Enable TLS for MySQL Clients

It is recommended to use the encrypted connection to ensure data security because non-encrypted connection might lead to an information leak.

The TiDB server supports the encrypted connection based on the TLS (Transport Layer Security). The protocol is consistent with MySQL encrypted connections and is directly supported by existing MySQL clients such as MySQL operation tools and MySQL drivers. TLS is sometimes referred to as SSL (Secure Sockets Layer). Because the SSL protocol has known security vulnerabilities, TiDB does not support it. TiDB supports the following versions: TLS 1.0, TLS 1.1, and TLS 1.2, TLS 1.3.

After using an encrypted connection, the connection has the following security properties:

Confidentiality: the traffic plaintext cannot be eavesdropped
Integrity: the traffic plaintext cannot be tampered
Authentication: (optional) the client and the server can verify the identity of both parties to avoid man-in-the-middle attacks

The encrypted connections in TiDB are disabled by default. To use encrypted connections in the client, you must first configure the TiDB server and enable encrypted connections. In short, to use encrypted connections, both of the following conditions must be met:

Enable encrypted connections in the TiDB server.
The client specifies to use an encrypted connection.

Similar to MySQL, the encrypted connections in TiDB consist of single connections. The encrypted connection is optional by default. For a TiDB server with encrypted connections enabled, you can choose to securely connect to the TiDB server through an encrypted connection, or to use a generally unencrypted connection. If the encrypted connections are enforced as required, both of the following two ways are available:

Configure the launch parameter --require-secure-transport to enable encrypted connections to the TiDB server for all users.
Specify require ssl when you create a user (create user), grant permissions (grant) or modify an existing user (alter user), which is to specify that specified users must use the encrypted connection to access TiDB. The following is an example of creating a user:
```
create user 'u1'@'%'  require ssl;
```

Note:
If the login user has configured using the TiDB Certificate-Based Authentication for Login, the user is implicitly required to enable the encrypted connection to TiDB.

Configure TiDB to use encrypted connections

See the following desrciptions about the related parameters to enable encrypted connections:

ssl-cert: specifies the file path of the SSL certificate
ssl-key: specifies the private key that matches the certificate
ssl-ca: (optional) specifies the file path of the trusted CA certificate

To enable encrypted connections in the TiDB server, you must specify both of the ssl-cert and ssl-key parameters in the configuration file when you start the TiDB server. You can also specify the ssl-ca parameter for client authentication (see Enable authentication).

All the files specified by the parameters are in PEM (Privacy Enhanced Mail) format. Currently, TiDB does not support the import of a password-protected private key, so it is required to provide a private key file without a password. If the certificate or private key is invalid, the TiDB server starts as usual, but the client cannot connect to the TiDB server through an encrypted connection.

The certificate or key is signed and generated using OpenSSL, or quickly generated using the mysql_ssl_rsa_setup tool in MySQL:

mysql_ssl_rsa_setup --datadir=./certs

This command generates the following files in the certs directory:

certs
├── ca-key.pem
├── ca.pem
├── client-cert.pem
├── client-key.pem
├── private_key.pem
├── public_key.pem
├── server-cert.pem
└── server-key.pem

The corresponding TiDB configuration file parameters are:

[security]
ssl-cert = "certs/server-cert.pem"
ssl-key = "certs/server-key.pem"

If the certificate parameters are correct, TiDB outputs secure connection is enabled when started; otherwise, it outputs secure connection is NOT ENABLED.

Reload certificate, key, and CA

To replace the certificate, the key or CA, first replace the corresponding files, then execute the ALTER INSTANCE RELOAD TLS statement on the running TiDB instance to reload the certificate (ssl-cert), the key (ssl-key), and the CA (ssl-ca) from the original configuration path. In this way, you do not need to restart the TiDB instance.

The newly loaded certificate, key, and CA take effect on the connection that is established after the statement is successfully executed. The connection established before the statement execution is not affected.

Configure the MySQL client to use encrypted connections

The client of MySQL 5.7 or later versions attempts to establish an encrypted connection by default. If the server does not support encrypted connections, it automatically returns to unencrypted connections. The client of MySQL earlier than version 5.7 uses the unencrypted connection by default.

You can change the connection behavior of the client using the following --ssl-mode parameters:

--ssl-mode=REQUIRED: The client requires an encrypted connection. The connection cannot be established if the server side does not support encrypted connections.
In the absence of the --ssl-mode parameter: The client attempts to use an encrypted connection, but the encrypted connection cannot be established if the server side does not support encrypted connections. Then the client uses an unencrypted connection.
--ssl-mode=DISABLED: The client uses an unencrypted connection.

For more information, see Client-Side Configuration for Encrypted Connections in MySQL.

Enable authentication

If the ssl-ca parameter is not specified in the TiDB server or MySQL client, the client or the server does not perform authentication by default and cannot prevent man-in-the-middle attack. For example, the client might "securely" connect to a disguised client. You can configure the ssl-ca parameter for authentication in the server and client. Generally, you only need to authenticate the server, but you can also authenticate the client to further enhance the security.

To authenticate the TiDB server from the MySQL client:
1. Specify the ssl-cert and ssl-key parameters in the TiDB server.
2. Specify the --ssl-ca parameter in the MySQL client.
3. Specify the --ssl-mode to VERIFY_CA at least in the MySQL client.
4. Make sure that the certificate (ssl-cert) configured in the TiDB server is signed by the CA specified by the client --ssl-ca parameter; otherwise, the authentication fails.
To authenticate the MySQL client from the TiDB server:
1. Specify the ssl-cert, ssl-key, and ssl-ca parameters in the TiDB server.
2. Specify the --ssl-cert and --ssl-key parameters in the client.
3. Make sure the server-configured certificate and the client-configured certificate are both signed by the ssl-ca specified by the server.

To perform mutual authentication, meet both of the above requirements.

By default, the server-to-client authentication is optional. Even if the client does not present its certificate of identification during the TLS handshake, the TLS connection can be still established. You can also require the client to be authenticated by specifying require 509 when creating a user (create user), granting permissions (grant), or modifying an existing user (alter user). The following is an example of creating a user:

create user 'u1'@'%'  require x509;

Note:
If the login user has configured using the TiDB Certificate-Based Authentication for Login, the user is implicitly required to enable the encrypted connection to TiDB.

Check whether the current connection uses encryption

Use the SHOW STATUS LIKE "%Ssl%"; statement to get the details of the current connection, including whether encryption is used, the encryption protocol used by encrypted connections, the TLS version number and so on.

See the following example of the result in an encrypted connection. The results change according to different TLS versions or encryption protocols supported by the client.

mysql> SHOW STATUS LIKE "%Ssl%";
......
| Ssl_verify_mode | 5                            |
| Ssl_version     | TLSv1.2                      |
| Ssl_cipher      | ECDHE-RSA-AES128-GCM-SHA256  |
......

For the official MySQL client, you can also use the STATUS or \s statement to view the connection status:

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

Supported TLS versions, key exchange protocols, and encryption algorithms

The TLS versions, key exchange protocols and encryption algorithms supported by TiDB are determined by the official Golang libraries.

Supported TLS versions

TLS 1.0
TLS 1.1
TLS 1.2
TLS 1.3

Supported key exchange protocols and encryption algorithms

TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_AES_128_CBC_SHA256
TLS_RSA_WITH_AES_128_GCM_SHA256
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_AES_128_GCM_SHA256
TLS_AES_256_GCM_SHA384
TLS_CHACHA20_POLY1305_SHA256

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