Security model for a computer is like an onion. Security levels surrounding the subject to be protected. Each layer isolates the subject and makes it more difficult to access otherwise than as it was planned.
1) Physical security is outside the security model and is, in general, locking computer equipment in an office or another site. Physical security deserve special consideration. The biggest problem is the backups for data backup and storage software supports saving and safety. In these situations, local networks are helpful: if all files residing on one server frequently changed, the same people (safe and reliable), which launches rescue mainframes can do the same and
the server. Computer, as any piece costly and should be protected. the danger of theft. Keeping out of public areas is one of the best forms of protection. Simple locking moves hidden equipment and will prevent theft. In a system in which processing is distributed, first physical security measures to be considered is to prevent access to equipment. To defeat any security measures must have physical access to equipment. This is common to all computing systems, distributed or not.
2) Logical Security consists of those methods that provide access control services Get the resources and systems. It has, in turn, more levels, divided into two main categories: security levels of access (SA) and security levels of service (SS).
3)• Secure Access (SA) includes:
Ø access system (AS), which is responsible for determining if and when the network is accessible to users. They may be also responsible for the decoupling of stations, as records management and access. AS runs also forced disconnection dictated by supervisor. AS may, for example, to prevent connecting outside office hours and to stop all sessions, after a certain time;
Ø account access (CA), which checks if the user is connected with a specific name and password there is a valid user profile;
Ø access rights (DA), which determines what the user has login privileges (for example, may account sessions totalling 4 hours per day or the account can use only station 27).
• Security Service (SS), which is under SA control access to system services such as waiting threads, I / O server’s disk management. From this level are:
Ø Control Service (CS), which is responsible for warning and reporting functions of state services, he also activate and deactivate various services;
Ø rights to services (DS), which determine exactly how use a given service account, for example, an account may only have the right to add files to a printer’s spooler, but has full rights to add and delete files to another printer.
Once the connection, validate and define the SA account. Operations to be performed are controlled by the SS, which prevents applications that are not specified in the user profile.Access a perfect security system must be made by these security levels, from top to bottom.Any system that lets you avoid one or more levels of security model involves the risk of being unsafe.
