BCAT Content Container

From Nintendo Switch Brew
Jump to navigation Jump to search

Content downloaded by BCAT normally uses this container.

Header

Offset Size Description
0x0 0x4 Magicnum "bcat"
0x4 0x1 ?
0x5 0x1 Crypto type: 0x1 = type1, 0x2 = type2, 0x3 = type3. Everything else indicates plaintext.
0x6 0x1 ?
0x7 0x1 Secret-data index
0x8 0x8 Normally zero?
0x10 0x10 Base IV/CTR
0x20 0x100 RSA-2048 signature

The header is 0x120-bytes.

Key generation

The AES keydata is the output from pkcs5_pbkdf2_hmac, with SHA256: password = <passphrase string loaded from file>, salt = <below salt string>, and iteration_count=4096.

The passphrase is loaded from "<basepath>/passphrase.bin". passphrase_len=strlen(passphrase). 0x40-bytes are read from the file, with 0x0 being written to passphrase[total_read_data]. salt_len = strlen(salt).

salt is the snprintf output from "%016llx%s", where the former is the titleID, while the latter is secretdata_str. secretdata_str = secretdata_array[<value of hdr+0x7>].

Settings config for 1-byte <"bcat", "production_mode"> is loaded, when retval!=1 or output_config!=0, then secretdata_array = secretdata_array0(retail), otherwise secretdata_array = secretdata_array1(devunit). The latter only contains empty strings, while the former contains lower-case hex strings. There are 16 entries in each array.