4. Ring Keychip

The Ring keychip is arguably simultaniously one of the most overkill while least utilised parts of the system. On-board is a PIC microcontroller, a dedicated cryptography chip, a hardware SHA engine for authentication, and flash storage.

4.1 Protocol

The PIC communicates with the system using a parallel bus. This bus is exposed physically on the keychip connector, and in software can be accessed using \\.\mxparallel. All bus communication is encrypted using AES 128 ECB, using a different key for each data direction. Send/receive is defined from the perspective of the Ring system. That is, the “Send” key handles data from the Ring to the keychip, and the “Receive” key handles data from the keychip to the Ring. The initial key values are:

4.1.1 Initial receive key:

75 6f 72 61 74 6e 65 6b 61 6d 69 68 73 75 6b 75

4.1.2 Initial send key:

66 6E 65 6B 65 72 61 77 64 72 61 68 61 67 65 73

All packets are first prefixed by a command ordinal (see below), then command-specific information. The base unit of transfer is 16 bytes due to AES 128. Unused bytes can contain anything, however mxkeychip chooses to pad using random bytes derrived from the current system time.

4.2 Storage locations

4.2.1 EEPROM

Stores entries detailing the tracedata metadata. There is a copy of the structure at 0x000 and a duplicate at 0x100. Each structure is comprised of 16 entries, where each entry first has a 4 byte CRC, then 12 bytes currently unknown.

4.2.2 NVRAM

Start	End	Content
1800_h	1bff_h	billing public key
1c00_h	1fff_h	ca certificate

Each block begins with a 4 byte integer indicating the length of the data following it (up to 1020 bytes).

4.2.3 Flash

Start	End	Content
00000_h	0ffff_h	tracedata sector 1
10000_h	1ffff_h	tracedata sector 2
20000_h	2ffff_h	tracedata sector 3
30000_h	3ffff_h	tracedata sector 4
40000_h	4ffff_h	tracedata sector 5
50000_h	5ffff_h	tracedata sector 6
60000_h	6ffff_h	tracedata sector 7
70000_h	70fff_h	nvram0
71000_h	71fff_h	nvram1
72000_h	72fff_h	nvram2
73000_h	73fff_h	nvram3
74000_h	74fff_h	nvram4
75000_h	75fff_h	nvram5
76000_h	76fff_h	nvram6
77000_h	77fff_h	nvram7
78000_h	78fff_h	nvram8
79000_h	79fff_h	nvram9
7a000_h	7a10b_h	billing info
7b000_h	7b10b_h	billing info dup

Each tracedata sector begins with a 128-byte bitfield (1024 bits) indicating which blocks in the sector have been populated. Following this are 1022 blocks, 64 bytes each. (the last two of the theorhetical 1024 would overlap into the next sector). Each slot is individually encrypted with DES ECB, using key 4D77F1748D6D1094.

This is implemented via the AT25DF041A 4Mbit flash chip on the keychip PCB. The maximum address is therefore 7ffff_h.

4.3 Command Ordinals

Ordinal	Command
`0`	4.4 SetKeyS
`1`	4.5 SetKeyR
`2`	4.6 SetIv
`3`	4.7 Decrypt
`4`	4.8 Encrypt
`5`	4.9 GetAppBootInfo
`6`	4.10 EepromWrite
`7`	4.11 EepromRead
`8`	4.12 NvramWrite
`9`	4.13 NvramRead
`10`	4.14 AddPlayCount
`11`	4.15 FlashRead
`12`	4.16 FlashErase
`13`	?
`14`	4.17 FlashWrite
`15`	?
`16`	?
`17`	?
`18`	?
`19`	?
`20`	4.18 KcGetVersion
`21`	4.19 SetMainId
`22`	4.20 GetMainId
`23`	4.21 SetKeyId
`24`	4.22 GetKeyId
`25`	4.23 GetPlayCounter

4.4 SetKeyS

Sets the “send” encryption key. The key is changed before communication of the reply.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	0	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	key

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
key	The send key

4.5 SetKeyR

Sets the “receive” encryption key. The key is changed before communication of the reply.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	1	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	key

