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MySQL 8.0 Reference Manual  /  ...  /  Configuring MySQL to Use Encrypted Connections

6.4.1 Configuring MySQL to Use Encrypted Connections

Several options are available to indicate whether to use encrypted connections, and to specify the appropriate certificate and key files. This section provides general guidance about configuring the server and clients for encrypted connections:

For a complete list of options related to establishment of encrypted connections, see Section 6.4.2, “Command Options for Encrypted Connections”. To create any required certificate and key files, see Section 6.4.3, “Creating SSL and RSA Certificates and Keys”.

Encrypted connections can be used between master and slave replication servers. See Section 17.3.9, “Setting Up Replication to Use Encrypted Connections”.

Encrypted connections are available through the MySQL C API. See Section 28.7.22, “C API Encrypted Connection Support”.

Server-Side Startup Configuration for Encrypted Connections

On the server side, the --ssl option specifies that the server permits but does not require encrypted connections. This option is enabled by default.

These options on the server side identify the certificate and key files the server uses when permitting clients to establish encrypted connections:

  • --ssl-ca: The path name of the Certificate Authority (CA) certificate file. (--ssl-capath is similar but specifies the path name of a directory of CA certificate files.)

  • --ssl-cert: The path name of the server public key certificate file. This can be sent to the client and authenticated against the CA certificate that it has.

  • --ssl-key: The path name of the server private key file.

For example, to enable the server for encrypted connections, start it with these lines in the my.cnf file, changing the file names as necessary:

[mysqld]
ssl-ca=ca.pem
ssl-cert=server-cert.pem
ssl-key=server-key.pem

Each option names a file in PEM format. If you need to create the required certificate and key files, see Section 6.4.3, “Creating SSL and RSA Certificates and Keys”. Alternatively, if you have a MySQL source distribution, you can test your setup using the demonstration certificate and key files in its mysql-test/std_data directory.

MySQL servers compiled using OpenSSL can generate missing certificate and key files automatically at startup. See Section 6.4.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”.

The server performs certificate and key file autodiscovery. If --ssl is enabled (possibly along with --ssl-cipher) and other --ssl-xxx options are not given to configure encrypted connections explicitly, the server attempts to enable support for encrypted connections automatically at startup:

  • If the server discovers valid certificate and key files named ca.pem, server-cert.pem, and server-key.pem in the data directory, it enables support for encrypted connections by clients. (The files need not have been generated automatically; what matters is that they have the indicated names and are valid.)

  • If the server does not find valid certificate and key files in the data directory, it continues executing but without support for encrypted connections.

If the server automatically enables support for encrypted connections, it writes a note to the error log. If the server discovers that the CA certificate is self-signed, it writes a warning to the error log. (The certificate is self-signed if created automatically by the server, or manually using mysql_ssl_rsa_setup.)

MySQL also provides these options for server-side SSL control:

  • --ssl-cipher: The list of permitted ciphers for connection encryption.

  • --ssl-crl: The path name of the file containing certificate revocation lists. (--ssl-crlpath is similar but specifies the path name of a directory of certificate revocation-list files.)

The server uses the values of the --ssl-xxx options as the values of the used certificate and key files to set the corresponding system variables (ssl_ca, ssl_cert, ssl_key, and so forth).

These system variables provide additional configuration control for encrypted connections:

Server-Side Runtime Configuration for Encrypted Connections

As of MySQL 8.0.16, the SSL context the server uses for new connections is reconfigurable at runtime. This capability may be useful, for example, to avoid restarting a MySQL server that has been running so long that its SSL certificate has expired.

The server creates the initial SSL context from the values that the context-related system variables have at startup. It also initializes a set of context-related status variables to indicate the values used in the context. The following table shows the system variables that define the SSL context and the corresponding status variables that indicate the currently active context values.


To reconfigure the SSL context at runtime, use this procedure:

  1. Set any SSL context-related system variables that should be changed to their new values.

  2. Execute ALTER INSTANCE RELOAD TLS. This statement reconfigures the active SSL context from the current values of the SSL context-related system variables. It also sets the context-related status variables to reflect the new active context values. The statement requires the CONNECTION_ADMIN privilege.

  3. New connections established after execution of ALTER INSTANCE RELOAD TLS use the new SSL context. Existing connections remain unaffected. If existing connections should be terminated, use the KILL statement.

The members of each pair of system and status variables may have different values temporarily due to the way the reconfiguration procedure works:

  • Changes to the system variables prior to ALTER INSTANCE RELOAD TLS do not change the SSL context. At this point, those changes have no effect on new connections, and corresponding context-related system and status variables may have different values. This enables you to make any changes required to the system variables, then update the active SSL context atomically with ALTER INSTANCE RELOAD TLS after all system variable changes have been made.

  • After ALTER INSTANCE RELOAD TLS, corresponding system and status variables have the same values. This remains true until the next change to the system variables.

In some cases, ALTER INSTANCE RELOAD TLS by itself may suffice to reconfigure the SSL context, without changing any system variables. Suppose that the certificate in the file named by ssl_cert has expired. It is sufficient to replace the existing file contents with a nonexpired certificate and execute ALTER INSTANCE RELOAD TLS to cause the new file contents to be read and used for new connections.

By default, the RELOAD TLS action rolls back with an error and has no effect if the configuration values do not permit creation of a new SSL context. The previous context values continue to be used for new connections.

If the optional NO ROLLBACK ON ERROR clause is given and a new context cannot be created, rollback does not occur. Instead, a warning is generated and SSL is disabled for new connections.

