pysim/pySim/utils.py

# -*- coding: utf-8 -*-

""" pySim: various utilities
"""

import json
from io import BytesIO
from typing import Optional, List, Dict, Any, Tuple

# Copyright (C) 2009-2010  Sylvain Munaut <tnt@246tNt.com>
# Copyright (C) 2021 Harald Welte <laforge@osmocom.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

# just to differentiate strings of hex nibbles from everything else
Hexstr = str

def h2b(s:Hexstr) -> bytearray:
	"""convert from a string of hex nibbles to a sequence of bytes"""
	return bytearray.fromhex(s)

def b2h(b:bytearray) -> Hexstr:
	"""convert from a sequence of bytes to a string of hex nibbles"""
	return ''.join(['%02x'%(x) for x in b])

def h2i(s:Hexstr) -> List[int]:
	"""convert from a string of hex nibbles to a list of integers"""
	return [(int(x,16)<<4)+int(y,16) for x,y in zip(s[0::2], s[1::2])]

def i2h(s:List[int]) -> Hexstr:
	"""convert from a list of integers to a string of hex nibbles"""
	return ''.join(['%02x'%(x) for x in s])

def h2s(s:Hexstr) -> str:
	"""convert from a string of hex nibbles to an ASCII string"""
	return ''.join([chr((int(x,16)<<4)+int(y,16)) for x,y in zip(s[0::2], s[1::2])
						      if int(x + y, 16) != 0xff])

def s2h(s:str) -> Hexstr:
	"""convert from an ASCII string to a string of hex nibbles"""
	b = bytearray()
	b.extend(map(ord, s))
	return b2h(b)

# List of bytes to string
def i2s(s:List[int]) -> str:
	"""convert from a list of integers to an ASCII string"""
	return ''.join([chr(x) for x in s])

def swap_nibbles(s:Hexstr) -> Hexstr:
	"""swap the nibbles in a hex string"""
	return ''.join([x+y for x,y in zip(s[1::2], s[0::2])])

def rpad(s:str, l:int, c='f') -> str:
	"""pad string on the right side.
	Args:
		s : string to pad
		l : total length to pad to
		c : padding character
	Returns:
		String 's' padded with as many 'c' as needed to reach total length of 'l'
	"""
	return s + c * (l - len(s))

def lpad(s:str, l:int, c='f') -> str:
	"""pad string on the left side.
	Args:
		s : string to pad
		l : total length to pad to
		c : padding character
	Returns:
		String 's' padded with as many 'c' as needed to reach total length of 'l'
	"""
	return c * (l - len(s)) + s

def half_round_up(n:int) -> int:
	return (n + 1)//2

# IMSI encoded format:
# For IMSI 0123456789ABCDE:
#
# |     byte 1      | 2 upper | 2 lower  | 3 upper | 3 lower | ... | 9 upper | 9 lower |
# | length in bytes |    0    | odd/even |    2    |    1    | ... |    E    |    D    |
#
# If the IMSI is less than 15 characters, it should be padded with 'f' from the end.
#
# The length is the total number of bytes used to encoded the IMSI. This includes the odd/even
# parity bit. E.g. an IMSI of length 14 is 8 bytes long, not 7, as it uses bytes 2 to 9 to
# encode itself.
#
# Because of this, an odd length IMSI fits exactly into len(imsi) + 1 // 2 bytes, whereas an
# even length IMSI only uses half of the last byte.

def enc_imsi(imsi:str):
	"""Converts a string IMSI into the encoded value of the EF"""
	l = half_round_up(len(imsi) + 1)	# Required bytes - include space for odd/even indicator
	oe = len(imsi) & 1			# Odd (1) / Even (0)
	ei = '%02x' % l + swap_nibbles('%01x%s' % ((oe<<3)|1, rpad(imsi, 15)))
	return ei

def dec_imsi(ef:Hexstr) -> Optional[str]:
	"""Converts an EF value to the IMSI string representation"""
	if len(ef) < 4:
		return None
	l = int(ef[0:2], 16) * 2		# Length of the IMSI string
	l = l - 1						# Encoded length byte includes oe nibble
	swapped = swap_nibbles(ef[2:]).rstrip('f')
	if len(swapped) < 1:
		return None
	oe = (int(swapped[0])>>3) & 1	# Odd (1) / Even (0)
	if not oe:
		# if even, only half of last byte was used
		l = l-1
	if l != len(swapped) - 1:
		return None
	imsi = swapped[1:]
	return imsi

