Encryption systems are important for protecting sensitive information that is transmitted online, such as credit card numbers, social security numbers, private messages, and company secrets. The document introduces symmetric-key encryption, where both parties have the same secret key, and public-key encryption, which uses a public and private key pair to securely communicate. It describes how secure sockets layer (SSL) is used to encrypt web traffic and ensure sensitive information is protected when browsing or conducting financial transactions online. Hashing algorithms are also introduced as a way to securely generate keys for public-key encryption systems.

1. 1.Introduction to How Encryption Systems
You are usually related to various encryption systems.
For example,
Credit-card information Social Security numbers
Private correspondence Personal details
Sensitive company information Bank-account information
Thus, encryption systems are very important.
In this article, you will learn about encryption and
authentication. You will also learn about public-key
and symmetric-key systems, as well as hash
algorithms.

2. 2.Security Encryption Systems
・Encryption
It is based on the science of cryptography.
・The first cipher (The Greeks used this way )
1 2 3 4 5 For example:
1 A B C D E I AM SPARTA
2 F G H I/J K → 42 11 23 34 53 11 24 44 11
3 L M N O P
4 Q R S T U I AM SATO
5 V W X Y Z → 42 11 23 34 11 44 43
If they could arrange the letters inside the grid in any
combination, you could not decode any message.
・Computer encryption sytems
- Symmetric-key encryption
- Public-key encryption

3. 3.Symmetric Key
● Computers using symmetric-key encryption to
send information between each other must
have the same key.
● In symmetric-key encryption, each computer
has a secret key (code) that it can use to
encrypt a packet of information before it is sent
over the network to another computer.
● Symmetric-key requires that you know which
computers will be talking to each other so you
can install the key on each one.

4. 4.Public key Encryption
・Encryption
Public-key encryption uses two different keys at
once to combine a private key and a public key.
・How to communicate securely
The private key is known only to your computer.
The public key is given to any computer.
1. An encrypted message is created by the public key.
- The public key only can encrypt information.
2. An encrypted message is sent the originating computer.
- The originating computer only can decode it.
The key pair is based on prime numbers, meaning key
has infinite possibilities and extremely secure.

5. 5.SSL and TLS
・Origin
Secure Sockets Layer (SSL) was developed by Netscape,
SSL is an Internet security protocol used by Internet
browser and Web servers.
SSL is packaged on Transport Layer Security.
・Locations
SSL is used by online bank or a payment transfer
service,such as PayPal or Google Checkout.
・How to know
If you could look the "https" in the addressbar, this web
page is used SSL to protect sensitive information and to
secure communication.
SSL's certificate is made from a trusted party.

6. 6.Hashing Algorithm
● The key in public-key encryption is based
on a hash value.
Hash is a value that is computed from a base
input number using a hashing algorithm.
Essentially, the hash value is a summary of the
original value. The important thing about a hash
value is that it is nearly impossible to derive the
original input number without knowing the data
used to create the hash value.