..::You can change the world with the knowledge::..

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.