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encryption algorithm

At present, the general encryption algorithm is divided into symmetric and asymmetric algorithms. Symmetric algorithm uses the same key for encryption and decryption. Commonly used symmetric encryption algorithm has AES, IDEA, RC2/RC4, DES, etc.. The most difficult problem is the key distribution problem, which must be exchanged by using a secure method in person or in a public transport system. Symmetric encryption because of fast encryption speed, easy to implement hardware, high security. It is still widely used to encrypt all kinds of information. However, there are some inherent shortcomings in the symmetric encryption: the key exchange is difficult, often using the same key for data encryption, to provide the attacker with the information and time to attack the key. Asymmetric algorithm, the use of public key encryption and decryption using the private key. The public key is public, anyone can access, data transmission with public key encrypted data is then transmitted to the data receiver, with their own private key to decrypt the recipient. The security of asymmetric encryption mainly depends on the difficult mathematical problem, and the length of key is much larger than that of symmetric encryption. Therefore, the encryption efficiency is low, mainly used in the field of identity authentication, digital signature and so on. Asymmetric encryption is slow, and it is not suitable for mass data encryption. Asymmetric encryption algorithms include RSA, DH, EC, DSS, etc.. At present, the most popular, the most famous asymmetric encryption algorithm is RSA.

The security of RSA lies in the difficulty of factoring large integers. The system structure is based on the Euler theorem of number theory:

(1). Take 2 different large prime numbers P and q;

(2). Calculate n=p * q;

(3). Random selection of integer e, and E (p-1) x (Q-1) are prime numbers;

(4). Find a number of D, to meet (E * d) mod[(p-1) x (Q-1)]=1 (n, e) is a public key (n, d) as the private key. For plaintext M, with public key (n, e) encryption can get ciphertext C, C=Me mod n; for ciphertext C, with the private key (n, d) can be decrypted plaintext M, M=Cd mod.

By using the predictive calculation ability, in decimal, with hundreds of thousands of years 2 250 product decomposition of prime numbers, the probability is small enough to be prime and exhausted or 2 computers by using the same prime numbers are ignored. Therefore, it is almost impossible to deduce the secret key from the public key and the ciphertext, or to attempt to use the public key to infer the private key. Therefore, this mechanism provides high security for information transmission.

From the above we can see that both the process of symmetric encryption and asymmetric encryption are done as follows:

(1). Generate key key;

(2). C=F (M, Key), that is, the use of the key has been generated by the encryption algorithm will be converted to plaintext ciphertext.

(3). Data transmission;

(4). M=F '(C, key), that is, the receiver uses the 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 long time, and the data transmission will take up a lot of network resources. That is, (2), (3), (4) the process will take up a lot of time and resources, if we can reduce the time of the 3 processes, it will save a lot of resources, improve the efficiency of data transmission. Through the use of Huffman coding to compress the file, you can greatly reduce the processing time of the above 3 links, and at the same time in the transmission process to reduce the computer resources and network resources.

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