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Python实现AES和DES

Python3实现AES和DES对称加密算法的

In [ ]:
print('python3')

对称算法编写

本实验是使用python来实现AES和DES加密和解密过程,并对加密解密过程的正确性进行验证。

1.实验目的

  1. 掌握分组加密的原理
  2. 掌握数据加密标准DES和高级数据加密标准AES的原理及其应用

2.实验工具

  • Jupyter Notebook
  • Python3.5

3.实验环境

  • Ubuntu16.04LTS操作系统
  • Python3标准库

4.实验步骤

4.1 回顾课程,查阅资料

4.2 熟悉AES的原理

AES(Advanced Encryption Standard)高级加密标准,在密码学中又称Rijndael加密法,是美国联邦政府采用的一种区块加密标准。这个标准用来替代原先的DES,已经被多方分析且广为全世界所使用。

AES加密过程是在一个4×4的字节矩阵上运作,这个矩阵又称为“体(state)”,其初值就是一个明文区块(矩阵中一个元素大小就是明文区块中的一个Byte)。(Rijndael加密法因支持更大的区块,其矩阵行数可视情况增加)加密时,各轮AES加密循环(除最后一轮外)均包含4个步骤:

  1. AddRoundKey—矩阵中的每一个字节都与该次回合密钥(round key)做XOR运算;每个子密钥由密钥生成方案产生。
  2. SubBytes—通过一个非线性的替换函数,用查找表的方式把每个字节替换成对应的字节。
  3. ShiftRows—将矩阵中的每个横列进行循环式移位。
  4. MixColumns—为了充分混合矩阵中各个直行的操作。这个步骤使用线性转换来混合每内联的四个字节。最后一个加密循环中省略MixColumns步骤,而以另一个AddRoundKey取代。

4.3 编写AES加密解密的测试用例

先使用其他已有工具计算出plaintext对应的

测试程序如下:

import unittest

class AES:
    def __init__(self, master_key):
        self.change_key(master_key)

    def change_key(self, master_key):
        pass

    def encrypt(self, plaintext):
        pass

    def decrypt(self, ciphertext):
        pass

class AES_TEST(unittest.TestCase):
    def setUp(self):
        master_key = 0x2b7e151628aed2a6abf7158809cf4f3c
        self.AES = AES(master_key)

    def test_encryption(self):
        plaintext = 0x3243f6a8885a308d313198a2e0370734
        encrypted = self.AES.encrypt(plaintext)

        self.assertEqual(encrypted, 0x3925841d02dc09fbdc118597196a0b32)

    def test_decryption(self):
        ciphertext = 0x3925841d02dc09fbdc118597196a0b32
        decrypted = self.AES.decrypt(ciphertext)

        self.assertEqual(decrypted, 0x3243f6a8885a308d313198a2e0370734)

if __name__ == '__main__':
    unittest.main()

4.4 编写DES算法的测试代码

4.5 编写AES和DES对称加密的python实现,并进行测试验证

代码和测试结果在报告最后

4.6 总结实验,编写实验报告

5. 实验总结

  • 需要善于借鉴前人经验,搜集资料
  • 实验只支持ascii码,对其他字符编码没有解决
  • 利用优秀的工具,如Jupyter可以提高学习效率

6. 实验完整代码

In [16]:
#!/usr/bin/env python
#-*- coding:utf-8 -*-

"""
ASE的python实现:
支持128位秘钥
支持秘钥和原文均为数字的AES加密解密
"""

Sbox = (
    0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
    0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
    0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
    0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
    0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
    0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
    0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
    0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
    0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
    0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
    0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
    0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
    0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
    0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
    0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
    0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16,
)

InvSbox = (
    0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
    0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
    0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
    0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
    0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
    0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
    0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
    0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
    0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
    0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
    0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
    0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
    0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
    0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
    0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
    0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D,
)


# 参考了C语言实现 http://cs.ucsb.edu/~koc/cs178/projects/JT/aes.c
xtime = lambda a: (((a << 1) ^ 0x1B) & 0xFF) if (a & 0x80) else (a << 1)


