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MD5 encryption

2022-07-02 15:28:00 【Killer is not too cold!】

MD5 encryption

Basic concept information

** First, what is encryption ？** encryption , Is a special algorithm to change the original information data , Enables unauthorized users to obtain encrypted information , But I don't know how to decrypt , Still unable to understand the content of the information .

** Symmetric encryption ？** Symmetric encryption uses the same key for encryption and decryption .

** Asymmetric encryption ？** Asymmetric encryption uses different keys for encryption and decryption . Cailin now wants to pass a piece of data to Bob , But if Kailin uses clear text transmission on the Internet , She is worried that her information will be obtained by others , So what to do ？ Cailin can get Bob's public key first , Then use Bob's public key to encrypt the plaintext , Encrypted into ciphertext , When Bob finally got the ciphertext , Then use your private key to decrypt , That's it .

Abstract algorithm ？ The digest algorithm is also called hash algorithm , Hash algorithm , Data of any length can be converted into a Fixed length , Irreversible numbers . What is fixed length ？ It's your data, no matter how long , Finally, it is converted into a summary, and then the length is fixed ; What is an irreversible number ？ Unlike symmetric algorithm and asymmetric algorithm , Because they can be decrypted after encryption , However, the abstract algorithm cannot obtain the original text through decryption after encryption , Its encryption is irreversible .
As long as the original text is different , The result of calculation must be different （ There is little need to consider repetition ）. The algorithm is used to compare whether the information sources are consistent , Because as long as the data source changes , The summary information obtained must be different , Usually used for signature verification .
The characteristics of message digest algorithm ：
No matter how long the message is entered , Always calculate the length of the message that comes out of the digest .
The message digest is not really random , Because the same message is used for two abstracts , The result must be the same .
The message digest function is a one-way function without trap gate , That is to say, only forward information summarization can be carried out , No message can be recovered from the digest , Even no information related to the original information can be found .
Common summary algorithms are ：MD5,SHA-1,MAC,CRC etc. .
It is widely used to verify the integrity of data and the transmission and storage of sensitive information .
MD5 Algorithm ：MD5 Information digest algorithm , A widely used cryptographic hash function , I can produce one 128 position （16 byte ） Hash value , Used to ensure complete and consistent transmission of information .2004 year , confirmed MD5 Algorithms can't prevent collisions （collision）, So it doesn't apply to security certification , Such as SSL Public key authentication or digital signature .
** What is called collision ？** We use MD5 Encrypted ciphertext cannot be restored , But if we have one to save common passwords and MD5 Encrypted database of ciphertext mapping relationship , Then we can compare the ciphertext , And then know what the corresponding original text is .

Basic applications

**md5-min.js and md5.js The difference between ？**md5.js Well formed js, It's for developers ;md5-min.js It's a compressed version js, It's for browsers .

md5 The front-end encryption is as follows ：

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <title>Document</title>
        <script type="text/javascript" src="./md5.js"></script>
        <script type="text/javascript"> /** * md5 After encryption  admin => 21232f297a57a5a743894a0e4a801fc3 * */ console.log("md5 => "+hex_md5("admin")); /** *  Add salt （MD5 There is no way to decrypt by algorithm , But it can be brutally cracked 【 Rainbow watch 】, Not enough security , The rainbow table is actually a plaintext and ciphertext  *  Mapped database tables ） *  Salt is a specific string （ Make it your own ） Of , Used to mix with encrypted content , The mixed content is carried out again md5 encryption , Data is more secure  *  such as ： * admin salt => 0x3d1eaaa *  Let the text and salt Mix （ at will ） * admin0x3d1eaaa *  Then the mixed text is md5 Encryption operation , In this way, even if our ciphertext is cracked , But it also doesn't know what our plaintext is  * */ </script>
    </head>
    <body class="index">
         I am a body
    </body>

</html>