There is free firewall software available that can run on minimal hardware and provide a good level of (71) to your network.

A．即使破译者能够加密任意数量的明文，也无法破译密文
B．破译者无法加密任意数量的明文
C．破译者无法破译密文
D．密钥有足够的长度

A．TCP
B．ARP
C．UDP
D．ICMP