def dec_iccid(ef:Hexstr) -> str:
	return swap_nibbles(ef).strip('f')

def enc_iccid(iccid:str) -> Hexstr:
	return swap_nibbles(rpad(iccid, 20))

def enc_plmn(mcc, mnc):
	"""Converts integer MCC/MNC into 3 bytes for EF"""
	if len(mnc) == 2:
		mnc += "F" # pad to 3 digits if needed
	return (mcc[1] + mcc[0]) + (mnc[2] + mcc[2]) + (mnc[1] + mnc[0])

def dec_plmn(threehexbytes:Hexstr) -> dict:
	res = {'mcc': 0, 'mnc': 0 }
	res['mcc'] = dec_mcc_from_plmn(threehexbytes)
	res['mnc'] = dec_mnc_from_plmn(threehexbytes)
	return res

def dec_spn(ef):
	byte1 = int(ef[0:2])
	hplmn_disp = (byte1&0x01 == 0x01)
	oplmn_disp = (byte1&0x02 == 0x02)
	name = h2s(ef[2:])
	return (name, hplmn_disp, oplmn_disp)

def enc_spn(name, hplmn_disp=False, oplmn_disp=False):
	byte1 = 0x00
	if hplmn_disp: byte1 = byte1|0x01
	if oplmn_disp: byte1 = byte1|0x02
	return i2h([byte1])+s2h(name)

def hexstr_to_Nbytearr(s, nbytes):
	return [s[i:i+(nbytes*2)] for i in range(0, len(s), (nbytes*2)) ]

# Accepts hex string representing three bytes
def dec_mcc_from_plmn(plmn:Hexstr) -> int:
	ia = h2i(plmn)
	digit1 = ia[0] & 0x0F		# 1st byte, LSB
	digit2 = (ia[0] & 0xF0) >> 4	# 1st byte, MSB
	digit3 = ia[1] & 0x0F		# 2nd byte, LSB
	if digit3 == 0xF and digit2 == 0xF and digit1 == 0xF:
		return 0xFFF # 4095
	return derive_mcc(digit1, digit2, digit3)

def dec_mnc_from_plmn(plmn:Hexstr) -> int:
	ia = h2i(plmn)
	digit1 = ia[2] & 0x0F		# 3rd byte, LSB
	digit2 = (ia[2] & 0xF0) >> 4	# 3rd byte, MSB
	digit3 = (ia[1] & 0xF0) >> 4	# 2nd byte, MSB
	if digit3 == 0xF and digit2 == 0xF and digit1 == 0xF:
		return 0xFFF # 4095
	return derive_mnc(digit1, digit2, digit3)

def dec_act(twohexbytes:Hexstr) -> List[str]:
	act_list = [
		{'bit': 15, 'name': "UTRAN"},
		{'bit': 14, 'name': "E-UTRAN"},
		{'bit':  7, 'name': "GSM"},
		{'bit':  6, 'name': "GSM COMPACT"},
		{'bit':  5, 'name': "cdma2000 HRPD"},
		{'bit':  4, 'name': "cdma2000 1xRTT"},
	]
	ia = h2i(twohexbytes)
	u16t = (ia[0] << 8)|ia[1]
	sel = []
	for a in act_list:
		if u16t & (1 << a['bit']):
			sel.append(a['name'])
	return sel

def dec_xplmn_w_act(fivehexbytes:Hexstr) -> Dict[str,Any]:
	res = {'mcc': 0, 'mnc': 0, 'act': []}
	plmn_chars = 6
	act_chars = 4
	plmn_str = fivehexbytes[:plmn_chars]				# first three bytes (six ascii hex chars)
	act_str = fivehexbytes[plmn_chars:plmn_chars + act_chars]	# two bytes after first three bytes
	res['mcc'] = dec_mcc_from_plmn(plmn_str)
	res['mnc'] = dec_mnc_from_plmn(plmn_str)
	res['act'] = dec_act(act_str)
	return res

