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import bchlib
import numpy as np
from typing import List, Tuple
import random
from copy import deepcopy
class RSC(object):
def __init__(self, data_bytes=16, ecc_bytes=4, verbose=False, **kwargs):
from reedsolo import RSCodec
self.rs = RSCodec(ecc_bytes)
if verbose:
print(f'Reed-Solomon ECC len: {ecc_bytes*8} bits')
self.data_len = data_bytes
self.dlen = data_bytes * 8 # data length in bits
self.ecc_len = ecc_bytes * 8 # ecc length in bits
def get_total_len(self):
return self.dlen + self.ecc_len
def encode_text(self, text: List[str]):
return np.array([self._encode_text(t) for t in text])
def _encode_text(self, text: str):
text = text + ' ' * (self.dlen // 8 - len(text))
out = self.rs.encode(text.encode('utf-8')) # bytearray
out = ''.join(format(x, '08b') for x in out) # bit string
out = np.array([int(x) for x in out], dtype=np.float32)
return out
def decode_text(self, data: np.array):
assert len(data.shape)==2
return [self._decode_text(d) for d in data]
def _decode_text(self, data: np.array):
assert len(data.shape)==1
data = ''.join([str(int(bit)) for bit in data])
data = bytes(int(data[i: i + 8], 2) for i in range(0, len(data), 8))
data = bytearray(data)
try:
data = self.rs.decode(data)[0]
data = data.decode('utf-8').strip()
except:
print('Error: Decode failed')
data = get_random_unicode(self.get_total_len()//8)
return data
def get_random_unicode(length):
# Update this to include code point ranges to be sampled
include_ranges = [
( 0x0021, 0x0021 ),
( 0x0023, 0x0026 ),
( 0x0028, 0x007E ),
( 0x00A1, 0x00AC ),
( 0x00AE, 0x00FF ),
( 0x0100, 0x017F ),
( 0x0180, 0x024F ),
( 0x2C60, 0x2C7F ),
( 0x16A0, 0x16F0 ),
( 0x0370, 0x0377 ),
( 0x037A, 0x037E ),
( 0x0384, 0x038A ),
( 0x038C, 0x038C ),
]
alphabet = [
chr(code_point) for current_range in include_ranges
for code_point in range(current_range[0], current_range[1] + 1)
]
return ''.join(random.choice(alphabet) for i in range(length))
class BCH(object):
def __init__(self, BCH_POLYNOMIAL = 137, BCH_BITS = 5, payload_len=100, verbose=True,**kwargs):
self.bch = bchlib.BCH(BCH_POLYNOMIAL, BCH_BITS)
self.payload_len = payload_len # in bits
self.data_len = (self.payload_len - self.bch.ecc_bytes*8)//7 # in ascii characters
assert self.data_len*7+self.bch.ecc_bytes*8 <= self.bch.n, f'Error! BCH with poly {BCH_POLYNOMIAL} and bits {BCH_BITS} can only encode max {self.bch.n//8} bytes of total payload'
if verbose:
print(f'BCH: POLYNOMIAL={BCH_POLYNOMIAL}, protected bits={BCH_BITS}, payload_len={payload_len} bits, data_len={self.data_len*7} bits ({self.data_len} ascii chars), ecc len={self.bch.ecc_bytes*8} bits')
def get_total_len(self):
return self.payload_len
def encode_text(self, text: List[str]):
return np.array([self._encode_text(t) for t in text])
def _encode_text(self, text: str):
text = text + ' ' * (self.data_len - len(text))
# data = text.encode('utf-8') # bytearray
data = encode_text_ascii(text) # bytearray
ecc = self.bch.encode(data) # bytearray
packet = data + ecc # payload in bytearray
packet = ''.join(format(x, '08b') for x in packet)
packet = [int(x) for x in packet]
packet.extend([0]*(self.payload_len - len(packet)))
packet = np.array(packet, dtype=np.float32)
return packet
def decode_text(self, data: np.array):
assert len(data.shape)==2
return [self._decode_text(d) for d in data]
def _decode_text(self, packet: np.array):
assert len(packet.shape)==1
packet = ''.join([str(int(bit)) for bit in packet]) # bit string
packet = packet[:(len(packet)//8*8)] # trim to multiple of 8 bits
packet = bytes(int(packet[i: i + 8], 2) for i in range(0, len(packet), 8))
packet = bytearray(packet)
# assert len(packet) == self.data_len + self.bch.ecc_bytes
data, ecc = packet[:-self.bch.ecc_bytes], packet[-self.bch.ecc_bytes:]
data0 = decode_text_ascii(deepcopy(data)).strip()
bitflips = self.bch.decode_inplace(data, ecc)
if bitflips == -1: # error, return random text
data = data0
else:
# data = data.decode('utf-8').strip()
data = decode_text_ascii(data).strip()
return data
def encode_text_ascii(text: str):
# encode text to 7-bit ascii
# input: text, str
# output: encoded text, bytearray
text_int7 = [ord(t) & 127 for t in text]
text_bitstr = ''.join(format(t,'07b') for t in text_int7)
if len(text_bitstr) % 8 != 0:
text_bitstr = '0'*(8-len(text_bitstr)%8) + text_bitstr # pad to multiple of 8
text_int8 = [int(text_bitstr[i:i+8], 2) for i in range(0, len(text_bitstr), 8)]
return bytearray(text_int8)
def decode_text_ascii(text: bytearray):
# decode text from 7-bit ascii
# input: text, bytearray
# output: decoded text, str
text_bitstr = ''.join(format(t,'08b') for t in text) # bit string
