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It's all that matters. Before a company / organization benefit from cloud computing, there are several aspects relating to Security and Privacy below that must be considered:

1. Risk Management and Compliance - organizations are starting to adopt the cloud still be responsible for aspects of security management, risk, and compliance with the rules applicable in the related industry. Risk and compliance management requires a strong internal team and the transparency of the process of cloud service providers.

Recommendation: cloud service providers have to use some or best practice frameworks such as MOF, or ITIL, and have certifications such as ISO / IEC 27001:2005, and publish the audit report to the SAS 70 Type II. In addition, according to provisions of a state, may also have to adhere to the PCI or FISMA.

2. Access and Identity Management - Identity can be obtained through some cloud service providers, and must be interoperable between different organizations, different cloud providers, and based on strong process.

Recommendation: Authentication is recommended to use several factors at once, such as biometrics, one time password tokens (such as token BCA), ID card with a chip, and a password.

3. Integrity of Service - cloud-based services must be built with a foundation of strong security, and operational processes must also be integrated with security management in the organization. The cloud service provider must follow the process that can be proven, well-defined, and clearly in integrating security and privacy in services ranging from the earliest point, at any point in the cycle, until the final. Besides security management and auditing must be aligned between cloud providers and customers.

Recommendation: Use such certification EAL4 + (for security evaluation), SDL (for application development), ISO / IEC 18 044 (for incident response)

4. Integrity Client - cloud services that are used on the client side should pay attention to aspects of security, compliance, and integrity on the client side. Integrity client can be improved by using a combination of best practices.

Recommendation: Strengthen the desktop system, make sure the health of desktop systems, apply the appropriate IT policy, identity federation, Network Access Protection and so on.

5. Information Protection - Services cloud requires a reliable process to protect the information before, during, and after the transaction. Take advantage of data classification to improve the control of the data is ready to be released into the clouds.
Recommendation: Use encryption technology and information rights management (IRM) prior to data released to the cloud.

Tips

If an interested company to implement cloud services, here are some tips:
Start with small things first, such as utilizing cloud services as below: Email, Calendars, Contact, Messenger, Storage, Document / Productivity, Photo, Group, News / Sport / Wheather, Synchronization Devices (live mesh), Family Safety, Mobile, Map
Map business requirements to a cloud service, do not do the opposite.
Not necessarily cheaper cloud services, calculate the overall cost if the system is used in full. Compare with the local system (on premise), and also studied the possibility of combining the cloud service with local system
Make the process of socialization and learning about cloud services to all employees in the company
Study the possibility of technical issues such as interoperability, architecture, and integration. Make sure that the format of files created through the cloud services are also exactly the same as a local application on the client side

"Cloud Computing" can be simply defined is "information technology services that can be used or accessed by customers through the Internet or bias as well". The words "Cloud" itself refers to the symbol of a cloud in the IT world is used to describe the Internet (Internet cloud). However not all existing services on the Internet can be categorized as Cloud Computing, there are at least several requirements that must be met:

1. Service is "On Demand", users can subscribe to just that he needs it, and pay only for what they use it. Suppose an Internet service provider providing a 5 different options or packages internet and the user simply takes a package of internet, the user only pays any packets captured.

2. Service is elastic / scalable, where users can add or reduce the type and capacity of services they want at any time and the system is always able to accommodate those changes. Suppose the user's Internet subscription in the bandwitchnya 512Kb / s and want to add speed to 512Kb / s then the user asks to call customer service and customer service additions bandwitch respond by changing bandwitc to 1Mb / s.

3. Services are fully managed by the provider / provider, the user is only required by the personal computer / laptop plus an Internet connection.

In terms of individual types of services, Cloud Computing, divided into 3 types of services, namely: Software as a Service (SaaS), Platform as a Service (PaaS) and Infrastructure as a Service (IaaS).

· Software as a Service SaaS is the Cloud Computing services are the most popular first. Software as a Service is a further evolution of the concept of ASP (Application Service Provider). As the name implies, SaaS makes it easy for users to be able to utilize the software with a subscription. So it does not need to spend a good investment for in-house development or purchase of a license. By subscription via the web, users can directly use the various features provided by the service provider. It's just that the concept of SaaS, the customer does not have complete control over their lease applications. Only the application features that have been provided by the providers that can be rented by the customer. And since SaaS application architecture is multi tenant, forcing providers to only provide the features of a general nature, not specific to the needs of specific users. However, customization does not necessarily prohibited, even if only for a limited scale and function. But with the development of markets and advances in programming technology, the limitations must be reduced in a time not too long. For an example of SaaS services, of course we must mention an online CRM service Salesforce.com--a dikomandai Marc Benioff and has become an icon of this SaaS. Additionally Zoho.com, with a very affordable price, providing SaaS services are quite diverse, ranging from services like Google Docs word processor, project management, to online invoicing. Online accounting service is also available, as given by Xero.com and much more. IBM with its Lotuslive.com can serve as an example for SaaS services in the areas of collaboration / unified communication. Unfortunately for the domestic market itself, as I have to say in a previous article, are still very few are willing to invest to provide this service SaaS.

· Platform as a Service (PaaS) that is As the name suggests, PaaS is a service that provides ready-made modules that can be used to develop an application, which of course can only run on that platform. As well as service SaaS, PaaS users do not have control over basic computing resources such as memory, storage, processing power, etc., which are all governed by the service provider. Pioneers in this area is Google AppEngine, which provides various tools for developing applications on the platform of Google, using the programming language Python and Django. Then Salesforce also provides services through Force.com PaaS, providing modules to develop applications on a platform that uses Salesforce Apex language. And maybe that rarely do we know that Facebook can also be considered to provide a service PaaS, which allows us to create applications on top.

· Infrastructure as a Service (IaaS) IaaS is located one level lower than PaaS. It is a service that "rent" the basic information technology resources, which includes media storage, processing power, memory, operating system, network capacity and others, which can be used by the tenant to run the applications it has. Business model similar to the data center providers that rent out space for co-location, but this is more to the micro level. Tenants do not need to know, with what machine and how IaaS providers to provide services. Importantly, their request on the basis of information technology resources can be met. The fundamental difference with current data center services is IaaS enables customers to do the addition / reduction of capacity in a flexible and automated. One of the pioneers in providing IaaS is that Amazon.com launched Amazon EC2 (Elastic Computing Cloud). Amazon's EC2 service provides a wide selection of rental starts the CPU, storage media, equipped with the operating system and application development platform that can be rented hourly calculations. For in their own country, the plan there are some providers that will provide a similar service starting this summer. whereas for the range of services, divided into 3 namely Public Cloud, Private Cloud and Hybrid Cloud.

1. Public Cloud's as simple as its name, type of cloud is dedicated to the public by the service provider. The services I mentioned earlier can be used as examples of public cloud in

2. Where a Private Cloud infrastructure cloud services, operated only for a particular organization. Infrastructure cloud could have been managed by the organization or by third parties. The location can be on-site or off-site. Usually organizations with large scale are able to have / manage this private cloud.

