|0x8||0x2||Type (always 2)|
|0xA||0x2||Version (always 1)|
The first step is to check the HMAC of the file. The process is to use the
Keystone HMAC Key from the Keys#PFS_Secret_Keys page to check the
keystone HMAC at position 0x40 in the file.
If it is correct, it proceeds to passcode HMAC check which is not present on retail units.
Passcode HMAC Key from the Keys#PFS_Secret_Keys to calculate HMAC of
passcode and check
passcode HMAC at offset 0x20.
passcode is a string of 0x20 bytes long that should match [A-Za-z0-9\-_] regex.