A blind signature algorithm for the message M uses a blinding factor, f; a modulus m; the private key, s, of the signer and the public key, q, of the signer. The sender, who generates f and knows q, presents the message to the signer in the form: Mf q (mod m) Thus, the message is not in a form readable by the signer since the signer does not know f. The signer signs Mf q (mod m) with his/her private key, returning (Mf q)s (mod m) This factor can be reduced to fMs (mod m) since s and q are inverses of each other. The sender then divides fMs (mod m) by the blinding factor, f, to obtain Ms (mod m) Ms (mod m) is, therefore, the message, M, signed with the private key, s, of the signer.
Answer Zero knowledge proof refers to a zero knowledge proof. In general, a zero knowledge proof involves a person, A, trying to prove that he/she knows something, S, to another person, B, without revealing S or anything about S.Answers Masked signature and Encrypted signature are distracters.

Delegation is the forwarding of a request by one object to another object.
Answer Polyresponse is a distracter.
Polyinstantiationis the development of a detailed version
of an object from another object. The new object uses values that are
different from those in the original object.

A trojan horse is any code that appears to have some useful purpose but also contains code that has a malicious or harmful purpose imbedded in it. A Trojan often also includes a trapdoor as a means to gain access to a computer system bypassing security controls.
Wikipedia defines it as:
A Trojan horse, or Trojan, in computing is a non-self-replicating type of malware program containing malicious code that, when executed, carries out actions determined by the nature of the Trojan, typically causing loss or theft of data, and possible system harm. The term is derived from the story of the wooden horse used to trick defenders of Troy into taking concealed warriors into their city in ancient Greece, because computer Trojans often employ a form of social engineering, presenting themselves as routine, useful, or interesting in order to persuade victims to install them on their computers.
The following answers are incorrect:
virus. Is incorrect because a Virus is a malicious program and is does not appear to be harmless, it's sole purpose is malicious intent often doing damage to a system. A computer virus is a type of malware that, when executed, replicates by inserting copies of itself
(possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be "infected".
worm. Is incorrect because a Worm is similiar to a Virus but does not require user intervention to execute. Rather than doing damage to the system, worms tend to self- propagate and devour the resources of a system. A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers.
Often, it uses a computer network to spread itself, relying on security failures on the target computer to access it. Unlike a computer virus, it does not need to attach itself to an existing program. Worms almost always cause at least some harm to the network, even if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.
trapdoor. Is incorrect because a trapdoor is a means to bypass security by hiding an entry point into a system. Trojan Horses often have a trapdoor imbedded in them.
References:
http://en.wikipedia.org/wiki/Trojan_horse_%28computing%29
and
http://en.wikipedia.org/wiki/Computer_virus
and
http://en.wikipedia.org/wiki/Computer_worm
and
http://en.wikipedia.org/wiki/Backdoor_%28computing%29

Explanation/Reference:
Explanation:
The 'value' of an information asset should be used to classify the information asset.
The rationale behind assigning values to different types of data is that it enables a company to gauge the amount of funds and resources that should go toward protecting each type of data, because not all data has the same value to a company. After identifying all important information, it should be properly classified. A company has a lot of information that is created and maintained. The reason to classify data is to organize it according to its sensitivity to loss, disclosure, or unavailability. Once data is segmented according to its sensitivity level, the company can decide what security controls are necessary to protect different types of data. This ensures that information assets receive the appropriate level of protection, and classifications indicate the priority of that security protection.
Incorrect Answers:
B: The age of an information asset is not the best criterion to consider in determining the classification of the information asset.
C: The useful life of an information asset is not the best criterion to consider in determining the classification of the information asset.
D: The personal association of an information asset is not the best criterion to consider in determining the classification of the information asset.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, p. 109