# Crypting and Decrypting Algorithms

Crypting is a method that uses for hiding a message. Purpose of symmetric encryption, which is one of encryption algorithms, is protect message that is between sender and receiver from foreigners. For that, It is used a common algorithm which is for encrypt and decrypt. All algorithms have a key for encrypting but only algorithms, which are double way, have a decrypting key or algorithm.

Provider of security in symmetric encryption is key. Because only thing that is hidden, is key. On the other hand encryption and decryption algorithms open to everyone. Thanks to different keys can be generated different encrypted texts by same text or same algorithms.

Symmetric encryption methods are grouped for two group according to transactions on texts. One of these is character based encryption which is conventional method (monoalphabetic or polialphabetic) and another one is bit based encryption which is modern encryption method. For examples of bit based encryption, we can say DES, TWOFISH, IRON and AES. Especially AES is still being used for important military encryptions and It is a standard encryption method of the NATO.

#### DES (Data Encryption Standard)

DES is one of most common algorithm in world. It is developed in 1975 by IBM and It was published by Federal Register. DES encrypts 64 bits of data to using a 56 bits of key. Used technics are to spreading and to mixing. The best disadvantage of the DES is that the key length is 56 bits. It isn’t enough this algorithm, that is published in 1975, for attacks from modern computing systems that is developed in nowadays. For more secure encryptions, DES is improved to Triple-DES that is more modern and more secure. Triple-DES uses 2 key that is 56 bits, for supporting to backward compatibility.

#### TWOFISH

This algorithm had created by Bruce Schneier, John Kelsey, Doug Whiting and David Wagner and published in 1998. It is one of the AES finalists and as fast as AES. It uses Feistel method like DES. The one of difference of the DES has changeable S-Boxes from created by using key. Moreover, It processes most of processes on 32 bits data by partitioning 128 bits to 32 bits. As different of the AES, It is slower 5 percent than AES because It has two rotation by 1 bit. Also It is costly than AES for causing increasing computing times.

#### IRON

It uses Feistel method like TWOFISH and DES. IRON is used to encryption 64 bits blocks by 128 bits key. Number of cycles is between 16 and 32. Subkeys is depend on cycles number. Number of subkeys is equal to number of cycles. Therefore, algorithm is dependent for key. Advantage of the algorithm is using 16 based number system as a substitute to bits. Disadvantage of it has been designed for software.

#### AES (The Advanced Encryption Standard)

AES had developed by John Daemen and Vincent Rijmen as named Rijndael. It standarded in 2002. AES uses block that fixed at 128 bits by with key that length is 128 bits or 192 bits or 256 bits. It is the most popular symmetric algorithm since 2006.

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