The Maximum Tolerable Downtime (MTD) is the maximum length of time a BUSINESS FUNCTION can endure without being restored, beyond which the BUSINESS is no longer viable
NIST SAYS: The ISCP Coordinator should analyze the supported mission/business processes and with the process owners, leadership and business managers determine the acceptable downtime if a given process or specific system data were disrupted or otherwise unavailable. Downtime can be identified in several ways.
Maximum Tolerable Downtime (MTD). The MTD represents the total amount of time the system owner/authorizing official is willing to accept for a mission/business process outage or disruption and includes all impact considerations. Determining MTD is important because it could leave contingency planners with imprecise direction on selection of an appropriate recovery method, and the depth of detail which will be required when developing recovery procedures, including their scope and content.
Other BCP and DRP terms you must be familiar with are: Recovery Time Objective (RTO). RTO defines the maximum amount of time that a system resource can remain unavailable before there is an unacceptable impact on other system resources, supported mission/business processes, and the MTD. Determining the information system resource RTO is important for selecting appropriate technologies that are best suited for meeting the MTD. When it is not feasible to immediately meet the RTO and the MTD is inflexible, a Plan of Action and Milestone should be initiated to document the situation and plan for its mitigation.
Recovery Point Objective (RPO). The RPO represents the point in time, prior to a disruption or system outage, to which mission/business process data can be recovered (given the most recent backup copy of the data) after an outage. Unlike RTO, RPO is not considered as part of MTD. Rather, it is a factor of how much data loss the mission/business process can tolerate during the recovery process. Because the RTO must ensure that the MTD is not exceeded, the RTO must normally be shorter than the MTD. For example, a system outage may prevent a particular process from being completed, and because it takes time to reprocess the data, that additional processing time must be added to the RTO to stay within the time limit established by the MTD.
References used for this question: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Page 276. and http://csrc.nist.gov/publications/nistpubs/800-34-rev1/sp800-34-rev1_errata-Nov11-2010.pdf

A block cipher breaks the plaintext into fixed-length blocks, commonly
64-bits, and encrypts the blocks into fixed-length blocks of
ciphertext. Another characteristic of the block cipher is that, if the
same key is used, a particular plaintext block will be transformed
into the same ciphertext block. Examples of block ciphers are DES,
Skipjack, IDEA, RC5 and AES. An example of a block cipher in a symmetric key cryptosystem is the Electronic Code Book (ECB) mode of operation. In the ECB mode, a plaintext block is transformed into a ciphertext block as shown in Figure. If the same key is used for
each transformation, then a Code Book can be compiled for each
plaintext block and corresponding ciphertext block.
Answer a is incorrect since it refers to a variable-length block of
plaintext being transformed into a fixed-length block of ciphertext.
Recall that this operation has some similarity to a hash function,
which takes a message of arbitrary length and converts it into a fixedlength message digest.
* Answers "An asymmetric key algorithm that operates on a variable-length block of plaintext and transforms it into a fixed-length block of ciphertext" and "An asymmetric key algorithm that operates on a fixed-length block of plaintext and transforms it into a fixed-length block of ciphertext"are incorrect because they involve asymmetric key algorithms, and the block cipher is used with symmetric key algorithms.
Exhibit:

image022
In other cryptographic modes of operation, such as Cipher Block
Chaining (CBC), the result of the encryption of the plaintext block, Pn, is fed into the encryption process of plaintext block Pn+1. Thus, the result of the encryption of one block affects the result of the encryption of the next block in the sequence.

This is the correct term, remember that Availability refers to get access to data when and where you need it. When we talk about destruction, we are saying the opposite, if your information is destroyed, you cant access to it neither when or where you want it. Delegation deals with permissions, distribution deals with deployment and documentation deals with information and how to's. The term we are looking here is definitively "destruction".

An information-system (IS) security mode of operation wherein each user with direct or indirect access to the system, its peripherals, remote terminals, or remote hosts, has all of the following: (a) a valid security clearance for all information within the system; (b) formal access approval and signed nondisclosure agreements for all the information stored and/or processed (including all compartments, sub compartments, and/or special access programs); and (c) a valid need-to-know for all information contained within the IS. When in the dedicated security mode, a system is specifically and exclusively dedicated to and controlled for the processing of one particular type or classification of information, either for full-time operation or for a specified period of time.

In cryptography, the one-time pad (OTP) is a type of encryption that is impossible to crack if used correctly. Each bit or character from the plaintext is encrypted by a modular addition with a bit or character from a secret random key (or pad) of the same length as the plaintext, resulting in a ciphertext. If the key is truly random, at least as long as the plaintext, never reused in whole or part, and kept secret, the ciphertext will be impossible to decrypt or break without knowing the key. It has also been proven that any cipher with the perfect secrecy property must use keys with effectively the same requirements as OTP keys. However, practical problems have prevented one-time pads from being widely used.
First described by Frank Miller in 1882, the one-time pad was re-invented in 1917 and patented a couple of years later. It is derived from the Vernam cipher, named after Gilbert
Vernam, one of its inventors. Vernam's system was a cipher that combined a message with a key read from a punched tape. In its original form, Vernam's system was vulnerable because the key tape was a loop, which was reused whenever the loop made a full cycle.
One-time use came a little later when Joseph Mauborgne recognized that if the key tape were totally random, cryptanalysis would be impossible.
The "pad" part of the name comes from early implementations where the key material was distributed as a pad of paper, so the top sheet could be easily torn off and destroyed after use. For easy concealment, the pad was sometimes reduced to such a small size that a powerful magnifying glass was required to use it. Photos show captured KGB pads that fit in the palm of one's hand, or in a walnut shell. To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose so they could be quickly burned.
The following are incorrect answers:
A running key cipher uses articles in the physical world rather than an electronic algorithm.
In classical cryptography, the running key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream.
Usually, the book to be used would be agreed ahead of time, while the passage to use would be chosen randomly for each message and secretly indicated somewhere in the message.
The Running Key cipher has the same internal workings as the Vigenere cipher. The difference lies in how the key is chosen; the Vigenere cipher uses a short key that repeats, whereas the running key cipher uses a long key such as an excerpt from a book. This means the key does not repeat, making cryptanalysis more difficult. The cipher can still be broken though, as there are statistical patterns in both the key and the plaintext which can be exploited.
Steganography is a method where the very existence of the message is concealed. It is the art and science of encoding hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message. it is sometimes referred to as Hiding in Plain Sight.
Cipher block chaining is a DES operating mode. IBM invented the cipher-block chaining
(CBC) mode of operation in 1976. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This way, each ciphertext block depends on all plaintext blocks processed up to that point. To make each message unique, an initialization vector must be used in the first block.
Reference(s) used for this question:
HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 8: Cryptography (page 555).
and
http://en.wikipedia.org/wiki/One-time_pad
http://en.wikipedia.org/wiki/Running_key_cipher
http://en.wikipedia.org/wiki/Cipher_block_chaining#Cipher-block_chaining_.28CBC.29