Amiibos are Nintendo figures with small RFID tags inside them that enables integration with some Wii U, 3DS, and Switch games. With a compatible RFID/NFC reader, the data from the tags can be extracted. This is called a dump.
The Amiibo RFID tags happen to be NXP Semiconductor’s NTAG215 (see also the NTAG page), which can hold 540 bytes. So Amiibo dumps should be 540 bytes. Sometimes, the configuration pages are omitted, incomplete dumps are 520 bytes.
NTAG215 offers password protection for memory access, which is used for Amiibos. The password is derived from the tag’s 7 byte UID:
pw = 0xAA ^ uid ^ uid pw = 0x55 ^ uid ^ uid pw = 0xAA ^ uid ^ uid pw = 0x55 ^ uid ^ uid
The first byte of the UID is always
0x04 for NXP tags, and so it doesn’t make sense to use it in the password.
On top of the password protection NTAG215 offers, cryptography is used to encrypt and sign some sections of the user data in the tag. Marcos Del Sol Vives’ reverse engineered the Amiibo cryptography in his excellent amiitool.
For more information, see the Master keys page.