def format_xplmn_w_act(hexstr):
	s = ""
	for rec_data in hexstr_to_Nbytearr(hexstr, 5):
		rec_info = dec_xplmn_w_act(rec_data)
		if rec_info['mcc'] == 0xFFF and rec_info['mnc'] == 0xFFF:
			rec_str = "unused"
		else:
			rec_str = "MCC: %03d MNC: %03d AcT: %s" % (rec_info['mcc'], rec_info['mnc'], ", ".join(rec_info['act']))
		s += "\t%s # %s\n" % (rec_data, rec_str)
	return s

def dec_loci(hexstr):
	res = {'tmsi': '',  'mcc': 0, 'mnc': 0, 'lac': '', 'status': 0}
	res['tmsi'] = hexstr[:8]
	res['mcc'] = dec_mcc_from_plmn(hexstr[8:14])
	res['mnc'] = dec_mnc_from_plmn(hexstr[8:14])
	res['lac'] = hexstr[14:18]
	res['status'] = h2i(hexstr[20:22])
	return res

def dec_psloci(hexstr):
	res = {'p-tmsi': '', 'p-tmsi-sig': '', 'mcc': 0, 'mnc': 0, 'lac': '', 'rac': '', 'status': 0}
	res['p-tmsi'] = hexstr[:8]
	res['p-tmsi-sig'] = hexstr[8:14]
	res['mcc'] = dec_mcc_from_plmn(hexstr[14:20])
	res['mnc'] = dec_mnc_from_plmn(hexstr[14:20])
	res['lac'] = hexstr[20:24]
	res['rac'] = hexstr[24:26]
	res['status'] = h2i(hexstr[26:28])
	return res

def dec_epsloci(hexstr):
	res = {'guti': '', 'mcc': 0, 'mnc': 0, 'tac': '', 'status': 0}
	res['guti'] = hexstr[:24]
	res['tai'] = hexstr[24:34]
	res['mcc'] = dec_mcc_from_plmn(hexstr[24:30])
	res['mnc'] = dec_mnc_from_plmn(hexstr[24:30])
	res['tac'] = hexstr[30:34]
	res['status'] = h2i(hexstr[34:36])
	return res

def dec_xplmn(threehexbytes:Hexstr) -> dict:
	res = {'mcc': 0, 'mnc': 0, 'act': []}
	plmn_chars = 6
	plmn_str = threehexbytes[:plmn_chars]				# first three bytes (six ascii hex chars)
	res['mcc'] = dec_mcc_from_plmn(plmn_str)
	res['mnc'] = dec_mnc_from_plmn(plmn_str)
	return res

def format_xplmn(hexstr:Hexstr) -> str:
	s = ""
	for rec_data in hexstr_to_Nbytearr(hexstr, 3):
		rec_info = dec_xplmn(rec_data)
		if rec_info['mcc'] == 0xFFF and rec_info['mnc'] == 0xFFF:
			rec_str = "unused"
		else:
			rec_str = "MCC: %03d MNC: %03d" % (rec_info['mcc'], rec_info['mnc'])
		s += "\t%s # %s\n" % (rec_data, rec_str)
	return s

def derive_milenage_opc(ki_hex:Hexstr, op_hex:Hexstr) -> Hexstr:
	"""
	Run the milenage algorithm to calculate OPC from Ki and OP
	"""
	from Crypto.Cipher import AES
	from Crypto.Util.strxor import strxor
	from pySim.utils import b2h

	# We pass in hex string and now need to work on bytes
	ki_bytes = bytes(h2b(ki_hex))
	op_bytes = bytes(h2b(op_hex))
	aes = AES.new(ki_bytes, AES.MODE_ECB)
	opc_bytes = aes.encrypt(op_bytes)
	return b2h(strxor(opc_bytes, op_bytes))

def calculate_luhn(cc) -> int:
	"""
	Calculate Luhn checksum used in e.g. ICCID and IMEI
	"""
	num = list(map(int, str(cc)))
	check_digit = 10 - sum(num[-2::-2] + [sum(divmod(d * 2, 10)) for d in num[::-2]]) % 10
	return 0 if check_digit == 10 else check_digit

