2.4 Integrity

Integrity is the ability to detect data manipulation by unauthorized entities. By data manipulation, we mean unauthorized acts such as the insertion, deletion, or substitution of individual data chunks or entire messages. It is not required that manipulations as such are rendered impossible; given the multitude of possible communication channels, this would be an impossible task. Clearly, a passively eavesdropping attacker such as Eve does not have the capability to perform data manipulation. We, therefore, assume a more active attacker named Mallory who also has the capability to write on the communication channel (see Figure 2.4).

Figure 2.4: The malicious attacker Mallory has the capabilities r,w to read all messages sent between Alice and Bob and to write on the unsecured channel. Mallory’s goal is to manipulate the messages in a way that is not noticed by Alice or Bob

At first glance, one might be tempted to think that a good encryption function...