3. Hybrid Cloud For this type, the available cloud infrastructure is composed of two or more cloud infrastructure (private, community, or public). Where the entity even though they still stand on their own, but connected by a technology / mechanism that enables data and application portability between the cloud it. For example, load balancing mechanism that antarcloud, so that the allocation of resources can be maintained at optimal levels. So little explanation of cloud models are abstracted from NIST. However, as recognized by this institution, and limits the definition of Cloud Computing itself is still looking for forms and standards. Where will pasarlah that will determine which model will survive and which model will die. But all agreed that cloud computing will be the future of the computing world. Even the prestigious research institute Gartner Group has stated that Cloud Computing is a discourse that is not to be missed by all stakeholders in the IT world, began at this time and in some future time.

Cloud Computing is a mechanism that allows us to "hire" of information technology resources (software, processing power, storage, etc.) through the Internet and exploit according to our needs and pay that is used by us alone. With this concept, the more people who can have access to and use of these resources, because they do not have to make massive investments. Especially in economic conditions like now, each organization will think long to issue an additional investment in the IT side.

Connecting two computers directly and simultaneously be referred to as Peer to Peer network. Where one computer can send data to a computer two and vice versa. The need to build a network Peer to Peer began to increase.
This type of connection in building the network is divided into two, namely the Cross and the Straight. Cross used to connect two devices together directly. As for connecting two devices are not directly, using the connection type Straight. As an example we will connect computer A to computer B. If we connect it directly, must use this type of cross connection. However, if computer A and B are connected via an intermediary (HUB), type of connections should be straight.

Types of connections in the network

 To make this type of cross connection, the tools that need to be prepared are as follows:
RJ-45 connector

RJ-45 connector

UTP cable

Crimping pliers

Crimping pliers and RJ-45 connectors

Now let's start how to make these types of cross connections. The first thing to do is cut UTP cable. Keep in mind, that the cut is only skin wrapping it. So that the cables will look colorful, amounting to 8 pin. In order to produce the correct pieces, use crimping pliers.

How to cut UTP cable

Next, straighten all that amounted to eight-pin cable on top. Arrange as shown below. Left to RJ-45 connector of the first and right for the latter.

The first connector (left) and the second connector (right)

When the cables have been made correctly, then the eighth input cable to the RJ-45 connector. Insert the cable into the RJ-45 connectors and clips using crimping pliers. Do a back way over to the other connector. However, with a different arrangement of cables or connectors for both.

How to clamp the RJ-45

The initial step to make the connection type Cross has been completed up to here. Next up is configuring the computer A and computer B.

To be continued

Wi-Fi is short for Wireless Fidelity, which has the sense of a set of standards used for Wireless Local Networks (Wireless Local Area Networks - WLAN) based on IEEE 802.11 specification. The latest standards of specification 802.11a or b, such as 802.16 g, is currently in preparation, the latest specification offers many improvements ranging from broad coverage further until transfer speed.

Wi-Fi was originally intended for the use of wireless devices and Local Area Network (LAN), but now more widely used for accessing the internet. This allows anyone with a computer with a wireless card (wireless card) or personal digital assistant (PDA) to connect to the internet using access point (otherwise known as hotspots) nearby.

TYPES OF WI-FI
Wi-Fi is designed based on the IEEE 802.11 specification. Today there are four variations of the 802.11, namely:

* 802.11a
* 802.11b
* 802.11g
* 802.11n

B is the first product specification Wi-Fi. Variations of g and n is one product that has the most sales in 2005.
Specifications Wi-Fi

SPESIFIKASI	SPEED	FREQUENCY BAND	FIT
802.11b	11 Mb/s	2.4 GHz	b
802.11a	54 Mb/s	5 GHz	a
802.11g	54 Mb/s	2.4 GHz	b,g
802.11n	100 Mb/s	2.4 GHz	b,g,n

A firewall is a way / system / mechanism that applies both to hardware, software or system itself in order to protect, either by filtering, limiting, or even reject one or all relations / activities of a segment on a private network with external network that is not a space scope. These segments can be a workstation, server, router, or local area network (LAN).
Firewalls generally designated to serve:
1. machine / computer
Any individual who is directly connected to outside networks or the Internet and wants all contained on their computers unprotected.
2. Network
Computer network consisting of more than one computer and various types of network topologies are used, both owned by companies, organizations, etc..

CHARACTERISTICS OF THE FIREWALL
1.All relations / events from the inside out, must pass through the firewall. This can be done by blocking / limiting physical access to all the local network, except through a firewall. Lots of networking possible.
2.Only activities listed / known which can pass through / have sex, this can be done by adjusting the local security policy configuration. There are so many types of firewalls to choose from as well as various types of policy offered.
3.Firewall itself must be strong or relatively invulnerable to attacks / weaknesses. this means the use of a reliable system with a relatively secure operating system.

TECHNIQUES USED BY THE FIREWALL
1.Service control (control of the service)
based on the types of services used on the Internet and be accessible both to into or out of the firewall. Usually the firewall will check the IP Address and also no port number in use both on TCP and UDP, can even be equipped with software for proxy which will receive and translate every demand for a service before recomendation . could be software on the server itself, such as services for the Web or to mail.
2.Direction Conrol (control of direction)
under the direction of the various requests (request) to the services that will be recognized and allowed to pass through the firewall.
3.User control (control of the user)
based on user / user to be able to run a service, meaning that a user can and some can not run a service, it is in because the user is not allowed to pass through the firewall. Typically used to restrict users from the local network to access the exit, but it can also be applied to restrict the users from the outside.
4.Behavior Control (control over their treatment)
based on how many services it has been used. For example, firewalls can filter emails to overcome / prevent spam.

