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Security mitigation

5 important questions on Security mitigation

Suppose that Bob receives a PGP message from Alice. How does Bob know for sure that Alice created the message (rather than, say, Trudy)? Does PGP use a MAC for message integrity?

PGP. It uses digital signatures for authentication and integrity.

What is the purpose of the random nonces in the SSL handshake?

The purpose of the random nonces in the handshake is to defend against the connection replay attack.

Stateful packet filters maintain two data structures. Name them and briefly describe what they do.

Filter table and connection table. The connection table keeps track of connections, allowing for a finer degree of packet filtering.

Why must an application gateway work in conjunction with a router filter to be effective?

If there isn’t a packet filter, than users inside the institution’s network will still be able to make direct connections to hosts outside the institution’s network. The filter forces the users to first connect to the application gateway.

Suppose Alice and Bob are communicating over an SSL session. Suppose an attacker, who does not have any of the shared keys, inserts a bogus TCP segment into a packet stream with correct TCP checksum and sequence numbers (and correct IP addresses and port numbers). Will SSL at the receiving side accept the bogus packet and pass the payload to the receiving application? Why or why not?

Message integrity can solve the issue. When router B receives a link-state message from router A, router B should verify that router A actually created the message and, further, that no one tampered with the message in transit.