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DES对称加密及三重DES（3DES）_des3加密

作者：从前慢现在也慢 | 2024-04-07 23:58:55

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des3加密

 一、DES

1 概述

DES算法全称为Data Encryption Standard，即数据加密算法，它是IBM公司于1975年研究成功并公开发表的。DES算法的入口参数有三个：Key、Data、Mode。其中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。

2 算法原理

DES算法把64位的明文输入块变为64位的密文输出块，它所使用的密钥也是64位，其算法主要分为两步：

（1）初始置换

其功能是把输入的64位数据块按位重新组合,并把输出分为L0、R0两部分，每部分各长32位，其置换规则为将输入的第58位换到第一位，第50位换到第2位……依此类推,最后一位是原来的第7位。L0、R0则是换位输出后的两部分，L0是输出的左32位，R0是右32位，例：设置换前的输入值为D1D2D3……D64，则经过初始置换后的结果为:L0=D58D50……D8；R0=D57D49……D7。

（2）逆置换

经过16次迭代运算后，得到L16、R16,将此作为输入，进行逆置换，逆置换正好是初始置换的逆运算，由此即得到密文输出。

二、 两个密钥的三重DES

由于DES密钥只有56bit，易于遭受穷举时攻击。作为一种替代加密方案，Tuchman提出使用两个密钥的三重DES加密方法，并在1985年成为美国的一个商用加密标准。该方法使用两个密钥，执行三次DES算法，如图2所示。加密的过程是加密-解密-加密，解密的过程是解密-加密-解密。

采用两个密钥进行三重加密的好处有：①两个密钥合起来有效密钥长度有112bit，可以满足商业应用的需要，若采用总长为168bit的三个密钥，会产生不必要的开销。②加密时采用加密-解密-加密，而不是加密-加密-加密的形式，这样有效的实现了与现有DES系统的向后兼容问题。因为当K1=K2时，三重DES的效果就和原来的DES一样，有助于逐渐推广三重DES。③三重DES具有足够的安全性，目前还没有关于攻破三重DES的报道。

 什么是三重DES

三重DES是为了增加DES的强度，将DES重复3次所得到的一种密码算法，通常缩写为3DES。

二 三重DSE加密

明文经过三次DES处理才能变成最后的密文，由于DES密钥长度实质是56位，因此3DES的密钥长度就是56*3=168比特。

注意：三重DES的三次DES加密是（加密->解密->加密），而不是（加密->加密->加密）,为什么这样设计呢？看看下面这张图就明白了。

如果三次DES加密的密钥都相同，前两次DES，相当于还原成了密文，这样看来，真正起作用的只是最后一次。这样做的好处是：三重DES对DES具备向下兼容性。

还有一种密码叫DES-EDE2,下面我们用图来描述这一种密码。

当然，只有三个密钥互不相等才是正宗的DES-EDE3。

三 三重DES解密

三重DES的解密过程和加密过程正好相反，是以密钥3、密钥2、密钥1的顺序执行解密->加密->解密的操作。

四 三重DES现状

尽管三重DES目前还被银行等机构使用，但其处理速度不高，除了特别重视向下兼容性的情况外，很少被用于新的用途。

pydes:
 

