/*****************************************************************************  

The main idea is that no password are sent between client & server on  

connection and that no password are saved in mysql in a decodable form.

  On connection a random string is generated and sent to the client.  

The client generates a new string with a random generator inited with  

the hash values from the password and the sent string.  

This ‘check‘ string is sent to the server where it is compared with  

a string generated from the stored hash_value of the password and the  

random string.

  The password is saved (in user.password) by using the PASSWORD() function in  

mysql.

  This is .c file because it‘s used in libmysqlclient, which is entirely in C.  

(we need it to be portable to a variety of systems).   Example:    

update user set password=PASSWORD("hello") where user="test"  

This saves a hashed number as a string in the password field.

  The new authentication is performed in following manner:

  　　SERVER:　public_seed=create_random_string()           

　　　　　　　　send(public_seed)

  　　CLIENT: 　recv(public_seed)   

　　　　　　　　hash_stage1=sha1("password")           

　　　　　　　　hash_stage2=sha1(hash_stage1)           

　　　　　　　　reply=xor(hash_stage1, sha1(public_seed,hash_stage2)

           　　　// this three steps are done in scramble()

           　　　　send(reply)

　　　SERVER:  recv(reply)

　　　　　　　　hash_stage1=xor(reply, sha1(public_seed,hash_stage2))           

　　　　　　　　candidate_hash2=sha1(hash_stage1)           

　　　　　　　　check(candidate_hash2==hash_stage2)

           　　// this three steps are done in check_scramble()

*****************************************************************************/

PASSWORD MySQL 5.6.21-1ubuntu14.04_amd64