What is MD5

What is? md5?

md5 Is an irreversible hash algorithm

1. Irreversible ： Ciphertext can be obtained from plaintext , But you can't get plaintext from ciphertext .
2. hash ： Get a mapping value through a function , It could be repetitive ！ But the probability of repetition is relatively low , For example, set characters + Case letters + Digital password , The probability of getting the same ciphertext through hashing is very, very low .

Application scenarios

1. Password storage ：
   On safety grounds , Native passwords cannot be stored directly in the database , If the data is leaked, it will cause many problems , therefore , Will pass the password md5 Encrypted and stored in the database , I'm sure you know that .

2. Consistency check ：
   This is a usage I found when making payment signatures , Not used before . When the client calls the third-party payment , Need is to use http（s） Transmission request , Once the request is blocked , Be modified , For example, payment 1000 element , Intercepted as 1 element , After successful payment , The third party returns the result of successful payment , It will cause serious damage .

   So people use a ciphertext , Process the request parameters into a string ： for example “amount=50&payMethod=native&id=012345”, Then encrypt the string , Send with the request . After receiving the request, make a consistency check with the plaintext parameters , Check the consistency of parameters .
   Of course , The real encryption means involving payment will be more complex , For example, certificates and so on , Using this example is just an illustration md5 It can be used as a means to verify the consistency of passwords .

How to improve security

1. Add salt
   Salt value is a meaningless random string , It can be a paragraph uuid, It can also be a random number . Adding salt can prevent hackers from using some comparison tables to crack simple passwords （ such as 123456,password These common passwords , The frequency of use is very high , You can find ）.

2. Multiple encryption
   Will be encrypted md5 Re encrypt the password , Cycle a few times , The ciphertext thus formed cannot be found through the comparison table .