by default.

Reading the Access and Kill Passwords on Gen2 RFID

Passwords are 0x00000000 by default

Example7-Write Passwords will show you how to write new passwords for the Access and Kill portions of memory.

Writing new passwords to RFID tag

New passwords have been written!

To verify these new passwords have been written load Example6 again.

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The new passwords are correctly recorded

It may seem odd that you can view the passwords. The Gen2 protocol has quite a few methods to lock out various portions of the memory preventing them from being read. Once the Access password is set the ability to read passwords, read user memory, and read portions of the EPC can all be controlled; this is called locking. Currently, locking is not supported in the Arduino library but it is available in the URA and in the Mercury API.

The final Example8-Kill Tag is the really fun one. It’s pretty rare that you’ll need to kill a tag but we find the concept fascinating and wanted to build in support for it.

Note: Killing a tag blows an internal fuse to the IC and makes the tag irreversibly dead.

It is very good to see that the protocol has the kill feature. Killing a tag makes sense after an item has been purchased (gallon of milk) or a process has been completed (dry cleaning has been picked up). By limiting the life-span of a tag you can help protect end user privacy and tracking.

The Gen2 protocol is well written and prevents a user from walking into a Wal-Mart and blasting away all the tags that haven’t been configured. The default Kill password is all 0s but any tag will ignore the kill command with the password set to 0s. Therefore, you must first write a non-zero kill password (using Example7) then you must issue the kill command using the new password.

Example of killing an RFID tag

Tag is now D E D, dead.

If you’re very paranoid about someone else using an UHF RFID reader/writer to reconfigure your tags consider writing new Access and Kill passwords to your tags then use the Universal Reader Assistant to lock the tags.