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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-II Authenticated Encryption mode.
This module provides the functions for authenticated encryption and decryption
using Lilliput-AE's nonce-misuse-resistant mode based on SCT-2.
"""
from .constants import BLOCK_BYTES
from .helpers import (
ArrayToBlockbytesMatrix,
BlockbytesMatrixToBytes,
BuildAuth,
Padding10LSB,
TagValidationError,
XorState
)
from . import tbc
TWEAK_BITS = 128
TWEAK_BYTES = TWEAK_BITS//8
def _TweakTag(j, padded):
tweak = [0 for byte in range(0, TWEAK_BYTES)]
tweak[TWEAK_BYTES - 1] |= ((j >> 120) & 0xf)
for byte in range(TWEAK_BYTES - 2, -1, -1):
tweak[byte] = (j >> (8 * byte)) & 0xff
if padded:
tweak[TWEAK_BYTES - 1] |= 0x40
return tweak
def _TweakTagEnd(N):
tweak = [0 for byte in range(0, TWEAK_BYTES)]
for byte in range(0, TWEAK_BYTES - 1):
tweak[byte] = N[byte]
tweak[TWEAK_BYTES - 1] = 0x10
return tweak
def _AddTagJ(tag, j):
array_j = [0 for byte in range(0, TWEAK_BYTES)]
for byte in range(0, TWEAK_BYTES):
array_j[byte] = (j >> (byte * 8))
xorr = XorState(tag, array_j)
xorr[TWEAK_BYTES - 1] |= 0x80
return xorr
def _MesssageAuthTag(M, N, Auth, key):
l = len(M)//BLOCK_BYTES
need_padding = len(M)%BLOCK_BYTES > 0
tag = list(Auth)
M = ArrayToBlockbytesMatrix(M)
for j in range(0, l):
tweak = _TweakTag(j, False)
encryption = tbc.encrypt(tweak, key, M[j])
tag = XorState(tag, encryption)
if need_padding:
tweak = _TweakTag(l, True)
m_padded = Padding10LSB(M[l])
encryption = tbc.encrypt(tweak, key, m_padded)
tag = XorState(tag, encryption)
tweak = _TweakTagEnd(N)
encryption = tbc.encrypt(tweak, key, tag)
tag = encryption
return tag
def _MessageEncryption(M, N, tag, key):
l = len(M)//BLOCK_BYTES
need_padding = len(M)%BLOCK_BYTES > 0
M = ArrayToBlockbytesMatrix(M)
C = []
for j in range(0, l):
tweak = _AddTagJ(tag, j)
padded_nonce = list(N) + [0x00]
encryption = tbc.encrypt(tweak, key, padded_nonce)
C.append(XorState(M[j], encryption))
if need_padding:
tweak = _AddTagJ(tag, l)
padded_nonce = list(N) + [0x00]
encryption = tbc.encrypt(tweak, key, padded_nonce)
C.append(XorState(M[l], encryption))
return C
################################################################################
def encrypt(A, M, N, key):
K = list(key)
Auth = BuildAuth(TWEAK_BITS, A, K)
tag = _MesssageAuthTag(M, N, Auth, K)
C = _MessageEncryption(M, N, tag, K)
return BlockbytesMatrixToBytes(C), bytes(tag)
def decrypt(A, C, N, tag, key):
K = list(key)
tag = list(tag)
M = BlockbytesMatrixToBytes(
_MessageEncryption(C, N, tag, K)
)
Auth = BuildAuth(TWEAK_BITS, A, K)
tag2 = _MesssageAuthTag(M, N, Auth, K)
if tag != tag2:
raise TagValidationError(tag, tag2)
return M
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