一、实验目的
1、了解对称密码体制基本原理
2、掌握编程语言实现对称加密、解密
二、实验原理
DES 使用一个 56 位的密钥以及附加的 8 位奇偶校验位，产生最大 64 位的分组大小。这是一个迭代的分组密码，使用称为 Feistel 的技术，其中将加密的文本块分成两半。使用子密钥对其中一半应用循环功能，然后将输出与另一半进行“异或”运算；接着交换这两半，这一过程会继续下去，但最后一个循环不交换。DES 使用 16 个循环，使用异或，置换，代换，移位操作四种基本运算。DES算法的入口参数有三个：Key、Data、Mode。Key为8个字节共64位，是DES算法的工作密钥；Data也为8个字节64位，是要被加密或被解密的数据；Mode为DES的工作方式，有两种：加密或解密。
三、实验代码
class DES():
# 初始化DES加密的参数
def __init__(self,key: str):
# 初始数据置换表IP，用于初始IP置换
self.IP = [
58, 50, 42, 34, 26, 18, 10, 2,
60, 52, 44, 36, 28, 20, 12, 4,
62, 54, 46, 38, 30, 22, 14, 6,
64, 56, 48, 40, 32, 24, 16, 8,
57, 49, 41, 33, 25, 17, 9, 1,
59, 51, 43, 35, 27, 19, 11, 3,
61, 53, 45, 37, 29, 21, 13, 5,
63, 55, 47, 39, 31, 23, 15, 7,
]
# 密钥初始置换表PC_1，用于获得最初的56位密钥
self.PC_1 = [
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,
]
# 密钥压缩置换表PC_2，用于获得子密钥
self.PC_2 = [
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,
]
# 密钥每一轮的对应左移位数
self.k0 = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1, ]
# E扩展表，用于将右半部分数据Rn从32位置换成48位
self.E = [
32, 1, 2, 3, 4, 5,
4, 5, 6, 7, 8, 9,
8, 9, 10, 11, 12, 13,
12, 13, 14, 15, 16, 17,
16, 17, 18, 19, 20, 21,
20, 21, 22, 23, 24, 25,
24, 25, 26, 27, 28, 29,
28, 29, 30, 31, 32, 1,
]
# S盒，将48位数据代替为32位数据
self.S = [
[
14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7,
0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8,
4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0,
15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13,
],
[
15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10,
3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5,
0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15,
13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9,
],
[
10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,
13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,
13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7,
1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12,
],
[
7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15,
13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9,
10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,
3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14,
],
[
2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9,
14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6,
4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14,
11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3,
],
[
12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,
10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,
9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,
4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13,
],
[
4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1,
13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6,
1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2,
6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12,
],
[
13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7,
1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2,
7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8,
2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11,
],
]
# P盒置换表，S盒代替运算的32位输出按照P盒进行置换
self.P = [
16, 7, 20, 21,
29, 12, 28, 17,
1, 15, 23, 26,
5, 18, 31, 10,
2, 8, 24, 14,
32, 27, 3, 9,
19, 13, 30, 6,
22, 11, 4, 25,
]
# 最终置换表IP_1，用于逆置换
self.IP_1 = [
40, 8, 48, 16, 56, 24, 64, 32,
39, 7, 47, 15, 55, 23, 63, 31,
38, 6, 46, 14, 54, 22, 62, 30,
37, 5, 45, 13, 53, 21, 61, 29,
36, 4, 44, 12, 52, 20, 60, 28,
35, 3, 43, 11, 51, 19, 59, 27,
34, 2, 42, 10, 50, 18, 58, 26,
33, 1, 41, 9, 49, 17, 57, 25,
]
# 设置密钥
self.K = self.convert_to_2(key)
# 进制转换——字符串转为二进制
def convert_to_2(self, string: str) -> str:
# 将字符串转成bytes类型，再转成list
str_list = list(bytes(string, 'utf8'))
result = []
for num in str_list:
# 用bin(num)将当前字节转换为二进制，然后使用[2:]切片操作去掉二进制字符串前面的"0b"标识。
# 用zfill(8)函数给二进制字符串添加前导零，确保二进制字符串长度为8位
# 一个字节由8个二进制位组成，保持一致性
result.append(bin(num)[2:].zfill(8))
# 将结果列表中的所有二进制字符串连接
return "".join(result)
# 进制转换——二进制转成字符串
def convert_to_str(self, binary: str) -> str:
# 将二进制字符串分组，每8位为一组
bin_list = [binary[i:i + 8] for i in range(0, len(binary), 8)]
# 存储每个8位二进制数字所代表的整数值
list_int = []
for b in bin_list:
# 将当前8位二进制数转换为对应的十进制整数
list_int.append(int(b, 2))
# 将整数列表转换为字节序列,再解码得到字符串
result = bytes(list_int).decode()
return result
# 对明文二进制进行分块，每64位为一块
def get_block(self, binary: str) -> list:
