Goal of Security

 Confidentiality(机密性)

what?(只有授权的人才能获取数据)

1.Data in transmission or stored in a storage system could be very sensitive and only authorized people are allowed to read.
2. Keeping data confidentiality means preventing unauthorized reading of data

how to?
1. Encryption & Decryption（加密和解密）
Use a secret 1-to-1 mapping (function) to map a plaintext m into a ciphertext

To recover the plaintext from the ciphertext ,apply the inverse mapping
 Q: How to do en(de)cryption, so that it is safe and efficient?（安全和有效）

 Integrity(完整性)

what?

For data in transmission or stored in a storage system the following could happen:
◦ Modification(篡改): It could be modified by an unauthorized person.
◦ Spoofing(欺骗): It could be replaced with another data by an unauthorized person.
◦ Repudiation(否认): The sender or receiver may deny sending or receiving the message.

how to?

 Keyed Hash Functions

Data authentication(When receiver receives c, how can he conclude whether c is authentic?)

Sender & receiver authentication
◦ Q: If you received a message with alleged sender X, how could you be sure that the sender is indeed X?
◦ Q: If you sent a message to a receiver Y ,how could you be sure that the receiver is indeed Y?

(Non)Repudiation
◦ Q: If you received a message with alleged sender X, how could you prove that the sender is indeed X evne if X denied?
◦ Q: If you sent a message to a receiver Y , how could you be sure that the receiver indeed received the message?
The solution is : Digital Signature(数字签名)

 Availability(可用性)

what?

The information created and stored by an organization needs to be available to authorized entities any time
Distributed Denial of Service (DDoS) attack