DES算法的python3实现

DES原理

DES原理 这里不予以复述， 有很多优秀的博客
原理可以参考这篇博客
https://www.cnblogs.com/songwenlong/p/5944139.html

DES实现

1. 主函数框架

DES 函数 传入参数为

• text（明文 或者 密文）
• key （解密的key）
• flag （是加密还是解密过程）

# DES 算法实现 flag是标志位 当为-1时， 是DES解密， flag默认为0
def DES (text, key, flag = "0"):
    # 初始字段
    # IP置换
    InitKeyCode = IP(text)
    # 产生子密钥 集合
    subkeylist = createSubkey(key)
    # 获得Ln 和 Rn
    Ln = InitKeyCode[0:32]
    Rn = InitKeyCode[32:]
	# 如果是解密的过程 把子密钥数字逆过来 就变成解密过程了
    if (flag == "-1") :
        subkeylist = subkeylist[::-1]


    for subkey in subkeylist:
        while len(Rn) < 32:
            Rn = "0" + Rn
        while len(Ln) < 32:
            Ln = "0" + Ln

        # 对右边进行E-扩展
        Rn_expand = E_expend(Rn)
        # 压缩后的密钥与扩展分组异或以后得到48位的数据，将这个数据送入S盒
        S_Input = int(Rn_expand, base=2) ^ int(subkey, base=2)

        # 进行S盒替代
        S_sub_str = S_sub(S_Input)

        #P盒置换  并且
        #  左、右半部分交换，接着开始另一轮
        (Ln, Rn) = P(Ln, S_sub_str, Rn)

        #进行下一轮轮置换

    # 最后一轮之后  左、右两半部分并未进行交换
    # 而是两部分合并形成一个分组做为末置换的输入。
    # 所以要重新置换 一次

    (Ln, Rn) = (Rn, Ln)
    # 末置换得到密文
    re_text = IP_inverse(Ln, Rn)

    return re_text

2. 各种置换矩阵的定义

DES有各种置换矩阵的定义， 所以提前定义好， 但是这里虽然说是矩阵 但是使用数组来表示的

# S盒 的置换矩阵
S_MATRIX = [(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置换的置换矩阵
P_MATRIX = [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]
# IP置换的 置换矩阵
IP_MATRIX = [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]

# 压缩置换矩阵  从56位里选48位
COMPRESS_MATRIXS = [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]
# E扩展置换矩阵

E_MATRIX = [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]
# IP逆置换矩阵
IP_INVERSE_MATRIX = [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]

3.IP置换函数

对于置换 我们的明文是用一个长度为64的字符01串构成的 所以置换 只需要新的字符串 然后按照置换矩阵的下表来把原字符串的单个字符加入

def IP(Mingwen):
    #如果长度不是64 就退出
    assert len(Mingwen) == 64

    ret = ""
    #通过循环 进行IP置换
    for i in IP_MATRIX:
        ret = ret + Mingwen[i - 1]
    return ret

4. 循环左移位数函数

对输入的str 按照shift_count的大小 左移shift_count位 这个函数主要用于子密钥生成

def shift(str, shift_count):
    try:
        if len(str) > 28:
            raise NameError
    except TypeError:
        pass

    str = str[shift_count:] + str[0:shift_count]
    return str

5.生成子密钥函数

此函数用来生成子密钥 生成16组子密钥 用于和扩展分组 异或

def createSubkey(key):
    # 如果key长度不是64 就退出
    assert len(key) == 64

    #DES的密钥由64位减至56位，每个字节的第8位作为奇偶校验位
    #把56位 变成 2个28位

    Llist = [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]
    Rlist = [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]

