Cryptography overview (1)
/ ***** At present, a few articles about password studies, good things, let everyone share **** /
So far, we have had a considerable understanding of the basic knowledge of the network, and even the TCP / IP protocol knows a lot, so I want to ask you a very simple question - rest assured, not test, this question is : Do you have free email? --99.99% of the possibility, is it? (What? You still don't know you, please apply for a !!!) Next, tell you a comparative fact, hey, do you know, your email is in the form of a plain text on the form of a clear text? Oh, I don't know it. --Ok, grace, everyone is doing, start lectures! !
Above we already know the need for encryption, now we look at the process of encryption with an example. Suppose you want to give you a secret message through the Internet, so you intend to encrypt it. You have changed it into an irregular code encrypted information in a complex way. In addition to your cousin, no one can explain it into a document that can be read, and she can understand it, but because you give She a decryption method, she will use it to make the encrypted message rule and restore its true look. The conventional single key encryption method is: Tell her encrypted password before you use it to encrypt. For example, a simple single key encryption method is to move 3 digits in the order of the alphabetical table in the original information. In this way, the single DOG changes to GRJ, the table below shows a document encrypted by a single key encryption scheme.
H a p p y n e w y e a r k d s s a c q h z c a h d u
After you receive your message, you will be able to decrypt the letters in the order of the alphabetic table, and then the solution is that it is such a sentence, and immediately lives. Three minutes. From China, the process of extracting encrypted decryption is as follows:
Ok, this is basically the process of encrypting decryption. Of course, we will also talk about the process of different key systems, so we now talk about the key system.
If the key system is standard, the cryptographic system can be divided into a single key password (also known as a symmetrical password or private key password) system and a two-key password (also known as an asymmetric password or public key password) system. Oh, yes, the so-called key is almost understandable. Under the single key system, the encryption key and the decryption key are the same, or in substantially equivalent, in which case the key passes through the secure key channel by the hairper. The characteristics of the single key password are the use of the same key whether encryption or decryption. Therefore, the security of this password system is the security of the key. If the key is leaked, this password system is broken. The most affected single key password is the DES algorithm issued by the 1977 National Standard Administration. The advantage of the single key password is: high security. Adding secret speed is fast. The disadvantage is: 1) With the expansion of the network size, the management of the key is a difficult point; 2) Unable to resolve the message confirmation problem; 3) Lack of automatic detection key leakage. In the two-key system, the encryption key and the decryption key are different. At this time, there is no need to transfer the key at all, and only the decryption key can be generated using the local key generator. The key password is: a new type of cryptosystem proposed in W. Diffie and M.E.heilin 1976. Since the encryption and decryption of the two key cryptographic system is different, but only the encryption key is disclosed, it only needs to be confidentially decryled, so the key password does not have key management issues. One advantage of the key password is that there are new features such as digital signatures. The most famous key cryptograph is: In 1977, the RSA password system proposed by Rivest, Shamir and Ad1eman. The disadvantage of the key password is that the key cryptographic algorithm is generally complicated and the add-on-speed is slow. Therefore, the encryption in the network generally uses a hybrid encryption system combined with a double key and a single key password, i.e., a single key password is used, and the key transfer is used. This has solved the difficulties of key management, and solves the problem of addeptical speed. At present, this method seems to be like this.
