Pre-General Availability Draft: 2017-12-16
MySQL provides two authentication plugins that implement SHA-256 hashing for user account passwords:
sha256_password: Implements basic SHA-256 authentication.
caching_sha2_password: Implements SHA-256 authentication (like
sha256_password), but uses caching for better performance and has additional features for wider applicability.
This section describes the caching SHA-2 authentication plugin. For information about the original basic (noncaching) plugin, see Section 22.214.171.124, “SHA-256 Pluggable Authentication”.
To connect to the server using an account that authenticates
caching_sha2_password plugin, you
must use either a secure connection or an unencrypted
connection that supports password exchange using an RSA key
pair, as described later in this section. Either way, the
caching_sha2_password plugin uses MySQL's
encryption capabilities. See
Section 6.4, “Using Encrypted Connections”.
In the name
“sha256” refers to the 256-bit digest length the
plugin uses for encryption. In the name
refers more generally to the SHA-2 class of encryption
algorithms, of which 256-bit encryption is one instance. The
latter name choice leaves room for future expansion of
possible digest lengths without changing the plugin name.
caching_sha2_password plugin has these
advantages, compared to
An in-memory cache enables faster reauthentication of users who have connected previously when they connect again.
RSA-based password exchange is available regardless of the SSL library against which MySQL is linked.
Support is provided for client connections that use the Unix socket-file and shared-memory protocols.
The following table shows the plugin names on the server and client sides.
Table 6.12 Plugin and Library Names for SHA-2 Authentication
|Server-side plugin name|
|Client-side plugin name|
|Library file name||None (plugins are built in)|
The following sections provide installation and usage information specific to caching SHA-2 pluggable authentication:
For general information about pluggable authentication in MySQL, see Section 6.3.10, “Pluggable Authentication”.
caching_sha2_password plugin exists in
server and client forms:
The server-side plugin is built into the server, need not be loaded explicitly, and cannot be disabled by unloading it.
The client-side plugin is built into the
libmysqlclientclient library and is available to any program linked against
The server-side plugin uses the
sha2_cache_cleaner audit plugin as a helper
to perform password cache management.
caching_sha2_password, is built in and need
not be installed.
To set up an account that uses the
caching_sha2_password plugin for SHA-256
password hashing, use the following statement, where
password is the desired account
CREATE USER 'sha2user'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'password';
The server assigns the
caching_sha2_password plugin to the account
and uses it to encrypt the password using SHA-256, storing
those values in the
authentication_string columns of the
mysql.user system table.
The preceding instructions do not assume that
caching_sha2_password is the default
authentication plugin. If
caching_sha2_password is the default
authentication plugin, a simpler
USER syntax can be used.
To start the server with the default authentication plugin set
caching_sha2_password, put these lines
in the server option file:
That causes the
plugin to be used by default for new accounts. As a result, it
is possible to create the account and set its password without
naming the plugin explicitly:
CREATE USER 'sha2user'@'localhost' IDENTIFIED BY 'password';
Another consequence of setting
caching_sha2_password is that, to use
some other plugin for account creation, you must specify that
plugin explicitly. For example, to use the
mysql_native_password plugin, use this
CREATE USER 'nativeuser'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';
caching_sha2_password supports connections
over secure transport. If you follow the RSA configuration
procedure given later in this section, it also supports
encrypted password exchange using RSA over unencrypted
connections. RSA support has these characteristics:
Two system variables name the RSA private and public key-pair files:
caching_sha2_password_public_key_path. The database administrator must set these variables at server startup if the key files to use have names that differ from the system variable default values.
As of MySQL 8.0.4, the server uses the
caching_sha2_password_auto_generate_rsa_keyssystem variable to determine whether to automatically generate the RSA key-pair files. See Section 6.4.3, “Creating SSL and RSA Certificates and Keys”.
