Digital certificate helps others verify that the public keys presented by users are genuine and valid. It is a form of Electronic credential proving that the person the certificate was issued to is who they claim to be.
The certificate is used to identify the certificate holder when conducting electronic transactions. It is issued by a certification authority (CA). It contains the name of an organization or individual, the business address, a serial number, expiration dates, a copy of the certificate
holder's public key (used for encrypting messages), and the digital signature of the
certificate-issuing authority so that a recipient can verify that the certificate is real. Some
digital certificates conform to a standard, X.509. Digital certificates can be kept in registries
so that authenticating users can look up other users' public keys.
Digital certificates are key to the PKI process. The digital certificate serves two roles. First,
it ensures the integrity of the public key and makes sure that the key remains unchanged
and in a valid state. Second, it validates that the public key is tied to the stated owner and
that all associated information is true and correct. The information needed to accomplish
these goals is added into the digital certificate.
A Certificate Authority (CA) is an entity trusted by one or more users as an authority in a
network that issues, revokes, and manages digital certificates.
A Registration Authority (RA) performs certificate registration services on behalf of a CA.
The RA, a single purpose server, is responsible for the accuracy of the information
contained in a certificate request. The RA is also expected to perform user validation
before issuing a certificate request.
A Digital Certificate is not like same as a digital signature, they are two different things, a
digital Signature is created by using your Private key to encrypt a message digest and a
Digital Certificate is issued by a trusted third party who vouch for your identity.
There are many other third parties which are providing Digital Certifictes and not just
Verisign, RSA.
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 14894-14903). Auerbach Publications. Kindle
Edition.
Gregg, Michael; Haines, Billy (2012-02-16). CASP: CompTIA Advanced Security
Practitioner Study Guide Authorized Courseware: Exam CAS-001 (p. 24). Wiley. Kindle
Edition.
Please refer to http://en.wikipedia.org/wiki/Digital_certificate
What is Digital certificate:
http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci211947,00.html
another deifination on http://www.webopedia.com/TERM/D/digital_certificate.html

Explanation/Reference:
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, page 197.
Also: THE source for all TCSEC "level" questions: http://csrc.nist.gov/publications/secpubs/rainbow/ std001.txt

"It [ACL] specifies a list of users [subjects] who are allowed access to each object" CBK, p. 188
A capability table is incorrect. "Capability tables are used to track, manage and apply controls based on the object and rights, or capabilities of a subject. For example, a table identifies the object, specifies access rights allowed for a subject, and permits access based on the user's posession of a capability (or ticket) for the object." CBK, pp. 191-192. The distinction that makes this an incorrect choice is that access is based on posession of a capability by the subject.
To put it another way, as noted in AIO3 on p. 169, "A capabiltiy table is different from an ACL because the subject is bound to the capability table, whereas the object is bound to the ACL."
An access control matrix is incorrect. The access control matrix is a way of describing the rules for an access control strategy. The matrix lists the users, groups and roles down the left side and the resources and functions across the top. The cells of the matrix can either indicate that access is allowed or indicate the type of access. CBK pp 317 - 318.
AIO3, p. 169 describes it as a table if subjects and objects specifying the access rights a certain subject possesses pertaining to specific objects.
In either case, the matrix is a way of analyzing 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.
A role-based matrix is incorrect. Again, a matrix of roles vs objects could be used as a tool for thinking about the access control to be applied to a set of objects. The results of the analysis could then be implemented using RBAC.
References:
CBK, Domain 2: Access Control.
AIO3, Chapter 4: Access Control

Explanation/Reference:
The SHA-1 is a hashing algorithm producing a 160-bit hash result from any data. It does not perform encryption.
In cryptography, SHA-1 is a cryptographic hash function designed by the United States National Security Agency and published by the United States NIST as a U.S. Federal Information Processing Standard.
SHA stands for "secure hash algorithm". The four SHA algorithms are structured differently and are distinguished as SHA-0, SHA-1, SHA-2, and SHA-3. SHA-1 is very similar to SHA-0, but corrects an error in the original SHA hash specification that led to significant weaknesses. The SHA-0 algorithm was not adopted by many applications. SHA-2 on the other hand significantly differs from the SHA-1 hash function.
SHA-1 is the most widely used of the existing SHA hash functions, and is employed in several widely used applications and protocols.
In 2005, cryptanalysts found attacks on SHA-1 suggesting that the algorithm might not be secure enough for ongoing use. NIST required many applications in federal agencies to move to SHA-2 after 2010 because of the weakness. Although no successful attacks have yet been reported on SHA-2, they are algorithmically similar to SHA-1.
In 2012, following a long-running competition, NIST selected an additional algorithm, Keccak, for standardization as SHA-3
NOTE:
A Cryptographic Hash Function is not the same as an Encryption Algorithm even thou both are Algorithms.
An algorithm is defined as a step-by-step procedure for calculations. Hashing Algorithm do not encrypt the data. People sometimes will say they encrypted a password with SHA-1 but really they simply created a Message Digest of the password using SHA-1, putting the input through a series of steps to come out with the message digest or hash value.
A cryptographic hash function is a hash function; that is, an algorithm that takes an arbitrary block of data and returns a fixed-size bit string, the (cryptographic) hash value, such that any (accidental or intentional) change to the data will (with very high probability) change the hash value. The data to be encoded are often called the "message," and the hash value is sometimes called the message digest or simply digest.
Encryption Algorithms are reversible but Hashing Algorithms are not meant to be reversible if the input is large enough.
The following are incorrect answers:
The Skipjack algorithm is a Type II block cipher with a block size of 64 bits and a key size of 80 bits that was developed by NSA and formerly classified at the U.S. Department of Defense "Secret" level.
Twofish is a freely available 128-bit block cipher designed by Counterpane Systems (Bruce Schneier et al.).
DEA is a symmetric block cipher, defined as part of the U.S. Government's Data Encryption Standard (DES). DEA uses a 64-bit key, of which 56 bits are independently chosen and 8 are parity bits, and maps a
64-bit block into another 64-bit block.
Reference(s) used for this question:
http://en.wikipedia.org/wiki/SHA-1
and
SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.
and
Counterpane Labs, at http://www.counterpane.com/twofish.html.

Means, motive, and opportunity are the three items needed to commit a crime.