Best Xor Encryption

def encryption(m,k):
    ret = ""
    for i in range(len(m)):
        ret += chr(ord(m[i])^ord(k[i%(len(m)-1)]))
    return ret
if __name__ == "__main__":
    print("Let's try the program!")
    m = input("Write the message to process: ")
    k = input("Write the key here: ")
    if len(k)<len(m):
        k = k*len(m)
    print("Your cyphertext is: \n %s" %encryption(m,k))