The server-side --ssl option has an effect only at server startup on whether the server accepts SSL connections. It is ignored by, and has no effect on the operation of, ALTER INSTANCE RELOAD TLS. For example, you can use --ssl=0 to start the server with SSL connections disabled, then reconfigure SSL and execute ALTER INSTANCE RELOAD TLS to enable SSL connections at runtime.

ALTER INSTANCE RELOAD TLS changes only the SSL context the server itself uses for new connections. It does not affect the SSL context used by other enabled server plugins or components such as X Plugin or Group Replication.

Note

Prior to MySQL 8.0.16, the SSL context-related system variables are not dynamic. They can be set at server startup, but cannot be changed thereafter. These system variables therefore reflect the SSL context values the server uses for new connections.

Client-Side Configuration for Encrypted Connections

By default, MySQL client programs attempt to establish an encrypted connection if the server supports encrypted connections, with further control available through the --ssl-mode option:

  • In the absence of an --ssl-mode option, clients attempt to connect using encryption, falling back to an unencrypted connection if an encrypted connection cannot be established. This is also the behavior with an explicit --ssl-mode=PREFFERED option.

  • With --ssl-mode=REQUIRED, clients require an encrypted connection and fail if one cannot be established.

  • With --ssl-mode=DISABLED, clients use an unencrypted connection.

  • With --ssl-mode=VERIFY_CA or --ssl-mode=VERIFY_IDENTITY, clients require an encrypted connection, and also perform verification against the server CA certificate and (with VERIFY_IDENTITY) against the server host name in its certificate.

The following options on the client side identify the certificate and key files clients use when establishing encrypted connections to the server. They are similar to the options used on the server side, but --ssl-cert and --ssl-key identify the client public and private key:

  • --ssl-ca: The path name of the Certificate Authority (CA) certificate file. This option, if used, must specify the same certificate used by the server. (--ssl-capath is similar but specifies the path name of a directory of CA certificate files.)

  • --ssl-cert: The path name of the client public key certificate file.

  • --ssl-key: The path name of the client private key file.

For additional security relative to that provided by the default encryption, clients can supply a CA certificate matching the one used by the server and enable host name identity verification. In this way, the server and client place their trust in the same CA certificate and the client verifies that the host to which it connected is the one intended:

Note

Host name identity verification with VERIFY_IDENTITY does not work with self-signed certificates created automatically by the server, or manually using mysql_ssl_rsa_setup (see Section 6.4.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”). Such self-signed certificates do not contain the server name as the Common Name value.

Host name identity verification also does not work with certificates that specify the Common Name using wildcards because that name is compared verbatim to the server name.

Depending on the encryption requirements of the MySQL account used by a client, the client may be required to specify certain options to connect using encryption to a MySQL server that supports encrypted connections.

Suppose that you want to connect using an account that has no special encryption requirements or was created using a CREATE USER statement that includes the REQUIRE SSL option. Assuming that the server supports encrypted connections, a client can connect using encryption with no --ssl-mode option or with an explicit --ssl-mode=PREFFERED option:

mysql

Or:

mysql --ssl-mode=PREFERRED

For an account with REQUIRE SSL, the connection attempt fails if an encrypted connection cannot be established. For an account with no special encryption requirements, the attempt falls back to an unencrypted connection if an encrypted connection cannot be established. To prevent fallback and fail if an encrypted connection cannot be obtained, connect like this:

mysql --ssl-mode=REQUIRED

If the account has more stringent security requirements, other options must be specified to establish an encrypted connection:

  • For accounts with REQUIRE X509, clients must specify at least --ssl-cert and --ssl-key. In addition, --ssl-ca (or --ssl-capath) is recommended so that the public certificate provided by the server can be verified. For example:

    mysql --ssl-ca=ca.pem \
          --ssl-cert=client-cert.pem \
          --ssl-key=client-key.pem
  • For accounts that have REQUIRE ISSUER or REQUIRE SUBJECT, the option requirements are the same as for REQUIRE X509, but the certificate must match the issue or subject, respectively, specified in the account definition.

For additional information about the REQUIRE clause, see the discussion in Section 13.7.1.3, “CREATE USER Syntax”.

To prevent use of encryption and override other --ssl-xxx options, invoke the client program with --ssl-mode=DISABLED:

mysql --ssl-mode=DISABLED

MySQL also provides these options for client-side SSL control:

  • --ssl-cipher: The list of permitted ciphers for connection encryption.

  • --ssl-crl: The path name of the file containing certificate revocation lists. (--ssl-crlpath is similar but specifies the path name of a directory of certificate revocation-list files.)

To specify permitted encryption protocols explicitly, use the --tls-version option; see Section 6.4.6, “Encrypted Connection Protocols and Ciphers”.

To determine whether the current connection with the server uses encryption, check the session value of the Ssl_cipher status variable. If the value is empty, the connection is not encrypted. Otherwise, the connection is encrypted and the value indicates the encryption cipher. For example:

mysql> SHOW SESSION STATUS LIKE 'Ssl_cipher';
+---------------+---------------------------+
| Variable_name | Value                     |
+---------------+---------------------------+
| Ssl_cipher    | DHE-RSA-AES128-GCM-SHA256 |
+---------------+---------------------------+

For the mysql client, an alternative is to use the STATUS or \s command and check the SSL line:

mysql> \s
...
SSL: Not in use
...

Or:

mysql> \s
...
SSL: Cipher in use is DHE-RSA-AES128-GCM-SHA256
...

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