  1. #-*- coding: utf8 -*-
  2.  
  3. #Initial permut matrix for the datas
  4. # IP initial permut
  5. PI = [58, 50, 42, 34, 26, 18, 10, 2,
  6.       60, 52, 44, 36, 28, 20, 12, 4,
  7.       62, 54, 46, 38, 30, 22, 14, 6,
  8.       64, 56, 48, 40, 32, 24, 16, 8,
  9.       57, 49, 41, 33, 25, 17, 9, 1,
  10.       59, 51, 43, 35, 27, 19, 11, 3,
  11.       61, 53, 45, 37, 29, 21, 13, 5,
  12.       63, 55, 47, 39, 31, 23, 15, 7]
  13.  
  14. #Initial permut made on the key
  15. CP_1 = [57, 49, 41, 33, 25, 17, 9,
  16.         1, 58, 50, 42, 34, 26, 18,
  17.         10, 2, 59, 51, 43, 35, 27,
  18.         19, 11, 3, 60, 52, 44, 36,
  19.         63, 55, 47, 39, 31, 23, 15,
  20.         7, 62, 54, 46, 38, 30, 22,
  21.         14, 6, 61, 53, 45, 37, 29,
  22.         21, 13, 5, 28, 20, 12, 4]
  23.  
  24. #Permut applied on shifted key to get Ki+1
  25. CP_2 = [14, 17, 11, 24, 1, 5, 3, 28,
  26.         15, 6, 21, 10, 23, 19, 12, 4,
  27.         26, 8, 16, 7, 27, 20, 13, 2,
  28.         41, 52, 31, 37, 47, 55, 30, 40,
  29.         51, 45, 33, 48, 44, 49, 39, 56,
  30.         34, 53, 46, 42, 50, 36, 29, 32]
  31.  
  32. #Expand matrix to get a 48bits matrix of datas to apply the xor with Ki
  33. E = [32, 1, 2, 3, 4, 5,
  34.      4, 5, 6, 7, 8, 9,
  35.      8, 9, 10, 11, 12, 13,
  36.      12, 13, 14, 15, 16, 17,
  37.      16, 17, 18, 19, 20, 21,
  38.      20, 21, 22, 23, 24, 25,
  39.      24, 25, 26, 27, 28, 29,
  40.      28, 29, 30, 31, 32, 1]
  41.  
  42. #SBOX
  43. S_BOX = [
  44.          
  45. [[14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
  46.  [0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
  47.  [4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
  48.  [15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13],
  49. ],
  50.  
  51. [[15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10],
  52.  [3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5],
  53.  [0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15],
  54.  [13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9],
  55. ],
  56.  
  57. [[10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8],
  58.  [13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1],
  59.  [13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7],
  60.  [1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12],
  61. ],
  62.  
  63. [[7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15],
  64.  [13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9],
  65.  [10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4],
  66.  [3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14],
  67. ],  
  68.  
  69. [[2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9],
  70.  [14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6],
  71.  [4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14],
  72.  [11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3],
  73. ], 
  74.  
  75. [[12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11],
  76.  [10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8],
  77.  [9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6],
  78.  [4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13],
  79. ], 
  80.  
  81. [[4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1],
  82.  [13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6],
  83.  [1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2],
  84.  [6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12],
  85. ],
  86.    
  87. [[13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7],
  88.  [1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2],
  89.  [7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8],
  90.  [2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11],
  91. ]
  92. ]
  93.  
  94. #Permut made after each SBox substitution for each round
  95. P = [16, 7, 20, 21, 29, 12, 28, 17,
  96.      1, 15, 23, 26, 5, 18, 31, 10,
  97.      2, 8, 24, 14, 32, 27, 3, 9,
  98.      19, 13, 30, 6, 22, 11, 4, 25]
  99.  
  100. #Final permut for datas after the 16 rounds
  101. PI_1 = [40, 8, 48, 16, 56, 24, 64, 32,
  102.         39, 7, 47, 15, 55, 23, 63, 31,
  103.         38, 6, 46, 14, 54, 22, 62, 30,
  104.         37, 5, 45, 13, 53, 21, 61, 29,
  105.         36, 4, 44, 12, 52, 20, 60, 28,
  106.         35, 3, 43, 11, 51, 19, 59, 27,
  107.         34, 2, 42, 10, 50, 18, 58, 26,
  108.         33, 1, 41, 9, 49, 17, 57, 25]
  109.  
  110. #Matrix that determine the shift for each round of keys
  111. SHIFT = [1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1]
  112.  
  113. def string_to_bit_array(text):#Convert a string into a list of bits
  114.     array = list()
  115.     for char in text:
  116.         binval = binvalue(char, 8)#Get the char value on one byte
  117.         array.extend([int(x) for x in list(binval)]) #Add the bits to the final list
  118.     return array
  119.  
  120. def bit_string_to_array(bitText):
  121.     array = list()
  122.     for bit in bitText.replace(" ",""):
  123.         array.append(int(bit))
  124.     return array
  125.  
  126. def bit_array_to_string(array): #Recreate the string from the bit array
  127.     res = ''.join([chr(int(y,2)) for y in [''.join([str(x) for x in _bytes]) for _bytes in  nsplit(array,8)]])
  128.     return res
  129.  
  130. # 根据ascil编码把字符转成对应的二进制
  131. def binvalue(val, bitsize): #Return the binary value as a string of the given size
  132.     binval = bin(val)[2:] if isinstance(val, int) else bin(ord(val))[2:]
  133.     if len(binval) > bitsize:
  134.         raise ("binary value larger than the expected size")
  135.     while len(binval) < bitsize:
  136.         binval = "0"+binval #Add as many 0 as needed to get the wanted size
