Amiibo are NFC figures made by Nintendo, used in games in different forms (different in each game). It can be used with the New3DS and the Old3DS with an IR peripheral.

Tag information

Model: NTAG215
Manufacturer: NXP Semiconductor
Page size: 4 bytes
Page count: 135 pages (540 bytes)
Data pages: 126 pages (504 bytes)

Page layout

Excluding the auth-related configuration pages at the end, the structure of the NFC pages is the following:

NFC page	Total pages	Raw byte offset in EEPROM	Total byte size	Writable	Description
0x0	0x3	0x0	0xC	No	Standard NTAG215: 9-byte serial-number, "internal" u8 value, then the two lock bytes which must match raw binary "0F E0".
0x3	0x1	0xC	0x4	No	Standard NTAG215: "Capability Container (CC)". Must match raw binary "F1 10 FF EE".
0x4	0x1	0x10	0x4	Yes	Last 3-bytes here are used with the following HMAC where the size is 0x1DF-bytes. The u16 starting at byte1 is used for the first two bytes in the 0x40-byte input buffer for Amiibo crypto init. The first byte must be 0xA5. The remaining bytes are initially(before the Amiibo is written to) all-zero. Byte[2](maybe big-endian u16 starting at byte1?) here is incremented each time the Amiibo is written to.
0x5	0x8	0x14	0x20	Yes	The system crypts 0x1A0-bytes with some data from here, see below.
0xD	0x8	0x34	0x20	No	SHA256-(HMAC?) hash. The first 0x18-bytes of this hash is section3 in the encrypted buffer.
0x15	0xB	0x54	0x2C	No	This is plaintext data, see below.
0x20	0x8	0x80	0x20	Yes	SHA256-HMAC hash over 0x1DF-bytes: first 3-bytes are from the last 3-bytes of page[4], the rest is over the first 0x1DC-bytes of the plaintext data.
0x28	0x45	0xA0	0x114	Yes	This is section1 in the encrypted buffer.
0x6D	0x15	0x1B4	0x54	Yes	This is section2 in the encrypted buffer.
0x82	0x1	0x208	0x4	No	Standard NTAG215: first 3-bytes are dynamic lock bytes. Must match raw binary "01 00 0F".
0x83	0x1	0x20C	0x4	No	Standard NTAG215: CFG0. Must match raw binary "00 00 00 04".
0x84	0x1	0x210	0x4	No	Standard NTAG215: CFG1. Must match raw binary "5F 00 00 00".

Specifications can be found on this image, which is a compilation of screenshots made by scanning a Samus amiibo with the Android App "NFC TagInfo":

See here regarding the Amiibo encryption.

Data structures

Structure of the data starting at page 0x15

Offset	Size	Description
0x0	0x8	Amiibo Identification Block
0x8	0x4	?
0xC	0x20	Probably a SHA256-(HMAC?) hash.

Structure of Amiibo Identification Block

Offset	Size	Description	Notes
0x0	0x2	Game & Character ID	First 10 bits are the Game ID and last 6 bits are Character ID.
0x2	0x1	Character variant
0x3	0x1	Amiibo Figure Type
0x4	0x2	Amiibo Model Number
0x6	0x1	Amiibo Series
0x7	0x1	Version	Always 0x02

Encrypted data buffer structure

Encrypted buffer offset	Raw byte offset in NFC EEPROM	NFC page	Byte size	Notes
0x0	0x14	0x5	0x20
0x20	0xA0	0x28	0x114
0x134	0x1B4	0x6D	0x54
0x188	0x34	0xD	0x18	This data is included in the crypto buffer, even though this data isn't actually encrypted(this is part of a hash).

Structure of the plaintext data

Offset	Size	Description
0x0	0xB0	Amiibo settings are stored within here.
0xB0	0xD8	AppData, for the user-application specified in the above Amiibo settings. The data stored here is application-specific. The data stored here is normally all big-endian, even when the user-application is only for 3DS systems. Note that this data is initially uninitialized, and at least some of it will stay that way unless an application clears/initializes all of it.
0x188	0x18	Not used in "decrypted" form, since this isn't encrypted to begin with.

