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

Availability assures that a system's authorized users have timely and uninterrupted access to the information in the system. The additional access control objectives are reliability and utility. These and other related objectives flow from the organizational security policy. This policy is a high-level statement of management intent regarding the control of access to information and the personnel who are authorized to receive that information. Three things that must be considered for the planning and implementation of access control mechanisms are the threats to the system, the system's vulnerability to these threats, and the risk that the threat may materialize
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the
Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 32

A TCP Segment is the group of TCP data tramsmitted at the Transport
Layer. TCP is segment based network technology.
The message is sent to the transport layer, where TCP does its magic on the data. The bundle of data is now a segment. If the message is being transmitted over TCP, it is referred to as a "segment."
Protocol Data Unit Layers
The following answers are incorrect:
TCP datagram. Is incorrect because a TCP datagram is only a distractor, IP datagram would be the proper terminology. TCP is segment based network technology.
TCP frame. Is incorrect because a TCP frame is only a distractor, Ethernet Frame would be the proper terminology. TCP is segment based network technology.
TCP packet. Is incorrect because a TCP packet is only a distractor. TCP is segment based network technology.
References(s) used for this question:
Wikipedia http://en.wikipedia.org/wiki/Transport_layer
Wikipedia
http://en.wikipedia.org/wiki/Transmission_Control_Protocol#TCP_segment_structure
TCP/IP Illustrated, Volume 1: The Protocols, Addison-Wesley, 1994, ISBN 0-201-63346-9.
http://www.infocellar.com/networks/osi-model.htm

Explanation/Reference:
Explanation:
Although society has evolved to be extremely dependent upon technology in the workplace, people are still the key ingredient to a successful company. But in security circles, people are often the weakest link.
Either accidentally through mistakes or lack of training, or intentionally through fraud and malicious intent, personnel causes more serious and hard-to-detect security issues than hacker attacks, outside espionage, or equipment failure. Although the future actions of individuals cannot be predicted, it is possible to minimize the risks by implementing preventive measures. These include hiring the most qualified individuals, performing background checks, using detailed job descriptions, providing necessary training, enforcing strict access controls, and terminating individuals in a way that protects all parties involved.
Incorrect Answers:
B: Software generally does what it is configured to do. It is not considered the weakest link in a security system.
C: It is easy to configure secure communications where they are required. Communications are not considered the weakest link in a security system.
D: Hardware generally does what it is configured to do. It is not considered the weakest link in a security system.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, p. 126

SSL use public-key cryptography to secure session key, while the session key (secret key) is used to secure the whole session taking place between both parties communicating with each other.
The SSL protocol was originally developed by Netscape. Version 1.0 was never publicly released; version 2.0 was released in February 1995 but "contained a number of security flaws which ultimately led to the design of SSL version 3.0." SSL version 3.0, released in
1996, was a complete redesign of the protocol produced by Paul Kocher working with
Netscape engineers Phil Karlton and Alan Freier.
All of the other answers are incorrect