lecture2-1 part one about cryptography.ppt

Editor's Notes

• #3: The NIST Computer Security Handbook [NIST95] defines the term computer security as shown on this slide. This definition introduces three key objectives that are at the heart of computer security as we see on the next slide.
• #4: We now provide some examples of applications that illustrate the requirements just enumerated. • Confidentiality - Student grade information is an asset whose confidentiality is considered to be highly important by students. Grade information should only be available to students, their parents, and employees that require the information to do their job. Student enrollment information may have a moderate confidentiality rating. While still coveredby FERPA, this information is seen by more people on a daily basis, is less likely to be targeted than grade information, and results in less damage if disclosed. Directory information, such as lists of students or faculty or departmental lists, may be assigned a low confidentiality rating or indeed no rating. This information is typically freely available to the public and published on a school's Web site. • Integrity – Consider a hospital patient's allergy information stored in a database. The doctor should be able to trust that the information is correct and current. Now suppose that an employee (e.g., a nurse) who is authorized to view and update this information deliberately falsifies the data to cause harm to the hospital. The database needs to be restored to a trusted basis quickly, and it should be possible to trace the error back to the person responsible. Patient allergy information is an example of an asset with a high requirement for integrity. Inaccurate information could result in serious harm or death to a patient and expose the hospital to massive liability. • Availability - The more critical a component or service, the higher is the level of availability required. Consider a system that provides authentication services for critical systems, applications, and devices. An interruption of service results in the inability for customers to access computing resources and staff to access the resources they need to perform critical tasks. The loss of the service translates into a large financial loss in lost employee productivity and potential customer loss.
• #5: The OSI security architecture focuses on security attacks, mechanisms, and services. These can be defined briefly as follows: • Security attack: Any action that compromises the security of information owned by an organization. • Security mechanism: A process (or a device incorporating such a process) that is designed to detect, prevent, or recover from a security attack. • Security service: A processing or communication service that enhances the security of the data processing systems and the information transfers of an organization. The services are intended to counter security attacks, and they make use of one or more security mechanisms to provide the service. In the literature, the terms threat and attack are commonly used to mean more or less the same thing. Table 1.1 provides definitions taken from RFC 2828, Internet Security Glossary. Threat - A potential for violation of security, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm. That is, a threat is a possible danger that might exploit a vulnerability. Attack - An assault on system security that derives from an intelligent threat; that is, an intelligent act that is a deliberate attempt (especially in the sense of a method or technique) to evade security services and violate the security policy of a system.
• #6: A useful means of classifying security attacks, used both in X.800 and RFC 2828, is in terms of passive attacks and active attacks. A passive attack attempts to learn or make use of information from the system but does not affect system resources. Passive attacks are in the nature of eavesdropping on, or monitoring of, transmissions. The goal of the opponent is to obtain information that is being transmitted. Two types of passive attacks are: + release of message contents - as shown above in Stallings Figure 1.2a here + traffic analysis - monitor traffic flow to determine location and identity of communicating hosts and could observe the frequency and length of messages being exchanged These attacks are difficult to detect because they do not involve any alteration of the data.
• #7: Active attacks involve some modification of the data stream or the creation of a false stream and can be subdivided into four categories: masquerade, replay, modification of messages, and denial of service: masquerade of one entity as some other replay previous messages (as shown above in Stallings Figure 1.3b) modify/alter (part of) messages in transit to produce an unauthorized effect denial of service - prevents or inhibits the normal use or management of communications facilities Active attacks present the opposite characteristics of passive attacks. Whereas passive attacks are difficult to detect, measures are available to prevent their success. On the other hand, it is quite difficult to prevent active attacks absolutely, because of the wide variety of potential physical, software, and network vulnerabilities. Instead, the goal is to detect active attacks and to recover from any disruption or delays caused by them.
• #8: To assess effectively the security needs of an organization and to evaluate and choose various security products and policies, the manager responsible for security needs some systematic way of defining the requirements for security and characterizing the approaches to satisfying those requirements. This is difficult enough in a centralized data processing environment; with the use of local and wide area networks the problems are compounded. ITU-T Recommendation X.800, Security Architecture for OSI, defines such a systematic approach. The OSI security architecture is useful to managers as a way of organizing the task of providing security.
• #9: authentication is concerned with assuring that a communication is authentic. Two specific authentication services are defined in X.800: Peer entity authentication: provides corroboration of the identity of a peer entity in an association; and Data origin authentication: provides corroboration of the source of a data unit. access control is the ability to limit and control the access to host systems and applications via communications links. confidentiality is the protection of transmitted data from passive attacks, and the protection of traffic flow from analysis. integrity assures that messages are received as sent, with no duplication, insertion, modification, reordering, replay, or loss. availability is the property of a system / resource being accessible and usable upon demand by an authorized system entity, according to performance specifications for the system.
• #10: specific security mechanisms Encipherment: the use of mathematical algorithms to transform data into a form that is not readable (Encryption). Digital signatures: data that is appended to the message that allows the recipient to prove source and the integrity data. Access controls : A variety of mechanisms that enforce access right to resources. Data integrity: : A variety of mechanisms that assure the integrity of the message. Authentication exchange : A mechanism intended to ensure the identity of entity. Notarization : a use of trusted 3rd party to assure certain properties of data exchange. ----------------------------------------------------------------------------------- pervasive security mechanisms: trusted functionality: That which is perceived to be correct with respect to some criteria, for example, as established by a security policy security labels: The marking bound to a resource (which may be a data unit) that names or designates the security attributes of that resource event detection: detection of security relevant events. security audit trails: Data collected and potentially used to facilitate a security audit . security recovery : deal with requests from mechanisms such as event handing
• #13: In considering the place of encryption, its useful to use the following two models from Stallings section 1.6. The first, illustrated in Figure 1.4, models information being transferred from one party to another over an insecure communications channel, in the presence of possible opponents. The two parties, who are the principals in this transaction, must cooperate for the exchange to take place. They can use an appropriate security transform (encryption algorithm), with suitable keys, possibly negotiated using the presence of a trusted third party
• #15: The second, illustrated in Figure 1.5, model is concerned with controlled access to information or resources on a computer system, in the presence of possible opponents. Here appropriate controls are needed on the access to and within the system, to provide suitable security. The security mechanisms needed to cope with unwanted access fall into two broad categories (as shown in this figure). The first category might be termed a gatekeeper function. It includes password-based login procedures that are designed to deny access to all but authorized users and screening logic that is designed to detect and reject worms, viruses, and other similar attacks. Once either an unwanted user or unwanted software gains access, the second line of defense consists of a variety of internal controls that monitor activity and analyze stored information in an attempt to detect the presence of unwanted intruders. These issues are explored in Part Four.