  137.     return binval
  138.  
  139. def nsplit(s, n):#Split a list into sublists of size "n"
  140.     return [s[k:k+n] for k in range(0, len(s), n)]
  141.  
  142. def showBits(s, n):#Split a list into sublists of size "n"
  143.     return " ".join(["".join([str(i) for i in s[k:k+n]]) for k in range(0, len(s), n)])
  144.  
  145. ENCRYPT=1
  146. DECRYPT=0
  147.  
  148. class des():
  149.     def __init__(self):
  150.         self.password = None
  151.         self.text = None
  152.         self.keys = list()
  153.         
  154.     def run(self, key, text, action=ENCRYPT):
  155.         self.password = key
  156.         self.text = text
  157.  
  158.         # 产生所有子密钥
  159.         self.generatekeys() #Generate all the keys
  160.         result = list()
  161.  
  162.         block = self.text
  163.         block = self.permut(block,PI)#Apply the initial permutation
  164.  
  165.         g, d = nsplit(block, 32) #g(LEFT), d(RIGHT)
  166.         tmp = None
  167.         for i in range(16): #Do the 16 rounds
  168.             d_e = self.expand(d, E) #Expand d to match Ki size (48bits)
  169.             if action == ENCRYPT:
  170.                 tmp = self.xor(self.keys[i], d_e)#If encrypt use Ki
  171.             else:
  172.                 tmp = self.xor(self.keys[15-i], d_e)#If decrypt start by the last key
  173.             tmp = self.substitute(tmp) #Method that will apply the SBOXes
  174.             tmp = self.permut(tmp, P)
  175.             tmp = self.xor(g, tmp)   # tmp = f(Rn-1,Kn)
  176.             g = d   # Ln = Rn-1
  177.             d = tmp # Rn = Ln-1 + f(Rn-1,Kn)
  178.             print(f"L{i+1}:{showBits(g, 8)}")
  179.             print(f"R{i + 1}:{showBits(d, 8)}")
  180.         result += self.permut(d+g, PI_1) #Do the last permut and append the result to result
  181.         final_res = "".join([str(i) for i in result])
  182.  
  183.         return final_res
  184.  
  185.         # if padding and action==DECRYPT:
  186.         #     return self.removePadding(final_res) #Remove the padding if decrypt and padding is true
  187.         # else:
  188.         #     return final_res #Return the final string of data ciphered/deciphered
  189.     
  190.     def substitute(self, d_e):#Substitute bytes using SBOX
  191.         subblocks = nsplit(d_e, 6)#Split bit array into sublist of 6 bits
  192.         result = list()
  193.         for i in range(len(subblocks)): #For all the sublists
  194.             block = subblocks[i]
  195.             row = int(str(block[0])+str(block[5]),2)#Get the row with the first and last bit
  196.             column = int(''.join([str(x) for x in block[1:][:-1]]),2) #Column is the 2,3,4,5th bits
  197.             val = S_BOX[i][row][column] #Take the value in the SBOX appropriated for the round (i)
  198.             bin = binvalue(val, 4)#Convert the value to binary
  199.             result += [int(x) for x in bin]#And append it to the resulting list
  200.         return result
  201.  
  202.     # 置换
  203.     def permut(self, block, table):#Permut the given block using the given table (so generic method)
  204.         return [block[x-1] for x in table]
  205.  
  206.     # 扩展
  207.     def expand(self, block, table):#Do the exact same thing than permut but for more clarity has been renamed
  208.         return [block[x-1] for x in table]
  209.     
  210.     def xor(self, t1, t2):#Apply a xor and return the resulting list
  211.         return [x^y for x,y in zip(t1,t2)]
  212.     
  213.     def generatekeys(self):#Algorithm that generates all the keys
  214.         self.keys = []
  215.         # 把密钥转成这个形式 00110100 11000010.....
  216.         key = self.password
  217.         key = self.permut(key, CP_1) #Apply the initial permut on the key
  218.         g, d = nsplit(key, 28) #Split it in to (g->LEFT),(d->RIGHT)
  219.         for i in range(16):#Apply the 16 rounds
  220.             g, d = self.shift(g, d, SHIFT[i]) #Apply the shift associated with the round (not always 1)
  221.             tmp = g + d #Merge them
  222.             self.keys.append(self.permut(tmp, CP_2)) #Apply the permut to get the Ki
  223.  
  224.     def shift(self, g, d, n): #Shift a list of the given value
  225.         return g[n:] + g[:n], d[n:] + d[:n]
  226.     
  227.     def addPadding(self):#Add padding to the datas using PKCS5 spec.
  228.         pad_len = 8 - (len(self.text) % 8)
  229.         self.text += pad_len * chr(pad_len)
  230.     
  231.     def removePadding(self, data):#Remove the padding of the plain text (it assume there is padding)
  232.         pad_len = ord(data[-1])
  233.         return data[:-pad_len]
  234.     
  235.     def encrypt(self, key, text):
  236.         return self.run(key, text, ENCRYPT)
  237.     
  238.     def decrypt(self, key, text):
  239.         return self.run(key, text, DECRYPT)
  240.  
  241.  
  242. if __name__ == '__main__':
  243.     plain_text = bit_string_to_array("00000001 00100011 01000101 01100111 10001001 10101011 11001101 11101111")
  244.     key = bit_string_to_array("00010011 00110100 01010111 01111001 10011011 10111100 11011111 11110001")
  245.     d = des()
  246.     r = d.encrypt(key,plain_text)
  247.     print(r)
  248.  
  249.     # 测试cyberchef
  250.     r = bit_string_to_array("01011010 11110101 00010101 10110000 01001011 11101111 01010010 01000001")
  251.     r2 = d.decrypt(key,r)
  252.     print("Ciphered: %r" % r)
  253.     print("Deciphered: ", r2)
  254.  
  255. # 07040502033636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636363636
  256. #
  257. # 6d6e6f68695c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c5c
  258.  
  259.  

