Hmm...
	What's the matter?
	When we use mail order site, we input Credit Card Number.
	Is it exploited by third party? Do you mean persoal information outflow?
	Yes, that's right. How do they prtect our personal information?
	Well, Let's examine encyption!

Internet is amasing but there are many anxiety.
One of them is persoal information outflow .
Why don't informations flow out?
Because we use encyption!

Encyption to make the secret difficult to read?

What is encyption?
It is a technology which enable secure communication.
It was used when war was happened.
Of course, we can use encyption.
What does complete encyption need?
It needs confidentiality, integrity, authentication.

Confidentiality

It means avoiding steal communication data of another person.
Even if your data is stolen, you can't notice.
Information browsing prohibition measures is encyption.

Integrity

We must protect our data from rewrite by third party.
One of countermeasure is digital signature.

Authentication

Spoofing is occur frequently.
So Certificate authority is playing an active role.
This organization publish a deed to prove that user don't fake.

Mechanism

Encyption has two types. One is Symmetric-key cryptography, and the other is Public key encryption.
These two keys encypt your important data, and decrypt.