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Python DES加密實(shí)現(xiàn)原理及實(shí)例解析

更新時(shí)間：2020年07月17日 08:54:18 作者：X1ace

這篇文章主要介紹了Python DES加密實(shí)現(xiàn)原理及實(shí)例解析,文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下

加密流程

首先說(shuō)一下置換的意思，比如說(shuō)有5678這個(gè)字符串，置換表為2143，置換表中的數(shù)表示的是位置，所以字符串變成6587。所有的置換表在程序中。（S盒置換不一樣，會(huì)另外說(shuō)明）

密鑰部分

把8位字符串密鑰變成2進(jìn)制（好像密鑰只可以是8位，這一塊我也沒(méi)有搞太清楚）
64位密鑰進(jìn)行PC1置換，變成56位，因?yàn)橐郧癉ES是用硬件實(shí)現(xiàn)的，所以8，16，24，32，40，48，56，64位為校驗(yàn)位，不記入密鑰部分。但是我們現(xiàn)在是用軟件實(shí)現(xiàn)，所以這8位需要去掉，再打亂順序。
將56位密鑰對(duì)半分L0和R0、分別對(duì)L0和R0進(jìn)行左循環(huán)移位，（當(dāng)輪數(shù)為第1、2、9、16輪時(shí)，移動(dòng)1位，其余時(shí)候移動(dòng)兩位）L0,R0移動(dòng)1位后得到L1，R1。L1和R0繼續(xù)進(jìn)行下一輪，進(jìn)行16輪。
上面移位得到的所以Li+Ri進(jìn)行PC2置換得到16個(gè)子密鑰（PC2置換把56位數(shù)據(jù)變成了48位）。

明文部分

先進(jìn)行明文填充，采用PKCS #5規(guī)則，如果剛好滿(mǎn)足每組有8個(gè)字節(jié)，則再添加一組，每個(gè)字節(jié)為000010000，如果最后一組沒(méi)有8個(gè)字節(jié)，則把這一組填充成8個(gè)字節(jié)，填充的字節(jié)為少掉的字節(jié)的數(shù)目，比如有7個(gè)字節(jié)，則填充00000001。
再進(jìn)行初始置換，把64位明文打亂。
進(jìn)行16輪feistel函數(shù)后在進(jìn)行逆初始運(yùn)算

以一組為例子來(lái)說(shuō)明，一組明文8個(gè)字節(jié)，64位。有16輪迭代，要運(yùn)行16次feistel函數(shù)。注意在16輪迭代前要把明文進(jìn)行初始置換，迭代后把左右兩邊數(shù)據(jù)合并成64位再進(jìn)行逆初始運(yùn)算。

把64位明文左右對(duì)半分成兩份。

右邊的先進(jìn)行部分進(jìn)行擴(kuò)展置換，32位變成48位。

再和對(duì)應(yīng)輪數(shù)的子密鑰進(jìn)行異或運(yùn)算。

再進(jìn)行S盒運(yùn)算，48位變成32位。S盒運(yùn)算具體操作方法是，把48位數(shù)據(jù)分成8份，每份就有6位數(shù)據(jù)，比如010110，把頭和尾結(jié)合位00，變成十進(jìn)制就是0，中間四位的十進(jìn)制為11，所以(x,y)為（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]

在上面這個(gè)表中表示的就是12，在把12變成2進(jìn)制就是1100，所以6位就變成了4位?？偣灿?份數(shù)據(jù)，也有8個(gè)表。每份對(duì)應(yīng)的運(yùn)算的表都不一樣。

