作者：Sri Sakthivel
MySQL 8.0 在密码管理方面有很多改善，本文将介绍以下两个特性。
- 密码重用策略
- 生成随机密码
| 1 密码重用策略
该策略简单说，就是设置新密码时，可以限制禁止使用曾经用过的密码。有以下两种策略：
- 历史密码 password_history
- 间隔时间 password_reuse_interval
1.1 历史密码
MySQL 官方手册描述：
If an account is restricted on the basis of number of password changes, a new password cannot be chosen from a specified number of the most recent passwords.
在实验环境中，创建用户并添加条件password history 2，历史密码中最近的两个不能被重新使用。
mysql> create user 'herc'@'localhost' identified by 'Percona@321' password history 2;
Query OK, 0 rows affected (0.02 sec)
mysql> select user, host, password_reuse_history from mysql.user where user='herc'\G
*************************** 1. row ***************************
user: herc
host: localhost
password_reuse_history: 2
1 row in set (0.00 sec)MySQL 将在 mysql.password_history 表上记录密码更改的信息。
mysql> select * from mysql.password_history;
+-----------+------+----------------------------+------------------------------------------------------------------------+
| Host | User | Password_timestamp | Password |
+-----------+------+----------------------------+------------------------------------------------------------------------+
| localhost | herc | 2021-09-20 15:44:42.295778 | $A$005$=R:q'M(Kh#D];c~SdCLyluq2UVHFobjWOFTwn2JYVFDyI042sl56B7DCPSK5 |
+-----------+------+----------------------------+------------------------------------------------------------------------+
1 row in set (0.00 sec)接下来我们尝试更改用户 herc@localhost 的密码。
mysql> alter user 'herc'@'localhost' identified by 'MySQL@321';
Query OK, 0 rows affected (0.02 sec)
mysql> select * from mysql.password_history\G
*************************** 1. row ***************************
Host: localhost
User: herc
Password_timestamp: 2021-09-20 15:49:15.459018
CGeRQT31UUwtw194KOKGdNbgj3558VUB.dxcoS8r4IKpG8
*************************** 2. row ***************************
Host: localhost
User: herc
Password_timestamp: 2021-09-20 15:44:42.295778
Password: $A$005$=R:q'M(Kh#D];c~SdCLyluq2UVHFobjWOFTwn2JYVFDyI042sl56B7DCPSK5
2 rows in set (0.00 sec)更改成功后，查看 mysql.password_history 表，可见该表存有最近两个密码的信息。
再次更改该用户密码，且密码为创建用户时设置的密码值（Percona@321）。
mysql> alter user 'herc'@'localhost' identified by 'Percona@321';
ERROR 3638 (HY000): Cannot use these credentials for 'herc@localhost' because they contradict the password history policy修改失败! 因为根据我们设置的限制策略，不能重用在 mysql.password_policy 表中被记录的最近的两个密码。因此，如果想再次重复使用第一个密码，就不能让该密码出现在 mysql.password_policy 表中。
再设置一个新密码后（第一个密码已经不是最近的两个密码了），再尝试用第一个密码值（Percona@321）进行修改，修改成功！
mysql> alter user 'herc'@'localhost' identified by 'Herc@321';
Query OK, 0 rows affected (0.01 sec)
mysql> alter user 'herc'@'localhost' identified by 'Percona@321';
Query OK, 0 rows affected (0.02 sec)也可以在启动时在全局配置 password_history。
#vi my.cnf
[mysqld]
password_history=6
#set global
mysql> set global password_history=5;
Query OK, 0 rows affected (0.00 sec)1.2 间隔时间
MySQL 官方手册描述：
If an account is restricted based on time elapsed, a new password cannot be chosen from passwords in the history that are newer than a specified number of days.