pad = len(text_bitstr) % 7
if pad != 0: # has padding, remove
text_bitstr = text_bitstr[pad:]
text_int7 = [int(text_bitstr[i:i+7], 2) for i in range(0, len(text_bitstr), 7)]
text_bytes = bytes(text_int7)
return text_bytes.decode('utf-8')
class ECC(object):
def __init__(self, BCH_POLYNOMIAL = 137, BCH_BITS = 5, **kwargs):
self.bch = bchlib.BCH(BCH_POLYNOMIAL, BCH_BITS)
def get_total_len(self):
return 100
def _encode(self, x):
# x: 56 bits, {0, 1}, np.array
# return: 100 bits, {0, 1}, np.array
dlen = len(x)
data_str = ''.join(str(x) for x in x.astype(int))
packet = bytes(int(data_str[i: i + 8], 2) for i in range(0, dlen, 8))
packet = bytearray(packet)
ecc = self.bch.encode(packet)
packet = packet + ecc # 96 bits
packet = ''.join(format(x, '08b') for x in packet)
packet = [int(x) for x in packet]
packet.extend([0, 0, 0, 0])
packet = np.array(packet, dtype=np.float32) # 100
return packet
def _decode(self, x):
# x: 100 bits, {0, 1}, np.array
# return: 56 bits, {0, 1}, np.array
packet_binary = "".join([str(int(bit)) for bit in x])
packet = bytes(int(packet_binary[i: i + 8], 2) for i in range(0, len(packet_binary), 8))
packet = bytearray(packet)
data, ecc = packet[:-self.bch.ecc_bytes], packet[-self.bch.ecc_bytes:]
bitflips = self.bch.decode_inplace(data, ecc)
if bitflips == -1: # error, return random data
data = np.random.binomial(1, .5, 56)
else:
data = ''.join(format(x, '08b') for x in data)
data = np.array([int(x) for x in data], dtype=np.float32)
return data # 56 bits
def _generate(self):
dlen = 56
data= np.random.binomial(1, .5, dlen)
packet = self._encode(data)
return packet, data
def generate(self, nsamples=1):
# generate random 56 bit secret
data = [self._generate() for _ in range(nsamples)]
data = (np.array([d[0] for d in data]), np.array([d[1] for d in data]))
return data # data with ecc, data org
def _to_text(self, data):
# data: {0, 1}, np.array
# return: str
data = ''.join([str(int(bit)) for bit in data])
all_bytes = [ data[i: i+8] for i in range(0, len(data), 8) ]
text = ''.join([chr(int(byte, 2)) for byte in all_bytes])
return text.strip()
def _to_binary(self, s):
if isinstance(s, str):
out = ''.join([ format(ord(i), "08b") for i in s ])
elif isinstance(s, bytes):
out = ''.join([ format(i, "08b") for i in s ])
elif isinstance(s, np.ndarray) and s.dtype is np.dtype(bool):
out = ''.join([chr(int(i)) for i in s])
elif isinstance(s, int) or isinstance(s, np.uint8):
out = format(s, "08b")
elif isinstance(s, np.ndarray):
out = [ format(i, "08b") for i in s ]
else:
raise TypeError("Type not supported.")
return np.array([float(i) for i in out], dtype=np.float32)
def _encode_text(self, s):
s = s + ' '*(7-len(s)) # 7 chars
s = self._to_binary(s) # 56 bits
packet = self._encode(s) # 100 bits
return packet, s
def encode_text(self, secret_list, return_pre_ecc=False):
"""encode secret with BCH ECC.
Input: secret (list of strings)
Output: secret (np array) with shape (B, 100) type float23, val {0,1}"""
assert np.all(np.array([len(s) for s in secret_list]) <= 7), 'Error! all strings must be less than 7 characters'
secret_list = [self._encode_text(s) for s in secret_list]
ecc = np.array([s[0] for s in secret_list], dtype=np.float32)
if return_pre_ecc:
return ecc, np.array([s[1] for s in secret_list], dtype=np.float32)
return ecc
def decode_text(self, data):
"""Decode secret with BCH ECC and convert to string.
Input: secret (torch.tensor) with shape (B, 100) type bool
Output: secret (B, 56)"""
data = self.decode(data)
data = [self._to_text(d) for d in data]
return data
def decode(self, data):
"""Decode secret with BCH ECC and convert to string.
Input: secret (torch.tensor) with shape (B, 100) type bool
Output: secret (B, 56)"""
data = data[:, :96]
data = [self._decode(d) for d in data]
return np.array(data)
def test_ecc():
ecc = ECC()
batch_size = 10
secret_ecc, secret_org = ecc.generate(batch_size) # 10x100 ecc secret, 10x56 org secret
# modify secret_ecc
secret_pred = secret_ecc.copy()
secret_pred[:,3:6] = 1 - secret_pred[:,3:6]
# pass secret_ecc to model and get predicted as secret_pred
secret_pred_org = ecc.decode(secret_pred) # 10x56
assert np.all(secret_pred_org == secret_org) # 10
def test_bch():
# test 100 bit
def check(text, poly, k, l):
bch = BCH(poly, k, l)
# text = 'secrets'
encode = bch.encode_text([text])
for ind in np.random.choice(l, k):
encode[0, ind] = 1 - encode[0, ind]
text_recon = bch.decode_text(encode)[0]
assert text==text_recon
check('secrets', 137, 5, 100)
check('some secret', 285, 10, 160)
if __name__ == '__main__':
test_ecc()
test_bch() |