Rcon = (
    0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40,
    0x80, 0x1B, 0x36, 0x6C, 0xD8, 0xAB, 0x4D, 0x9A,
    0x2F, 0x5E, 0xBC, 0x63, 0xC6, 0x97, 0x35, 0x6A,
    0xD4, 0xB3, 0x7D, 0xFA, 0xEF, 0xC5, 0x91, 0x39,
)


def text2matrix(text):
    matrix = []
    for i in range(16):
        byte = (text >> (8 * (15 - i))) & 0xFF
        if i % 4 == 0:
            matrix.append([byte])
        else:
            matrix[int(i / 4)].append(byte)
    return matrix


def matrix2text(matrix):
    text = 0
    for i in range(4):
        for j in range(4):
            text |= (matrix[i][j] << (120 - 8 * (4 * i + j)))
    return text


class AES:
    def __init__(self, master_key):
        self.change_key(master_key)

    def change_key(self, master_key):
        self.round_keys = text2matrix(master_key)
        # print self.round_keys

        for i in range(4, 4 * 11):
            self.round_keys.append([])
            if i % 4 == 0:
                byte = self.round_keys[i - 4][0]        \
                     ^ Sbox[self.round_keys[i - 1][1]]  \
                     ^ Rcon[int(i / 4)]
                self.round_keys[i].append(byte)

                for j in range(1, 4):
                    byte = self.round_keys[i - 4][j]    \
                         ^ Sbox[self.round_keys[i - 1][(j + 1) % 4]]
                    self.round_keys[i].append(byte)
            else:
                for j in range(4):
                    byte = self.round_keys[i - 4][j]    \
                         ^ self.round_keys[i - 1][j]
                    self.round_keys[i].append(byte)

        # print self.round_keys

    def encrypt(self, plaintext):
        self.plain_state = text2matrix(plaintext)

        self.__add_round_key(self.plain_state, self.round_keys[:4])

        for i in range(1, 10):
            self.__round_encrypt(self.plain_state, self.round_keys[4 * i : 4 * (i + 1)])

        self.__sub_bytes(self.plain_state)
        self.__shift_rows(self.plain_state)
        self.__add_round_key(self.plain_state, self.round_keys[40:])

        return matrix2text(self.plain_state)

    def decrypt(self, ciphertext):
        self.cipher_state = text2matrix(ciphertext)

        self.__add_round_key(self.cipher_state, self.round_keys[40:])
        self.__inv_shift_rows(self.cipher_state)
        self.__inv_sub_bytes(self.cipher_state)

        for i in range(9, 0, -1):
            self.__round_decrypt(self.cipher_state, self.round_keys[4 * i : 4 * (i + 1)])

        self.__add_round_key(self.cipher_state, self.round_keys[:4])

        return matrix2text(self.cipher_state)

    def __add_round_key(self, s, k):
        for i in range(4):
            for j in range(4):
                s[i][j] ^= k[i][j]


    def __round_encrypt(self, state_matrix, key_matrix):
        self.__sub_bytes(state_matrix)
        self.__shift_rows(state_matrix)
        self.__mix_columns(state_matrix)
        self.__add_round_key(state_matrix, key_matrix)


    def __round_decrypt(self, state_matrix, key_matrix):
        self.__add_round_key(state_matrix, key_matrix)
        self.__inv_mix_columns(state_matrix)
        self.__inv_shift_rows(state_matrix)
        self.__inv_sub_bytes(state_matrix)

    def __sub_bytes(self, s):
        for i in range(4):
            for j in range(4):
                s[i][j] = Sbox[s[i][j]]


    def __inv_sub_bytes(self, s):
        for i in range(4):
            for j in range(4):
                s[i][j] = InvSbox[s[i][j]]


    def __shift_rows(self, s):
        s[0][1], s[1][1], s[2][1], s[3][1] = s[1][1], s[2][1], s[3][1], s[0][1]
        s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
        s[0][3], s[1][3], s[2][3], s[3][3] = s[3][3], s[0][3], s[1][3], s[2][3]


    def __inv_shift_rows(self, s):
        s[0][1], s[1][1], s[2][1], s[3][1] = s[3][1], s[0][1], s[1][1], s[2][1]
        s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
        s[0][3], s[1][3], s[2][3], s[3][3] = s[1][3], s[2][3], s[3][3], s[0][3]

