local aes = require "resty.aes"
local str = require "resty.string"
local secret_key = "1234abcdefg"
local aes_128_cbc_md5 = aes:new(secret_key)
local encrypt_msg = aes_128_cbc_md5:encrypt("it is secret message")
local encrypt_msg_hex = str.to_hex(encrypt_msg)
请问如何通过encrypt_msg_hex得到encrypt_msg?即str.to_hex的逆函数是什么?谢谢