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"""
OCB 3 for lilliput ae i
"""
from enum import Enum
from .constants import BLOCK_BYTES, NONCE_BYTES
from .helpers import (
ArrayToBlockbytesMatrix,
BlockbytesMatrixToBytes,
BuildAuth,
Padding10LSB,
TagValidationError,
XorState
)
from . import tbc
TWEAK_BITS = 192
TWEAK_BYTES = TWEAK_BITS//8
def LowPart(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 = 0b000
NO_PADDING = 0b0001
PAD = 0b0100
FINAL = 0b0101
def TweakMessage(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 TreatMessageEnc(M, N, key):
checksum = [0 for byte in range(0, BLOCK_BYTES)]
l = len(M)//BLOCK_BYTES
padding_bytes = len(M)%BLOCK_BYTES
M = ArrayToBlockbytesMatrix(M)
C = []
for j in range(0, l):
checksum = XorState(checksum, M[j])
tweak = TweakMessage(N, j, _MessageTweak.BLOCK)
C.append(tbc.encrypt(tweak, key, M[j]))
if padding_bytes == 0:
tweak = TweakMessage(N, l, _MessageTweak.NO_PADDING)
Final = tbc.encrypt(tweak, key, checksum)
else:
m_padded = Padding10LSB(M[l])
checksum = XorState(checksum, m_padded)
tweak = TweakMessage(N, l, _MessageTweak.PAD)
pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
lower_part = LowPart(pad, padding_bytes*8)
C.append(XorState(M[l], lower_part))
tweak_final = TweakMessage(N, l+1, _MessageTweak.FINAL)
Final = tbc.encrypt(tweak_final, key, checksum)
return (Final, C)
def TreatMessageDec(C, N, key):
checksum = [0 for byte in range(0, BLOCK_BYTES)]
l = len(C)//BLOCK_BYTES
padding_bytes = len(C)%BLOCK_BYTES
C = ArrayToBlockbytesMatrix(C)
M = []
for j in range(0, l):
tweak = TweakMessage(N, j, _MessageTweak.BLOCK)
M.append(tbc.decrypt(tweak, key, C[j]))
checksum = XorState(checksum, M[j])
if padding_bytes == 0:
tweak = TweakMessage(N, l, _MessageTweak.NO_PADDING)
Final = tbc.encrypt(tweak, key, checksum)
else:
tweak = TweakMessage(N, l, _MessageTweak.PAD)
pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
lower_part = LowPart(pad, padding_bytes*8)
M.append(XorState(C[l], lower_part))
m_padded = Padding10LSB(M[l])
checksum = XorState(checksum, m_padded)
tweak_final = TweakMessage(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 = BuildAuth(TWEAK_BITS, A, K)
(Final, C) = TreatMessageEnc(M, N, K)
tag = XorState(Auth, Final)
return BlockbytesMatrixToBytes(C), bytes(tag)
def decrypt(A, C, N, tag, key):
K = list(key)
tag = list(tag)
Auth = BuildAuth(TWEAK_BITS, A, K)
(Final, M) = TreatMessageDec(C, N, K)
tag2 = XorState(Auth, Final)
if tag != tag2:
raise TagValidationError(tag, tag2)
return BlockbytesMatrixToBytes(M)
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