Python DES加密實現原理及實例解析
加密流程
首先說一下置換的意思，比如說有5678這個字符串，置換表為2143，置換表中的數表示的是位置，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，會另外說明）
密鑰部分
明文部分
先進行明文填充，采用PKCS #5規則，如果剛好滿足每組有8個字節，則再添加一組，每個字節為000010000，如果最后一組沒有8個字節，則把這一組填充成8個字節，填充的字節為少掉的字節的數目，比如有7個字節，則填充00000001。 再進行初始置換，把64位明文打亂。 進行16輪feistel函數后在進行逆初始運算
以一組為例子來說明，一組明文8個字節，64位。有16輪迭代，要運行16次feistel函數。注意在16輪迭代前要把明文進行初始置換，迭代后把左右兩邊數據合并成64位再進行逆初始運算。
把64位明文左右對半分成兩份。
右邊的先進行部分進行擴展置換，32位變成48位。
再和對應輪數的子密鑰進行異或運算。
再進行S盒運算，48位變成32位。S盒運算具體操作方法是，把48位數據分成8份，每份就有6位數據，比如010110，把頭和尾結合位00，變成十進制就是0，中間四位的十進制為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]
在上面這個表中表示的就是12，在把12變成2進制就是1100，所以6位就變成了4位?？偣灿?份數據，也有8個表。每份對應的運算的表都不一樣。
再進行P盒運算。
最后和左邊的32位進行異或運算。
解密
解密部分除了在feistel函數中調用子密鑰的順序相反外，其他都一樣。加密調用的順序是1-16，解密是16-1。
代碼
#################################輔助函數####################################### 十進制轉成二進制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]# 二進制轉字符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位密鑰對半分L0和R0、分別對L0和R0進行左循環移位，# （當輪數為第1、2、9、16輪時，移動1位，其余時候移動兩位）L0,R0移動1位# 后得到L1，R1，L1+R0進行PC2置換得到密鑰K1，L1和R0繼續進行下一輪，直到生成16個子密鑰# 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def GenerateSubkey(Key): # 字符串轉二進制 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規則，如果剛好滿足每組有8個字節，則再添加一組，每個字節為# 000010000，如果最后一組沒有8個字節，則把這一組填充成8個字節，填充的字節為少掉的# 字節的數目，比如有7個字節，則填充00000001# 對明文進行填充，分組def InitPlaintext(Plaintext): DecimalList = [] BytesList = [] BinList = [] # 字符串轉成10機制 i_byte = bytes(Plaintext, encoding=’utf-8’) for i_bin in i_byte: DecimalList.append(i_bin) # 剛好滿足分組 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進制轉2進制 for i in BytesList: TMP = ’’ for j in i: TMP += INT_BIN(j) BinList.append(TMP) return BinList###########################################################################################################feistel函數#################################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def feistel(L, R, K): # 擴展置換 Expand = Replace(R,EExten) # 異或運算 Expand = XOR(Expand[0],K) # S盒運算 Expand = S(Expand[0]) # P盒 Expand = Replace(Expand,PBOX) # 異或運算 Expand = XOR(L[0],Expand[0]) return Expand[0]###########################################################################################################加、解密函數################################# 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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