- (Topic 5)
Which of the following is NOT a known type of Message Authentication Code (MAC)?
Correct Answer:
C
There is no such thing as a Signature-Based MAC. Being the wrong choice in the list, it is the best answer to this question.
WHAT IS A Message Authentication Code (MAC)?
In Cryptography, a MAC (Message Authentication Code) also known as a cryptographic checksum, is a small block of data that is generated using a secret key and then appended to the message. When the message is received, the recipient can generate their own MAC using the secret key, and thereby know that the message has not changed either accidentally or intentionally in transit. Of course, this assurance is only as strong as the trust that the two parties have that no one else has access to the secret key.
A MAC is a small representation of a message and has the following characteristics:
A MAC is much smaller than the message generating it.
Given a MAC, it is impractical to compute the message that generated it.
Given a MAC and the message that generated it, it is impractical to find another message generating the same MAC.
See the graphic below from Wikipedia showing the creation of a MAC value:
C:\Users\MCS\Desktop\1.jpg
Message Authentication Code MAC HMAC
In the example above, the sender of a message runs it through a MAC algorithm to produce a MAC data tag. The message and the MAC tag are then sent to the receiver. The receiver in turn runs the message portion of the transmission through the same MAC algorithm using the same key, producing a second MAC data tag. The receiver then compares the first MAC tag received in the transmission to the second generated MAC tag. If they are identical, the receiver can safely assume that the integrity of the message was not compromised, and the message was not altered or tampered with during transmission.
However, to allow the receiver to be able to detect replay attacks, the message itself must contain data that assures that this same message can only be sent once (e.g. time stamp, sequence number or use of a one-time MAC). Otherwise an attacker could — without even understanding its content — record this message and play it back at a later time, producing the same result as the original sender.
NOTE: There are many ways of producing a MAC value. Below you have a short list of some implementation.
The following were incorrect answers for this question:
They were all incorrect answers because they are all real type of MAC implementation.
In the case of DES-CBC, a MAC is generated using the DES algorithm in CBC mode, and the secret DES key is shared by the sender and the receiver. The MAC is actually just the last block of ciphertext generated by the algorithm. This block of data (64 bits) is attached to the unencrypted message and transmitted to the far end. All previous blocks of
encrypted data are discarded to prevent any attack on the MAC itself. The receiver can just generate his own MAC using the secret DES key he shares to ensure message integrity and authentication. He knows that the message has not changed because the chaining function of CBC would significantly alter the last block of data if any bit had changed anywhere in the message. He knows the source of the message (authentication) because only one other person holds the secret key.
A Keyed-hash message authentication code (HMAC) is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret cryptographic key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authentication of a message. Any cryptographic hash function, such as MD5, SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key.
A message authentication code based on universal hashing, or UMAC, is a type of message authentication code (MAC) calculated choosing a hash function from a class of hash functions according to some secret (random) process and applying it to the message. The resulting digest or fingerprint is then encrypted to hide the identity of the hash function used. As with any MAC, it may be used to simultaneously verify both the data integrity and the authenticity of a message. UMAC is specified in RFC 4418, it has provable cryptographic strength and is usually a lot less computationally intensive than other MACs.
What is the MicMac (confusion) with MIC and MAC?
The term message integrity code (MIC) is frequently substituted for the term MAC, especially in communications, where the acronym MAC traditionally stands for Media Access Control when referring to Networking. However, some authors use MIC as a distinctly different term from a MAC; in their usage of the term the MIC operation does not use secret keys. This lack of security means that any MIC intended for use gauging message integrity should be encrypted or otherwise be protected against tampering. MIC algorithms are created such that a given message will always produce the same MIC assuming the same algorithm is used to generate both. Conversely, MAC algorithms are designed to produce matching MACs only if the same message, secret key and initialization vector are input to the same algorithm. MICs do not use secret keys and, when taken on their own, are therefore a much less reliable gauge of message integrity than MACs. Because MACs use secret keys, they do not necessarily need to be encrypted to provide the same level of assurance.
Reference(s) used for this question:
Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 15799-15815). Auerbach Publications. Kindle Edition.
and http://en.wikipedia.org/wiki/Message_authentication_code and
http://tools.ietf.org/html/rfc4418
- (Topic 6)
Upon which of the following ISO/OSI layers does network address translation operate?
Correct Answer:
D
Network address translation (NAT) is concerned with IP address translation between two networks and operates at the network layer (layer 3).
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw- Hill/Osborne, 2002, Chapter 3: Telecommunications and Network Security (page 440).
- (Topic 2)
Who can best decide what are the adequate technical security controls in a computer- based application system in regards to the protection of the data being used, the criticality of the data, and it's sensitivity level ?
