These attacks involve some modification of the data stream or the creation of a false stream. These
attacks can be classified in to four categories:
Masquerade – One entity pretends to be a different entity.
Replay – involves passive capture of a data unit and its subsequent transmission to produce an
unauthorized effect.
Modification of messages – Some portion of message is altered or the messages are delayed or
recorded, to produce an unauthorized effect.
Denial of service – Prevents or inhibits the normal use or management of communication
facilities. Another form of service denial is the disruption of an entire network, either by disabling
the network or overloading it with messages so as to degrade performance.
It is quite difficult to prevent active attacks absolutely, because to do so would require physical
protection of all communication facilities and paths at all times. Instead, the goal is to detect them
and to recover from any disruption or delays caused by them.