    # 初试生成 左右两组28位密钥
    L0 = ""
    R0 = ""

    for i in Llist:
        L0 += key[i - 1]
    for i in Rlist:
        R0 += key[i - 1]

    assert len(L0) == 28
    assert len(R0) == 28

    #轮函数生成 48位密钥

    #定义轮数
    Movetimes = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1]
    #定义返回的subKey
    retkey = []
    #开始轮置换
    for i in range(0, 16):
        #获取左半边 和 右半边  shift函数用来左移生成轮数
        L0 = shift(L0, Movetimes[i])
        R0 = shift(R0, Movetimes[i])
        #合并左右部分
        mergedKey = L0 + R0

        tempkey = ""
        # 压缩置换矩阵  从56位里选48位
        #选出48位子密钥
        for i in COMPRESS_MATRIXS:
            tempkey += mergedKey[i - 1]
        assert len(tempkey) == 48
        #加入生成子密钥
        retkey.append(tempkey)

    return retkey

6.E扩展置换

用于把右边的32位扩展成48位

def E_expend(Rn):

    retRn = ""
    for i in E_MATRIX:
        retRn += Rn[i - 1]
    assert len(retRn) == 48
    return retRn

7.S盒替换函数

压缩后的密钥与扩展分组异或以后得到48位的数据，将这个数据送入S盒，进行替代运算。替代由8个不同的S盒完成，每个S盒有6位输入4位输出。48位输入分为8个6位的分组，一个分组对应一个S盒，对应的S盒对各组进行代替操作。

# S盒替代运算
def S_sub(S_Input):
    #从第二位开始的子串  去掉0X
    S_Input = bin(S_Input)[2:]

    while len(S_Input) < 48:
        S_Input = "0" + S_Input

    index = 0
    retstr = ""

    for Slist in S_MATRIX:
        # 输入的高低两位做为行数row
        row = int(S_Input[index] + S_Input[index + 5], base=2)
        # 中间四位做为列数L
        col = int(S_Input[index + 1:index + 5], base=2)
        # 得到 result的 单个四位输出
        ret_single = bin(Slist[row * 16 + col])[2:]

        while len(ret_single) < 4:
            ret_single = "0" + ret_single

        # 合并单个输出
        retstr += ret_single
        # index + 6 进入下一个六位输入
        index += 6

    assert len(retstr) == 32

    return retstr

8.P置换

S盒代替运算的32位输出按照P盒进行置换

最后，P盒置换的结果与最初的64位分组左半部分L0异或，然后左、右半部分交换，接着开始另一轮。

def P(Ln, S_sub_str, oldRn):
    # P 盒置换
    tmp = ""
    for i in P_MATRIX:
        tmp += S_sub_str[i - 1]
    # P盒置换的结果与最初的64位分组左半部分L0异或
    LnNew = int(tmp, base=2) ^ int(Ln, base=2)
    LnNew = bin(LnNew)[2:]
    while len(LnNew) < 32:
        LnNew = "0" + LnNew
    assert len(LnNew) == 32
    # 左、右半部分交换，接着开始另一轮
    (Ln, Rn) = (oldRn, LnNew)

    return (Ln, Rn)

9. IP逆置换

末置换是初始置换的逆过程，DES最后一轮后，左、右两半部分并未进行交换，而是两部分合并形成一个分组做为末置换的输入
置换后得到密文或者解密的明文

def IP_inverse(L16, R16):
    tmp = L16 + R16
    retstr = ""
    for i in IP_INVERSE_MATRIX:
        retstr += tmp[i - 1]
    assert len(retstr) == 64
    return retstr

10. TEST函数

用来测试效果

if __name__ == "__main__":
    key =     "0101101000110101010101110111100110010011001100110100111101100111"
    Mingwen = "1001101010110101011001110011001001010001010101110011010110110011"

    #打印明文的16进制形式
    print("明文的16进制形式:         " + hex(int(Mingwen, base=2)).upper())

    ciphertext = DES(Mingwen, key)

    #打印加密后的密文
    print("加密后的密文:             " + hex(int(ciphertext, base=2)).upper())

    falseKey = "0001101000110101010101110111100110010011001100110100111101100111"

    decode_ciphertext = DES(ciphertext, key, "-1")
    #打印解密后的明文  看是否相同
    print("解密后的明文:             " + hex(int(decode_ciphertext, base=2)).upper())

    decode_ciphertext = DES(ciphertext, falseKey, "-1")
    # 打印给定错误的key 解密后的明文  看是否不同
    print("给定错误的key 解密后的明文:" + hex(int(decode_ciphertext, base=2)).upper())

实现结果

代码传送门