Memory Card
Partitions
Memory Card can be accessed with SceMsif module. It has the following partitions:
| code | type | offset | size | name | description |
|---|---|---|---|---|---|
| 0xD | raw | 0x400000 | 0x400000 | Some data | |
| 0x8 | exfat | 0x800000 | (mc size - 0x800000) | ux0 | Memory Card contents |
mediaid
Memory Card raw partition contains so called mediaid data. It can be accessed as sdstor0:mcd-lp-act-mediaid. One of the important fields in this partition is a field that stores special sleep_session_id. This is a random number that is generated and stored there before PS Vita goes to sleep mode. Upon wakeup this sleep_session_id is verified and error is shown if the value is unexpected, which leads to power off. Hence why one cannot swap Memory Card while PS Vita is in sleep mode.
Findings about Memory Card
It turns out that Memory Card supports standard Memory Stick protocol (TPC).
SceMsif driver allows to read and write single values on Memory Card according to the (TPC) protocol. It can also read and write chunks of data from Memory Card using (TPC) protocol.
It is still not confirmed, however based on some findings in SceMsif driver, it is hypothesized that PSVita Memory Card is simply a new generation of Memory Stick with additional authentication layer. These findings include:
- Support of TPC protocol.
- SceMsif driver contains code that can handle
Model Name Device Information Entry(in attribute area of the Memory Card). This code clearly shows that standard Memory Stick should be supported. - Dump of real Memory Card shows that
Attribute Information Area Confirmation Structureis valid.
Memory Card Initialization
Much like SD standard allows execution of vendor specific commands through CMD56, PS Vita Memory Card has specific commands 0x48, 0x49, 0x4A and 0x4B. To be able to read from Memory Card, it has to be properly initialized with commands 0x48 and 0x49 first. It is not completely tested yet, but commands 0x4A and 0x4B are probably not required, and used by PS Vita to check that Memory Card is genuine.
Memory card initialization also uses rmauth_sm.self functions 1 and 2. Function 1 is used to obtain some data from Cmep (1 byte). Function 2 is used to set key, that is obtained from Memory Card, into keyring 0x1C of SceSblDMAC5DmacKRBase keyring. For encryption during Memory Card authentication, SceMsif driver uses 3-DES-CBC-CTS cipher. Key that is returned from Memory Card is unique to that Memory Card and is signed with ECDSA-224 signature (custom curve). This signature is verified by SceMsif driver.
Table of ECDSA-224 parameters is stored in data section of SceMsif driver. Table of ECDSA-224 parameters is encrypted with AES-128-CBC (and some tweak?, this still have to be double-checked). AES keys are stored in data section of SceMsif driver. There are multiple keys from which - one is chosen. But it seems to be same key. AES keys are encrypted. They are decrypted with encdec_w_portability_sm.self function 0x2000A.
The ECDSA signature received from the memory card looks fixed regardless of session_id. So there is no private key in the memory card and it is possible that the signature is embedded in the factory.
Faking Memory Card with hardware
Faking Memory Card with hardware is not entirely possible because ECDSA-224 private key for command 0x4B is still unknown. In theory, specific key and signature pair can be taken (dumped) and put into clone Memory Cards. However they can be blacklisted in next System Software update.
Patching in software
Commands 0x48 and 0x49 are only used to verify that Memory Card is genuine. Data given from Memory Card is used to calculate IV and compare it with IV that is calculated by the Memory Card. This can be removed by patching.
Command 0x4A is used by Memory Card to verify that PS Vita is genuine. Another IV is computed and sent to Memory Card to initialize it. This unlocks all I/O operations. This can be removed by patching.
Command 0x4B is used by PS Vita to verify that Memory Card is genuine. This is done by checking the Memory Card key that is signed with ECDSA-224 signature. This can be removed by patching.