def mcc_from_imsi(imsi:str) -> Optional[str]:
	"""
	Derive the MCC (Mobile Country Code) from the first three digits of an IMSI
	"""
	if imsi == None:
		return None

	if len(imsi) > 3:
		return imsi[:3]
	else:
		return None

def mnc_from_imsi(imsi:str, long:bool=False) -> Optional[str]:
	"""
	Derive the MNC (Mobile Country Code) from the 4th to 6th digit of an IMSI
	"""
	if imsi == None:
		return None

	if len(imsi) > 3:
		if long:
			return imsi[3:6]
		else:
			return imsi[3:5]
	else:
		return None

def derive_mcc(digit1:int, digit2:int, digit3:int) -> int:
	"""
	Derive decimal representation of the MCC (Mobile Country Code)
	from three given digits.
	"""

	mcc = 0

	if digit1 != 0x0f:
		mcc += digit1 * 100
	if digit2 != 0x0f:
		mcc += digit2 * 10
	if digit3 != 0x0f:
		mcc += digit3

	return mcc

def derive_mnc(digit1:int, digit2:int, digit3:int=0x0f) -> int:
	"""
	Derive decimal representation of the MNC (Mobile Network Code)
	from two or (optionally) three given digits.
	"""

	mnc = 0

	# 3-rd digit is optional for the MNC. If present
	# the algorythm is the same as for the MCC.
	if digit3 != 0x0f:
		return derive_mcc(digit1, digit2, digit3)

	if digit1 != 0x0f:
		mnc += digit1 * 10
	if digit2 != 0x0f:
		mnc += digit2

	return mnc

def dec_msisdn(ef_msisdn:Hexstr) -> Optional[Tuple[int,int,Optional[str]]]:
	"""
	Decode MSISDN from EF.MSISDN or EF.ADN (same structure).
	See 3GPP TS 31.102, section 4.2.26 and 4.4.2.3.
	"""

	# Convert from str to (kind of) 'bytes'
	ef_msisdn = h2b(ef_msisdn)

	# Make sure mandatory fields are present
	if len(ef_msisdn) < 14:
		raise ValueError("EF.MSISDN is too short")

	# Skip optional Alpha Identifier
	xlen = len(ef_msisdn) - 14
	msisdn_lhv = ef_msisdn[xlen:]

	# Parse the length (in bytes) of the BCD encoded number
	bcd_len = msisdn_lhv[0]
	# BCD length = length of dial num (max. 10 bytes) + 1 byte ToN and NPI
	if bcd_len == 0xff:
		return None
	elif bcd_len > 11 or bcd_len < 1:
		raise ValueError("Length of MSISDN (%d bytes) is out of range" % bcd_len)

	# Parse ToN / NPI
	ton = (msisdn_lhv[1] >> 4) & 0x07
	npi = msisdn_lhv[1] & 0x0f
	bcd_len -= 1

	# No MSISDN?
	if not bcd_len:
		return (npi, ton, None)

	msisdn = swap_nibbles(b2h(msisdn_lhv[2:][:bcd_len])).rstrip('f')
	# International number 10.5.118/3GPP TS 24.008
	if ton == 0x01:
		msisdn = '+' + msisdn

	return (npi, ton, msisdn)

def enc_msisdn(msisdn:str, npi:int=0x01, ton:int=0x03) -> Hexstr:
	"""
	Encode MSISDN as LHV so it can be stored to EF.MSISDN.
	See 3GPP TS 31.102, section 4.2.26 and 4.4.2.3. (The result
	will not contain the optional Alpha Identifier at the beginning.)

