def gen_otp(timestamp, secret): part1 = timestamp // 30 total = part1 + secret digits = str(part1)[::-1] for d in digits: d = int(d) if d == 0: continue total = d * total s = str(total) s = s.rstrip('0') if s == '': s = '0' otp = s[-6:] if len(s) >= 6 else s.zfill(6) return otp # Known OTPs shoulder-surfed from the suspect's phone targets = { 1785818743: "995543", 1785818761: "399222", 1785818823: "988976", } # Brute-force every possible 8-bit secret key (0-255) for secret in range(256): ok = True for ts, expected in targets.items(): got = gen_otp(ts, secret) if got != expected: ok = False break if ok: print("Found secret:", secret) # Once found, generate OTPs for the required timestamps secret = 38 for ts in [123456789, 1798156817, 1798761646]: print(ts, gen_otp(ts, secret))