The classic methods in the current network security transmission scheme are divided into symmetric encryption and asymmetric encryption. Symmetric encryption operation is fast but easy to be attacked and cracked; asymmetric encryption algorithm is complex and not easy to be cracked, but the encryption speed is slow, which is not suitable for transmitting large amounts of security data. Through the research on the Huffman compression method, it can be known that different data files can form different Huffman compression coding tables and compressed files with a small amount of data after Huffman compression. Through the scheme of asymmetric encryption design on the Huffman coding table, the number of bytes encrypted by the asymmetric encryption algorithm can be reduced, and asymmetric encryption of large data files can be realized. At the same time, by compressing large data files, you can reduce the entire file size and improve network transmission efficiency. The program has been applied in multiple network security transmission projects and can fully meet the network transmission security requirements. In recent years, with the rapid development of computer and network technology, more and more social groups, agencies, enterprises and institutions have established computer networks, and people have shifted their focus to social activities, office work, and scientific research. In the network, a huge interconnected network composed of local area networks as nodes is formed. More and more data exchange tasks between internet nodes need to be completed in order to realize the sharing of computer software, hardware resources and information resources. Data exchange in an open system such as the Internet is critical for data with high security requirements, and data security during transmission. The core of network data transmission security is to encrypt data in each link of data transmission, network transmission, and data reception to achieve the purpose of data security. Protect the confidentiality, integrity, authenticity, reliability, availability, and non-repudiation of data transmitted, exchanged, and stored in public network information systems. The encryption technology is the core of data transmission security. It encrypts data from plaintext to ciphertext through encryption algorithm and communicates. Even if the ciphertext is intercepted by hackers, it is difficult to be deciphered, and then decodes the ciphertext to restore the plaintext through corresponding decoding technology. At present, the commonly used encryption methods in the world mainly include symmetric encryption and asymmetric encryption. Different encryption methods have different characteristics. They are widely used in network systems with high data transmission security and high requirements, such as e-commerce and mail transmission. aspect. 1 Status of encryption algorithms Cryptography is a science to ensure that the data transmitted between the sender and the receiver is not obtained by a third party, but the data to be transmitted is encrypted to obtain confidentiality. The transmitted data is usually called plain text. In order to protect the plain text, it is transformed into an unrecognized cipher text in some way. This conversion process is called encryption; on the other hand, the cipher text can be restored to the plain text through the corresponding inverse transformation. This process is called decryption. The encryption algorithm can be seen as a complex function transformation: C = F (M, Key) In the formula: C stands for cipher text, that is, the character sequence obtained after encryption; M stands for plain text, that is, the character sequence to be encrypted; Key represents the key, which is a secretly selected character sequence. After the encryption is completed, the ciphertext can be sent to the data receiver through an insecure channel. Only the data receiver who has the decryption key can decrypt the ciphertext, that is, the inverse transform obtains the plaintext. The key must be passed through a secure channel. Current general encryption algorithms are mainly divided into symmetric and asymmetric algorithms. The symmetric algorithm uses the same key for encryption and decryption. Commonly used symmetric encryption algorithms are AES, IDEA, RC2 / RC4, DES, etc. The biggest difficulty is the issue of key distribution. The keys must be exchanged through secure methods in person or in public transmission systems. Symmetric encryption is still widely used to encrypt various information due to its fast encryption speed, easy hardware implementation, and high security strength. However, symmetric encryption also has inherent shortcomings: it is difficult to replace the key, and the same key is often used for data encryption, which provides attackers with information and time to attack the key. Asymmetric algorithm, using public key for encryption and private key for decryption. The public key can be made public and can be obtained by anyone. The data sender uses the public key to encrypt the data and then transmits it to the data receiver. The receiver uses its own private key to decrypt it. The security of asymmetric encryption mainly depends on difficult mathematical problems. The length of the key is much larger than that of symmetric encryption, so the encryption efficiency is low. It is mainly used in the fields of identity