	Default NPI / ToN values:
	  - NPI: ISDN / telephony numbering plan (E.164 / E.163),
	  - ToN: network specific or international number (if starts with '+').
	"""

	# If no MSISDN is supplied then encode the file contents as all "ff"
	if msisdn == "" or msisdn == "+":
		return "ff" * 14

	# Leading '+' indicates International Number
	if msisdn[0] == '+':
		msisdn = msisdn[1:]
		ton = 0x01

	# An MSISDN must not exceed 20 digits
	if len(msisdn) > 20:
		raise ValueError("msisdn must not be longer than 20 digits")

	# Append 'f' padding if number of digits is odd
	if len(msisdn) % 2 > 0:
		msisdn += 'f'

	# BCD length also includes NPI/ToN header
	bcd_len = len(msisdn) // 2 + 1
	npi_ton = (npi & 0x0f) | ((ton & 0x07) << 4) | 0x80
	bcd = rpad(swap_nibbles(msisdn), 10 * 2) # pad to 10 octets

	return ('%02x' % bcd_len) + ('%02x' % npi_ton) + bcd + ("ff" * 2)


def dec_st(st, table="sim") -> str:
	"""
	Parses the EF S/U/IST and prints the list of available services in EF S/U/IST
	"""

	if table == "isim":
		from pySim.ts_31_103 import EF_IST_map
		lookup_map = EF_IST_map
	elif table == "usim":
		from pySim.ts_31_102 import EF_UST_map
		lookup_map = EF_UST_map
	else:
		from pySim.ts_51_011 import EF_SST_map
		lookup_map = EF_SST_map

	st_bytes = [st[i:i+2] for i in range(0, len(st), 2) ]

	avail_st = ""
	# Get each byte and check for available services
	for i in range(0, len(st_bytes)):
		# Byte i contains info about Services num (8i+1) to num (8i+8)
		byte = int(st_bytes[i], 16)
		# Services in each byte are in order MSB to LSB
		# MSB - Service (8i+8)
		# LSB - Service (8i+1)
		for j in range(1, 9):
			if byte&0x01 == 0x01 and ((8*i) + j in lookup_map):
				# Byte X contains info about Services num (8X-7) to num (8X)
				# bit = 1: service available
				# bit = 0: service not available
				avail_st += '\tService %d - %s\n' % ((8*i) + j, lookup_map[(8*i) + j])
			byte = byte >> 1
	return avail_st

def first_TLV_parser(bytelist):
	'''
	first_TLV_parser([0xAA, 0x02, 0xAB, 0xCD, 0xFF, 0x00]) -> (170, 2, [171, 205])

	parses first TLV format record in a list of bytelist
	returns a 3-Tuple: Tag, Length, Value
	Value is a list of bytes
	parsing of length is ETSI'style 101.220
	'''
	Tag = bytelist[0]
	if bytelist[1] == 0xFF:
		Len = bytelist[2]*256 + bytelist[3]
		Val = bytelist[4:4+Len]
	else:
		Len = bytelist[1]
		Val = bytelist[2:2+Len]
	return (Tag, Len, Val)

def TLV_parser(bytelist):
	'''
	TLV_parser([0xAA, ..., 0xFF]) -> [(T, L, [V]), (T, L, [V]), ...]

	loops on the input list of bytes with the "first_TLV_parser()" function
	returns a list of 3-Tuples
	'''
	ret = []
	while len(bytelist) > 0:
		T, L, V = first_TLV_parser(bytelist)
		if T == 0xFF:
			# padding bytes
			break
		ret.append( (T, L, V) )
		# need to manage length of L
		if L > 0xFE:
			bytelist = bytelist[ L+4 : ]
		else:
			bytelist = bytelist[ L+2 : ]
	return ret

def enc_st(st, service, state=1):
	"""
	Encodes the EF S/U/IST/EST and returns the updated Service Table

	Parameters:
		st - Current value of SIM/USIM/ISIM Service Table
		service - Service Number to encode as activated/de-activated
		state - 1 mean activate, 0 means de-activate

	Returns:
		s - Modified value of SIM/USIM/ISIM Service Table

	Default values:
		- state: 1 - Sets the particular Service bit to 1
	"""
	st_bytes = [st[i:i+2] for i in range(0, len(st), 2) ]

	s = ""
	# Check whether the requested service is present in each byte
	for i in range(0, len(st_bytes)):
		# Byte i contains info about Services num (8i+1) to num (8i+8)
		if service in range((8*i) + 1, (8*i) + 9):
			byte = int(st_bytes[i], 16)
			# Services in each byte are in order MSB to LSB
			# MSB - Service (8i+8)
			# LSB - Service (8i+1)
			mod_byte = 0x00
			# Copy bit by bit contents of byte to mod_byte with modified bit
			# for requested service
			for j in range(1, 9):
				mod_byte = mod_byte >> 1
				if service == (8*i) + j:
					mod_byte = state == 1 and mod_byte|0x80 or mod_byte&0x7f
				else:
					mod_byte = byte&0x01 == 0x01 and mod_byte|0x80 or mod_byte&0x7f
				byte = byte >> 1

