Review Questions
17.1 What are the advantages of each of the three approaches shown in Figure 17.1?
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17.2 What protocols comprise SSL?
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17.3 What is the difference between an SSL connection and an SSL session?
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17.4 List and briefly define the parameters that define an SSL session state.
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17.5 List and briefly define the parameters that define an SSL session connection.
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17.6 What services are provided by the SSL Record Protocol?
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17.7 What steps are involved in the SSL Record Protocol transmission?
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17.8 What is the purpose of HTTPS?
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17.9 For what applications is SSH useful?
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17.10 List and briefly define the SSH protocols.
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Problems
17.1 In SSL and TLS, why is there a separate Change Cipher Spec Protocol rather than
including a change_cipher_spec message in the Handshake Protocol?
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17.2 What purpose does the MAC serve during the change cipher spec SSL exchange?
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17.3 Consider the following threats to Web security and describe how each is countered by
a particular feature of SSL.
a. Brute-Force Cryptanalytic Attack: An exhaustive search of the key space for a
conventional encryption algorithm.
b. Known Plaintext Dictionary Attack: Many messages will contain predictable
plaintext, such as the HTTP GET command. An attacker constructs a dictionary
containing every possible encryption of the known-plaintext message. When
an encrypted message is intercepted, the attacker takes the portion containing
the encrypted known plaintext and looks up the ciphertext in the dictionary. The
ciphertext should match against an entry that was encrypted with the same secret
key. If there are several matches, each of these can be tried against the full ciphertext
to determine the right one. This attack is especially effective against small key
sizes (e.g., 40-bit keys).
c. Replay Attack: Earlier SSL handshake messages are replayed.
d. Man-in-the-Middle Attack: An attacker interposes during key exchange, acting as
the client to the server and as the server to the client.
e. Password Sniffing: Passwords in HTTP or other application traffic are eavesdropped.
f. IP Spoofing: Uses forged IP addresses to fool a host into accepting bogus data.
g. IP Hijacking: An active, authenticated connection between two hosts is disrupted
and the attacker takes the place of one of the hosts.
h. SYN Flooding: An attacker sends TCP SYN messages to request a connection but
does not respond to the final message to establish the connection fully. The attacked
TCP module typically leaves the “half-open connection” around for a few
minutes. Repeated SYN messages can clog the TCP module.
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17.4 Based on what you have learned in this chapter, is it possible in SSL for the receiver
to reorder SSL record blocks that arrive out of order? If so, explain how it can be
done. If not, why not?
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17.5 For SSH packets, what is the advantage, if any, of not including the MAC in the scope
of the packet encryption?
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