In this section, we discuss two DoS attacks on the client. Since we assume the attacker could have full control of the network, some DoS attacks such as delay or drop packets are always possible. Delay packets could cause packets to violate the security condition and hence not to be authenticated. On the other hand, speeding up packets does not do anything at all. The receiver even benefits from this since she might be able to use a chain with a short disclosure delay that she could not use otherwise. We can show that replay packets cannot do much harm either. First, a duplicated packet is only accepted by the receiver within a short time period, since the security condition drops packets if they are replayed with a long delay. Second we can prevent the replay attack by adding a sequence number to each packet and by including the sequence number in the MAC. The TESLA protocol in the network layer or in the application layer will filter out duplicate packets.
In the rest of the subsection, we discuss some more complicated DoS attacks and show how to mitigate or prevent the attacks. First we discuss a flooding attack which fills up the receiver buffers. Second we discuss an attack that tries to waste the receiver's computation resources by unnecessarily re-computing the key chain.