TYPE of FIREWALL
1.Packet Filtering Router
Packet filtering is applied in a way to set all the IP packet toward the good, past or will be addressed by this type of packet; its packet will be arranged whether it will be received and forwarded, or in this packet refused. configured to filter packets that are going on transfer in both directions (either from or to the local network). Filtering rules based on IP header and transport header, including the beginning address (IP) and destination address (IP), transport protocol in use (UDP, TCP), as well as the port number used.
The advantages of this type are easy to implement, transparent to users, faster
The weakness is quite complicated to set its packet to be filtered appropriately, and weak in terms of authentication.
The attacks that can occur on the firewall with this type are:
+ IP address spoofing: An intruder (intruder) from the outside can do this a way to include / use the ip address local network has allowed through the firewall.
+ Source routing attacks: This type does not analyze the routing information source IP, making it possible to bypass the firewall.
+ Tiny fragment attacks: an intruder (intruder) into the IP divides the parts (fragments) that are smaller and forced division of the TCP header information. This type of attack designed to fool the filtering rules that depend on information from the TCP header. Attackers expect only a part (fragment) The first course will be in check and the rest will be able to pass freely. This can be in the tackle by rejecting all the packets with the TCP protocol and has offset = 1 in the IP fragment (the IP)
2.Application-Level Gateway
Application-level Gateway is also commonly known as a proxy server which serves to reinforce / deliver the application flow. This type of relationship that will govern all use the application layer, be it FTP, HTTP, GOPHER, etc..
The way it works is if there are users who use an application such as FTP to access remotely, the gateway will require the user to enter the address on the remote host will send the user access. User ID and other information that is appropriate then the gateway will do the relationships of the application located on the remote host, and distribute data between the two points. if the data does not match then the firewall will not forward the data or reject it. Furthermore, in this type of firewall can be configured to only support multiple applications and rejected any other applications to pass through the firewall.
The surplus is relatively safer than the type of packet filtering router is easier to check (audit) and record (log) all the incoming data stream at the application level.
The drawback is an excessive additional processing on every relationship. which will result in a connection there are two connections between the user and the gateway, where gateway will check and forward all flows from two directions.
3.Circuit-level Gateway
This third type can be a stand-alone system, or can also be a special function that is formed from the type of application-level gateway.tipe does not allow TCP connections end to end (direct)
how it works: Gateway will manage both the tcp connection, one between himself (i) with TCP on the local user (inner host) and 1 more between himself (i) with TCP users outside (outside host). When the two relations is done, the gateway will deliver TCP segments from one relationship to another without checking its contents. The security function lies in the determination of which relationships are allowed.
Use of this type is usually because administrators believe with internal users (internal users).
FIREWALL CONFIGURATION
1.Screened host firewall system (single-homed bastion)
In this configuration, the firewall function will be performed by packet filtering routers and bastion hosts *. This router is configured such that for all the current data from the Internet, only the IP packet to the bastion host are allowed. As for the flow of data (traffic) from the internal network, only IP packets of the bastion host are allowed to exit.
This configuration supports fleksibilitas in Internet access directly, for example if there is a web server on the network can then configure it so that the web server can be accessed directly from the internet.
Bastion Host performs the function of the Authentication and functions as a proxy. This configuration provides a better level of security than packet-filtering router or application-level gateway independently.
2.Screened Host Firewall System (Dual-homed bastion)
In this configuration, there will physically break / gap in the network. The surplus is the presence of a separating two line physically it will further enhance the security configuration than the first, while for the servers that require direct access (direct access) it can be put into place / segment are directly related to internet
This can be done by using 2 pieces of NICs (network interface card) on the bastion host.
3.Screened subnet firewall
This is the configuration of the highest level of security. why? because in this configuration in use 2 pieces of packet filtering router, first between the Internet and the bastion host, while a longer among bastian host and local network configuration to form an isolated subnet.
As for the advantages are:
+ There are 3 layers / levels of defense against an intruder / intruders.
+ External router serves only the relationship between the Internet and the bastion host so that the local network becomes invisible (invisible)
+ Local network can not mengkonstuksi routing directly to the internet, or in other words, the Internet became Invinsible (not mean it can not connect to the internet).
STEPS TO BUILD FIREWALL
1.identification form a network that is owned
Knowing the particular form of network owned toplogi that is in use as well as network protocol, will facilitate the design of a firewall
2.determine Policy or policies
Determination or Policy is policy that should be done, good or bad in the wake of a firewall is determined by the policy / policy is enforced. Among them:
1. Determine what needs to be on serve. That is, what will be subjected to the policy or policies that we will make
2. Determine the individuals or groups who will be subject to policy or policy
3. Determining the services needed by each of the individuals or groups who use the network
4. Based on each service that is in use by individuals or groups will be determined how best configuration that would make it more secure
5. Apply any policy or policy
3.prepare Software or hardware that will be used Whether it's operating system that supports or supporting specialized software firewall such as ipchains, or iptables on Linux, etc.. And hardware configuration that will support the firewall.
4.doing test configuration
Tests on the firewall that has been completed in the wake must be done, especially to know the results that we will get, how to use the usual tools tools such as nmap to audit.
* Bastion Host is a system / part are considered the strongest in the network security system by administrator.atau can be considered as blind leading the most powerful in blocking an attack, so it becomes the most important part in securing the network, usually the firewall component or the outer portion of the public system. Bastion hosts generally will use the operating system that can handle all the needs (eg, Unix, Linux, NT)

Transmission medium is a medium that can be used to transmit information from one place to another. In a network, all media that can distribute electricity or electromagnetic waves or light can be used as the sender of the media, both for sending and receiving data. Choice of transmission media (the sender) for the purposes of data communication depends on several factors, such as price, network performance is desired, whether or not the medium.

A. Copper Media
Copper media is all the media data transmissions are made of copper. People usually refer to the name of the cable. Data sent over the wire, it's the electric signals (voltage or current) digital.
The types of cables used for data transmission on the network:
1. Coaxial Cable
These cables are often used as an antenna cable TV. Known also as cable BNC (Bayonet Naur Connector). These cables are cable's most widely used on the LAN, since it has protection against higher noise, inexpensive, and able to transmit data with standard speed.
There are four types of coaxial cable, namely:
• Thinnet or RG-58 (10Base2)

 • Thicknet or RG-8 (10Base5).

• RG-59

• RG-6

There are three types of connectors on coaxial cable, that is, T connectors, I connector (socket) and BNC connectors. The advantage of using coaxial cable is less expensive than fiber optic cable and quite far-reaching range of cable types UTP / STP using repeaters as reinforcements. The drawback is difficult at the time of installation, both the connector and cable installation. For now the coaxial cable is no longer recommended intuk network installation.

2. Twisted-Pair cable
Twisted Pair consists of two types:

 STP cable (Shielded Twisted Pair)
The advantage of using STP cable is more resistant to interference from electromagnetic waves both from within and from outside. The drawback is expensive, difficult at the time of installation (especially the grounding problem), and the distance range is only 100m.
UTP (Unshielded Twisted Pair)
The advantages of using UTP cable is cheap and easy to install. The drawback is vulnerable to electromagnetic wave interference, and distance range is only 100m.
There are several categories for Twisted Pair cable, namely:
• Category 1 (Cat-1).
Generally use standard AWG solid conductors as much as 22 or 24 pin with a wide impedance range. Used in telephone connections and not recommended for data transmission.
• Category 2 (Cat-2).
Impedance range is wide, often used in PBX systems and alarm systems. ISDN data transmission using the cable category 2, with a maximum bandwidth of 1 MBps.
• Category 3 (Cat-3).
Often called voice grade cable, use a solid conductor as many as 22 or 24 pin with impedance of 100 Ω and serves up to 16 MBps. Can be used for 10BaseT and Token Ring network with a bandwidth of 4 Mbps.
• Category 4 (Cat-4).
As category 3 with a bandwidth of 20 MBps, Token Ring network is applied to a bandwidth of 16 Mbps.
• Category 5 (Cat-5).
Twisted Pair Cable is the best (data grade) with a bandwidth of 100 Mbps and the maximum transmission range of 100 m.

