tailieunhanh - Bảo mật hệ thống mạng part 35

Mã hoá CÔNG CHÍNH Công khoá mật mã là một phát minh mới hơn mã hóa khóa riêng. Sự khác biệt chính giữa hai loại mã hóa là số lượng các phím được sử dụng trong hoạt động. Trường hợp sử dụng mã hóa khóa riêng một chìa khóa để cả hai mã hóa và giải mã trong hình, mã hóa khóa công khai sử dụng hai phím. Một khóa được sử dụng để mã hóa và một phím khác nhau được dùng để giải mã thông tin | 219 Chapter 12 Encryption Skipjack Skipjack was developed by the United States government for use with the Clipper Chip. It uses an 80-bit key which may be marginal in the near future. Blowfish Blowfish allows for variable length keys up to 448 bits and was optimized for execution on 32-bit processors. CAST-128 CAST-128 uses a 128-bit key. It is used in newer versions of PGP. GOST GOST is a Russian standard that was developed in answer to DES. It uses a 256-bit key. Any of these algorithms may appear in security products. All of them are likely to be strong enough for general use. Keep in mind that it is not only the algorithm but also the implementation and the use of the system that define its overall security. PUBLIC KEY ENCRYPTION Public key encryption is a more recent invention than private key encryption. The primary difference between the two types of encryption is the number of keys used in the operation. Where private key encryption uses a single key to both encrypt and decrypt information public key encryption uses two keys. One key is used to encrypt and a different key is then used to decrypt the information. What Is Public Key Encryption Figure 12-9 shows the basic public key or asymmetric encryption operation. As you can see both the sender and the receiver of the information must have a key. The keys are related to each other hence they are called a key pair but they are different. The relationship Figure 12-9. Public key encryption n Network Security A Beginner s Guide between the keys is such that information encrypted by K1 can only be decrypted by its pair K2. If K2 encrypts the information it can only be decrypted by K1. In practice one key is called the private key and the other is called the public key. The private key is kept secret by the owner of the key pair. The public key is published with information as to who the owner is. Another property of public key encryption is that if you have one of the keys of a pair you cannot compute the .