测试前，创建了用户 sri@localhost，并设置用户密码可重用的时间间隔为五天。
mysql> create user 'sri'@'localhost' identified by 'Percona@321' password reuse interval 5 day;
Query OK, 0 rows affected (0.01 sec)
mysql> select user, host, password_reuse_time from mysql.user where user='sri'\G
*************************** 1. row ***************************
user: sri
host: localhost
password_reuse_time: 5
1 row in set (0.00 sec)这意味着每个密码生效后，在五天内都不能再被重复设置。
mysql> select * from mysql.password_history where user='sri'\G
*************************** 1. row ***************************
Host: localhost
User: sri
Password_timestamp: 2021-09-20 16:09:27.918585
Password: $A$005$+B e3!C9&8m
eFRG~IqRWX4b6PtzLA8I4VsdYvWU3qRs/nip/QRhXXR5phT6
1 row in set (0.00 sec)执行 ALTER 来更改密码。
mysql> alter user 'sri'@'localhost' identified by 'Herc@321';
Query OK, 0 rows affected (0.02 sec)
mysql> select * from mysql.password_history where user='sri'\G
*************************** 1. row ***************************
Host: localhost
User: sri
Password_timestamp: 2021-09-20 16:17:51.840483
Password: $A$005$~k7qp8.OP=^#e79qwtiYd7/cmCFLvHM7MHFbvfX2WlhXqzjmrN03gGZ4
*************************** 2. row ***************************
Host: localhost
User: sri
Password_timestamp: 2021-09-20 16:09:27.918585
Password: $A$005$+B e3!C9&8m
eFRG~IqRWX4b6PtzLA8I4VsdYvWU3qRs/nip/QRhXXR5phT6
2 rows in set (0.00 sec)现在尝试再次设置为第一个密码。
mysql> alter user 'sri'@'localhost' identified by 'Percona@321';
ERROR 3638 (HY000): Cannot use these credentials for 'sri@localhost' because they contradict the password history policy设置失败！
也可以在启动时在全局配置 password_reuse_interval。
#vi my.cnf
[mysqld]
password_reuse_interval=365
#set global
mysql> set global password_reuse_interval=365;
Query OK, 0 rows affected (0.00 sec)| 2 随机密码
从 MySQL 8.0.18 开始，MySQL 能够为用户帐户创建随机密码。这意味着可以不必分配指定密码。它支持以下语句：
- 创建用户
- 更改用户
- 设置密码
我们需要使用 RANDOM PASSWORD 以避免修改密码时屏幕上有明文显示。例如：
mysql> create user 'sakthi'@'localhost' identified by random password;
+--------+-----------+----------------------+
| user | host | generated password |
+--------+-----------+----------------------+
| sakthi | localhost | .vZYy+<<BO7l1;vtIufH |
+--------+-----------+----------------------+
1 row in set (0.01 sec)
mysql> alter user 'sri'@'localhost' identified by random password;
+------+-----------+----------------------+
| user | host | generated password |
+------+-----------+----------------------+
| sri | localhost | 5wb>2[]q*jbDsFvlN-i_ |
+------+-----------+----------------------+
1 row in set (0.02 sec)密码哈希值将存储在 mysql.user 表中。
mysql> select user, authentication_string from mysql.user where user in ('sakthi','sri')\G
*************************** 1. row ***************************
user: sakthi
authentication_string: $A$005$L`PYcedj%3tz*J>ioBP1.Rsrj7H8wtelqijvV0CFnXVnWLNIc/RZL0C06l4oA
*************************** 2. row ***************************
user: sri
authentication_string: $A$005$/k?aO&ap.#b=
^zt[E|x9q3w9uHn1oEumXUgnqNMH8xWo4xd/s26hTPKs1AbC2
2 rows in set (0.00 sec)默认情况下，密码长度为 20 个字符。我们可以使用变量 generated_random_password_length 定义密码长度，允许的长度范围是 5 到 255。
mysql> select @@generated_random_password_length;
+------------------------------------+
| @@generated_random_password_length |
+------------------------------------+
| 20 |
+------------------------------------+
1 row in set (0.00 sec)如果 validate_password 组件已经安装，对随机密码策略不会有影响。
还有一些特性，将在下一篇文章中介绍。
参考
MySQL 手册：
mysql
**粗体** _斜体_ [链接](http://example.com) `代码` - 列表 > 引用。你还可以使用@来通知其他用户。