python实现DES加密

Posted 2020-12-16 x1ace

加密流程

? 首先说一下置换的意思，比如说有5678这个字符串，置换表为2143，置换表中的数表示的是位置，所以字符串变成6587。所有的置换表在程序中。（S盒置换不一样，会另外说明）

密钥部分

• 把8位字符串密钥变成2进制（好像密钥只可以是8位，这一块我也没有搞太清楚）
• 64位密钥进行PC1置换，变成56位，因为以前DES是用硬件实现的，所以8，16，24，32，40，48，56，64位为校验位，不记入密钥部分。但是我们现在是用软件实现，所以这8位需要去掉，再打乱顺序。
• 将56位密钥对半分L0和R0、分别对L0和R0进行左循环移位，（当轮数为第1、2、9、16轮时，移动1位，其余时候移动两位）L0,R0移动1位后得到L1，R1。L1和R0继续进行下一轮，进行16轮。
• 上面移位得到的所以Li+Ri进行PC2置换得到16个子密钥（PC2置换把56位数据变成了48位）。

明文部分

• 先进行明文填充，采用PKCS #5规则，如果刚好满足每组有8个字节，则再添加一组，每个字节为000010000，如果最后一组没有8个字节，则把这一组填充成8个字节，填充的字节为少掉的字节的数目，比如有7个字节，则填充00000001。
• 再进行初始置换，把64位明文打乱。
• 进行16轮feistel函数后在进行逆初始运算

feistel函数

? 以一组为例子来说明，一组明文8个字节，64位。有16轮迭代，要运行16次feistel函数。注意在16轮迭代前要把明文进行初始置换，迭代后把左右两边数据合并成64位再进行逆初始运算。

• 把64位明文左右对半分成两份。

• 右边的先进行部分进行扩展置换，32位变成48位。

• 再和对应轮数的子密钥进行异或运算。

• 再进行S盒运算，48位变成32位。S盒运算具体操作方法是，把48位数据分成8份，每份就有6位数据，比如010110，把头和尾结合位00，变成十进制就是0，中间四位的十进制为11，所以(x,y)为（0,11）

  [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]
  

  在上面这个表中表示的就是12，在把12变成2进制就是1100，所以6位就变成了4位。总共有8份数据，也有8个表。每份对应的运算的表都不一样。

• 再进行P盒运算。

• 最后和左边的32位进行异或运算。

解密

解密部分除了在feistel函数中调用子密钥的顺序相反外，其他都一样。加密调用的顺序是1-16，解密是16-1。

代码

#################################辅助函数######################################

# 十进制转成二进制
def INT_BIN(NUM):
    i = bin(NUM)[2:]
    if len(i) != 8:
        i = ((8 - len(i)) * ‘0‘) + i

    return i

# 置换函数
def Replace(ARR,change):
    ARR1 = []
    for i in ARR:
        a = ‘‘
        for j in change:
            a += i[j-1]
        ARR1.append(a)
    return ARR1

# 异或运算
def XOR(a,b):
    c=""
    for i,j in zip(a,b):
        if i==j:
            c+=‘0‘
        else:
            c+=‘1‘
    return [c]

# 二进制转字符
def ASCII(A):
    text = ‘‘
    for i in A:
        for j in range(8):
            b = i[j*8:(j+1)*8]
            text += chr(int(b,2))
    return text

##############################################################################

#################################密钥生成######################################
# 先PC1置换、将56位密钥对半分L0和R0、分别对L0和R0进行左循环移位，
# （当轮数为第1、2、9、16轮时，移动1位，其余时候移动两位）L0,R0移动1位
# 后得到L1，R1，L1+R0进行PC2置换得到密钥K1，L1和R0继续进行下一轮，直到生成16个子密钥

# PC-1置换表
PC1 = [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]

# PC-2置换表
PC2 = [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]

# 生成子密钥函数
def GenerateSubkey(Key):
    # 字符串转二进制
    K = ""
    i_byte = bytes(Key, encoding=‘utf-8‘)
    for i_bin in i_byte:
        K += INT_BIN(i_bin)

    # PC1置换
    ReplacePc1 = Replace([K],PC1)

    # 生成16组子密钥
    Lmi = []
    Rmi = []
    Lmi.append(ReplacePc1[0][:28])
    Rmi.append(ReplacePc1[0][28:])
    for i in range(1,17):
        if i in (1, 2, 9, 16):
            Lmi.append(Lmi[i-1][1:]+Lmi[i-1][:1])
            Rmi.append(Rmi[i-1][1:]+Rmi[i-1][:1])
        else:
            Lmi.append(Lmi[i-1][2:]+Lmi[i-1][:2])
            Rmi.append(Rmi[i-1][2:]+Rmi[i-1][:2])
    del Lmi[0]
    del Rmi[0]
    del ReplacePc1[0]
    for i in range(16):
        ReplacePc1.append(Lmi[i]+Rmi[i])