  1. l = [1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0]
  2. def showBits(s, n):#Split a list into sublists of size "n"
  3.     return " ".join(["".join([str(i) for i in s[k:k+n]]) for k in range(0, len(s), n)])
  4.  
  5. print(showBits(l, 8))

CBC模式调用：

  1. from pyDes import des, CBC, PAD_PKCS5
  2. import binascii
  3.  
  4. # 秘钥
  5. KEY = 'Codeoooo'
  6.  
  7.  
  8. def des_encrypt(s):
  9.     """
  10.     DES 加密
  11.     :param s: 原始字符串
  12.     :return: 加密后字符串，16进制
  13.     """
  14.     secret_key = KEY  # 密码
  15.     iv = secret_key  # 偏移
  16.     # secret_key:加密密钥，CBC:加密模式，iv:偏移, padmode:填充
  17.     des_obj = des(secret_key, CBC, iv, pad=None, padmode=PAD_PKCS5)
  18.     # 返回为字节
  19.     secret_bytes = des_obj.encrypt(s, padmode=PAD_PKCS5)
  20.     # 返回为16进制
  21.     return bytes.decode(binascii.b2a_hex(secret_bytes))
  22.  
  23.  
  24. def des_descrypt(s):
  25.     """
  26.     DES 解密
  27.     :param s: 加密后的字符串，16进制
  28.     :return:  解密后的字符串
  29.     """
  30.     secret_key = KEY
  31.     iv = secret_key
  32.     des_obj = des(secret_key, CBC, iv, pad=None, padmode=PAD_PKCS5)
  33.     decrypt_str = des_obj.decrypt(binascii.a2b_hex(s), padmode=PAD_PKCS5)
  34.     return bytes.decode(decrypt_str)
  35.  
  36. print(des_encrypt('codeooo'))
  37. print(des_descrypt('4ff67fd9b661f01d'))

ECB模式调用：

  1. from pyDes import des, ECB, PAD_PKCS5
  2. import base64
  3.  
  4. DES_SECRET_KEY = '12345678'
  5. data = 'codeooo'
  6. des_obj = des(DES_SECRET_KEY, ECB, DES_SECRET_KEY, padmode=PAD_PKCS5)
  7. secret_bytes = str(base64.b64encode(des_obj.encrypt(data)), encoding = 'utf-8')
  8. print(secret_bytes)

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