1. What is encryption ?
A encryption is code for security and when we use a computer
, it is necessary . The code has several form and use .

2. Security Encryption Systems
Computer's code is based on cryproqraphy . This code was
used for military on purpose . Let introduce following code .
First , the code which uses scytale and write your message
along its length . When someone removed the paper from the
cylinder , he can't read the message . Only person who has a
scytale of similar size can read it . Second , the code which
uses ciplers . This code uses a table which a number
correspond to character .

3. Symmetric key
A code needs a key to decode the massage which is
coincided . When two person exchange the message
to each other , the message is coincided not to be
read by someone . Only they have a key . For
example , if key is “shift by 2” . Code send the key to
them .
The key called DES was used in the U.S in the 1970's
.DES uses a 56-bit key . DES has 70 quadrillion
combinations . But it was cracked by brute force . So
DES has since been replaced by AES . AES uses a
256-bit key .

4. Public key encryption
One of the weaknesses point out about symmetric key
encryption is that two users must have same key . In November
1976 , public key encryption was released in the journal IEEE .
This key uses two different keys at once . The private key is
given by your coomputer to any computer . You need private
key and public key to decode message . These key consist of
prime number .

5. SSL and TLS
A popular implementation of public-key encryption is the
Secure Sockets Layer (SSL) . SSL is an Internet security
protocol used by Internet browsers . TLS is a secure protocol .
You can see that the “http” in the address line is replaced with
“https” when you are accessing sensitive information , such as
an online bank You will know your information will most likely
pass along securely .

6. Hashing Algorithm
The key in public-key encryption is based on a hash
value , Hash value 's feature is that it is nearly
impossible to derive the original number without
knowing the data used to create the hash value
.Hashing algorithm can create very large hash value
including 40-bit or even 128-bit numbers .