    def __mix_single_column(self, a):
        # please see Sec 4.1.2 in The Design of Rijndael
        t = a[0] ^ a[1] ^ a[2] ^ a[3]
        u = a[0]
        a[0] ^= t ^ xtime(a[0] ^ a[1])
        a[1] ^= t ^ xtime(a[1] ^ a[2])
        a[2] ^= t ^ xtime(a[2] ^ a[3])
        a[3] ^= t ^ xtime(a[3] ^ u)


    def __mix_columns(self, s):
        for i in range(4):
            self.__mix_single_column(s[i])


    def __inv_mix_columns(self, s):
        # see Sec 4.1.3 in The Design of Rijndael
        for i in range(4):
            u = xtime(xtime(s[i][0] ^ s[i][2]))
            v = xtime(xtime(s[i][1] ^ s[i][3]))
            s[i][0] ^= u
            s[i][1] ^= v
            s[i][2] ^= u
            s[i][3] ^= v

        self.__mix_columns(s)
        
        



master_key = 0x2b7e151628aed2a6abf7158809cf4f3c
AESbar = AES(master_key)

def test_encryption():
    plaintext = 0x3243f6a8885a308d313198a2e0370734
    encrypted = AESbar.encrypt(plaintext)
    print('加密得密文: 0x%x'  % encrypted)
    assert encrypted == 0x3925841d02dc09fbdc118597196a0b32
    print('加密结果正确')

def test_decryption():
    ciphertext = 0x3925841d02dc09fbdc118597196a0b32
    decrypted = AESbar.decrypt(ciphertext)
    print('解密得原文: 0x%x' % decrypted)
    assert decrypted == 0x3243f6a8885a308d313198a2e0370734
    print('解密成功')

if __name__ == '__main__':
    print('开始单元测试:')
    test_encryption()
    test_decryption()
    print('单元测试成功')
开始单元测试:
加密得密文: 0x3925841d02dc09fbdc118597196a0b32
加密结果正确
解密得原文: 0x3243f6a8885a308d313198a2e0370734
解密成功
单元测试成功
In [19]:
#!/usr/bin/env python
#-*- coding:utf-8 -*-

'''
DES加密解密的Python3实现
'''

#Initial permut matrix for the datas
PI = [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]

#Initial permut made on the key
CP_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]

#Permut applied on shifted key to get Ki+1
CP_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]

#Expand matrix to get a 48bits matrix of datas to apply the xor with Ki
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]

#SBOX
S_BOX = [
         
[[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],
]
]

#Permut made after each SBox substitution for each round
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]

#Final permut for datas after the 16 rounds
PI_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]

#Matrix that determine the shift for each round of keys
SHIFT = [1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1]

def string_to_bit_array(text):#Convert a string into a list of bits
    array = list()
    for char in text:
        binval = binvalue(char, 8)#Get the char value on one byte
        array.extend([int(x) for x in list(binval)]) #Add the bits to the final list
    return array

def bit_array_to_string(array): #Recreate the string from the bit array
    res = ''.join([chr(int(y,2)) for y in [''.join([str(x) for x in bytes]) for bytes in  nsplit(array,8)]])   
    return res

def binvalue(val, bitsize): #Return the binary value as a string of the given size 
    binval = bin(val)[2:] if isinstance(val, int) else bin(ord(val))[2:]
    if len(binval) > bitsize:
        raise "binary value larger than the expected size"
    while len(binval) < bitsize:
        binval = "0"+binval #Add as many 0 as needed to get the wanted size
    return binval

def nsplit(s, n):#Split a list into sublists of size "n"
    return [s[k:k+n] for k in range(0, len(s), n)]