B. Optical Media

There are three types of fiber optic cable that is normally used, ie single mode, multi mode optical fiber and plastic that serves as a hint of light from the cable end to the other cable end. From the transmitter ^ receiver, which converts electronic pulses into light and vice versa, in the form of light-emitting laser diodeataupun. Single mode fiber optic cable is a single glass fiber with a diameter of 8.3 to 10 micrometers, have one type of transmission that can deliver large-capacity data at high speeds for long distances, and requires a light source with a smaller width of the spectrum. Cable capabilities in delivering the type of single mode transmission is 50 times faster than multimode cable types, because it has a smaller core so as to eliminate any distortion and overlapping light pulses.

  Multimode fiber optic cable is made of fiberglass with a larger diameter, ie 50 to 100 micrometers that can deliver large-capacity data at high speed to medium range. If the distance is more than 3000 feet, the signal distortion will occur at the receiver side which resulted in transmission of data to be inaccurate. Medium plastic optical'fiber is the latest plastic-based cable which ensures the same level of performance with glass fiber in a short distance with a much cheaper cost. Currently, fiber optic cable has been used as a standard physical layer dalambiding data or telecommunications networks, such as cable TV devices, as well as security systems that use Closed Circuit Television (CCTV), etc. The basic ingredients of optical media is glass with a very small size (micron scale). Usually known as fiber optic cables (fiber optic). The data is passed in this medium in the form of light (laser or infrared).
Single fiber optic cable consists of two fibers, one function for Transmit (Tx) and one for Receive (Rx) so that communication with the fiber optic can occur both directions simultaneously (full duplex).
C. Wireless Network
Are now widely used wireless network (wireless network), data transmission using infrared rays or microwaves to deliver data. Although it sounds practical, but the obstacles faced here is the problem of distance, bandwidth, and high cost. However, for the needs of the LAN in the building, the current wireless technology already developed for the Active Hub (Wireless Access Point) and the Wireless LAN Card (NIC replacement), so that it can reduce the chaotic cable data transmission on computer networks. Wireless Access Point can also be combined (up-link) with ActiveHub of the existing network.
   Wireless transmission media using high-frequency radio waves. Usually the electromagnetic waves with a frequency of 2.4 GHz and 5 GHz. Digital data sent over wireless will be modulated into these electromagnetic waves.

WiMAX is a platform that is used on the Metropolitan Area Network (MAN) previously used fiber optic cables, GSB, FSL. WiMAX stands for Worldwide Interoperability for Microwave Access. This is one form of wireless technology is becoming the focus of telecom operators, businesses and Internet users in the world.

WiMAX (Worldwide Interoperability for Microwave Access) is present as a solution to limited access to Wi-Fi is designed for use in space. Technology that uses OFDM is able to provide speed data services up to 70 Mbps within a radius of 50 km. Radius is enough to make WiMax as a broadband telecommunications network replaces fixedline technology. When compared with fixedline WiMAX network installation cost is much cheaper.

Development of Ethernet 
When the early days of Metcalfe develops Ethernet, a computer network created by connecting with a single copper cable. Physical limitations of a piece of copper wire record electrical signals is limited how far away from each other computers on an Ethernet. Repeater help ease the distance limitations. Repeater is a small tool that regenerates the electrical signals on the strength of the original signal. This process allows Ethernet to be able to extend across the floor of the office that may be beyond the reach of Ethernet limits. The addition or removal of devices on a wired Ethernet network, to all other connected devices. device called an Ethernet hub to solve this problem.
First, each port on the hub is actually a repeater.
Second, an Ethernet hub simplifies troubleshooting and administration. As the network grows larger, companies must comply more and more computers to an Ethernet.
Repeter hub and is working on the Physical Layer in the OSI model. Functions of Hub and Repeater is simple it is forwarding data packets sent from the PC without having the intelligence of a router that has a good destination IP filtering, MAC Address and others that only have the ability to forward it to the address that will be addressed.
Data sent by a computer will be delivered to the destination by spreading the news (broadcast) to all computers connected in a single terminal (Hub / Repeater), consequently all computers are connected to receive data packets, and if at the same time there is another computer that sends packets of data then there is the crush or collision data, and this will affect the smooth flow of data within the network. Computer-computers that are in the same LAN will have the same broadcast domain or so-called broadcast. Hub and Repeater does not have the ability to forward data to another computer that is in the broadcast domain or network ID of another, therefore the IP address given to computers that are in the same LAN usually have the same network.
For example is a single broadcast domain is: 
A PC that is in a network and a terminal with the IP 192.168.1.4 to 192.168.1.52 with subnet 255.255.255.0 and PC B is located in an other network and a terminal with the IP 192.168.2.6 to 192.168.2.70 with a subnet 255 255 .255.0 then A PC that is on network 192.168.1.4 is called a broadcast domain and PC B is located on the network 192.168.2.6 is in another broadcast domain.
The protocol used is IEEE 802.3 Ethernet uses a data-flow patterns Carrier Sense Multiple Access Collision Detection (CSMA-CD), by definition: that is a way of networking computers to check whether there is transmission of data by other parties. If there is no transmission of data, data by the other party will be sent. Ethernet networks are generally used only for half-duplex transmission, ie at a time can only send or receive only.
Hub and Repeater has only one collision domain, so that all computers are connected if one port is busy then the other ports will have to wait.
Why do we have to learn the Ethernet
Ethernet was developed in 1972 as a way to connect computers with laser printers which was newly created.
It was recognized even then as an outstanding technological breakthrough.
However, few people thought that the success of generating technology for connecting computers and devices will transform human communication on the same scale with the invention of the telephone business and change on the scale of the Industrial Revolution.
Several competing protocols have emerged since 1972, but remains the dominant standard Ethernet to connect computers to local area network (LAN). For many years the dominant Ethernet home networks as well.
Ethernet is a way of sharing resources in which the end stations (computers, servers, etc.) all have access to the transmission medium at the same time. The result is that only one device can transmit information at a time.
Given these limitations, there are two viable solutions:
• Use sharing mechanism: If all the end stations are forced to share the data via data cable, there must be rules to ensure that any end station to wait its turn before transmitting. In the case of simultaneous transmission, there must be rules to transmit.
• Divide the segment share, and protect them:
Another solution is the limitations of shared resources by using a device that reduces the number of stations to end the sharing of resources at any given time.

