import string,os

def   vigenereEncrypt(msg,key):
    size = len(key)
    result = []
    cnt = 0
    for i in msg:
      if i.upper() in string.uppercase:
        #offset相当于是 ki
        offset = string.uppercase.find(key[cnt%size])
        t = string.uppercase[(string.uppercase.find(i.upper())+offset)%26] #这里相当于是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密码############
 
letter_list='ABCDEFGHIJKLMNOPQRSTUVWXYZ' #字母表
 
#根据输入的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
 
#加密函数
def Encrypt(plaintext,key_list):
 ciphertext=""
 
 i=0
 for ch in plaintext: #遍历明文
  if 0==i%len(key_list):
   i=0
  if ch.isalpha(): #明文是否为字母,如果是,则判断大小写,分别进行加密
   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: #如果密文不为字母,直接添加到密文字符串里
   ciphertext+=ch
 return ciphertext
 
#解密函数
def Decrypt(ciphertext,key):
 plaintext=""
 
 i=0
 for ch in ciphertext: #遍历密文
  if 0==i%len(key_list):
   i=0
  if ch.isalpha(): #密文为否为字母,如果是,则判断大小写,分别进行解密
   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: #如果密文不为字母,直接添加到明文字符串里
   plaintext+=ch
 return plaintext
 
if __name__=='__main__':
 print("加密请按D,解密请按E:")
 user_input=input();
 while(user_input!='D' and user_input!='E'):#输入合法性判断
  print("输入有误!请重新输入:")
  user_input=input()
 
 print("请输入密钥:")
 key=input()
 while(False==key.isalpha()):#输入合法性判断
  print("输入有误!密钥为字母,请重新输入:")
  key=input()
 
 key_list=Get_KeyList(key)
 
 if user_input=='D':
  #加密
  print("请输入明文:")
  plaintext=input()
  ciphertext=Encrypt(plaintext,key_list)
  print("密文为:\n%s" % ciphertext)
 else:
  #解密
  print("请输入密文:")
  ciphertext=input()
  plaintext=Decrypt(ciphertext,key_list)
  print("明文为:\n%s" % plaintext)