[网络协议]凯撒加密的实现（Python）

????????凯撒明文的要点在于循环移位，在计算机中实现利用ASCII码增加或者减少来对明文进行加密或者解密，凯撒加密类比于一次函数y=x+a，其中x代表字符的ASCII码值与a或者A的ASCII码值的差，a代表循环移位的位数。

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import time
def encryption(word,key):
    list_text = list(word)
    encrypt = []
    for letter in list_text:
        if letter.isalpha():#判断是否为英文字符
            if letter.isupper():#判断是否为大写
                text = letter.lower()#是大写就转化为小写
                n = chr(((ord(text) - ord("a") + key) % 26) + ord("a"))
                encrypt.append(n.upper())#加密后返还大写字符
            elif letter == " ":#加入输入明文中的空格
                encrypt.append(" ")
            else:
                n = chr(((ord(letter) - ord("a") + key) % 26) + ord("a"))
                encrypt.append(n)
    print(f"The Output is {''.join(encrypt)}！\n")
def decryption(word,key):#解密是加密的逆过程
    list_text = list(word)
    decrypt = []
    for letter in list_text:
        if letter.isalpha():
            if letter.isupper():
                text = letter.lower()
                n = chr(((ord(text) - ord("a") - key) % 26) + ord("a"))
                decrypt.append(n.upper())
            elif letter == " ":
                decrypt.append(" ")
            else:
                n = chr(((ord(letter) - ord("a") - key) % 26) + ord("a"))
                decrypt.append(n)
    print(f"The Output is {''.join(decrypt)}！\n")
type_writter = ['L','e','t',"'",'s',' ','P','l','a','y',' ','G','a','m','e','!']
for n in type_writter:
    time.sleep(0.4)
    print(n,end='')
time.sleep(1)
print("\n********凯撒明文********")
while True:
    time.sleep(1)
    choice = int(input('''Please enter your choice:
1.Encrypt The Word
2.Decipher The Word
3.End The program
Your Chioce:'''))
    if choice == 1:
        plaintext = input("Enter The Plaintext:")
        key = int(input("Enter the Key:"))
        time.sleep(1)
        encryption(plaintext,key)
    elif choice == 2:
        ciphertext = input("Enter The Ciphertext:")
        key = int(input("Enter the Key:"))
        time.sleep(1)
        decryption(ciphertext,key)
    else:
        time.sleep(1)
        print("The process is DONE!!!")
        break