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from constants import BLOCK_BITS, BLOCK_BYTES
import tbc
def ArrayToBlockbytesMatrix(array):
vector = list(array)
blocks_nb = len(vector)//BLOCK_BYTES
block_starts = (
i*BLOCK_BYTES for i in range(blocks_nb)
)
matrix = [
vector[start:start+BLOCK_BYTES] for start in block_starts
]
padding_len = len(vector)%BLOCK_BYTES
if padding_len > 0:
padding = vector[-padding_len:]
matrix.append(padding)
return matrix
def BlockbytesMatrixToBytes(matrix):
return bytes(byte for block in matrix for byte in block)
def XorState(state1, state2):
return [s1^s2 for (s1, s2) in zip(state1, state2)]
def Padding10LSB(X):
zeroes = [0] * (BLOCK_BYTES-len(X)-1)
return zeroes + [0b10000000] + X
def _tweakAssociatedData(t, i, padded):
t_bytes = t//8
tweak = [0]*(t_bytes)
mask = 0xff
for byte in range(t_bytes-1):
tweak[byte] = (i & mask) >> (byte * 8)
mask = mask << 8
mask = (0xf << (8 * t_bytes-1))
tweak[-1] = (i & mask) >> ((t_bytes-1)*8)
if not padded:
tweak[-1] |= 0x20
else:
tweak[-1] |= 0x60
return tweak
def BuildAuth(t, A, key):
Auth = [0 for byte in range(0, BLOCK_BYTES)]
l_a = len(A)//BLOCK_BYTES
need_padding = len(A)%BLOCK_BYTES > 0
A = ArrayToBlockbytesMatrix(A)
for i in range(0, l_a):
tweak = _tweakAssociatedData(t, i, padded=False)
enc = tbc.encrypt(tweak, key, A[i])
Auth = XorState(Auth, enc)
if not need_padding:
return Auth
tweak = _tweakAssociatedData(t, l_a, padded=True)
ad_padded = Padding10LSB(A[l_a])
enc = tbc.encrypt(tweak, key, ad_padded)
Auth = XorState(Auth, enc)
return Auth
class TagValidationError(Exception):
def __init__(self, announced, computed):
msg = '\n'.join((
'Invalid tag:',
announced.hex().upper()+' (announced)',
computed.hex().upper()+' (computed)'
))
super().__init__(msg)
self._announced = announced
self._computed = computed
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