			s += ('%02x' % (mod_byte))
		else:
			s += st_bytes[i]

	return s

def dec_addr_tlv(hexstr):
	"""
	Decode hex string to get EF.P-CSCF Address or EF.ePDGId or EF.ePDGIdEm.
	See 3GPP TS 31.102 version 13.4.0 Release 13, section 4.2.8, 4.2.102 and 4.2.104.
	"""

	# Convert from hex str to int bytes list
	addr_tlv_bytes = h2i(hexstr)

	s = ""

	# Get list of tuples containing parsed TLVs
	tlvs = TLV_parser(addr_tlv_bytes)

	for tlv in tlvs:
		# tlv = (T, L, [V])
		# T = Tag
		# L = Length
		# [V] = List of value

		# Invalid Tag value scenario
		if tlv[0] != 0x80:
			continue

		# Empty field - Zero length
		if tlv[1] == 0:
			continue

		# First byte in the value has the address type
		addr_type = tlv[2][0]
		# TODO: Support parsing of IPv6
		# Address Type: 0x00 (FQDN), 0x01 (IPv4), 0x02 (IPv6), other (Reserved)
		if addr_type == 0x00: #FQDN
			# Skip address tye byte i.e. first byte in value list
			content = tlv[2][1:]
			s += "\t%s # %s\n" % (i2h(content), i2s(content))
		elif addr_type == 0x01: #IPv4
			# Skip address tye byte i.e. first byte in value list
			# Skip the unused byte in Octect 4 after address type byte as per 3GPP TS 31.102
			ipv4 = tlv[2][2:]
			content = '.'.join(str(x) for x in ipv4)
			s += "\t%s # %s\n" % (i2h(ipv4), content)

	return s

def enc_addr_tlv(addr, addr_type='00'):
	"""
	Encode address TLV object used in EF.P-CSCF Address, EF.ePDGId and EF.ePDGIdEm.
	See 3GPP TS 31.102 version 13.4.0 Release 13, section 4.2.8, 4.2.102 and 4.2.104.

	Default values:
	  - addr_type: 00 - FQDN format of Address
	"""

	s = ""

	# TODO: Encoding of IPv6 address
	if addr_type == '00': #FQDN
		hex_str = s2h(addr)
		s += '80' + ('%02x' % ((len(hex_str)//2)+1)) + '00' + hex_str
	elif addr_type == '01': #IPv4
		ipv4_list = addr.split('.')
		ipv4_str = ""
		for i in ipv4_list:
			ipv4_str += ('%02x' % (int(i)))

		# Unused bytes shall be set to 'ff'. i.e 4th Octet after Address Type is not used
		# IPv4 Address is in octet 5 to octet 8 of the TLV data object
		s += '80' + ('%02x' % ((len(ipv4_str)//2)+2)) + '01' + 'ff' + ipv4_str

	return s

def is_hex(string:str, minlen:int=2, maxlen:Optional[int]=None) -> bool:
	"""
	Check if a string is a valid hexstring
	"""

	# Filter obviously bad strings
	if not string:
		return False
	if len(string) < minlen or minlen < 2:
		return False
	if len(string) % 2:
		return False
	if maxlen and len(string) > maxlen:
		return False

