tailieunhanh - Bảo mật hệ thống mạng part 34

Có hai loại chính của mã hóa: tư nhân chủ chốt và công chính. mã hóa khóa cá nhân yêu cầu tất cả các bên được phép đọc thông tin để có các phím tương tự. Điều này sau đó làm giảm tổng thể của vấn đề bảo vệ thông tin cho một trong những bảo vệ chính. mã hóa khóa cá nhân là loại được sử dụng rộng rãi nhất của mã hóa. | 211 Chapter 12 Encryption The lesson here is that the surrounding system is just as important to the overall security of encryption as the algorithm and the key. PRIVATE KEY ENCRYPTION There are two primary types of encryption private key and public key. Private key encryption requires all parties who are authorized to read the information to have the same key. This then reduces the overall problem of protecting the information to one of protecting the key. Private key encryption is the most widely used type of encryption. It provides confidentiality of information and some guarantee that the information was not changed while in transit. What Is Private Key Encryption Private key encryption is also known as symmetric key encryption because it uses the same key to encrypt information as is needed to decrypt information. Figure 12-2 shows the basic private key encryption function. As you can see from the figure both the sender and the receiver of the information must have the same key. Private key encryption provides for the confidentiality of the information while it is encrypted. Only those who know the key can decrypt the message. Any change to the message while it is in transit will also be noticed as the decryption will not work properly. Private key encryption does not provide authentication as anyone with the key can create encrypt and send a valid message. Generally speaking private key encryption is fast and can be easy to implement in hardware or software. Sender z------- Message Receiver z-------- Message Figure 12-2. Private key encryption 212 Network Security A Beginner s Guide Substitution Ciphers Substitution ciphers have been around for as much as 2 500 years. The earliest known example is the Atbash cipher. It was used around 600 . and consisted of reversing the Hebrew alphabet. Julius Caesar used a substitution cipher call the Caesar cipher. This cipher consisted of replacing each letter with the letter three positions later in the alphabet. .