Section: Access Control
Explanation/Reference:
The Answer: authentication. Kerberos is an authentication service. It can use single-factor or multi-factor authentication methods.
The following answers are incorrect:
non-repudiation. Since Kerberos deals primarily with symmetric cryptography, it does not help with non- repudiation.
confidentiality. Once the client is authenticated by Kerberos and obtains its session key and ticket, it may use them to assure confidentiality of its communication with a server; however, that is not a Kerberos service as such.
authorization. Although Kerberos tickets may include some authorization information, the meaning of the authorization fields is not standardized in the Kerberos specifications, and authorization is not a primary Kerberos service.
The following reference(s) were/was used to create this question:
ISC2 OIG,2007 p. 179-184
Shon Harris AIO v.3 152-155

Explanation/Reference:
IPSec can be run in either tunnel mode or transport mode. Each of these modes has its own particular uses and care should be taken to ensure that the correct one is selected for the solution:
Tunnel mode is most commonly used between gateways, or at an end-station to a gateway, the gateway acting as a proxy for the hosts behind it.
Transport mode is used between end-stations or between an end-station and a gateway, if the gateway is being treated as a host-for example, an encrypted Telnet session from a workstation to a router, in which the router is the actual destination.
As Figure 1 shows, basically transport mode should be used for end-to-end sessions and tunnel mode should be used for everything else. (Refer to the figure for the following discussion.) Figure 1 Tunnel and transport modes in IPSec.
Figure 1 displays some examples of when to use tunnel versus transport mode:
Tunnel mode is most commonly used to encrypt traffic between secure IPSec gateways, such as between the Cisco router and PIX Firewall (as shown in example A in Figure 1). The IPSec gateways proxy IPSec for the devices behind them, such as Alice's PC and the HR servers in Figure 1. In example A, Alice connects to the HR servers securely through the IPSec tunnel set up between the gateways.
Tunnel mode is also used to connect an end-station running IPSec software, such as the Cisco Secure VPN Client, to an IPSec gateway, as shown in example B.
In example C, tunnel mode is used to set up an IPSec tunnel between the Cisco router and a server running IPSec software. Note that Cisco IOS software and the PIX Firewall sets tunnel mode as the default IPSec mode.
Transport mode is used between end-stations supporting IPSec, or between an end-station and a gateway, if the gateway is being treated as a host. In example D, transport mode is used to set up an encrypted Telnet session from Alice's PC running Cisco Secure VPN Client software to terminate at the PIX Firewall, enabling Alice to remotely configure the PIX Firewall securely.
AH Tunnel Versus Transport Mode
Figure 2 shows the differences that the IPSec mode makes to AH. In transport mode, AH services protect the external IP header along with the data payload. AH services protect all the fields in the header that don't change in transport. The header goes after the IP header and before the ESP header, if present, and other higher-layer protocols.
In tunnel mode, the entire original header is authenticated, a new IP header is built, and the new IP header is protected in the same way as the IP header in transport mode.
Figure 2 AH tunnel versus transport mode.
AH is incompatible with Network Address Translation (NAT) because NAT changes the source IP address, which breaks the AH header and causes the packets to be rejected by the IPSec peer.
ESP Tunnel Versus Transport Mode
Figure 3 shows the differences that the IPSec mode makes to ESP. In transport mode, the IP payload is encrypted and the original headers are left intact. The ESP header is inserted after the IP header and before the upper-layer protocol header. The upper-layer protocols are encrypted and authenticated along with the ESP header. ESP doesn't authenticate the IP header itself.
NOTE
Higher-layer information is not available because it's part of the encrypted payload.
When ESP is used in tunnel mode, the original IP header is well protected because the entire original IP datagram is encrypted. With an ESP authentication mechanism, the original IP datagram and the ESP header are included; however, the new IP header is not included in the authentication.
When both authentication and encryption are selected, encryption is performed first, before authentication.
One reason for this order of processing is that it facilitates rapid detection and rejection of replayed or bogus packets by the receiving node. Prior to decrypting the packet, the receiver can detect the problem and potentially reduce the impact of denial-of-service attacks.
Figure 3 ESP tunnel versus transport mode.
ESP can also provide packet authentication with an optional field for authentication. Cisco IOS software and the PIX Firewall refer to this service as ESP hashed message authentication code (HMAC).
Authentication is calculated after the encryption is done. The current IPSec standard specifies SHA-1 and MD5 as the mandatory HMAC algorithms.
The main difference between the authentication provided by ESP and AH is the extent of the coverage.
Specifically, ESP doesn't protect any IP header fields unless those fields are encapsulated by ESP (tunnel mode). Figure 4 illustrates the fields protected by ESP HMAC.
Figure 4 ESP encryption with a keyed HMAC.
IPSec Transforms
An IPSec transform specifies a single IPSec security protocol (either AH or ESP) with its corresponding security algorithms and mode. Example transforms include the following:
The AH protocol with the HMAC with MD5 authentication algorithm in tunnel mode is used for authentication.
The ESP protocol with the triple DES (3DES) encryption algorithm in transport mode is used for confidentiality of data.
The ESP protocol with the 56-bit DES encryption algorithm and the HMAC with SHA-1 authentication algorithm in tunnel mode is used for authentication and confidentiality.
Transform Sets
A transform set is a combination of individual IPSec transforms designed to enact a specific security policy for traffic. During the ISAKMP IPSec security association negotiation that occurs in IKE phase 2 quick mode, the peers agree to use a particular transform set for protecting a particular data flow. Transform sets combine the following IPSec factors:
Mechanism for payload authentication-AH transform
Mechanism for payload encryption-ESP transform
IPSec mode (transport versus tunnel)
Transform sets equal a combination of an AH transform, plus an ESP transform, plus the IPSec mode (either tunnel or transport mode).
This brings us to the end of the second part of this five-part series of articles covering IPSec. Be sure to catch the next installment.
Cisco Press at: http://www.ciscopress.com/articles/printerfriendly.asp?p=25477 and
Source: TIPTON, Harold F & KRAUSE, MICKI, Information Security Management Handbook, 4th Edition, Volume 2, 2001, CRC Press, NY, Pages 166-167.

