1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
|
from collections import defaultdict
from dataclasses import dataclass, field, replace
from typing import Any, Dict, Optional, Tuple
from .constants import GROUP_PREFIX_LENGTH_WORDS
from .shamir import ShareGroup, recover_ems
from .share import Share, ShareCommonParameters
from .utils import MnemonicError
UNDETERMINED = -1
class RecoveryState:
"""Object for keeping track of running Shamir recovery."""
def __init__(self) -> None:
self.last_share: Optional[Share] = None
self.groups: Dict[int, ShareGroup] = defaultdict(ShareGroup)
self.parameters: Optional[ShareCommonParameters] = None
def group_prefix(self, group_index: int) -> str:
"""Return three starting words of a given group."""
if not self.last_share:
raise RuntimeError("Add at least one share first")
fake_share = replace(self.last_share, group_index=group_index)
return " ".join(fake_share.words()[:GROUP_PREFIX_LENGTH_WORDS])
def group_status(self, group_index: int) -> Tuple[int, int]:
"""Return completion status of given group.
Result consists of the number of shares already entered, and the threshold
for recovering the group.
"""
group = self.groups[group_index]
if not group:
return 0, UNDETERMINED
return len(group), group.member_threshold()
def group_is_complete(self, group_index: int) -> bool:
"""Check whether a given group is already complete."""
return self.groups[group_index].is_complete()
def groups_complete(self) -> int:
"""Return the number of groups that are already complete."""
if self.parameters is None:
return 0
return sum(
self.group_is_complete(i) for i in range(self.parameters.group_count)
)
def is_complete(self) -> bool:
"""Check whether the recovery set is complete.
That is, at least M groups must be complete, where M is the global threshold.
"""
if self.parameters is None:
return False
return self.groups_complete() >= self.parameters.group_threshold
def matches(self, share: Share) -> bool:
"""Check whether the provided share matches the current set, i.e., has the same
common parameters.
"""
if self.parameters is None:
return True
return share.common_parameters() == self.parameters
def add_share(self, share: Share) -> bool:
"""Add a share to the recovery set."""
if not self.matches(share):
raise MnemonicError(
"This mnemonic is not part of the current set. Please try again."
)
self.groups[share.group_index].add(share)
self.last_share = share
if self.parameters is None:
self.parameters = share.common_parameters()
return True
def __contains__(self, obj: Any) -> bool:
if not isinstance(obj, Share):
return False
if not self.matches(obj):
return False
if not self.groups:
return False
return obj in self.groups[obj.group_index]
def recover(self, passphrase: bytes) -> bytes:
"""Recover the master secret, given a passphrase."""
# Select a subset of shares which meets the thresholds.
reduced_groups: Dict[int, ShareGroup] = {}
for group_index, group in self.groups.items():
if group.is_complete():
reduced_groups[group_index] = group.get_minimal_group()
# some groups have been added so parameters must be known
assert self.parameters is not None
if len(reduced_groups) >= self.parameters.group_threshold:
break
encrypted_master_secret = recover_ems(reduced_groups)
return encrypted_master_secret.decrypt(passphrase)
|
