python实现入侵检测的多模式匹配算法的具体代码
时间: 2023-12-21 12:05:06 浏览: 28
多模式匹配算法在入侵检测系统中是非常常用的一种算法,其中最常见的算法是AC自动机算法。下面是使用Python实现AC自动机算法的代码:
```python
class TrieNode:
def __init__(self, char: str):
self.char = char
self.children = {}
self.failure_link = None
self.is_end = False
class AC:
def __init__(self, patterns: List[str]):
self.root = TrieNode('')
self.patterns = patterns
self.build_trie()
def build_trie(self):
for pattern in self.patterns:
node = self.root
for char in pattern:
if char not in node.children:
node.children[char] = TrieNode(char)
node = node.children[char]
node.is_end = True
def build_failure_links(self):
queue = [self.root]
while queue:
node = queue.pop(0)
for char, child in node.children.items():
if node == self.root:
child.failure_link = self.root
else:
failure_node = node.failure_link
while failure_node:
if char in failure_node.children:
child.failure_link = failure_node.children[char]
break
failure_node = failure_node.failure_link
if not failure_node:
child.failure_link = self.root
queue.append(child)
def search(self, text: str) -> bool:
node = self.root
for i, char in enumerate(text):
while node != self.root and char not in node.children:
node = node.failure_link
if char in node.children:
node = node.children[char]
if node.is_end:
return True
return False
```
其中,TrieNode是Trie树的节点类,AC是AC自动机类,包含了Trie树的构建、失败指针的构建和搜索等方法。构建Trie树和失败指针的方法在build_trie和build_failure_links中实现,搜索方法在search中实现。在构建Trie树时,将模式串添加到Trie树中,并将最后一个节点标记为is_end=True;在构建失败指针时,对每个节点,从父节点的失败指针开始,向上查找直到找到一个节点的子节点包含当前字符,或者到达根节点为止,将该子节点作为当前节点的失败指针;在搜索时,从根节点开始,对每个字符,像Trie树一样逐层匹配,如果匹配到最后一个字符的节点的is_end属性为True,则说明匹配成功。
使用示例:
```python
patterns = ['attack', 'hack', 'intrusion', 'malware']
ac = AC(patterns)
ac.build_failure_links()
text = 'There was a malware attack on the system'
print(ac.search(text)) # True
```