The reference monitor concept is an abstract machine that ensures that all subjects have the necessary access rights before accessing objects. Therefore, the kernel will mediates all accesses to objects by subjects and will do so by validating through the reference monitor concept.
The kernel does not decide whether or not the access will be granted, it will be the Reference Monitor which is a subset of the kernel that will say YES or NO.
All access requests will be intercepted by the Kernel, validated through the reference monitor, and then access will either be denied or granted according to the request and the subject privileges within the system.
1. The reference monitor must be small enough to be full tested and valided
2. The Kernel must MEDIATE all access request from subjects to objects
3. The processes implementing the reference monitor must be protected
4. The reference monitor must be tamperproof

To understand the whys in crime, many times it is necessary to understand the Motivations, Opportunities, and Means (MOM). Motivations are the who and why of a crime. Opportunities are the where and when of a crime, and Means pertains to the capabilities a criminal would need to be successful. Methods is not a component of MOM.

Section: Cryptography
Explanation/Reference:
When a concealment cipher is used, every X number of words within a text, is a part of the real message. The message is within another message.
A concealment cipher is a message within a message. If my other super-secret spy buddy and I decide our key value is every third word, then when I get a message from him, I will pick out every third word and write it down.
Suppose he sends me a message that reads, "The saying, 'The time is right' is not cow language, so is now a dead subject." Because my key is every third word, I come up with "The right cow is dead." This again means nothing to me, and I am now turning in my decoder ring.
Concealment ciphers include the plaintext within the ciphertext. It is up to the recipient to know which letters or symbols to exclude from the ciphertext in order to yield the plaintext. Here is an example of a concealment cipher:
i2l32i5321k34e1245ch456oc12ol234at567e
Remove all the numbers, and you'll have i like chocolate. How about this one?
Larry even appears very excited. No one worries.
The first letter from each word reveals the message leave now. Both are easy, indeed, but many people have crafted more ingenious ways of concealing the messages. By the way, this type of cipher doesn't even need ciphertext, such as that in the above examples.
Consider the invisible drying ink that kids use to send secret messages. In a more extreme example, a man named Histiaeus, during 5th century B.C., shaved the head of a trusted slave, then tattooed the message onto his bald head. When the slave's hair grew back, Histiaeus sent the slave to the message's intended recipient, Aristagoros, who shaved the slave's head and read the message instructing him to revolt.
The following answers are incorrect:
A transposition cipher uses permutations.
A substitution cipher replaces bits, characters, or blocks of characters with different bits, characters or blocks.
Steganography refers to hiding the very existence of the message.
Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 1).
and also see:
http://www.go4expert.com/forums/showthread.php?t=415

In 1973 Bell and LaPadula created the first mathematical model of a multi-level security system.
The following answers are incorrect:
Diffie and Hellman. This is incorrect because Diffie and Hellman was involved with cryptography.
Clark and Wilson. This is incorrect because Bell and LaPadula was the first model. The Clark- Wilson model came later, 1987.
Gasser and Lipner. This is incorrect, it is a distractor. Bell and LaPadula was the first model.