As of MySQL 8.0.4, the
Caching_sha2_password_rsa_public_keystatus variable displays the RSA public key value used by the
Clients that have the RSA public key can perform RSA key pair-based password exchange with the server during the connection process, as described later.
For connections by accounts that authenticate using
caching_sha2_passwordand RSA key pair-based password exchange, the server does not send the RSA public key to clients by default. Clients can use a client-side copy of the required public key, or request the public key from the server.
Use of a trusted local copy of the public key enables the client to avoid a round trip in the client/server protocol, and is more secure than requesting the public key from the server. On the other hand, requesting the public key from the server is more convenient (it requires no management of a client-side file) and may be acceptable in secure network environments.
For command-line clients, use the
--server-public-key-pathoption to specify the RSA public key file. Use the
--get-server-public-keyoption to request the public key from the server. The following programs support the two options: mysql, mysqladmin, mysqlbinlog, mysqlcheck, mysqldump, mysqlimport, mysqlpump, mysqlshow, mysqlslap, mysqltest, mysql_update.
For programs that use the C API, call
mysql_options()to specify the RSA public key file by passing the
MYSQL_SERVER_PUBLIC_KEYoption and the name of the file, or request the public key from the server by passing the
For replication slaves, use the
CHANGE MASTER TOstatement with the
MASTER_PUBLIC_KEY_PATHoption to specify the RSA public key file, or the
GET_MASTER_PUBLIC_KEYoption to request the public key from the master. For Group Replication, the
group_replication_recovery_get_public_keysystem variables serve the same purpose.
In all cases, if the option is given to specify a valid public key file, it takes precedence over the option to request the public key from the server.
For clients that use the
caching_sha2_password plugin, passwords are
never exposed as cleartext when connecting to the server. How
password transmission occurs depends on whether a secure
connection or RSA encryption is used:
If the connection is secure, an RSA key pair is unnecessary and is not used. This applies to encrypted TCP connections that use TLS, as well as Unix socket-file and shared-memory connections. The password is sent as cleartext but cannot be snooped because the connection is secure.
If the connection is not secure, an RSA key pair is used. This applies to unencrypted TCP connections without TLS and named-pipe connections. RSA is used only for password exchange between client and server, to prevent password snooping. When the server receives the encrypted password, it decrypts it. A scramble is used in the encryption to prevent repeat attacks.
To enable use of an RSA key pair for password exchange during the client connection process, use the following procedure:
Create the RSA private and public key-pair files using the instructions in Section 6.4.3, “Creating SSL and RSA Certificates and Keys”.
If the private and public key files are located in the data directory and are named
public_key.pem(the default values of the
caching_sha2_password_public_key_pathsystem variables), the server uses them automatically at startup.
Otherwise, to name the key files explicitly, set the system variables to the key file names in the server option file. If the files are located in the server data directory, you need not specify their full path names:
[mysqld] caching_sha2_password_private_key_path=myprivkey.pem caching_sha2_password_public_key_path=mypubkey.pem
If the key files are not located in the data directory, or to make their locations explicit in the system variable values, use full path names:
[mysqld] caching_sha2_password_private_key_path=/usr/local/mysql/myprivkey.pem caching_sha2_password_public_key_path=/usr/local/mysql/mypubkey.pem
Restart the server, then connect to it and check the
Caching_sha2_password_rsa_public_keystatus variable value. The value will differ from that shown here, but should be nonempty:
mysql> SHOW STATUS LIKE 'Caching_sha2_password_rsa_public_key'\G *************************** 1. row *************************** Variable_name: Caching_sha2_password_rsa_public_key Value: -----BEGIN PUBLIC KEY----- MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDO9nRUDd+KvSZgY7cNBZMNpwX6 MvE1PbJFXO7u18nJ9lwc99Du/E7lw6CVXw7VKrXPeHbVQUzGyUNkf45Nz/ckaaJa aLgJOBCIDmNVnyU54OT/1lcs2xiyfaDMe8fCJ64ZwTnKbY2gkt1IMjUAB5Ogd5kJ g8aV7EtKwyhHb0c30QIDAQAB -----END PUBLIC KEY-----
If the value is empty, the server found some problem with the key files. Check the error log for diagnostic information.
