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Encryption and Decryption

What is Encryption and Decryption?
Encryption is the process of changing intelligible data into unintelligible data. Decryption is the opposite of encryption it decrypt the encrypted data into intelligible data. 

Most information in  today's world are free to use, for example internet has huge information, you can ask any topics you get terabytes of information in your finger tips, however some information is not meant for public eyes and has to be secured, for example military operations, financial information, medical reports, bank transaction, private data are all types of information must keep secret. this where the data encryption takes place. It also know as cryptography.

Cryptography which comes from Greek words kryptos or hidden and graphein or to write  is the science of secret communication. It is a methodology for transforming the representation or appearance of a message through a position scrambling process or through some method of transformation of letters or characters without changing its information content.

The original message is called plaintext or cleartext and the transformed message is known as the ciphertext, which is also some times called cryptogram.

A wide range of encryption technique have been devised. Some are simple, whereas others are incredibly complex. Obviously, the simpler the encryption technique, the easier it is to crack, Also as commuter hardware are get faster and more efficient, they become more capable of cracking existing encryption techniques. The encryption function has two inputs, one of which is the plain text and the other is called key. The key consists of a finite number of bits which are usually expressed as decimal, hexadecimal, or alphanumeric character strings.

The effectiveness of the encryption technique dose not depend on whether or not the encryption algorithm is secret. Instead its success in preventing information security breaches depends on the degree of difficulty required to decipher it without the knowledge of the decryption key, A property of the decryption key is that it should not be derivable by any one who has the knowledge of the encryption key, ciphertext and the plain text. The amount of work required to break the code should be prohibitively expensive compared to the value of the information being protected.

The theory and practice of uncovering a secret from either cipher text or encryption keys without the authorization of the sender is know as the cryptanalysis. The means of doing this is called the method of attack.

Data Encryption Standard (DES)
DES was developed by the U.S. National Bureau of Standards in 1975 in an attempt to devise an encryption method that could be used in government applications. It has become one of the world's most used encryption techniques.

DES encrypts data in 64-bit blocks of text, using a 56-bit key. DES has then benefit of being a known quantity with familiar strengths and weakness. In typical applications it is unlikely to be vulnerable to any attack specially brute force. In the late 1980's the public cryptanalysis, which proved to be effective against DES under a narrow and impractical set of conditions. Many users are drawn to DES beacuse it is U.S. government. This provides justification for its use, which other crypto algorithm lack.

Later version of DES such as 3-Round DES (Triple DES) as 6-Round DES, encrypt data multiple times using the same encryption method but different keys. potentially using a different 56-bit key each time. Typical applications use a 112-bit key constructed of a pair of 56-bit keys, key1 and key2, with key1 being reused for the final encrypt operation. A triple DES device can interoperate with conventional DES encryption  by using and identical key value for key1, key2, key3. This is because the second step is decrypt operation, using the same key in all three steps yields the same result as encrypting only once with key. Typical approaches use two conventional DES keys, yielding a length of 112 bits. Some applications use three different keys, yielding a total key size of 128 bits, which is truly enormous for a symmetric cipher. The longer the key (that is, the more bits is uses) the more difficult it is to crack.

International Data Encryption Algorithm (IDEA)
IDEA is a block cipher that appeared in 1990 as the replacement for DES. Xuejia Lai and James Massey developed IDEA as the Swiss Federal Institute of Technology. IDEA is more efficient to implement in software than DES or 3 DES, and its 128 bit key makes it more attractive than conventional DES. Its is a block based algorithm text are split into 16-bit blocks taht are each encrypted separately. A long sequence of calculations and bit operation are performed on the data and then the 16-bit blocks of encrypted data are combined together to once again form a 64-bit block.

Many experts are optimistic about IDEA and its likelihood stand the test of time, it is one of the most secure encryption method ever devised, and it has not yet been broken, Of course, that might change in the near future, as new methods of cryptanalysis are created.

Rives Cipher #4 (RC4)
RC4 is a stream cipher marketed by RSA Data Security. Although its key size can vary, it is often used with a 128-bit key. originally the cipher was protected as trade secret, only to be leaked to the crypto community via internet. The most cited problem is its use with short key lengths. Typical implementation use a very short key length and suffer from corresponding vulnerability to brute force craking.

SKIPJACK is a block encryption algorithm developed by the NSA. It encrypts 64-bit bloks using an 80 bit key. The usual block cipher modes may be used with it to encrypt streams. It is provided with prepackaged encryption chip sets and in fortezza crypto card, a PC card contain a crypto processor and storage for keying material.

The SKIPJACK algorithm is classified, when dramatically limits how much is publicly known about its essential cryptographic properties. The algorithm is at least as resistance as the best commercial algorithms.

Pretty Good Privacy (PGP)
PGP is created by Phil Zimmermann, PGP uses a public/private key encryption strategy, where two different keys are used for encryption and decryption. One key is made public, and one is kept secret. The public key is used for encryption, so any one can encrypt the data with public key. To decrypt data it requires private key. It is best use in untrusted network channel like internet where any body can send data by encrypting it with public key without knowing the private only authorized person with private key can decrypt the data.

PGP has the capability of using large keys up to 2047-bits in size, PGP is one of the best secure methods of data encryption ever devised. PGP uses IDEA method for its data encryption. It also uses elements of other encryption methods such as RSA (Rivest-Shamir-Adelman) and MD5 (Message of Digest 5) to manage its keys as well as for data hashing and compression.

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