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
key	The receive key

4.6 SetIv

Reset the game key IV to its initial value

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	2	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

4.7 Decrypt

Decrypt a block of data using the game key

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	3	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
	ct

Receive	pt

Variable
ct	The encrypted ciptertext
pt	The decrypted plaintext

4.8 Encrypt

Encrypt a block of data using the game key

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	4	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	pt

Receive	ct

Variable
pt	The decrypted plaintext
ct	The encrypted ciptertext

4.9 GetAppBootInfo

Request the AppBoot structure from the keychip. The AppBoot structure is 256 bytes, thus requires 16 packets.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	5	0	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	CRC				Format				Game ID				Region	Model type	System flag	?
	Platform ID			DVD flag	Network address

	206 bytes padding

	Seed

Variable
CRC	CRC32 checksum of the reamining 252 bytes
Format	AppBoot format type. The described type is format `1`
Game ID	Four character game ID. For example, `SBTR`
Region	Region bitmask
Model type	Model type this keychip is for
System flag	System flag bitmask
DVD flag	Is update from DVD allowed
Network address	Permitted subnet. Fourth octet is null

Note: I’m not sure what the 0 is for here. Surprises await for anything other than 0 :D

4.10 EepromWrite

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	6	reg	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	data

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
reg	EEPROM register to write. EEPROM is divided into 16x16 byte registers
data	The data to write

4.11 EepromRead

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	7	reg	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	data

Variable
reg	EEPROM register to read. EEPROM is divided into 16x16 byte registers
data	The data read

4.12 NvramWrite

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	8	addr		blocks	*	*	*	*	*	*	*	*	*	*	*	*
Send	data

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
addr	Absolute offset in NVRAM to write at
blocks	The number of 16 bytes blocks to write
data	The data to write. This will require `blocks` packets

4.13 NvramRead

	0	1	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	8	addr	blocks	*	*	*	*	*	*	*	*	*	*	*	*

Receive	data

Variable
addr	Absolute offset in NVRAM to read at
blocks	The number of 16 bytes blocks to read
data	The read data. This will require `blocks` packets

4.14 AddPlayCount

Increment the playcount value

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	10	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

4.15 FlashRead

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	11	addr			# bytes			*	*	*	*	*	*	*	*	*

Variable
addr	Absolute offset in flash to read at
# bytes	The number of bytes to read

Important: Data is returned as raw bytes transmitted over parallel, without encryption or packet encapsulation.

4.16 FlashErase

Honestly not actually sure if this is an erase or what. Still working on it!

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	12	addr			*	*	*	*	*	*	*	*	*	*	*	*

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

4.17 FlashWrite

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	14	addr			# bytes			*	*	*	*	*	*	*	*	*

Receive	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
addr	Absolute offset in flash to write at
# bytes	The number of bytes to write

Important: Data is transmitted immediately following transmission of the first packet. Is it transmitted as raw bytes over parallel, without encryption or packet encapsulation. The response packet is transmitted after # bytes have been received in this manner.

4.18 KcGetVersion

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	20	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	version		*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
version	Two-byte version number. Keychips are observed to return 01,04.

4.19 SetMainId

Set the Main ID on the keychip, if not already set.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	21	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	Main ID

Receive	err	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
Main ID	The new keychip Main ID. No validation is performed of this value.
err	? (0?) when succesful, FF_h otherwise

4.20 GetMainId

Get the Main ID on the keychip.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	22	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	Main ID

Variable
Main ID	The keychip Main ID

4.21 SetKeyId

Set the Key ID on the keychip, if not already set.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	23	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*
Send	Key ID

Receive	err	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Variable
Key ID	The new keychip ID. No validation is performed of this value.
err	? (0?) when succesful, FF_h otherwise

4.22 GetKeyId

Get the Key ID on the keychip.

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	24	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	Key ID

Variable
Key ID	The keychip ID

4.23 GetPlayCounter

Get the current playcount value

	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F
Send	24	*	*	*	*	*	*	*	*	*	*	*	*	*	*	*

Receive	playcount				*	*	*	*	*	*	*	*	*	*	*	*

Variable
playcount	The billing playcount value