Certificate extraction tool

The tools and information in this repository are used to extract the device certificates and key from mfg.dat & calibration_01.bin files of BGW gateway devices. The certificates and key can be used to configure EAP authentication between a network gateway and an AT&T ONT device.

Instructions

• Method #1: Use a pre-built release binary. Download and unzip the latest Linux, Mac or Windows binary from a release: here. Place the binary application and an mfg.dat or calibration_01.bin file into the same folder and run the application. The application will create a .tar.gz file containing the key, certificates and example wpa_supplicant.conf file.
  • If the mfg.dat or calibration_01.bin file is in a different directory or has a different file name then the full path to the file can be passed as the first argument to the program. Example: $ decoder-windows-amd64 path/to/my/mfg.dat
• Method #2: Build & run the Go code. Ensure that you have Go installed (https://go.dev/doc/install).

  git clone https://github.com/abrender/mfgdat.git
  cd mfgdat
  go get .
  go run . path/to/my/mfg.dat
  

• Method #3. Bash script. This method only works with BGW210-700 devices. Download and run the parse-mfg-dat.sh script from this repository. The script will output the device key, certificates and MAC address to the console. The wpa_supplicant.conf.template file can be used as a template for creating your own configuration file. If there are multiple CA certificates (this is likely) then they can all be appended and placed into the same file.

Supported devices

This code supports the following devices models:

• BGW210-700
• BGW320-500
• BGW320-505
• BGW620-700

Certificate storage format details

Location

• mfg.dat: The certificate section begins at -0x4000 (-16,384) bytes from the end of mfg.dat. Given an mfg.dat of size 256k (0x40000), the certificate section begins at 0x40000 + (-0x4000) = 0x3C000.

• calibration_01.bin: The certificate section begins at the start of the file.

Format

The header and entries are encoded in 4-byte words, with the MSB (most significant byte) stored at the smallest memory address (big endian).

Starting Address	Length	Details
0x3C000	5 words	Header
0x3C014	(4 words) x (number_of_entries)	Entries
0x3C014 + (16 x number_of_entries)	variable	Raw data

Header

The header contains metadata information about the certificate section and entries. Each field is a 4-byte word.

Word	Value	Details
1	Magic	Always: 0x0E0C0A08
2	Magic	Always: 0x02040607
3	Length	Length of the certificate section, in bytes. This is relative to the start of the certificate section (at 0x3C000), therefore the first 2 (magic) words and this length field are included in the length.
4	Number of entries	Number of entries in the certificate section
5	Unknown	Unknown. Set to 0x0

Entries

Entries contains metadata about the type of entry and where to locate the entry's raw data.

Each entry is composed of 4x 4-byte words as described in the table below.

Word	Value	Details
1	Offset	Starting address for the entry's raw data. The offset is in bytes relative to the certificate sections's Raw data starting address.
2	Length	Length, in bytes, of the entry's raw data.
3	Type	2 = X509 Client Certificate in ASN.1 DER format. 3 = X509 CA Certificates (Intermediate and Root certificates) in ASN.1 DER format. 4 = AES-128 Encrypted Private Key in PKCS8 ASN.1 DER form.
4	Unknown	Set to 1 for the encrypted private key, 0 otherwise.

Encrypted Private Key

The device's private key is contained in a single entry of type 4 which points to a section of raw data.

For BGW210-700 devices, the raw data is laid out as follows:

Word	Value	Details
1	Unknown	The value must be 1
2	Unknown	Maybe a length
3+	Encrypted Private Key	AES-128 encrypted private key, in PKCS8 ASN.1 DER form.

For all other models, the raw data is the AES-128 encrypted private key, in PKCS8 ASN.1 DER form.

Information on decrypting the keys can be found in the source code.

Raw Data

Certificate entries point to raw data contained in this section.

Credit

Credit to rss (@rssor) and d (@slush0_) of 8311 for information about the private key decryption.

Resources

• extract_bgw_certs Python version authored by @rssor & @slush0_ from 8311.
• mfg_dat_decode the original closed-source implementation from devicelocksmith, with support for all but the BGW620-700
• 0x888e/certs software-only method to get the necessary files out of a BGW210 or BGW320