Python 凯撒密码

凯撒密码

class CaesarCipher:
    def __init__(self, alphabet, shift):
        self.alphabet = alphabet
        self.asize = len(alphabet)
        self.shift = shift
        self._dict = {}
        for i, c in enumerate(ALPHABET):
            self._dict[c] = i
    
    def _encode(self, c):
        return self.alphabet[(self._dict[c]+self.shift)%self.asize]
    
    
    def encode(self, s):
        o = ''
        for c in s:
            o += self._encode(c)
        return o

if __name__ == '__main__':
	ALPHABET = 'abcdefghijklmnopqrstuvwxyz'
    cipher = CaesarCipher(ALPHABET, 3)
    code = cipher.encode('hello')
    print(code)

ROT13

即把 凯撒密码 的偏置参数设成 13，由于字母表的长度为 26，故 ROT13 既是加密算法，也是解密算法：
$$ROT13(ROT13(s))=s$$