python實現(xiàn)維吉尼亞加密法

import string,os

def   vigenereEncrypt(msg,key):
    size = len(key)
    result = []
    cnt = 0
    for i in msg:
      if i.upper() in string.uppercase:
        #offset相當(dāng)于是 ki
        offset = string.uppercase.find(key[cnt%size])
        t = string.uppercase[(string.uppercase.find(i.upper())+offset)%26] #這里相當(dāng)于是c1 = (mi+ki)(mod 26) ,t = c1
        if i.isupper():
          result.append(t)
        else:
          result.append(t.lower())
        cnt+=1
      else:
        result.append(i)
    return "".join(result)
def   main():

    msg = "Common sense is not so common"
    cipher = vigenereEncrypt(msg,"PIZZA")#key = "PIZZA:

    print cipher
if   __name__=="__main__":
    main()

##########Vigenere密碼############
 
letter_list='ABCDEFGHIJKLMNOPQRSTUVWXYZ' #字母表
 
#根據(jù)輸入的key生成key列表
def Get_KeyList(key):
 key_list=[]
 for ch in key:
  key_list.append(ord(ch.upper())-65)
 return key_list
 
#加密函數(shù)
def Encrypt(plaintext,key_list):
 ciphertext=""
 
 i=0
 for ch in plaintext: #遍歷明文
  if 0==i%len(key_list):
   i=0
  if ch.isalpha(): #明文是否為字母,如果是,則判斷大小寫,分別進行加密
   if ch.isupper(): 
    ciphertext+=letter_list[(ord(ch)-65+key_list[i]) % 26]
    i+=1
   else:
    ciphertext+=letter_list[(ord(ch)-97+key_list[i]) % 26].lower()
    i+=1
  else: #如果密文不為字母,直接添加到密文字符串里
   ciphertext+=ch
 return ciphertext
 
#解密函數(shù)
def Decrypt(ciphertext,key):
 plaintext=""
 
 i=0
 for ch in ciphertext: #遍歷密文
  if 0==i%len(key_list):
   i=0
  if ch.isalpha(): #密文為否為字母,如果是,則判斷大小寫,分別進行解密
   if ch.isupper():
    plaintext+=letter_list[(ord(ch)-65-key_list[i]) % 26]
    i+=1
   else:
    plaintext+=letter_list[(ord(ch)-97-key_list[i]) % 26].lower()
    i+=1
  else: #如果密文不為字母,直接添加到明文字符串里
   plaintext+=ch
 return plaintext
 
if __name__=='__main__':
 print("加密請按D,解密請按E:")
 user_input=input();
 while(user_input!='D' and user_input!='E'):#輸入合法性判斷
  print("輸入有誤!請重新輸入:")
  user_input=input()
 
 print("請輸入密鑰:")
 key=input()
 while(False==key.isalpha()):#輸入合法性判斷
  print("輸入有誤!密鑰為字母,請重新輸入:")
  key=input()
 
 key_list=Get_KeyList(key)
 
 if user_input=='D':
  #加密
  print("請輸入明文:")
  plaintext=input()
  ciphertext=Encrypt(plaintext,key_list)
  print("密文為:\n%s" % ciphertext)
 else:
  #解密
  print("請輸入密文:")
  ciphertext=input()
  plaintext=Decrypt(ciphertext,key_list)
  print("明文為:\n%s" % plaintext)