Ethernet Collisions 
In a traditional LAN, the user will all share the same ports on network devices and will fight for bandwidth.
The main limitation of such a setup is that only one device can transmit at a time. Segments that share resources in this way is called a collision domain, since if two or more devices transmit at the same time, information that "collide," and both end points must resend their information (at different times). Usually the device either to wait some random time before attempting to retransmit.
This method works well for a small number of user segments, where each has a relatively low bandwidth requirements. Due to the increasing number of users, the efficiency of collision domains decreased sharply, to the point where traffic will occur overhead (management and control) network.
Small segment
Segments can be divided to reduce the number of users and increase the bandwidth available to each user in this segment. Each new segment is created generating new collision domain.
Traffic from one segment or collision domain does not interfere with any other segment, thereby increasing the available bandwidth of each segment. In the following figure, each segment has a greater bandwidth, but all segments are on the same backbone and must share the available bandwidth.
This approach works best when care is taken to ensure that the largest users of bandwidth are placed in separate segments.
There are several basic methods for dividing an Ethernet LAN to a collision domains more:
• Use bridges to divide collision domains.
• Use the switch to provide a dedicated domain for each host.
• Use a router to route traffic between domains (and not route traffic that is not important to another domain).

Encapsulation is a process to hide or protect a process from the possibility of outside interference or misuse of the system while simplifying the use of the system itself, also makes one type of network data packets to other data types. Encapsulation occurs when a protocol that is on the lower layer receives data from the protocol that is at a higher layer and put the data into a data format that is understood by the protocol. Access to the internal system so arranged through a set of interfaces.
With the encapsulation of data into an identity. A simple example encapsulation process in the process of mail delivery, if a letter would be sent but without the envelope, address and postage. The letter should have an identity in order to get to the destination, if it does not have an identity then the letter will not be able to get to the destination. Envelopes with address and stamp the same as the data encapsulation.
Encapsulation process varies in each layernya, the following process:

1. Initially the data was made, when starting the process of sending, the data fell through the application layer (layer 7)
responsible for the exchange of information from the computer to the network, basically this is an interface layer between network applications used by users. Can also be mentioned that this layer serves to define the request of the user. Then the data passed to the Presentation layer (layer 6), which layer is responsible for determining whether he needs to do the encryption on this request or to other forms of translational
data. If the process is complete, the next ditambahakan necessary information. Then forwarded to the session layer (layer 5) in which this layer will check whether an application requesting the information and verify that the services requested on the server. Any information will be passed down an added header of each layer. However, the processing layer 5, 6 and 7 sometimes it is not necessary to the header. This dikarena her no new information that needs to be processed.

2. Data arrived at the Transport layer (layer 4), ensuring that he already possessed a proper connection with the server and start the process by converting the information into the form of segments. Error checking and merging data coming from the same application done in this transport layer and the wholeness
data is guaranteed here as well. L4PDU formed from this process.

3. The next segment is forwarded to the Network layer (layer 3), here the segments received earlier and added the network address for the station to request and network address for the requested server. Segments will be converted into a packet-packet, then network layer makes
Network header, in which there are also addresses the network layer, and placed L4PDU behind it, and formed L3PDU.

4. Then the packet-packet was passed to the Data Link layer (layer 2) and the packages were arranged and then be wrapped again into the individual frames, one example of this process is to provide the MAC address of destination and source MAC address which is then used that information to make a trailer.
Because a packet can be delivered via many devices and routers, this is where the role of MAC addresses in packets sent between a router and other routers. Then be transmitted to the media. All
yanng information added by each layer before (as an actual file requests) must fit into a size of 46-1500 bytes of data fields in the ethernet frame. The data link layer is responsible for sending the frame according to the topology used. L2PDU formed in this process.

5. Finally, the data arrived at the Physical layer (layer 1), information will be taken from the source to the destination. Since the physical layer frame is not known, he would pass that information into the form of bits. The addition of the header does not occur at this layer. The Physical layer is associated with the hardware. Finally, the bits
They'll be synchronized and then converted into electrical signals in the form of high and low voltage and then transmitted through the media. Example of the cable to the destination, it is in accordance with the characteristics that determine the physical layer of a layer sequence of events in which the bit stream moving through a physical medium.
At each layer there is LxPDU (Layer N Protocol Data Unit), which is a form of bytes in the header-trailer on the data. PDU is the processes on each layer of the OSI model. At each layer is also formed a new formation, the layer 2 PDU including the header and trailer is called the frame formation. In the third layer is called packet (packet). While in layer 4 are called segments (segments).
After the encapsulation process, and then sent to the server and the server will perform this process in reverse, ie from the physical layer to application layer, this process is called decapsulation. If the encapsulation performed
packaging, then the decapsulation will perform the opening of the sheaths was through his layers.

Decapsulation process 
Decapsulation is the inverse of the encapsulation process. Encapsulation is the process of wrapping the data while the decapsulation process is a process of opening packs. The process was reversed from the encapsulation process. Encapsulation The process starts from the uppermost layer (Application Layer) to the lowest layer (Physical layer) while the decapsulation process starts from the lowest layer (Physical Layer) to the uppermost layer (Application Layer)

The main purpose use of the OSI model is to help network designers understand the function of each layer are associated with the flow of data communications. Including the types and methods of transmission network protoklol. The model is divided into 7 layers, with the characteristics and functions of each. Each layer must be able to communicate with the layer above it and below it directly through a series of protocols and standards.
Application Layer: Provides services for user applications. This layer is responsible for the exchange of information between computer programs, such as e-mail programs, and other service roads on the network, such as a printer server or other computer applications.

Presentation Layer: Concerned with how data is converted and formatted for data transfer. Example conversion of ASCII text format for documents,. Gif and JPG for images. This layer performs code conversion, data translation, encryption and conversion. Session Layer: Determines how two devices establish, maintain and manage a connection - how they talk to each other. These connections are called "session".

Transport Layer: Responsible for breaking data into segments, logical connection "end-to-end" between the terminals, and provide error handling (error handling).

Network Layer: Responsible for determining the network address, specify the route to be taken during the trip, and keep the network traffic congestion. The data on this layer-shaped package.
Data Link Layer: Provides links to data, packaged into frames associated with the "hardware" and then transported through the medium of communication with the network card, set the physical layer communications between connecting systems and error handling.

Physical Layer: Responsible for the process data into bits and transfers them via the media, like cable, and maintain the physical connection between systems.

Introduction to Model Open Systems Interconnection (OSI)

Model Open Systems Interconnection (OSI) was created by the International Organization for Standardization (ISO) that provides a logical framework Structured how processes interact via a data communications network. Standards were developed for the computer industry can communicate on different networks efficiently.

OSI Layer Model

There are seven layers in the OSI model. Each layer is responsible for a particular in the process of data communication. For example, one layer may be responsible for establishing connections between devices, while another layer is responsible to correct the "errors" during the data transfer process takes place.
Layers of the OSI model is divided into two groups: "upper layer" and "lower layer". "Upper Layer" focus on user applications and how to file represented in the computer. For Network Engineers, a major part of
became the focus is on "lower layer". Lower layer is the essence actual data communication over a network.

