Authenticity and integrity

Authenticity and integrity

by Ilias Marwane Merigh -
Number of replies: 2

Good afternoon,

I will take as example the Homework 8, "Providing all three properties", question 1.

If Alice sends a message Ks{m} to Bob. Let's assume that Persa is in the path between Alice and Bob. Persa could modify the msg arbitrarily and send it to Bob.

So Bob will receive two messages : one from Alice and one from Persa.

My question : How can Persa block Alice's msg, so only one reaches Bob ?

In reply to Ilias Marwane Merigh

Re: Authenticity and integrity

by Devrim Celik -
Hello Illias,

my take on this is, that if Persa is one of the machines of which the traffic from A to B is relayed, then she can choose to not forward the package. Since it is stated that Persa can "modify" traffic, this would be implied in my opinion.
If she would be only "observing" the traffic (i.e., is not part of the communication link but can see it), it would not be possible to "modify".