Google TOTP decode and self-generate

Pre-requirements

An ubuntu system
- with python3 supports
- with python3-pip
- with package installer, likes apt

Step1. Export TOTP

Export your TOTP from Google Authenticator by using "Transfer Codes". Take a screenshot of the generated QR-Code.

Step 2. Decode the exportsexport

Step 2-1. Decode QR-code

Install dependencies

sudo apt install -y libzbar0 protobuf-compiler

pip install pyzbar pillow

Write the protobuf created by Google

cat > migration.proto <<'EOF'
syntax = "proto3";

message MigrationPayload {
  repeated OTPParameters otp_parameters = 1;
}

message OTPParameters {
  bytes secret = 1;
  string name = 2;
  string issuer = 3;
  Algorithm algorithm = 4;
  DigitCount digits = 5;
  OTPType type = 6;
  int64 counter = 7;
}

enum Algorithm {
  ALGORITHM_UNSPECIFIED = 0;
  SHA1 = 1;
  SHA256 = 2;
  SHA512 = 3;
}
EOF

protoc --python_out=. migration.proto
# File migration_pb2.py is generated

Run the script

import base64
import migration_pb2
import pickle
from pyzbar.pyzbar import decode
from PIL import Image
from urllib.parse import unquote


img = Image.open('google_auth.jpg')

decoded_objects = decode(img)

if len(decoded_objects) == 0:
    print('No decoded object from given QRCode')
    exit()

migrations = [datum
                for obj in decoded_objects:decoded_objects
                print('Type:',if obj.type)type print(== 'Data:',QRCODE' and 
                    (datum := unquote(obj.data.decode('utf-8'))) and
                    datum.startswith('otpauth-migration://')]

if len(migrations) == 0:
    print('No valid migration extracted from given QRCode')
    exit()

prots = [base64.b64decode(migration.replace('otpauth-migration://offline?data=', '\n'', 1))
            for migration in migrations]

if len(prots) == 0:
    print('No correctly-formed migration extracted from given QRCode')
    exit()

totps = []

payload = migration_pb2.MigrationPayload()
payload.ParseFromString(prots[0])

for otp in payload.otp_parameters:
    totps.append({
        "issuer": otp.issuer,
        "name": otp.name,
        "secret": otp.secret,
    })

with open('google_auth.bin', 'wb') as fout:
    pickle.dump(totps, fout)

The script ~~output~~output, the decoded data, should be saved in file google_auth.bin

Step 3. Generate the TOTP codes

You only need google_auth.bin and following python script to re-generate TOTP codes

Type:import QRCODEhmac
Data:import otpauth-migration:hashlib
import pickle
import struct
import time


def gen_totp_code(secret, digits=6, period=30, algo=hashlib.sha1):
    counter = int(time.time() //offline?data= period)
    msg = struct.pack(">Q", counter)
    h = hmac.new(secret, msg, algo).digest()
    offset = h[-1] & 0x0F
    code = struct.unpack(">I", h[offset:offset+4])[0] & 0x7fffffff
    return str(code % (10 ** digits))..zfill(digits)

def load_totp_raws():
    with open('google_auth.bin', 'rb') as fin:
        return pickle.load(fin)

for otp in load_totp_raws():
    print(otp['issuer'])
    print(otp['name'])
    print(gen_totp_code(otp['secret']))
    print()

~~Just save the string after~~ data ~~paramater~~