"Open" in OSI "
"Open" in the OSI network model is to declare that conduct regardless of the hardware interconnect / "hardware" is used, all in accordance with standard communications software. It is notdirect cause "modularity" (can be dismantled pairs).

Modularity
"Modularity" refers to the exchange of protocol at a certain level without affecting or damaging relationships or functions of other levels. In a layer, protocol interchangeable, and allows communication continues. This exchange took place based on the hardware"hardware" from different vendors and a variety of reasons or a desire different.

next post I will discuss about OSI layer model. thanks you very much.

LAN describes a network that reaches a limited area, such as a single office building, where the computer that has network is physically adjacent to one another. A large LAN for example on an office or corporate complex, where it can be separated into multiple workgroup to further facilitate manejemennya. In this case, a workgroup comprised of user who do share the same resources, such as files, printers and application programs. For example, on a LAN of a company you can create a workgroup to different departments, such as sales, finance, human resources. The distance is approximately up to 10 km.
Advantages jaingan LAN is
1. Exchange of files (file sharing)
2. Use the printer can be done by all clients (printer sharing)
3. The data files can be stored on the server, so it can be accessed from any client securities according to the authorization of all employees, which can be made based on the company's organizational structure so that data security is assured.
4. Data files in / out from / to the server can be controlled
5. The process of backing up data quick and easy
6. The risk of losing data by a computer virus becomes very small
7. Communication between employees can be done using email and chat

Some applications will listen (listen) incoming connections (incoming) or do something to another computer. Programs like this model is called the application server. TSB program. created to provide services for other computers that request it. To truly understand the role of some components of family TCP / IP, of course, keep in mind what can be done at the network bases TCP / IP. Here I will give an explanation about some of the same practice commonly used with TCP / IP, okay next on:

• Telnet 

Telnet program provides the ability to do remote login. With this program, a user on a computer can log in (go) to another computer and act as if he was directly in front of the computer both the call. Access can be done from any network, provided the user has a valid permit does not matter in a local network or any network.

• File Transfer Protocol

Also called FTP. Allows a file on a computer system is copied to other systems. Users do not need a full user loginsebagai like telnet but need access permission (username, password and IP). If the connection has occurred, allowing FTP to copy files from a remote computer to a local computer that we use.
Simple Mail Transfer Protocol. Also called SMTP. Used to transfer electronic mail (e-mail). When using e-mail program, behind the scenes SMTP will connect itself to the remote computer and transfer the e-mail messages as well as an FTP program to transfer files, but we never realized the work "stealth" (SMTP) is.
Remote Procedure Call. Also called RPC. A set of functions that allow an application to communicate to another computer (server). RPC will provide the programming functions, return codes, predefined variables to support distributed computing.

• User Datagram Protocol

Also called UDP. The protocol bersifatconnectionless. UDP is the opposite of TCP connection-oriented. UDP is not reliable but it is designed for special purposes.

• Transmission Control Protocol. 

Also called TCP. Communication protocol that provides reliable data transfer. TCP is responsible for organizing and preparing (assembling) dilewatikan data from the layer (layer) application into a standard package and ensure that the data has been sent correctly.
Internet protocol. Also called IP. Section is responsible for moving packets of data that has been in-assembling the TCP or UDP (User datagram protocol) over the network. IP uses a set of unique addresses for each device in the network so that he can define and handle the travel path (route) and destination address.

• Domain Nname System. 

Also called DNS. Allows a computer with a common name are converted to specific network addresses. For example, a computer with a normal name DIMAS, can not be accessed by other computers on the same network or other networks, if there is no method to check the local machine name and replace it with a physical address (hardware) machine. DNS provides the conversion from local name to the physical address of a connection.

Server is a computer system that provides a specific service type within a computer network. Servers are supported with processors that are scalable and large RAM, also equipped with a special operating system, called the network operating system or network operating system. Server is also running administrative software that controls access to networks and resources contained in it, like a file or printer device (printer), and provide access to the workstation network members.
Type Server
1. Application Server (Application server)
2. Server Data (Data Server)
3. Proxy Server (Proxy Server).

Server function
1. Application Servers 
Server used to store various kinds of applications that can be accessed by the client, the server data itself is used to store data that is used either directly or client data that is processed by the server application.
2. Proxy Server 
Serves to regulate traffic on the network through proxy settings. People are more familiar with the proxy server to connect client computers to the Internet.

although a bit hopefully my post useful, maybe the next post I will discuss more details about the computer server. thank you

Open Web Application Security Project (OWASP) is an open source project that was built to find the cause of insecurity is a software and discover how to handle it. There are 10 web application security loopholes are found and their recommendations about the deal as a minimum safety standard of the web application.
Here are 10 hole, and the way that we can resolve the issue.

I. Unvalidated input 
All web application displaying data from the HTTP request made by the user and uses that data to perform operations. Hackers can manipulate the parts on request (query string, cookie information, headers) to bypass the security mechanisms.
Here are three types of attacks associated with this problem:
• Cross site scripting 
• Buffer overflows 
• Injection flaws 
There are several things to note when dealing with the validation of our application. First, it is not good to believe in the web application on the client side scripting. The script usually stop form submission when there is an incorrect input. However, the script can not prevent hackers to create their own HTTP request, which is free of the form. Using a client-side validation can still make a vulnerable web application.
Second, some applications use a "negative" (negative approach) on the validation: The application tries to detect if there is a dangerous element in the request parameters. Problems of this type of approach is only able to protect against some attacks, namely: only attacks that are recognized by the validation code that is preventable. There are many ways in which hackers can bypass the security of unvalidated input; There is still a possibility that the new way is not recognized by the application can bypass validation and do the destruction. Is a better way to use a "positive" (positive approach), namely: limiting a format or pattern to the permitted values ​​and ensure input in accordance with the format.

II. Broken Access Control 
Many applications are user-user should categorize into different roles and different levels to interact with content that is distinguished from these categories. One example, many applications that are user role and admin role: only the admin role are allowed to access specific pages or administration action.
The problem is that some applications are not effective for this work force so that authorization. For example, some programs only use a checkpoint where only selected users can access: for further processing, the user must prove himself authorized by using the user name and password. However, they do not run the checks from the previous checkpoint: which if the user successfully passes the login page, they can freely run the operation.

Another problem associated with access control are:
• Insecure IDs - Some sites use the id or key that points to the user or function. ID can also be guessed, and if the hackers can easily guess the ID of the user who terautorisasi, then the site will be easily attacked.
• File Permissions - Many web and application server is believed to external file that holds a list of authorized users and resources anywhere that can and / or inaccessible. If the file is readable from the outside, then the hacker can easily modify to add itself to the list of permitted users.
What steps can be done to solve it? In these examples, we can develop a filter or a component that can be run on sensitive resources. Filters or components can be designated to ensure only authorized users can mengakases. To protect from insecure IDS, we must develop our application in order not to believe in the confidentiality of the IDs that can provide access control. On the issue of file permissions, the files must be in a location not accessible by web browsers and only certain roles can access them.

