The Answer: Call back Systems; Callback systems provide access protection by calling back the number of a previously authorized location, but this control can be compromised by call forwarding. Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 35.

Commercial firewalls are a dime-a-dozen in todays world. Black firewall and whitewall are just distracters.

RESCORLA, Eric, SSL and TLS: Designing and Building Secure Systems, 2000, Addison Wesley Professional; SMITH, Richard E., Internet Cryptography, 1997, Addison-Wesley Pub Co.

CHAP is not used within IPSEC or IKE. CHAP is an authentication scheme used by Point to Point Protocol (PPP) servers to validate the identity of remote clients. CHAP periodically verifies the identity of the client by using a three-way handshake. This happens at the time of establishing the initial link (LCP), and may happen again at any time afterwards. The verification is based on a shared secret (such as the client user’s password).
After the completion of the link establishment phase, the authenticator sends a “challenge” message to the peer. The peer responds with a value calculated using a one-way hash function on the challenge and the secret combined. The authenticator checks the response against its own calculation of the expected hash value. If the values match, the authenticator acknowledges the authentication; otherwise it should terminate the connection. At random intervals the authenticator sends a new challenge to the peer and repeats steps 1 through 3.
The following were incorrect answers:
Pre Shared Keys In cryptography, a pre-shared key or PSK is a shared secret which was previously shared between the two parties using some secure channel before it needs to be used. To build a key from shared secret, the key derivation function should be used. Such systems almost always use symmetric key cryptographic algorithms. The term PSK is used in WiFi encryption such as WEP or WPA, where both the wireless access points (AP) and all clients share the same key.
The characteristics of this secret or key are determined by the system which uses it; some system designs require that such keys be in a particular format. It can be a password like ‘bret13i’, a passphrase like ‘Idaho hung gear id gene’, or a hexadecimal string like ’65E4 E556 8622 EEE1′. The secret is used by all systems involved in the cryptographic processes used to secure the traffic between the systems. Certificat Based Authentication
The most common form of trusted authentication between parties in the wide world of Web commerce is the exchange of certificates. A certificate is a digital document that at a minimum includes a Distinguished Name (DN) and an associated public key.
The certificate is digitally signed by a trusted third party known as the Certificate Authority (CA). The CA vouches for the authenticity of the certificate holder. Each principal in the transaction presents certificate as its credentials. The recipient then validates the certificate’s signature against its cache of known and trusted CA certificates. A “personal certificate” identifies an end user in a transaction; a “server certificate” identifies the service provider.
Generally, certificate formats follow the X.509 Version 3 standard. X.509 is part of the Open Systems Interconnect (OSI) X.500 specification.
Public Key Authentication Public key authentication is an alternative means of identifying yourself to a login server, instead of typing a password. It is more secure and more flexible, but more difficult to set up.
In conventional password authentication, you prove you are who you claim to be by proving that you know the correct password. The only way to prove you know the password is to tell the server what you think the password is. This means that if the server has been hacked, or spoofed an attacker can learn your password.
Public key authentication solves this problem. You generate a key pair, consisting of a public key (which everybody is allowed to know) and a private key (which you keep secret and do not give to anybody). The private key is able to generate signatures. A signature created using your private key cannot be forged by anybody who does not have a copy of that private key; but anybody who has your public key can verify that a particular signature is genuine.
So you generate a key pair on your own computer, and you copy the public key to the server. Then, when the server asks you to prove who you are, you can generate a signature using your private key. The server can verify that signature (since it has your public key) and allow you to log in. Now if the server is hacked or spoofed, the attacker does not gain your private key or password; they only gain one signature. And signatures cannot be re-used, so they have gained nothing.
There is a problem with this: if your private key is stored unprotected on your own computer, then anybody who gains access to your computer will be able to generate signatures as if they were you. So they will be able to log in to your server under your account. For this reason, your private key is usually encrypted when it is stored on your local machine, using a passphrase of your choice. In order to generate a signature, you must decrypt the key, so you have to type your passphrase.
References: RFC 2409: The Internet Key Exchange (IKE); DORASWAMY, Naganand & HARKINS, Dan
Ipsec: The New Security Standard for the Internet, Intranets, and Virtual Private Networks, 1999, Prentice Hall PTR; SMITH, Richard E.
Internet Cryptography, 1997, Addison-Wesley Pub Co.; HARRIS, Shon, All-In-One CISSP Certification Exam Guide, 2001, McGraw-Hill/Osborne, page 467.
http://en.wikipedia.org/wiki/Pre-shared_key http://www.home.umk.pl/~mgw/LDAP/RS.C4.JUN.97.pdf http://the.earth.li/~sgtatham/putty/0.55/htmldoc/Chapter8.html#S8.1

Reference: RFC 2409: The Internet Key Exchange (IKE); DORASWAMY, Naganand & HARKINS, Dan, Ipsec: The New Security Standard for the Internet, Intranets, and Virtual Private Networks, 1999, Prentice Hall PTR; SMITH, Richard E., Internet Cryptography, 1997, Addison-Wesley Pub Co.

Reference: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, 2001, McGraw-Hill/Osborne, page 467; SMITH, Richard E., Internet Cryptography, 1997, Addison-Wesley Pub Co.

HTTP is Port 80. Reference: MAIWALD, Eric, Network Security: A Beginner’s Guide, McGraw-Hill/Osborne Media, 2001, page 135.

Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, pages 76, 157.

The following answers are incorrect: Sniffers alter the source address of a computer to disguise and exploit weak authentication methods. IP Spoofing is a network-based attack, which involves altering the source address of a computer to disguise the attacker and exploit weak authentication methods.
Sniffers take over network connections. Session Hijacking tools allow an attacker to take over network connections, kicking off the legitimate user or sharing a login.
Sniffers send IP fragments to a system that overlap with each other. Malformed Packet attacks are a type of DoS attack that involves one or two packets that are formatted in an unexpected way. Many vendor product implementations do not take into account all variations of user entries or packet types. If software handles such errors poorly, the system may crash when it receives such packets. A classic example of this type of attack involves sending IP fragments to a system that overlap with each other (the fragment offset values are incorrectly set. Some unpatched Windows and Linux systems will crash when the encounter such packets.
The following reference(s) were/was used to create this question:
Source: TIPTON, Harold F. & KRAUSE, MICKI, Information Security Management Handbook, 4th Edition, Volume 2, Auerbach, NY, NY 2001, Chapter 22, Hacker Tools and Techniques by Ed Skoudis. ISC2 OIG, 2007 p. 137-138, 419

The main responsibility of the network layer is to insert information into the packet’s header so that it can be properly routed. The protocols at the network layer must determine the best path for the packet to take. The following answers are incorrect: Session layer. The session layer is responsible for establishing a connection between two applications. Physical layer. The physical layer if responsible for converting electronic impulses into bits and vice-versa. Transport layer. The transport layer is responsible for data transmission and error detection.
The following reference(s) were/was used to create this question: Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, v3, chapter 7: Telecommunications and Network Security (page 422-428).
ISC2 Official ISC2 Guide to the CBK (OIG) 2007, p. 409-412