After the server has been configured with the RSA key files,
accounts that authenticate with the
caching_sha2_password plugin have the
option of using those key files to connect to the server. As
mentioned previously, such accounts can use either a secure
connection (in which case RSA is not used) or an unencrypted
connection that performs password exchange using RSA. Suppose
that an unencrypted connection is used. For example:
shell> mysql --ssl-mode=DISABLED -u sha2user -p Enter password: password
For this connection attempt by
the server determines that
caching_sha2_password is the appropriate
authentication plugin and invokes it (because that was the
plugin specified at
time). The plugin finds that the connection is not encrypted
and thus requires the password to be transmitted using RSA
encryption. However, the server does not send the public key
to the client, and the client provided no public key, so it
cannot encrypt the password and the connection fails:
ERROR 2061 (HY000): Authentication plugin 'caching_sha2_password' reported error: Authentication requires secure connection.
To request the RSA public key from the server, specify the
shell> mysql --ssl-mode=DISABLED -u sha2user -p --get-server-public-key Enter password: password
In this case, the server sends the RSA public key to the client, which uses it to encrypt the password and returns the result to the server. The plugin uses the RSA private key on the server side to decrypt the password and accepts or rejects the connection based on whether the password is correct.
Alternatively, if the client has a file containing a local
copy of the RSA public key required by the server, it can
specify the file using the
shell> mysql --ssl-mode=DISABLED -u sha2user -p --server-public-key-path=file_name Enter password: password
In this case, the client uses the public key to encrypt the password and returns the result to the server. The plugin uses the RSA private key on the server side to decrypt the password and accepts or rejects the connection based on whether the password is correct.
The public key value in the file named by the
should be the same as the key value in the server-side file
named by the
system variable. If the key file contains a valid public key
value but the value is incorrect, an access-denied error
occurs. If the key file does not contain a valid public key,
the client program cannot use it.
Client users can obtain the RSA public key two ways:
The database administrator can provide a copy of the public key file.
A client user who can connect to the server some other way can use a
SHOW STATUS LIKE 'Caching_sha2_password_rsa_public_key'statement and save the returned key value in a file.
caching_sha2_password uses an in-memory
cache for faster authentication of clients who have connected
previously. Entries consist of account-name/password-hash
pairs. The cache works like this:
When a client connects,
caching_sha2_passwordchecks whether the client and password match some cache entry. If so, authentication succeeds.
If there is no matching cache entry, the plugin attempts to verify the client against the credentials in the
mysql.usersystem table. If this succeeds,
caching_sha2_passwordadds an entry for the client to the hash. Otherwise, authentication fails and the connection is rejected.
In this way, when a client first connects, authentication
mysql.user table occurs. When
the client connects subsequently, faster authentication
against the cache occurs.
Password cache operations other than adding entries are
handled by the
plugin, which performs these actions on behalf of
It clears the cache entry for any account that is renamed or dropped, or any account for which the credentials or authentication plugin are changed.
It empties the cache when the
FLUSH PRIVILEGESstatement is executed.
It empties the cache at server shutdown. (This means the cache is not persistent across server restarts.)
Cache clearing operations affect the authentication requirements for subsequent client connections. For each user account, the first client connection for the user after any of the following operations must use a secure connection (made using TCP using TLS credentials, a Unix socket file, or shared memory) or RSA key pair-based password exchange:
FLUSH PRIVILEGES clears the
entire cache and affects all accounts that use the
caching_sha2_password plugin. The other
operations clear specific cache entries and affect only
accounts that are part of the operation.
Once the user authenticates successfully, it is entered into the cache and subsequent connections do not require a secure connection or the RSA key pair, until another cache clearing event occurs that affects the user account.