III. Broken Authentication and Session Management 
Authentication and session management refers to all aspects of managing user authentication and management of an active session. Here are a few things to note:
• Password strength - our application should provide a minimum level of security of a password, which can be seen by looking at the length of the password and complexity. For example an application where there are new users that will register: the application does not allow passwords with a length of 3-4 characters or simple words that can be easily guessed by hackers.
• Password use - The application we have to restrict users who access the application to log back into the system at a certain time limit. In this way the application can be protected from a brute force attack where hackers can attack repeatedly to successfully log into the system. In addition, the log in which failed should be noted as information to the administrator to indicate the possibility that the attack occurred.
• Password storage - the password should not be stored in the application. Passwords should be stored in encrypted format and stored in another file like a database file or password file. This can ensure that sensitive information such as passwords are not propagated into the application.
Another related issue: the password should not be in the form of hardcoded in the source code.
• Session ID Protection - servers usually use the session Id to identify the user who entered the session. However, if the session ID can be seen by someone on the same network, the person may become a client.
One way that can be used to prevent the invisibility of the session ID by someone in a similar network is to connect the communication between servers and clients on an SSL-protected channel.

IV.Cross site scripting 
Cross site scripting occurs when a person makes a web application through script to another user. This is done by an attacker to add content (such as JavaScript, ActiveX, Flash) in the request that can create HTML output that can be viewed by other users. If there are other users who access content, the browser does not know that the page can not be trusted.
Way that can be used to prevent cross-site scripting attacks is to validate the data entry of user requests (such as headers, cookies, user parameters, ...). How to not use negative approach: try to filter active content that is not an effective way.

V. Buffer overflows 
Attackers can use buffer overflows to damage the web application. This is done because the attacker sends requests that cause the server to run code sent by the attacker.
Buffer overflow weakness is usually difficult to detect and hard done by hackers. But the attacker still can find these weaknesses and make the buffer overflow on some web application.
Thanks for the design of the Java environment, where applications running on J2EE servers are safe from this type of attack.
To ensure security, the best way is to conduct surveillance if there are any patches or bug reports for the server products that are used.

VI. Injection flaws
One disadvantage is that popular injection flaw, which the hacker can send or menginject request to the operating system or to external sources such as databases.
One form is SQL injection. Here is one example of SQL injection:
http://someServer/someApp/someAction?searchString=jedi 
URL above will process the search with the keyword 'Jedi'. Implementations where there is no input validation is like the following SQL code:
select * from someTable where someField = 'value' 
where the value is the value of searchString parameters that exist in the HTTP request.
What if, hackers do input from the URL like this:
http://someServer/someApp/someAction?searchString=jedi '% 20and% 20true; 
% 20DROP% 20DATABASE; ' 
SQL query is formed like this:
select * from someTable where someField = 'Jedi' AND true; DROP DATABASE;'' 
Initial statement would be acceptable where there is a clause AND TRUE. And then the DROP DATABASE statement will also be execution that will give damage to the application.
This attack could possibly occur because the input is not validated. There are two ways you can do to prevent this attack are:
• Instead of using SELECT statements, INSERT, UPDATE and DELETE statements, can be made a function that do the same. By using the existing safeguards against the parameters expected. In addition to the function, the parameters that enter must be the same as the data type of the declared parameters.
• Right to access the application should also be restricted. For example, if the application seeks only to see the data, need not be given permissions to perform INSERT, UPDATE or DELETE. Do not use an admin account on a web application for mengakases database. It can also meminimailkan attacks from hackers.

VIII. Insecure storage 
Web applications typically need to store sensitive information like passwords, credit card information, and others. Because these items are sensitive items that need to be encrypted to prevent access directly. However, several encryption methods are still weak and still be attacked.
Here are some common mistakes:
• Mistakes to encrypt critical data
• No safe keys, certificates, and passwords
• Lack of safe storage location of data
• Lack of randomization count
• Errors selection algorithm
• Trying to create a new encryption algorithm
Based on the following scenario: There is an application, where there is a password on the user object. However, the application stores the user object into the session after the user login. The problems that will arise in this scenario is that the password can be viewed by someone who can see the session of that user.
One way to avoid mistakes made storage of sensitive information is: do not make the password as an attribute of a class that represents user information; Rather than encrypting credit card numbers from the user, it is better to ask about it whenever needed.
In addition, using existing encryption algorithms will be better than making your own algorithm. You just make sure the algorithm to be used has been recognized by the public and totally reliable.

IX. Denial of Service 
Denial of Service is an attack made by a hacker who sends the request in a very large amount and at the same time. Due to these requests, the server becomes overloaded and can not serve other users.
DoS attacks are able to spend bandwidth on the server machine. Moreover, it can also spend a memory, database connections, and other sources.
It is generally very difficult to protect these applications from attacks. However, there are still ways to do such as limiting the resources that are accessible user in a minimal amount. An idea / a good way to make the load quotas that limit the amount of load data to be accessible to users of the system.
One example is the implementation of the bulletin board: user restrictions at the time of search, where these operations can only be done every 20 seconds. In this way it is certain that the user can not spend the connection from the database.
Another solution is to design a web application where users are not authorized to have access to only a little or no access to web content associated with the database.

X. Insecure Configuration Management 
Usually the group (group) who developed different applications to groups that arrange the hosting of the application. This could be dangerous, because security is reliable only in terms of application: sedangakan terms of the server also has the security aspects that need attention. An error of server configuration can pass through the security aspect in terms of application.
Here is a server configuration error that could cause problems:
• Vulnerabilities that have not patched the software on the server - the administrator is not to patch existing software on the server.
• Vulnerabilities in which the server can display a list of directory or a directory traversal attack also.
• backup files or file sample (sample file), script files, configuration files are left behind / not necessary.
• Right to access the directory or file is wrong.
• Presence services such as remote administration and content management are still active.
• Use the default account and default password.
• administrative functions or debugging functions that can be accessed.
• There is an informative error messages from a technical point.
• configuration error SSL certificate and encryption settings.
• Use self-Signet certificates for authentication.
• Use the default certificate.
• Errors authentication with external systems.

A discussion of web programming is not complete unless they have been learning about safety in the application. Abundant facilities, a function that will not mean very much if we fail in terms of application data security.
In this chapter, we will learn how to secure communication between server and client via SSL.

SSL has become the de facto standard in the community to secure communication between client and server. SSL stands for Secure Socket Layer is; SSL is a protocol layer that resides between the TCP / IP standard protocol on top of the application-level protocol like HTTP. SSL allows a server to perform authentication with the client and then encrypt the communication.
A discussion of the SSL operations in this chapter aims so that we know the use of this technology to secure communications between the server and client.

