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**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**

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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