关于python实现凯撒密码、凯撒加解密算法的案例

def casar(message):
# *************begin************#
 message1=message.upper() #把明文字母变成大写
 message1=list(message1) #将明文字符串转换成列表
 list1=[]
 for i in range(len(message1)):
 if message1[i]==' ':
  list1.append(message1[i]) #若为空格不用移动
 elif ord(message1[i]) <= 90-3+1: #A-X右移三位
  list1.append(chr(ord(message1[i]) + 3))
  result = ''.join(list1) #列表转换成字符串
 else:
  list1.append(chr(ord(message1[i]) - (26-3))) #Y和Z回到A、B
  result = ''.join(list1)
 print(result)
# **************end*************# 
 
 
def main():
 message = input()
 casar(message)
if __name__=='__main__':
 main()

def casar(mode,message,key):
# *************begin************#
 if mode==1: #加密
 message1 = message.upper() # 把明文字母变成大写
 message1 = list(message1) # 将明文字符串转换成列表
 list1 = []
 for i in range(len(message1)):
  if message1[i] == ' ':
  list1.append(message1[i]) # 若为空格不用移动
  elif ord(message1[i]) <= 65 +key-1: 
  list1.append(chr(ord(message1[i]) + key)) # 右移key位
  result = ''.join(list1) # 列表转换成字符串
  else:
  list1.append(chr(ord(message1[i]) - key)) 
  result = ''.join(list1)
 print(result)
 elif mode==0: #解密
 message2 = list(message) # 将明文字符串转换成列表
 list2 = []
 for i in range(len(message2)):
  if message2[i] == ' ':
  list2.append(message2[i]) # 若为空格不用移动
  elif ord(message2[i]) <= 65+ key -1: 
  list2.append(chr(ord(message2[i]) + (26-key))) # 右移三位
  result = ''.join(list2) # 列表转换成字符串
  else:
  list2.append(chr(ord(message2[i]) - key)) 
  result = ''.join(list2)
 result = result.lower()
 print(result)

# **************end*************# 

def main():
 mode = int(input()) # 1代表加密，0代表解密
 message = input() #待加密或解密的消息
 key = int(input()) # key的范围0~25之间
 casar(mode,message,key)
if __name__=='__main__':
 main()

#仿射密码

def encrypt(k1,k2,message):
# *************begin************#
 message1 = list(message)
 list1=list(map(chr,range(ord('a'),ord('z')+1)))
 list2=list(map(chr,range(ord('A'),ord('Z')+1)))
 for i in range(len(list1)):
 list1.append(list2[i])
 y=[]
 for i in range(len(message)):
 if message1[i]==' ':
  y.append(message1[i])
 else:
  for j in range(52):
  if message1[i]==list1[j]:
   y.append(list1[(k1*j + k2) % 52])
   result = ''.join(y)
 return result
# **************end*************# 

def decrypt(k1,k2,message):
# *************begin************#
	#扩展欧几里得算法求逆元法
 # x1, x2, x3 = 1, 0, 52 
 # y1, y2, y3 = 0, 1, k1
 # while True:
 # if y3 == 0:
 #  return 'None'
 #  break
 # elif y3 == 1:
 #  a_reverse =y2 % 52
 #  break
 # else:
 #  Q = x3 // y3
 #  t1, t2, t3 = x1 - Q * y1, x2 - Q * y2, x3 - Q * y3
 #  x1, x2, x3 = y1, y2, y3
 #  y1, y2, y3 = t1, t2, t3
 
 #已知模求逆元
 for i in range(1,53):
 if k1 * i % 52 == 1:
  a_reverse = i

 message1 = list(message)
 list1=list(map(chr,range(ord('a'),ord('z')+1)))
 list2=list(map(chr,range(ord('A'),ord('Z')+1)))
 for i in range(len(list1)):
 list1.append(list2[i])
 x=[]
 for i in range(len(message1)):
 if message1[i]==' ':
  x.append(message1[i])
 else:
  for j in range(52):
  if message1[i]==list1[j]:
   x.append(list1[(a_reverse * (j-k2) )% 52])
   result = ''.join(x)
 return result
  
# **************end*************# 

def main():
 mode = int(input()) # 1代表加密，0代表解密
 message = input() #待加密或解密的消息
 key1 = int(input()) # key的范围0~51之间
 key2 = int(input()) # key的范围0~51之间
 if mode == 1:
 translated = encrypt(key1,key2,message)
 else:
 translated = decrypt(key1,key2,message)
 print(translated)

if __name__=='__main__':
 main()