# 首先获取给定二进制字符串的长度
len_binary = len(binary)
if len_binary % 64 != 0:
# 如果不能整除，说明按每64块分块不能刚好分块，需要添加前导零。
new_binary = ("0" * (64 - (len_binary % 64))) + binary
# 分块
return [new_binary[i:i + 64] for i in range(0, len(new_binary), 64)]
else:
# 能被64整除，就不用补零，直接分块
return [binary[j:j + 64] for j in range(0, len(binary), 64)]
# 按照给定的置换表进行置换
def replace(self, table: str, replace_table: list) -> str:
new_table = ""
for i in replace_table:
# 因为列表的索引是从0开始的，而替换表中的位置索引是从1开始的，所以需要进行减1的操作。
new_table += table[i - 1]
return new_table
# 返回加密过程中16轮的子密钥
def get_sonkey(self):
# 56位密钥由密钥初始置换表（PC_1）置换默认密钥获得
key = self.replace(self.K, self.PC_1)
# 将56位的密钥分成两部分，每部分28位
left_key = key[0:28]
right_key = key[28:56]
# 存储子密钥
keys = []
for i in range(0, 16):
# 由轮换表确定当前轮次的移动次数
move = self.k0[i]
# 对左右部分分别进行移位操作
move_left = left_key[move:28] + left_key[0:move]
move_right = right_key[move:28] + right_key[0:move]
# 更新left_key和right_key
left_key = move_left
right_key = move_right
# 合并形成当前轮次的子密钥
move_key = left_key + right_key
# 按照密钥压缩置换表（PC_2）进行置换，得到长度为48位的子密钥ki，并将其添加到keys列表中。
ki = self.replace(move_key, self.PC_2)
keys.append(ki)
# 返回加密过程中的16轮子密钥。
return keys
# 异或操作
def xor(self, xor1: str, xor2: str):
size = len(xor1)
result = ""
for i in range(0, size):
result += '0' if xor1[i] == xor2[i] else '1'
return result
# S盒代替
def s_box(self, xor_result: str):
result = ""
# 迭代8轮，每轮处理6位二进制数据
for i in range(0, 8):
# 将48位数据分为8组，循环进行
block = xor_result[i * 6:(i + 1) * 6]
# 首尾比特得行数
line = int(block[0] + block[5], 2)
# 中间四位比特得列数
column = int(block[1:5], 2)
# 在S盒中查找，将所得转为二进制并通过[2:]切片去除二进制字符串的前缀"0b"
res = bin(self.S[i][line * column])[2:]
if len(res) < 4:
# 如果结果的长度不足4位，则在左边用'0'进行填充
res = '0' * (4 - len(res)) + res
result += res
# result中存储了经过S盒替换后的32位二进制数据
return result
# F函数，进行E扩展，与key异或操作，S盒替代及P盒置换操作后返回32位01字符串
def F_function(self, right: str, key: str):
# 对right进行E扩展
e_result = self.replace(right, self.E)
# 与key 进行异或操作
xor_result = self.xor(e_result, key)
# 进入S盒子
s_result = self.s_box(xor_result)
# 进行P置换
p_result = self.replace(s_result, self.P)
return p_result
# 16轮迭代加密
def iteration(self, bin_plaintext: str, key_list: list):
# 分组切分
left = bin_plaintext[0:32]
right = bin_plaintext[32:64]
for i in range(0, 16):
# L(n) = R(n-1)
# R(n) = L(n-1)⊕F(R(n-1),K(n))
next_left = right
f_result = self.F_function(right, key_list[i])
next_right = self.xor(left, f_result)
left = next_left
right = next_right
# 最后R在左边,L在右边
return right + left
# DES加密函数
def encrypt(self, plaintext):
# 将给定明文转换为二进制
plaintext_2 = self.convert_to_2(plaintext)
# 将二进制明文分为64位一组的块
plaintext_block = self.get_block(plaintext_2)
# 存储加密后的分组
ciphertext_block = []
# 获取生成的16个子密钥列表
key_list = self.get_sonkey()
for block in plaintext_block:
# 初代IP置换
replaced_IP = self.replace(block, self.IP)
# 16轮迭代操作
ite_result = self.iteration(replaced_IP, key_list)
# 逆IP置换
replaced_IP_1 = self.replace(ite_result, self.IP_1)
# 密文块replaced_IP_1添加到ciphertext_block列表中，以便后续拼接
ciphertext_block.append(replaced_IP_1)
ciphertext = ''.join(ciphertext_block)
return ciphertext
#DES解密函数
def decrypt(self, ciphertext):
# 存储解密后的分组
plaintext_block = []
# 获取生成的16个子密钥列表
key_list = self.get_sonkey()
# 解密时密钥的使用顺序与加密时的顺序应当相反。
key_list = key_list[::-1]
# 将二进制密文分为64位一组的块
ciphertext_block = [ciphertext[i:i + 64] for i in range(0, len(ciphertext), 64)]
for block in ciphertext_block:
# 初代IP置换
replaced_IP = self.replace(block, self.IP)
# 16轮迭代操作
ite = self.iteration(replaced_IP, key_list)
# 逆IP置换
replaced_IP_1 = self.replace(ite, self.IP_1)
# 明文块replaced_IP_1添加到plaintext_block列表中，以便后续拼接
plaintext_block.append(replaced_IP_1)
# 拼接，并移除其中的所有全零块。
# 消除加密过程中可能引入的填充块，使得最终的二进制明文表示更加紧凑和直观。
plaintext = ''.join(plaintext_block).replace('00000000', '')
# 将二进制明文转为字符串返回
return self.convert_to_str(plaintext)
def main():
#select = input("输入1加密；输入2解密；输入3退出程序；请输入：\n")
while True:
select = input("输入1加密；输入2解密；输入3退出程序；请输入：\n")
if select == '1':
plaintext = input("输入要加密的明文：")
key = input("输入要加密的密钥：")
des = DES(key) # 创建DES对象时传入密钥
ciphertext = des.encrypt(plaintext)
print("加密得:{}".format(ciphertext))
elif select == '2':
ciphertext = input("输入要解密的密文：")
key = input("输入要解密的密钥：")
des = DES(key) # 创建DES对象时传入密钥
plaintext = des.decrypt(ciphertext)
print("解密得:{}".format(plaintext))
elif select == '3':
break
else:
print("重新选择！")
select = input("输入1加密；输入2解密；输入3退出程序；请输入：\n") # 重新获取选择
if __name__ == '__main__':
main()
四、运行结果
