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# Implementation of the Lilliput-AE tweakable block cipher.
#
# Authors, hereby denoted as "the implementer":
# Kévin Le Gouguec,
# Léo Reynaud
# 2019.
#
# For more information, feedback or questions, refer to our website:
# https://paclido.fr/lilliput-ae
#
# To the extent possible under law, the implementer has waived all copyright
# and related or neighboring rights to the source code in this file.
# http://creativecommons.org/publicdomain/zero/1.0/
"""Lilliput-I Authenticated Encryption mode.
This module provides the functions for authenticated encryption and decryption
using Lilliput-AE's nonce-respecting mode based on ΘCB3.
"""
from enum import Enum
from .constants import BLOCK_BYTES, NONCE_BYTES
from .ae_common import (
bytes_to_block_matrix,
block_matrix_to_bytes,
build_auth,
pad10,
TagValidationError,
xor
)
from . import tbc
TWEAK_BITS = 192
TWEAK_BYTES = TWEAK_BITS//8
def _low_part(array, number_bits):
shifted = 0
for byte in range(0, len(array)):
shifted |= (array[byte] << (8 * byte))
mask = 0
for bit in range(0, number_bits):
mask |= (0x1 << bit)
lower_part = shifted & mask
will_pad = 0
if number_bits % 8 != 0:
will_pad = 1
lower_part_byte = []
nb_bytes = number_bits//8 + will_pad
for byte in range(nb_bytes):
lower_part_byte.append(lower_part & 0xff)
lower_part = lower_part >> 8
return lower_part_byte
class _MessageTweak(Enum):
BLOCK = 0b0000
NO_PADDING = 0b0001
PAD = 0b0100
FINAL = 0b0101
def _tweak_message(N, j, padding):
tweak = [0 for byte in range(0, TWEAK_BYTES)]
for byte in range(NONCE_BYTES-1, -1, -1):
tweak[byte + (TWEAK_BYTES-NONCE_BYTES)] |= (N[byte] & 0xf0) >> 4
tweak[byte + (TWEAK_BYTES-NONCE_BYTES-1)] |= (N[byte] & 0x0f) << 4
tweak[TWEAK_BYTES-NONCE_BYTES-1] |= ((j >> 64) & 0xf)
for byte in range(TWEAK_BYTES-NONCE_BYTES-2, -1, -1):
tweak[byte] = (j >> (8 * byte)) & 0xff
tweak[-1] |= padding.value<<4
return tweak
def _treat_message_enc(M, N, key):
checksum = [0 for byte in range(0, BLOCK_BYTES)]
l = len(M)//BLOCK_BYTES
padding_bytes = len(M)%BLOCK_BYTES
M = bytes_to_block_matrix(M)
C = []
for j in range(0, l):
checksum = xor(checksum, M[j])
tweak = _tweak_message(N, j, _MessageTweak.BLOCK)
C.append(tbc.encrypt(tweak, key, M[j]))
if padding_bytes == 0:
tweak = _tweak_message(N, l, _MessageTweak.NO_PADDING)
Final = tbc.encrypt(tweak, key, checksum)
else:
m_padded = pad10(M[l])
checksum = xor(checksum, m_padded)
tweak = _tweak_message(N, l, _MessageTweak.PAD)
pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
lower_part = _low_part(pad, padding_bytes*8)
C.append(xor(M[l], lower_part))
tweak_final = _tweak_message(N, l+1, _MessageTweak.FINAL)
Final = tbc.encrypt(tweak_final, key, checksum)
return (Final, C)
def _treat_message_dec(C, N, key):
checksum = [0 for byte in range(0, BLOCK_BYTES)]
l = len(C)//BLOCK_BYTES
padding_bytes = len(C)%BLOCK_BYTES
C = bytes_to_block_matrix(C)
M = []
for j in range(0, l):
tweak = _tweak_message(N, j, _MessageTweak.BLOCK)
M.append(tbc.decrypt(tweak, key, C[j]))
checksum = xor(checksum, M[j])
if padding_bytes == 0:
tweak = _tweak_message(N, l, _MessageTweak.NO_PADDING)
Final = tbc.encrypt(tweak, key, checksum)
else:
tweak = _tweak_message(N, l, _MessageTweak.PAD)
pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
lower_part = _low_part(pad, padding_bytes*8)
M.append(xor(C[l], lower_part))
m_padded = pad10(M[l])
checksum = xor(checksum, m_padded)
tweak_final = _tweak_message(N, l+1, _MessageTweak.FINAL)
Final = tbc.encrypt(tweak_final, key, checksum)
return (Final, M)
def encrypt(A, M, N, key):
K = list(key)
Auth = build_auth(TWEAK_BITS, A, K)
(Final, C) = _treat_message_enc(M, N, K)
tag = xor(Auth, Final)
return block_matrix_to_bytes(C), bytes(tag)
def decrypt(A, C, N, tag, key):
K = list(key)
tag = list(tag)
Auth = build_auth(TWEAK_BITS, A, K)
(Final, M) = _treat_message_dec(C, N, K)
tag2 = xor(Auth, Final)
if tag != tag2:
raise TagValidationError(tag, tag2)
return block_matrix_to_bytes(M)
|