Explanation/Reference:
The reference monitor, not the security kernel is an access control concept.
The security kernel is made up of software, and firmware components that fall within the TCB and implements and enforces the reference monitor concept. The security kernel mediates all access and functions between subjects and objects. The security kernel is the core of the TCB and is the most commonly used approach to building trusted computing systems.
There are three main requirements of the security kernel:
* It must provide isolation for the processes carrying out the reference monitor concept, and the processes must be tamperproof.
* It must be invoked for every access attempt and must be impossible to circumvent. Thus, the security kernel must be implemented in a complete and foolproof way.
* It must be small enough to be able to be tested and verified in a complete and comprehensive manner.
The following answers are incorrect:
The security kernel is made up of mechanisms that fall under the TCB and implements and enforces the reference monitor concept. Is incorrect because this is the definition of the security kernel.
The security kernel must provide isolation for the processes carrying out the reference monitor concept and they must be tamperproof. Is incorrect because this is one of the three requirements that make up the security kernel.
The security kernel must be small enough to be able to be tested and verified in a complete and comprehensive manner. Is incorrect because this is one of the three requirements that make up the security kernel.

With mandatory access control (MAC), the authorization of a subject's access to an object is dependant upon labels, which indicate the subject's clearance. Identity-based access control is a type of discretionary access control. A role-based access control is a type of non-discretionary access control.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 2: Access control systems (page 33).

Section: Access Control
Explanation/Reference:
MAC provides high security by regulating access based on the clearance of individual users and sensitivity labels for each object. Clearance levels and sensitivity levels cannot be modified by individual users -- for example, user Joe (SECRET clearance) cannot reclassify the "Presidential Doughnut Recipe" from "SECRET" to "CONFIDENTIAL" so that his friend Jane (CONFIDENTIAL clearance) can read it. The administrator is ultimately responsible for configuring this protection in accordance with security policy and directives from the Data Owner.
DAC is incorrect. In DAC, the data owner is responsible for controlling access to the object.
Access control matrix is incorrect. The access control matrix is a way of thinking about the access control needed by a population of subjects to a population of objects. This access control can be applied using rules, ACL's, capability tables, etc.
TACACS is incorrect. TACACS is a tool for performing user authentication.
References:
CBK, p. 187, Domain 2: Access Control.
AIO3, Chapter 4, Access Control.