Correct Answer:
B
The data or information owner also referred to as "Data Owner" would be the best person. That is the individual or officer who is ultimately responsible for the protection of the information and can therefore decide what are the adequate security controls according to the data sensitivity and data criticality. The auditor would be the best person to determine the adequacy of controls and whether or not they are working as expected by the owner.
The function of the auditor is to come around periodically and make sure you are doing what you are supposed to be doing. They ensure the correct controls are in place and are being maintained securely. The goal of the auditor is to make sure the organization complies with its own policies and the applicable laws and regulations.
Organizations can have internal auditors and/ or external auditors. The external auditors commonly work on behalf of a regulatory body to make sure compliance is being met. For example CobiT, which is a model that most information security auditors follow when evaluating a security program. While many security professionals fear and dread auditors, they can be valuable tools in ensuring the overall security of the organization. Their goal is to find the things you have missed and help you understand how to fix the problem.
The Official ISC2 Guide (OIG) says:
IT auditors determine whether users, owners, custodians, systems, and networks are in compliance with the security policies, procedures, standards, baselines, designs, architectures, management direction, and other requirements placed on systems. The auditors provide independent assurance to the management on the appropriateness of the security controls. The auditor examines the information systems and determines whether they are designed, configured, implemented, operated, and managed in a way ensuring that the organizational objectives are being achieved. The auditors provide top company management with an independent view of the controls and their effectiveness.
Example:
Bob is the head of payroll. He is therefore the individual with primary responsibility over the payroll database, and is therefore the information/data owner of the payroll database. In Bob's department, he has Sally and Richard working for him. Sally is responsible for making changes to the payroll database, for example if someone is hired or gets a raise. Richard is only responsible for printing paychecks. Given those roles, Sally requires both read and write access to the payroll database, but Richard requires only read access to it. Bob communicates these requirements to the system administrators (the "information/data custodians") and they set the file permissions for Sally's and Richard's user accounts so that Sally has read/write access, while Richard has only read access.
So in short Bob will determine what controls are required, what is the sensitivily and criticality of the Data. Bob will communicate this to the custodians who will implement the requirements on the systems/DB. The auditor would assess if the controls are in fact providing the level of security the Data Owner expects within the systems/DB. The auditor does not determine the sensitivity of the data or the crititicality of the data.
The other answers are not correct because:
A "system auditor" is never responsible for anything but auditing... not actually making control decisions but the auditor would be the best person to determine the adequacy of controls and then make recommendations.
A "system manager" is really just another name for a system administrator, which is actually an information custodian as explained above.
A "Data or information user" is responsible for implementing security controls on a day-to- day basis as they utilize the information, but not for determining what the controls should be or if they are adequate.
References:
Official ISC2 Guide to the CISSP CBK, Third Edition , Page 477
Schneiter, Andrew (2013-04-15). Official (ISC)2 Guide to the CISSP CBK, Third Edition : Information Security Governance and Risk Management ((ISC)2 Press) (Kindle Locations 294-298). Auerbach Publications. Kindle Edition.
Harris, Shon (2012-10-25). CISSP All-in-One Exam Guide, 6th Edition (Kindle Locations 3108-3114).
Information Security Glossary
Responsibility for use of information resources
- (Topic 3)
As a result of a risk assessment, your security manager has determined that your organization needs to implement an intrusion detection system that can detect unknown attacks and can watch for unusual traffic behavior, such as a new service appearing on the network. What type of intrusion detection system would you select?
Correct Answer:
D
Traffic anomaly-based is the correct choice. An anomaly based IDS can detect unknown attacks. A traffic anomaly based IDS identifies any unacceptable deviation from expected behavior based on network traffic.
Protocol anomaly based is not the best choice as while a protocol anomaly based IDS can identify unknown attacks, this type of system is more suited to identifying deviations from established protocol standards such as HTTP. This type of IDS faces problems in analyzing complex or custom protocols.
Pattern matching is not the best choice as a pattern matching IDS cannot identify unknown attacks. This type of system can only compare packets against signatures of known attacks.
Stateful matching is not the best choice as a statful matching IDS cannot identify unknown attacks. This type of system works by scanning traffic streams for patterns or signatures of attacks.
Reference:
Official guide to the CISSP CBK. pages 198 to 201
- (Topic 4)
How often should tests and disaster recovery drills be performed?
Correct Answer:
C
Tests and disaster recovery drills should be performed at least once a year. The company should have no confidence in an untested plan. Since systems and processes can change, frequent testing will aid in ensuring a plan will succeed.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw- Hill/Osborne, 2002, chapter 9: Disaster Recovery and Business continuity (page 621).
