It is unconditionally secure (i.e. secure against a spy who has sufficient time and computer power), and needless of any private key exchange before the actual communication.

• 量子密码具有无条件安全的特性(即不会遭受拥有足够时间和计算机能力的窃听者攻击的危险)，而在实际通信发生之前，不需要交换私钥。