authentication and digital signature. Asymmetric encryption has a slow encryption speed and is not suitable for encrypted transmission of large amounts of data. Asymmetric encryption algorithms include RSA, DH, EC, DSS, etc. At present, the most popular and most famous asymmetric encryption algorithm is RSA. The security of RSA lies in the difficulty of factorization of large integers. Its system construction is based on Euler's theorem of number theory. The method of generating public and secret keys is: (1) Take two mutually different large prime numbers p and q; (2) Calculate n = p & TImes; q; (3) Randomly select the integer e, and e and (p-1) & TImes; (q-1) are prime numbers of each other; (4) Find another number d to satisfy (e & TImes; d) mod [(p-1) & TImes; (q-1)] = 1; (n, e) is the public key; (n, d) Is the private key. For plaintext M, encrypt with public key (n, e) to get ciphertext C, C = Me mod n; for ciphertext C, decrypt with private key (n, d) to get plaintext M, M = Cd mod n. With today's predictable computing power, it takes hundreds of thousands of years to decompose the product of two 250-bit prime numbers in decimal, and the probability that the prime numbers are used up or two computers accidentally use the same prime number is too small to be ignored. It can be seen that attempts to infer plaintext using public keys and ciphertexts or inference of private keys using public keys are extremely difficult and almost impossible. Therefore, this mechanism provides high security for information transmission. It can be found from the above content that both symmetric encryption and asymmetric encryption processes complete the following processes: (1) Generate key key; (2) C = F (M, Key), that is, use the generated key to convert the plain text into cipher text through the encryption algorithm. (3) Data transmission; (4) M = F '(C, key), that is, the receiver uses a decryption algorithm to convert the ciphertext to plaintext. If the plaintext data to be transmitted is huge, the encryption and decryption algorithm will take a very long time, and the data transmission will also take up a lot of network resources. That is, the above three processes (2), (3), (4) will occupy a lot of time and resources. If the time of these three processes can be reduced, a lot of resources will be saved and the efficiency of data transmission will be improved. By using Huffman coding to compress the file, the processing time of the above three links can be greatly reduced, and at the same time, the occupation of computer resources and network resources can be reduced during the transmission process. 2 Introduction to Huffman coding Huffman coding was developed by Professor Huffman in the 1950s. It uses the tree structure in the data structure to construct an optimal binary tree with the support of the Huffman algorithm. For the Huffman tree. Therefore, to be precise, Huffman coding is a coding form constructed on the basis of the Huffman tree, which itself has a very wide range of applications. 2.1 Basic principles The theoretical basis for data to be compressed is as follows: Definition 1 For a given source and code symbol set, if there is a unique decodable and the average code length L is less than all other unique decodable, then this code is called compact code or best code. Theorem 1 Huffman coding is a compact code. Computer files are composed of bytes, and the value of each byte ranges from 0 to 255. Each byte is regarded as a character, a total of 256 kinds of characters. Therefore, each byte is represented by a fixed-length code of 8 binary bits. Since this fixed-length code is also the only decodable, according to Theorem 1, L≤8. If a file is composed of N bytes, the total length of the file is 8N bits. If the file is Huffman encoded, the total length of the file is LN bits. Since L≤8, LN≤8. Therefore, as long as the file satisfies L <8, Huffman encoding can always compress it. Huffman coding is a variable-length coding, that is, by using a shorter codeword to encode a source symbol with a higher probability of occurrence, and a source symbol with a lower probability of occurrence is encoded with a longer codeword, thus Make the average code length the shortest to achieve the best coding purpose. Since Huffman coding can only encode source symbols whose probabilities are known, it is a kind of statistical coding.
Drum
type Rice Cooker
Features
This type rice cooker is famous with drum type appearance, which
is easy operation and easy clean.
There are two type of inner pot , one type called white pot which is without non-stick but cheaper price
.another one called non-stick pot is polished with emery, Also there are two
type non-stick with different price ,it`s depending on different demands to
use.
And the inner pot cannot be burned on the stove, which will make
the pot transfigured and bad contact with the heating plate. While cooking , the
heating plate or the fuse is most likely to be burned for the bad contact of
the inner pot and the heating plate, Besides, make sure to dry the pot before
putting into the outer shell of the rice cooker ,or else the drops of water
flowing on the heating plate, will make the heating plate rusted.
Applications
Many
peoples are used drum type rice cooker for congee and soup, some of peoples are
prefer to use this type rice cooker for steaming.
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