Enabling SSL on the application.
To know the advantages SSL on the application, we need to configure the server to accept SSL connections. On a different servlet container will be different ways to do it anyway. Here we will learn about configuring Sun Application Server 8.1

Certificates
One part of the configuration we need to establish SSL communications on the server is a security certificate. Can we imagine a certificate in this case like a passport: where have important information that the owner can be known by others. The certificate is usually spread by Certification Authorities (CA). A CA is similar such as passports office: where the CA on duty to perform certificate validation certificate to the owner and the mark can not be forged.
Until now many well-known Certification Authorities enough, one of which is Verisign. Determining election of CA is the responsibility or authority of an admin to give a valid security certificate on the server.
If a case is found in the absence of the CA certificate, a temporary certificate (temporary) can be created using tools from the Java 1.4 SDK. You need to note that the client typically does not continue the transaction that requires a high level of security and found that the certificate used is certificate that we created.
11.2.3 Creating a private key certificate
To simplify this problem, it would be easier if the operation in which the certificate is stored. It can be found to do the% APP_SERVER_HOME% / domains/domain1/config.
Open the directory using the command line. then call the following command:

keytool-genkey-alias keyAlias
-RSA-keypass keyalg keypassword
-Storepass storepassword
-Keystore keystore.jks

• keyAlias ​​- which is an alias or ID of this certificate will designate to whom.
• keypassword - is the password for the private key used in the encryption process.
• storepassword - is used for the keystore password.
In this case might be a little confusing where the two passwords are needed to create a certificate. To overcome this, we can remember that the key is inserted is also called keystore. Keystore can hold one or several keys. Keypassword is the password of the private key to be used on the certificate, while storepassword is the password of an existing key in the keystore. In the directory in which we operate already have a keystore file with a password, so we need to set the value storepass be: changeit.
This password can be changed using keytool like this:

keytool-keystore-storepass keystore.jks Newpassword

One of the things that are important in communication using a computer to ensure the confidentiality of the data is encrypted. Encryption is a process that changes a code of conduct that can be understood to be a code that can not be understood (not legible). Encryption can be interpreted as a code or cipher. A coding system using a table or a dictionary that has been defined to replace the words of the information or that are part of the information sent. A cipher uses an algorithm that can encode all data streams (stream) bits of a message into an incomprehensible cryptogram (unitelligible). Because cipher technique is a system that has been prepared for the automation, then the technique used in computer and network security systems.
In the next section we will discuss a variety of encryption techniques commonly used in security systems of computer systems and networks.

A. Conventional encryption. 
This encryption process can be described as follows:
Plain text -> Encryption Algorithm -> Cipher text -> Algorithm Dekrispsi -> Plain Text
                            User A |                                     | User B
                           |---------------------- Key (Key) --------------------|

Origin of information that can be understood in simbolkan by Plain text, which is then translated by the encryption algorithm into information that can not be to understand which is symbolized by the cipher text. The process of encryption consists of two algorithms and keys. The key is usually a short string of bits that control the algorithm. Encryption algorithm will produce different results depending on which key is used. Changing the encryption key will change the output of the encryption algorithms.
Once the cipher text has been generated, then transmitted. In the next recipient of the received cipher text is converted back to plain text and key algorithm and the same.
Security of conventional encryption depends on several factors. The first encryption algorithm must be sufficiently strong so that makes it very difficult to decrypt the cipher text by the basic cipher text. Furthermore the security of conventional encryption algorithms rely on the secrecy of the key is not the algorithm. That is assuming that is not very practical to decrypt the cipher text with basic information and knowledge about the algorithm descriptions / encryption. Or in other words, we do not need to maintain the secrecy of the algorithm, but enough with the secrecy of the key.
The benefits of a conventional encryption algorithm is the ease in use widely. With the fact that this algorithm does not need to be kept secret with the intent that the makers can and do make an implementation in the form of chips at a cheap price. These chips can be widely available and also provided for some types of products. With the use of conventional encryption, the security principle is to maintain the security of the key.
Encryption model is a widely used model based on data encrytion standard (DES), taken by the U.S. Bureau of the national standard in 1977. DES encryption for data in the 64-bit blocks using a 56-bit key. By using this key, 64 input data converted to a sequence of methods to 64 bit output. The same process with the same key is used to change the encryption back.

B. Public-Key Encryption 
One of the main difficulties of the conventional encryption is the need to distribute the keys used in secure circumstances. An appropriate way has been found to overcome this weakness with an encryption model that surprisingly does not require a key to be distributed. This method is known as public-key encryption and was first introduced in 1976.
Plain text -> Encryption Algorithm -> Cipher text -> Algorithm Dekrispsi -> Plain Text
                           User A |                                 | User B
                                                                Private Key ----| B
                          |---------------------- Key (Key) --------------------|

Algorithms such as that depicted in the image above. For conventional encryption, the key used in encryption and decryption cent is the same. But this is not actually the required conditions. However it is possible to construct an algorithm that uses one key for encryption and her partner, a different key, for decryption. Furthermore it is possible to create an algorithm that is where the knowledge of the encryption algorithm the encryption key plus is not enough to determine the key dekrispi. So the following techniques will be performed:
1. Respectively - each of the system in the network will create a pair of keys used for encryption and decryption of information received.
2. Each - each of the system will publish the encryption key (public key) to install in public registers or files, are being maintained as a partner private key (private key).
3. If A wants mengisim message to B, then A will encrypt the message with the public key of B.
4. When B receives the message from A, then B will use the private key to decrypt the message from A.
As we see, public-key distribution because it does not solve the problem needed a key to be distributed. All participants have access to a public key (public key) and private key is generated locally by each participant, so no need to be distributed. During each control system - each private key with both the communication becomes secure communications. Each system is changing the private key public key partner will replace the old public key. The weakness of public key encryption method is compared with conventional encryption methods encryption algorithm has a more complex algorithm. So for comparison of size and price of the hardware, the public key method will produce lower performance. The following table will show the various important aspects of conventional and public key encryption.

Conventional encryption 
Required to work:
1. The same algorithm with the same key can be used for the decryption process - the encryption.
2. Sender and receiver must share the same algorithm and key.
What is needed for security:
1. Keys must be kept secret.
2. It is impossible or highly impractical to translate the information that has been encrypted.
3. Knowledge of algorithms and sample of an encrypted word is not sufficient to determine kunc untu.
Public Key Encryption
Required to work:
1. The algorithm used for encryption and decryption with a key pair, one for encryption one for decryption.
2. Sender and receiver must have a suitable key pair.
What is needed for security:
1. One of the key must be kept secret.
2. It is impossible or highly impractical to translate the information that has been encrypted.
3. Knowledge of algorithms and sample of an encrypted word untu insufficient to determine the key.