popufare/busunit-PIU/scripts/rfid_filter

#!/usr/bin/python
#
# Copyright (c) 2019 Clementine Computing LLC.
#
# This file is part of PopuFare.
#
# PopuFare is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# PopuFare is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with PopuFare.  If not, see <https://www.gnu.org/licenses/>.
#

# The output format is `<bit-length>|<payload>`, where the
# <bit-length> and <payload> field are in ascii hex.
#
# Input is expected to come from stdin and as the result of the
# `proxmark3` LUA script setup for low frequency read.
# Input text is seached for a matching prefix of:
#
#   #db# TAG ID:
#
# Once found, the ascii hex string is read, it's converted to binary
# and parsed.
# The first run of two '1' bits is removed from the 'left'.
# The remaing number of bits is the bit length and the remaining
# bit string is converted back to ascii.
# Note the 'paylaod' can be a non exact multiple of 4 or 2.
#
# For example, if the following string was found:
#
#     #db# TAG ID: 200712054a (677)
#
# This is converted to:
#
#    2    0    0      7     1    2    0    5    4    a
# 0010 0000 0000  01 11  0001 0010 0000 0101 0100 1010
#                   |                                 |
#                   -----------------------------------
#                               26 bits
# 
# To evenually give the final result:
#
#    23|43F6311B2
#


import os
import re
import sys
import time

rate_limit_ms = 3000.0

def convert_tagid(s):
  binstr = ""
  for c in s:
    v = int(c, 16)

    _b = bin(int(c, 16))[2:]

    __b = "0"*(4-len(_b)) + _b
    binstr = binstr + __b

    #print("c:", c, "v:", v, "_b:", _b, "binstr:", binstr)

  #print("binstr:", binstr)

  f, s,  = -1, -1
  for idx, b in enumerate(binstr):
    if (b == '1') and (f < 0):
      f = idx
    elif (b == '1') and (s < 0):
      s = idx
      break

  #print("first:", f, "second:", s)

  filt_binstr = binstr[s+1:]
  n = len(filt_binstr)
  bitlen = n
  fin_hex = ""
  while n >= 4:

    _b = filt_binstr[n-4:n]
    fin_hex = hex(int(_b, 2))[2:] + fin_hex

    #print("n:", n, "_b:", _b, "fin_hex:", fin_hex)
    
    n -= 4
  if n>0:
    _b = filt_binstr[0:n]
    fin_hex = hex(int(_b, 2))[2:] + fin_hex

    #print("n:", n, "_b:", _b, "fin_hex:", fin_hex)


  #print("bitlen:", bitlen)
  #print("binstr:", binstr)
  #print("fin_hex:", fin_hex)

  return hex(bitlen)[2:] + "|" + fin_hex


t_prv = time.time()*1000.0
t_now = t_prv

last_tok = ""

while True:
  line = sys.stdin.readline()
  line = line.strip()

  m = re.match("#db# TAG ID: ([^ ]*)", line)
  if m:
    #print("match:", m.group(1))

    t_now = time.time()*1000.0

    tok = convert_tagid(m.group(1)).upper()
    if last_tok != tok:
      print(tok)
      sys.stdout.flush()
      t_prv = t_now
      last_tok = tok
    elif (t_now - t_prv) >= rate_limit_ms:
      print(tok)
      sys.stdout.flush()
      t_prv = t_now
      last_tok = tok
    else:
      #print("#ignore")
      pass