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from dataclasses import dataclass
from typing import Iterable, List, NamedTuple
from . import rs1024, wordlist
from .constants import (
CUSTOMIZATION_STRING_EXTENDABLE,
CUSTOMIZATION_STRING_ORIG,
EXTENDABLE_FLAG_LENGTH_BITS,
ID_EXP_LENGTH_WORDS,
ITERATION_EXP_LENGTH_BITS,
METADATA_LENGTH_WORDS,
MIN_MNEMONIC_LENGTH_WORDS,
RADIX,
RADIX_BITS,
)
from .utils import MnemonicError, bits_to_bytes, bits_to_words, int_to_indices
WordIndex = int
def _int_to_word_indices(value: int, length: int) -> List[WordIndex]:
"""Converts an integer value to a list of base 1024 indices in big endian order."""
return list(int_to_indices(value, length, radix_bits=RADIX_BITS))
def _int_from_word_indices(indices: Iterable[WordIndex]) -> int:
"""Converts a list of base 1024 indices in big endian order to an integer value."""
value = 0
for index in indices:
value = value * RADIX + index
return value
def _customization_string(extendable: bool) -> bytes:
if extendable:
return CUSTOMIZATION_STRING_EXTENDABLE
else:
return CUSTOMIZATION_STRING_ORIG
class ShareCommonParameters(NamedTuple):
"""Parameters that are common to all shares of a master secret."""
identifier: int
extendable: bool
iteration_exponent: int
group_threshold: int
group_count: int
class ShareGroupParameters(NamedTuple):
"""Parameters that are common to all shares of a master secret, which belong to the same group."""
identifier: int
extendable: bool
iteration_exponent: int
group_index: int
group_threshold: int
group_count: int
member_threshold: int
@dataclass(frozen=True)
class Share:
"""Represents a single mnemonic share and its metadata"""
identifier: int
extendable: bool
iteration_exponent: int
group_index: int
group_threshold: int
group_count: int
index: int
member_threshold: int
value: bytes
def common_parameters(self) -> ShareCommonParameters:
"""Return values that uniquely identify a matching set of shares."""
return ShareCommonParameters(
self.identifier,
self.extendable,
self.iteration_exponent,
self.group_threshold,
self.group_count,
)
def group_parameters(self) -> ShareGroupParameters:
"""Return values that uniquely identify shares belonging to the same group."""
return ShareGroupParameters(
self.identifier,
self.extendable,
self.iteration_exponent,
self.group_index,
self.group_threshold,
self.group_count,
self.member_threshold,
)
def _encode_id_exp(self) -> List[WordIndex]:
id_exp_int = self.identifier << (
ITERATION_EXP_LENGTH_BITS + EXTENDABLE_FLAG_LENGTH_BITS
)
id_exp_int += self.extendable << ITERATION_EXP_LENGTH_BITS
id_exp_int += self.iteration_exponent
return _int_to_word_indices(id_exp_int, ID_EXP_LENGTH_WORDS)
def _encode_share_params(self) -> List[WordIndex]:
# each value is 4 bits, for 20 bits total
val = self.group_index
val <<= 4
val += self.group_threshold - 1
val <<= 4
val += self.group_count - 1
val <<= 4
val += self.index
val <<= 4
val += self.member_threshold - 1
# group parameters are 2 words
return _int_to_word_indices(val, 2)
def words(self) -> List[str]:
"""Convert share data to a share mnemonic."""
value_word_count = bits_to_words(len(self.value) * 8)
value_int = int.from_bytes(self.value, "big")
value_data = _int_to_word_indices(value_int, value_word_count)
share_data = self._encode_id_exp() + self._encode_share_params() + value_data
checksum = rs1024.create_checksum(
share_data, _customization_string(self.extendable)
)
return list(wordlist.words_from_indices(share_data + checksum))
def mnemonic(self) -> str:
"""Convert share data to a share mnemonic."""
return " ".join(self.words())
@classmethod
def from_mnemonic(cls, mnemonic: str) -> "Share":
"""Convert a share mnemonic to share data."""
mnemonic_data = wordlist.mnemonic_to_indices(mnemonic)
if len(mnemonic_data) < MIN_MNEMONIC_LENGTH_WORDS:
raise MnemonicError(
"Invalid mnemonic length. The length of each mnemonic "
f"must be at least {MIN_MNEMONIC_LENGTH_WORDS} words."
)
padding_len = (RADIX_BITS * (len(mnemonic_data) - METADATA_LENGTH_WORDS)) % 16
if padding_len > 8:
raise MnemonicError("Invalid mnemonic length.")
id_exp_data = mnemonic_data[:ID_EXP_LENGTH_WORDS]
id_exp_int = _int_from_word_indices(id_exp_data)
identifier = id_exp_int >> (
EXTENDABLE_FLAG_LENGTH_BITS + ITERATION_EXP_LENGTH_BITS
)
extendable = bool((id_exp_int >> ITERATION_EXP_LENGTH_BITS) & 1)
iteration_exponent = id_exp_int & ((1 << ITERATION_EXP_LENGTH_BITS) - 1)
if not rs1024.verify_checksum(mnemonic_data, _customization_string(extendable)):
raise MnemonicError(
'Invalid mnemonic checksum for "{} ...".'.format(
" ".join(mnemonic.split()[: ID_EXP_LENGTH_WORDS + 2])
)
)
share_params_data = mnemonic_data[ID_EXP_LENGTH_WORDS : ID_EXP_LENGTH_WORDS + 2]
share_params_int = _int_from_word_indices(share_params_data)
share_params = int_to_indices(share_params_int, 5, 4)
(
group_index,
group_threshold,
group_count,
index,
member_threshold,
) = share_params
if group_count < group_threshold:
raise MnemonicError(
'Invalid mnemonic "{} ...". Group threshold cannot be greater than group count.'.format(
" ".join(mnemonic.split()[: ID_EXP_LENGTH_WORDS + 2])
)
)
value_data = mnemonic_data[
ID_EXP_LENGTH_WORDS + 2 : -rs1024.CHECKSUM_LENGTH_WORDS
]
value_byte_count = bits_to_bytes(RADIX_BITS * len(value_data) - padding_len)
value_int = _int_from_word_indices(value_data)
try:
value = value_int.to_bytes(value_byte_count, "big")
except OverflowError:
raise MnemonicError(
'Invalid mnemonic padding for "{} ...".'.format(
" ".join(mnemonic.split()[: ID_EXP_LENGTH_WORDS + 2])
)
) from None
return cls(
identifier,
extendable,
iteration_exponent,
group_index,
group_threshold + 1,
group_count + 1,
index,
member_threshold + 1,
value,
)
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