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skiplist.py
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skiplist.py
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from typing import List, Union, Tuple
from random import random
from hashlib import sha256
from typing import Union
import binascii
def hash_fun(x: bytes, y: bytes) -> bytes:
return sha256(bytes(binascii.a2b_hex(min(x.hex(), y.hex()) + max(x.hex(), y.hex())))).digest()
class AuthenticResponse:
def __init__(self, timestamp: bytes, item, proof, result: bool):
self.timestamp = timestamp.hex()
self.item = item.hex()
ls = [x.hex() for x in proof]
self.proof = ls
self.result = result
def subject_contained(self):
return self.result
def validates_against(self, timestamp: Union[bytes, None] = None):
if timestamp is None:
timestamp = self.timestamp
acc = binascii.a2b_hex(self.proof[0])
for value in self.proof[1:]:
acc = hash_fun(acc, binascii.a2b_hex(value))
return timestamp == acc
class Node:
def __init__(self, item, height: int = 1):
self.item = item
self.height = height
self.refs: List[Union[Node, None]] = [None] * height
self.hashes: List[Union[bytes, None]] = [None] * height
def compute_hashes(self) -> None:
for i in range(self.height):
self.hashes[i] = self.compute_hash(i)
def compute_hash(self, index) -> bytes:
if self.refs[index] is None:
return hash_fun(SkipList.zero, SkipList.zero)
else:
if index == 0:
w = self.refs[index]
if w.height - 1 > index:
return hash_fun(bytes(self.item), bytes(w.item))
else:
return hash_fun(bytes(self.item), w.hashes[index])
else:
w = self.refs[index]
if w.height - 1 > index:
return self.hashes[index - 1]
else:
return hash_fun(self.hashes[index - 1], w.hashes[index])
def __str__(self):
return "Node<" + str(self.item) + ">"
class SkipList:
seed = b'\xd1\xf7\xb7\xd5\xa6\xbd\xef^\x9f\xeb\xcfy\xe9\xff\x1d\xef\xc7|m\xd7\xb7\xf5\xc6\xbay\xde]\xe7\xbe\xf5' \
b'\xe7w]\xe1\xf7\xfc\xeb\xa6\x9a\xe9\xf7\x1d}\xde\xfb\xd9\xee\x9a'
zero = b'{N\xbay\xf7\xb5\xe5\xd6\xde\xdb\xce\xf5\xef\x87{\xe3\xdf\x1em\xf7\x1bw\xa7=m\xd6\xfc\xf7\xb6\xbc' \
b'\xdb\xbex\xeb~:\xdd\xfft\xef\x96\xfdi\xf7_\xf3\x9e\x1f'
def __init__(self):
self.tail: Node = Node(self.zero, 2)
self.tail.compute_hashes()
self.head: Node = Node(self.seed)
self.head.refs[0] = self.tail
self.head.compute_hashes()
self.length: int = 0
self.level: int = 1
self.timestamp: bytes = self.head.hashes[0]
def __len__(self):
return self.length
def __str__(self):
l = []
node = self.head
while node is not None:
l.append((node.item, list(map(lambda r: "None" if r is None else r.item, node.refs))))
node = node.refs[0]
return "Skiplist<" + str(l) + ">"
def __head_hash(self) -> bytes:
return self.head.hashes[self.level - 1]
@staticmethod
def __gen_height(_height: Union[int, None]) -> int:
if _height is not None:
return _height
height = 1
while random() < 0.5:
height += 1
return height
def __find_node(self, item) -> Node:
node = self.head
height = self.level - 1
while height >= 0:
next = node.refs[height]
if next is not self.tail and next.item <= item:
node = next
else:
height -= 1
return node
def __find_update(self, item) -> List[Node]:
node = self.head
update: List[Union[Node, None]] = [None] * self.level
height = self.level - 1
while height >= 0:
next = node.refs[height]
if next is not self.tail and next.item < item:
node = next
else:
update[height] = node
height -= 1
return update
def contains(self, item) -> bool:
return self.__find_node(item).item == item
__contains__ = contains
def insert(self, item, _height: Union[int, None] = None) -> None:
height = self.__gen_height(_height)
head = self.head
tail = self.tail
before = head.height
if before < height:
tail.height = height + 1
head.height = height
for i in range(before, height):
tail.refs.append(None)
tail.hashes.append(tail.compute_hash(i))
head.refs.append(self.tail)
head.hashes.append(head.compute_hash(i))
if self.level < height:
self.level = height
update = self.__find_update(item)
p = self.__get_p(item)
node = Node(item, height)
for i in range(height):
node.refs[i] = update[i].refs[i]
update[i].refs[i] = node
node.compute_hashes()
for n, h in p.__reversed__():
n.hashes[h] = n.compute_hash(h)
for i in range(before, height):
head.hashes[i] = head.compute_hash(i)
self.length += 1
def delete(self, item):
if self.length == 0:
return None
update = self.__find_update(item)
p = self.__get_p(item)
node = update[0].refs[0]
if node is not None and node.item == item:
for i in range(node.height):
update[i].refs[i] = node.refs[i]
while self.level > 1 and self.head.refs[self.level - 1] is self.tail:
self.level -= 1
self.length -= 1
for n, h in p.__reversed__():
n.hashes[h] = n.compute_hash(h)
return item
return None
def __get_p(self, item) -> List[Tuple[Node, int]]:
update = self.__find_update(item)
p: List[Tuple[Node, int]] = []
node = self.head
for i in range(len(update) - 1, -1, -1):
while node is not update[i]:
p.append((node, i))
node = node.refs[i]
p.append((node, i))
return p
def update(self, insertion: bool, item, timestamp: Union[bytes, None] = None, height: Union[int, None] = None)\
-> None:
if insertion:
self.insert(item, height)
else:
self.delete(item)
if timestamp is None:
timestamp = self.__head_hash()
self.timestamp = timestamp
def verify(self, item) -> AuthenticResponse:
p = self.__get_p(item)
p.append((p[-1][0].refs[0], 0))
plen = len(p)
q = []
wv, _ = p.pop()
zw = wv.refs[0]
if wv.height == 1:
if zw.height == 1:
q.append(zw.hashes[0])
else:
q.append(zw.item)
q.append(wv.item)
result = wv.item == item
j = 1
pv = wv
for i in range(1, plen):
v, h = p.pop()
w = v.refs[h]
if h == 0 or w.height - 1 == h:
j += 1
if w is not pv:
q.append(w.hashes[h])
else:
if h == 0:
q.append(v.item)
else:
q.append(v.hashes[h - 1])
pv = v
return AuthenticResponse(self.timestamp, item, q, result)