    # PC2置换
    return Replace(ReplacePc1,PC2)

###########################################################################

#################################明文处理###################################
# 明文填充，采用PKCS #5规则，如果刚好满足每组有8个字节，则再添加一组，每个字节为
# 000010000，如果最后一组没有8个字节，则把这一组填充成8个字节，填充的字节为少掉的
# 字节的数目，比如有7个字节，则填充00000001

# 对明文进行填充，分组
def InitPlaintext(Plaintext):
    DecimalList = []
    BytesList = []
    BinList = []
    
    # 字符串转成10机制
    i_byte = bytes(Plaintext, encoding=‘utf-8‘)
    for i_bin in i_byte:
        DecimalList.append(i_bin)

    # 刚好满足分组
    if len(DecimalList) % 8 == 0:
        for i in range(8):
            DecimalList.append(8)
        for i in range(int(len(DecimalList)/8)):
            BytesList.append(DecimalList[i*8:(i+1)*8])
    # 不满足分组
    else:
        INT = 8 - len(DecimalList) % 8
        for i in range(INT):
            DecimalList.append(INT)
        for i in range(int(len(DecimalList)/8)):
            BytesList.append(DecimalList[i*8:(i+1)*8])
    
    # 10进制转2进制
    for i in BytesList:
        TMP = ‘‘
        for j in i:
           TMP += INT_BIN(j)
        BinList.append(TMP)
    
    return BinList

###########################################################################

################################feistel函数################################
#ip初始置换表
IPINIT = [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]

#扩展E置换表
EExten = [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]

#P盒置换表
PBOX = [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]

#逆初始置换表
P1 = [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]

#8个s盒
S_1 = [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]
 
S_2 = [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]
 
S_3 = [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]
 
S_4 = [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]
 
S_5 = [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]
 
S_6 = [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]
 
S_7 = [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]
 
S_8 = [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]

S_9 = []
S_9.append(S_1)
S_9.append(S_2)
S_9.append(S_3)
S_9.append(S_4)
S_9.append(S_5)
S_9.append(S_6)
S_9.append(S_7)
S_9.append(S_8)

# S盒置换
def S(R):
    s = ‘‘
    for i in range(8):
        a = R[i*6:(i+1)*6]
        x = int(a[0]+a[-1],2)
        y = int(a[1:5],2)
        s += INT_BIN(S_9[i][x*15+y])[4:]
    return[s]


# feistel函数
def feistel(L, R, K):
    # 扩展置换
    Expand = Replace(R,EExten)
    # 异或运算
    Expand = XOR(Expand[0],K)
    # S盒运算
    Expand = S(Expand[0])
    # P盒
    Expand = Replace(Expand,PBOX)
    # 异或运算
    Expand = XOR(L[0],Expand[0])

    return Expand[0]

###########################################################################

################################加、解密函数################################
# 加密
def Encrypt(PlanText,Key):
    # 初始置换
    IP1 = Replace(InitPlaintext(PlanText),IPINIT)
    # 生成子密钥
    SubkeyList = GenerateSubkey(Key)

    # 16轮迭代
    Ciphertext = []
    for i in IP1:
        L = i[:32]
        R = i[32:]
        for k in SubkeyList:
            TMP = feistel([L],[R],k)
            L = R
            R = TMP
        # 逆初始置换
        Ciphertext.append(Replace([R+L],P1)[0])
    return Ciphertext,SubkeyList

# 解密
def Decrypt(Ciphertext,Key):
    # 初始置换
    IP1 = Replace(Ciphertext,IPINIT) 

    # 16轮迭代
    PlanText = []
    for i in IP1:
        L = i[:32]
        R = i[32:]
        for k in Key[::-1]:
            TMP = feistel([L],[R],k)
            L = R
            R = TMP
        # 逆初始置换
        PlanText.append(Replace([R+L],P1)[0])
    return PlanText

###########################################################################

if __name__ == "__main__":
    miwen,miyao = Encrypt(‘computer‘,‘networks‘)
    print(miwen)
    print(ASCII(Decrypt(miwen,miyao)))

参考

https://zhuanlan.zhihu.com/p/133516777