NTAG is NXP Semiconductor’s name for a family of NFC RFID products. Amiibos use NTAG215 internally. NXP’s NTAG213/215/216 datasheet is truly excellent and worth a read. (The code is based on Rev. 3.2 / 2 June 2015 / 265332.)
Many constants/properties for interpreting Amiibo/NTAG215 dumps are sourced from the datasheet; where possible the exact section is indicated.
ISO/IEC 14443:2016 is the standard for “Identification cards – Contactless integrated circuit cards – Proximity cards”, which NFC (and therefore NTAG) products implement. There are four parts:
- Part 1: Physical characteristics
- Part 2: Radio frequency power and signal interface
- Part 3: Initialization and anticollision
- Part 4: Transmission protocol
For interpreting NTAG dumps, only part 3 is interesting, because it details the way the UID is stored and validated.
Unfortunately, getting a PDF of the standard costs real money. They are also very tedious - stick to the NTAG213/215/216 datasheet instead!