实现DES轮密钥扩展算法
简介
DES（Data Encryption Standard）是一种对称加密算法，其中的一个重要步骤是密钥扩展。在DES加密过程中，需要生成多轮的子密钥来对数据进行加密。本文将教你如何使用Python实现DES轮密钥扩展算法。
流程图
flowchart TD
A[生成初始密钥] --> B[PC-1置换]
B --> C[循环左移]
C --> D[PC-2置换]
类图
classDiagram
class DESKeyExpansion {
+__init__(key)
-_key
-_pc_1_table
-_pc_2_table
-_shift_table
-_round_keys
+get_round_keys()
-_pc_1_permute()
-_pc_2_permute()
-_left_shift()
}
代码实现
首先，我们需要定义一个DESKeyExpansion类，用于进行密钥扩展操作。
class DESKeyExpansion:
def __init__(self, key):
self._key = key
self._pc_1_table = [57, 49, 41, 33, 25, 17, 9, 1,
58, 50, 42, 34, 26, 18, 10, 2,
59, 51, 43, 35, 27, 19, 11, 3,
60, 52, 44, 36, 63, 55, 47, 39,
31, 23, 15, 7, 62, 54, 46, 38,
30, 22, 14, 6, 61, 53, 45, 37,
29, 21, 13, 5, 28, 20, 12, 4]
self._pc_2_table = [14, 17, 11, 24, 1, 5, 3, 28,
15, 6, 21, 10, 23, 19, 12, 4,
26, 8, 16, 7, 27, 20, 13, 2,
41, 52, 31, 37, 47, 55, 30, 40,
51, 45, 33, 48, 44, 49, 39, 56,
34, 53, 46, 42, 50, 36, 29, 32]
self._shift_table = [1, 1, 2, 2, 2, 2, 2, 2,
1, 2, 2, 2, 2, 2, 2, 1]
self._round_keys = []
def _pc_1_permute(self):
pc_1_key = []
for index in self._pc_1_table:
pc_1_key.append(self._key[index - 1])
return pc_1_key
def _pc_2_permute(self, key):
pc_2_key = []
for index in self._pc_2_table:
pc_2_key.append(key[index - 1])
return pc_2_key
def _left_shift(self, key, shift):
left = key[:28]
right = key[28:]
left = left[shift:] + left[:shift]
right = right[shift:] + right[:shift]
return left + right
def get_round_keys(self):
pc_1_key = self._pc_1_permute()
left = pc_1_key[:28]
right = pc_1_key[28:]
for shift in self._shift_table:
left = self._left_shift(left, shift)
right = self._left_shift(right, shift)
pc_2_key = self._pc_2_permute(left + right)
self._round_keys.append(pc_2_key)
return self._round_keys
接下来，我们可以使用这个类来生成DES轮密钥。
key = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
des_key_expansion = DESKeyExpansion(key)
round_keys = des_key_expansion.get_round_keys()
print("Round Keys:")
for index, round_key in enumerate(round_keys):
print("Round {0}: {1}".format(index + 1, round_key))
