def _block_to_indices(block):
if len(block) > 4:
raise ValueError("block too big")
# `menmonicode` uses little-endian numbers.
num = from_base(256, reversed(block))
indices = list(reversed(to_base(1626, num)))
# Pad the list of indices to the correct size.
length = {
1: 1,
2: 2,
3: 3,
4: 3,
}[len(block)]
indices += [0] * (length - len(indices))
# The third byte in a block slightly leaks into the third word. A
# different set of words is used for this case to distinguish it from the
# four byte case.
if len(block) == 3:
indices[-1] += 1626
return indices
def _block_to_indices(block):
if len(block) > 4:
raise ValueError("block too big")
# menmonicode uses little-endian numbers
num = from_base(256, reversed(block))
indices = list(reversed(to_base(1626, num)))
# pad the list of indices to the correct size
length = {
1: 1,
2: 2,
3: 3,
4: 3,
}[len(block)]
indices += [0] * (length - len(indices))
# The third byte in a block slightly leaks into the third word. A
# different set of words is used for this case to distinguish it from the
# four byte case
if len(block) == 3:
indices[-1] += 1626
return indices
def _words_to_block(words):
if not isinstance(words, tuple):
raise TypeError("expected tuple of words")
if len(words) == 0:
raise ValueError("no words in block")
if len(words) > 3:
raise ValueError("too many words in block")
try:
indices = list(word_to_index(word) for word in words)
except KeyError as e:
raise ValueError("word not recognized") from e
# calculate length of block.
# both three byte and four byte blocks map to three words but can be
# distinguished as a different word list is used to encode the last word
# in the three byte case
length = {
1: 1,
2: 2,
3: 3 if indices[-1] >= 1626 else 4,
}[len(words)]
if length == 3:
indices[2] -= 1626
# check that words in the second word list don't appear anywhere else in
# the block
for index in indices:
if index > 1626:
raise ValueError(
"unexpected three byte word: %s" % index_to_word(index)
)
num = from_base(1626, reversed(indices))
block = bytes(reversed(to_base(256, num)))
# pad to correct length
return block.ljust(length, b'\x00')
def _words_to_block(words):
if not isinstance(words, tuple):
raise TypeError("expected tuple of words")
if len(words) == 0:
raise ValueError("no words in block")
if len(words) > 3:
raise ValueError("too many words in block")
try:
indices = list(word_to_index(word) for word in words)
except KeyError as e:
raise ValueError("word not recognized") from e
# Calculate length of block.
# Both three byte and four byte blocks map to three words but can be
# distinguished as a different word list is used to encode the last word
# in the three byte case.
length = {
1: 1,
2: 2,
3: 3 if indices[-1] >= 1626 else 4,
}[len(words)]
if length == 3:
indices[2] -= 1626
# Check that words in the second word list don't appear anywhere else in
# the block.
for index in indices:
if index > 1626:
raise ValueError((
"unexpected three byte word: {word!r}"
).format(word=index_to_word(index)))
num = from_base(1626, reversed(indices))
block = bytes(reversed(to_base(256, num)))
# Pad to correct length.
return block.ljust(length, b'\x00')
def test_encode_base_ten(self):
self.assertEqual([1, 2, 3, 4, 5, 6], to_base(10, 123456))
def test_encode_zero(self):
self.assertEqual([], to_base(12, 0))
def test_encode_base_ten(self):
self.assertEqual([1, 2, 3, 4, 5, 6], to_base(10, 123456))
def test_encode_zero(self):
self.assertEqual([], to_base(12, 0))