ENCRYPT=1
DECRYPT=0

class des():
    def __init__(self):
        self.password = None
        self.text = None
        self.keys = list()
        
    def run(self, key, text, action=ENCRYPT, padding=False):
        if len(key) < 8:
            raise "Key Should be 8 bytes long"
        elif len(key) > 8:
            key = key[:8] #If key size is above 8bytes, cut to be 8bytes long
        
        self.password = key
        self.text = text
        
        if padding and action==ENCRYPT:
            self.addPadding()
        elif len(self.text) % 8 != 0:#If not padding specified data size must be multiple of 8 bytes
            raise "Data size should be multiple of 8"
        
        self.generatekeys() #Generate all the keys
        text_blocks = nsplit(self.text, 8) #Split the text in blocks of 8 bytes so 64 bits
        result = list()
        for block in text_blocks:#Loop over all the blocks of data
            block = string_to_bit_array(block)#Convert the block in bit array
            block = self.permut(block,PI)#Apply the initial permutation
            g, d = nsplit(block, 32) #g(LEFT), d(RIGHT)
            tmp = None
            for i in range(16): #Do the 16 rounds
                d_e = self.expand(d, E) #Expand d to match Ki size (48bits)
                if action == ENCRYPT:
                    tmp = self.xor(self.keys[i], d_e)#If encrypt use Ki
                else:
                    tmp = self.xor(self.keys[15-i], d_e)#If decrypt start by the last key
                tmp = self.substitute(tmp) #Method that will apply the SBOXes
                tmp = self.permut(tmp, P)
                tmp = self.xor(g, tmp)
                g = d
                d = tmp
            result += self.permut(d+g, PI_1) #Do the last permut and append the result to result
        final_res = bit_array_to_string(result)
        if padding and action==DECRYPT:
            return self.removePadding(final_res) #Remove the padding if decrypt and padding is true
        else:
            return final_res #Return the final string of data ciphered/deciphered
    
    def substitute(self, d_e):#Substitute bytes using SBOX
        subblocks = nsplit(d_e, 6)#Split bit array into sublist of 6 bits
        result = list()
        for i in range(len(subblocks)): #For all the sublists
            block = subblocks[i]
            row = int(str(block[0])+str(block[5]),2)#Get the row with the first and last bit
            column = int(''.join([str(x) for x in block[1:][:-1]]),2) #Column is the 2,3,4,5th bits
            val = S_BOX[i][row][column] #Take the value in the SBOX appropriated for the round (i)
            bin = binvalue(val, 4)#Convert the value to binary
            result += [int(x) for x in bin]#And append it to the resulting list
        return result
        
    def permut(self, block, table):#Permut the given block using the given table (so generic method)
        return [block[x-1] for x in table]
    
    def expand(self, block, table):#Do the exact same thing than permut but for more clarity has been renamed
        return [block[x-1] for x in table]
    
    def xor(self, t1, t2):#Apply a xor and return the resulting list
        return [x^y for x,y in zip(t1,t2)]
    
    def generatekeys(self):#Algorithm that generates all the keys
        self.keys = []
        key = string_to_bit_array(self.password)
        key = self.permut(key, CP_1) #Apply the initial permut on the key
        g, d = nsplit(key, 28) #Split it in to (g->LEFT),(d->RIGHT)
        for i in range(16):#Apply the 16 rounds
            g, d = self.shift(g, d, SHIFT[i]) #Apply the shift associated with the round (not always 1)
            tmp = g + d #Merge them
            self.keys.append(self.permut(tmp, CP_2)) #Apply the permut to get the Ki

    def shift(self, g, d, n): #Shift a list of the given value
        return g[n:] + g[:n], d[n:] + d[:n]
    
    def addPadding(self):#Add padding to the datas using PKCS5 spec.
        pad_len = 8 - (len(self.text) % 8)
        self.text += pad_len * chr(pad_len)
    
    def removePadding(self, data):#Remove the padding of the plain text (it assume there is padding)
        pad_len = ord(data[-1])
        return data[:-pad_len]
    
    def encrypt(self, key, text, padding=False):
        return self.run(key, text, ENCRYPT, padding)
    
    def decrypt(self, key, text, padding=False):
        return self.run(key, text, DECRYPT, padding)
    
if __name__ == '__main__':
    key = "secret_k"
    text= "Hello wo"
    d = des()
    r = d.encrypt(key,text)
    r2 = d.decrypt(key,r)
    print("Ciphered: %r" % r)
    print("Deciphered: ", r2)
    assert r2 == text
    print('成功实现DES加密解密')
Ciphered: 'ßåýåÚ\x9f\\\x9d'
Deciphered:  Hello wo
成功实现DES加密解密

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