再進(jìn)行P盒運(yùn)算。

最后和左邊的32位進(jìn)行異或運(yùn)算。

解密

解密部分除了在feistel函數(shù)中調(diào)用子密鑰的順序相反外，其他都一樣。加密調(diào)用的順序是1-16，解密是16-1。

代碼

#################################輔助函數(shù)######################################

# 十進(jìn)制轉(zhuǎn)成二進(jìn)制
def INT_BIN(NUM):
  i = bin(NUM)[2:]
  if len(i) != 8:
    i = ((8 - len(i)) * '0') + i

  return i

# 置換函數(shù)
def Replace(ARR,change):
  ARR1 = []
  for i in ARR:
    a = ''
    for j in change:
      a += i[j-1]
    ARR1.append(a)
  return ARR1

# 異或運(yùn)算
def XOR(a,b):
  c=""
  for i,j in zip(a,b):
    if i==j:
      c+='0'
    else:
      c+='1'
  return [c]

# 二進(jìn)制轉(zhuǎn)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

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

#################################密鑰生成######################################
# 先PC1置換、將56位密鑰對(duì)半分L0和R0、分別對(duì)L0和R0進(jìn)行左循環(huán)移位，
# （當(dāng)輪數(shù)為第1、2、9、16輪時(shí)，移動(dòng)1位，其余時(shí)候移動(dòng)兩位）L0,R0移動(dòng)1位
# 后得到L1，R1，L1+R0進(jìn)行PC2置換得到密鑰K1，L1和R0繼續(xù)進(jìn)行下一輪，直到生成16個(gè)子密鑰

# PC-1置換表
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置換表
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]

# 生成子密鑰函數(shù)
def GenerateSubkey(Key):
  # 字符串轉(zhuǎn)二進(jìn)制
  K = ""
  i_byte = bytes(Key, encoding='utf-8')
  for i_bin in i_byte:
    K += INT_BIN(i_bin)

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

  # 生成16組子密鑰
  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置換
  return Replace(ReplacePc1,PC2)

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

#################################明文處理###################################
# 明文填充，采用PKCS #5規(guī)則，如果剛好滿(mǎn)足每組有8個(gè)字節(jié)，則再添加一組，每個(gè)字節(jié)為
# 000010000，如果最后一組沒(méi)有8個(gè)字節(jié)，則把這一組填充成8個(gè)字節(jié)，填充的字節(jié)為少掉的
# 字節(jié)的數(shù)目，比如有7個(gè)字節(jié)，則填充00000001

# 對(duì)明文進(jìn)行填充，分組
def InitPlaintext(Plaintext):
  DecimalList = []
  BytesList = []
  BinList = []
  
  # 字符串轉(zhuǎn)成10機(jī)制
  i_byte = bytes(Plaintext, encoding='utf-8')
  for i_bin in i_byte:
    DecimalList.append(i_bin)

  # 剛好滿(mǎn)足分組
  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])
  # 不滿(mǎn)足分組
  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進(jìn)制轉(zhuǎn)2進(jìn)制
  for i in BytesList:
    TMP = ''
    for j in i:
      TMP += INT_BIN(j)
    BinList.append(TMP)
  
  return BinList

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

################################feistel函數(shù)################################
#ip初始置換表
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]

#擴(kuò)展E置換表
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盒置換表
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]

#逆初始置換表
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個(gè)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盒置換
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函數(shù)
def feistel(L, R, K):
  # 擴(kuò)展置換
  Expand = Replace(R,EExten)
  # 異或運(yùn)算
  Expand = XOR(Expand[0],K)
  # S盒運(yùn)算
  Expand = S(Expand[0])
  # P盒
  Expand = Replace(Expand,PBOX)
  # 異或運(yùn)算
  Expand = XOR(L[0],Expand[0])

  return Expand[0]

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

################################加、解密函數(shù)################################
# 加密
def Encrypt(PlanText,Key):
  # 初始置換
  IP1 = Replace(InitPlaintext(PlanText),IPINIT)
  # 生成子密鑰
  SubkeyList = GenerateSubkey(Key)

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

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

  # 16輪迭代
  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
    # 逆初始置換
    PlanText.append(Replace([R+L],P1)[0])
  return PlanText

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

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

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