Structure of Amiibo settings

Offset	Size	Description
0x0	0x1	Flags. The low 4-bits here are copied to the struct used with NFC:GetAmiiboSettings. The below setup date is only loaded when bit4 and/or bit5 here are set, otherwise value 0 is used instead for the date. Bit4=1 indicates that the Amiibo was setup with amiibo Settings: NFC:GetAmiiboSettings will return an all-zero struct when this is not set. Bit5=1 indicates that the AppData was initialized. NFC:InitializeWriteAppData will return an error if this is value 1, when successful that command will then set this bit to value 1.
0x1	0x1	Country Code ID, from the system which setup this amiibo. This is copied to the struct used with NFC:GetAmiiboSettings.
0x2	0x2	This big-endian u16 counter is incremented each time that the CRC32 at offset 0x8 gets updated by NFC:InitializeWriteAppData, due to that value not matching the calculated one. When this value is already 0xFFFF, this counter won't be updated anymore.
0x4	0x2	u16 big-endian date value, see below. This is the date for when the Amiibo was initially setup in amiibo Settings. This is also written by NFC:InitializeWriteAppData.
0x6	0x2	u16 big-endian date value, see below. This is the date for when the Amiibo was last written to.
0x8	0x4	Big-endian CRC32 value with initialval=~0, with the 8-byte output from Cfg:GenHashConsoleUnique. This is written by NFC:InitializeWriteAppData, when the current value doesn't match the calculated one.
0xC	0x14(10*2)	UTF-16BE Amiibo nickname.
0x20	0x60	Owner Mii.
0x80	0x8	Big-endian application programID/titleID from the application which initialized the AppData, zero otherwise. This is only written, not compared with the user application titleID: doing the latter would break games' cross-platform compatibility with 3DS<>Wii U(Super Smash Bros 3DS/Wii U for example).
0x88	0x2	u16 big-endian. This value is incremented each time the Amiibo is written to. When this value is already 0xFFFF, this counter won't be updated anymore.
0x8A	0x4	Big-endian u32 Amiibo AppID.
0x8E	0x2	?
0x90	0x20	Probably a SHA256-HMAC hash.

Format of the big-endian date values:

Bit	Description
0-4	Day
5-8	Month
9-15	Year, relative to 2000.

3DS read/write procedure

Note this is the procedure used by the console, but isn't the only way of reading them.

Read procedure

GET_VERSION
READ, startpage=0x03.
PWD_AUTH. Key is based on UID.
FAST_READ: startpage=0x00, endpage=0x3B
FAST_READ: startpage=0x3C, endpage=0x77
FAST_READ: startpage=0x78, endpage=0x86

Therefore, *all* pages from the Amiibo NFC tag are read, including the configuration pages at the end.

Write procedure

GET_VERSION
READ, startpage=0x03.
PWD_AUTH. Key is based on UID.
Multiple WRITE commands for writing to pages 0x04..0x0C. The first byte for page[4] is zero here.
Multiple WRITE commands for writing to pages 0x20..0x81.
Use the last 3 commands from the above reading section.
WRITE: page=0x04, same data as before except first byte is 0xA5 this time.
FAST_READ: startpage=0x04, endpage=0x04

Games using Amiibo AppData

The following is a list of games which actually store game-specific data on Amiibo, not *just* using Amiibo for checking character IDs:

Name	Available for (New)3DS	Available for Wii U	Amiibo AppID	AppData structure / link to info	AppData modification for exploitation notes.
Super Smash Bros	Yes	Yes	0x10110E00	[1]	No crash ever triggered via AppData fuzzing.
Mario Party 10	No	Yes	?	N/A	N/A
Animal Crossing: Happy Home Designer	Yes	No	0x0014F000	N/A	The initial AppData handling doesn't appear to have any vuln(s), going by manual code-RE for update v2.0. Fuzzing wasn't attempted.
Chibi-Robo!: Zip Lash	Yes	No	0x00152600	The entire AppData is read by the game, but only the first 0x10-bytes are actually used.	No crash ever triggered via AppData fuzzing.
Mario & Luigi: Paper Jam	Yes	No	0x00132600	Starts with the process-name("MILLION"). The rest seems to be bitmasks maybe?	No crash ever triggered via AppData fuzzing, when viewing "character cards"(just unlocks various cards).
The Legend of Zelda: Twilight Princess HD	No	Yes	0x1019C800	Unknown.	No crash/hang ever occurred when using amiibo in-game for "Cave of Shadows". With the amiibo quick-start option at the title-screen, only errors ever occurred(<quick-start data not found> / <quick-start data is for another user>).

External links

Wii U Gamepad and Amiibo information on WiiUBrew.