	# Try actual encoding to be sure
	try:
		try_encode = h2b(string)
		return True
	except:
		return False

def sanitize_pin_adm(pin_adm, pin_adm_hex = None) -> Hexstr:
	"""
	The ADM pin can be supplied either in its hexadecimal form or as
	ascii string. This function checks the supplied opts parameter and
	returns the pin_adm as hex encoded string, regardless in which form
	it was originally supplied by the user
	"""

	if pin_adm is not None:
		if len(pin_adm) <= 8:
			pin_adm = ''.join(['%02x'%(ord(x)) for x in pin_adm])
			pin_adm = rpad(pin_adm, 16)

		else:
			raise ValueError("PIN-ADM needs to be <=8 digits (ascii)")

	if pin_adm_hex is not None:
		if len(pin_adm_hex) == 16:
			pin_adm = pin_adm_hex
			# Ensure that it's hex-encoded
			try:
				try_encode = h2b(pin_adm)
			except ValueError:
				raise ValueError("PIN-ADM needs to be hex encoded using this option")
		else:
			raise ValueError("PIN-ADM needs to be exactly 16 digits (hex encoded)")

	return pin_adm

def enc_ePDGSelection(hexstr, mcc, mnc, epdg_priority='0001', epdg_fqdn_format='00'):
	"""
	Encode ePDGSelection so it can be stored at EF.ePDGSelection or EF.ePDGSelectionEm.
	See 3GPP TS 31.102 version 15.2.0 Release 15, section 4.2.104 and 4.2.106.

	Default values:
		- epdg_priority: '0001' - 1st Priority
		- epdg_fqdn_format: '00' - Operator Identifier FQDN
	"""

	plmn1 = enc_plmn(mcc, mnc) + epdg_priority + epdg_fqdn_format
	# TODO: Handle encoding of Length field for length more than 127 Bytes
	content = '80' + ('%02x' % (len(plmn1)//2)) + plmn1
	content = rpad(content, len(hexstr))
	return content

def dec_ePDGSelection(sixhexbytes):
	"""
	Decode ePDGSelection to get EF.ePDGSelection or EF.ePDGSelectionEm.
	See 3GPP TS 31.102 version 15.2.0 Release 15, section 4.2.104 and 4.2.106.
	"""

	res = {'mcc': 0, 'mnc': 0, 'epdg_priority': 0, 'epdg_fqdn_format': ''}
	plmn_chars = 6
	epdg_priority_chars = 4
	epdg_fqdn_format_chars = 2
	# first three bytes (six ascii hex chars)
	plmn_str = sixhexbytes[:plmn_chars]
	# two bytes after first three bytes
	epdg_priority_str = sixhexbytes[plmn_chars:plmn_chars + epdg_priority_chars]
	# one byte after first five bytes
	epdg_fqdn_format_str = sixhexbytes[plmn_chars + epdg_priority_chars:plmn_chars + epdg_priority_chars + epdg_fqdn_format_chars]
	res['mcc'] = dec_mcc_from_plmn(plmn_str)
	res['mnc'] = dec_mnc_from_plmn(plmn_str)
	res['epdg_priority'] = epdg_priority_str
	res['epdg_fqdn_format'] = epdg_fqdn_format_str == '00' and 'Operator Identifier FQDN' or 'Location based FQDN'
	return res

def format_ePDGSelection(hexstr):
	ePDGSelection_info_tag_chars = 2
	ePDGSelection_info_tag_str = hexstr[:2]
	s = ""
	# Minimum length
	len_chars = 2
	# TODO: Need to determine length properly - definite length support only
	# Inconsistency in spec: 3GPP TS 31.102 version 15.2.0 Release 15, 4.2.104
	# As per spec, length is 5n, n - number of PLMNs
	# But, each PLMN entry is made of PLMN (3 Bytes) + ePDG Priority (2 Bytes) + ePDG FQDN format (1 Byte)
	# Totalling to 6 Bytes, maybe length should be 6n
	len_str = hexstr[ePDGSelection_info_tag_chars:ePDGSelection_info_tag_chars+len_chars]

	# Not programmed scenario
	if int(len_str, 16) == 255 or int(ePDGSelection_info_tag_str, 16) == 255:
		len_chars = 0
		ePDGSelection_info_tag_chars = 0
	if len_str[0] == '8':
		# The bits 7 to 1 denotes the number of length octets if length > 127
		if int(len_str[1]) > 0:
			# Update number of length octets
			len_chars = len_chars * int(len_str[1])
			len_str = hexstr[ePDGSelection_info_tag_chars:len_chars]

	content_str = hexstr[ePDGSelection_info_tag_chars+len_chars:]
	# Right pad to prevent index out of range - multiple of 6 bytes
	content_str = rpad(content_str, len(content_str) + (12 - (len(content_str) % 12)))
	for rec_data in hexstr_to_Nbytearr(content_str, 6):
		rec_info = dec_ePDGSelection(rec_data)
		if rec_info['mcc'] == 0xFFF and rec_info['mnc'] == 0xFFF:
			rec_str = "unused"
		else:
			rec_str = "MCC: %03d MNC: %03d ePDG Priority: %s ePDG FQDN format: %s" % \
					(rec_info['mcc'], rec_info['mnc'], rec_info['epdg_priority'], rec_info['epdg_fqdn_format'])
		s += "\t%s # %s\n" % (rec_data, rec_str)
	return s

def get_addr_type(addr):
	"""
	Validates the given address and returns it's type (FQDN or IPv4 or IPv6)
	Return: 0x00 (FQDN), 0x01 (IPv4), 0x02 (IPv6), None (Bad address argument given)

	TODO: Handle IPv6
	"""

	# Empty address string
	if not len(addr):
		return None

	addr_list = addr.split('.')

	# Check for IPv4/IPv6
	try:
		import ipaddress
		# Throws ValueError if addr is not correct
		ipa = ipaddress.ip_address(addr)

		if ipa.version == 4:
			return 0x01
		elif ipa.version == 6:
			return 0x02
	except Exception as e:
		invalid_ipv4 = True
		for i in addr_list:
			# Invalid IPv4 may qualify for a valid FQDN, so make check here
			# e.g. 172.24.15.300
			import re
			if not re.match('^[0-9_]+$', i):
				invalid_ipv4 = False
				break

		if invalid_ipv4:
			return None

	fqdn_flag = True
	for i in addr_list:
		# Only Alpha-numeric characters and hyphen - RFC 1035
		import re
		if not re.match("^[a-zA-Z0-9]+(?:-[a-zA-Z0-9]+)?$", i):
			fqdn_flag = False
			break

	# FQDN
	if fqdn_flag:
		return 0x00

	return None

def sw_match(sw:str, pattern:str) -> bool:
	"""Match given SW against given pattern."""
	# Create a masked version of the returned status word
	sw_lower = sw.lower()
	sw_masked = ""
	for i in range(0, 4):
		if pattern[i] == '?':
			sw_masked = sw_masked + '?'
		elif pattern[i] == 'x':
			sw_masked = sw_masked + 'x'
		else:
			sw_masked = sw_masked + sw_lower[i]
	# Compare the masked version against the pattern
	return sw_masked == pattern

def tabulate_str_list(str_list, width:int = 79, hspace:int = 2, lspace:int = 1,
					  align_left:bool = True) -> str:
	"""Pretty print a list of strings into a tabulated form.

	Args:
		width : total width in characters per line
		space : horizontal space between cells
		lspace : number of spaces before row
		align_lef : Align text to the left side
	Returns:
		multi-line string containing formatted table
	"""
	if str_list == None:
		return ""
	if len(str_list) <= 0:
		return ""
	longest_str = max(str_list, key=len)
	cellwith = len(longest_str) + hspace
	cols = width // cellwith
	rows = (len(str_list) - 1) // cols + 1
	table = []
	for i in iter(range(rows)):
		str_list_row = str_list[i::rows]
		if (align_left):
			format_str_cell = '%%-%ds'
		else:
			format_str_cell = '%%%ds'
		format_str_row = (format_str_cell % cellwith) * len(str_list_row)
		format_str_row = (" " * lspace) + format_str_row
		table.append(format_str_row % tuple(str_list_row))
	return '\n'.join(table)

class JsonEncoder(json.JSONEncoder):
    """Extend the standard library JSONEncoder with support for more types."""
    def default(self, o):
        if isinstance(o, BytesIO) or isinstance(o, bytes) or isinstance(o, bytearray):
            return b2h(o)
        return json.JSONEncoder.default(self, o)

def boxed_heading_str(heading, width=80):
	"""Generate a string that contains a boxed heading."""
	# Auto-enlarge box if heading exceeds length
	if len(heading) > width - 4:
		width = len(heading) + 4

	res = "#" * width
	fstr = "\n# %-" + str(width - 4) + "s #\n"
	res += fstr % (heading)
	res += "#" * width
	return res