MySQL 5.7 C API Developer Guide  /  ...  /  Support for Encrypted Connections

3.6.1 Support for Encrypted Connections

This section describes how C applications use the C API capabilities for encrypted connections. By default, MySQL programs attempt to connect using encryption if the server supports encrypted connections, falling back to an unencrypted connection if an encrypted connection cannot be established (see Configuring MySQL to Use Encrypted Connections). For applications that require control beyond the default behavior over how encrypted connections are established, the C API provides these capabilities:

Options for Encrypted Connections

mysql_options() provides the following options for control over use of encrypted connections. For option details, see Section 5.4.50, “mysql_options()”.

  • MYSQL_OPT_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.

  • MYSQL_OPT_SSL_CAPATH: The path name of the directory that contains trusted SSL CA certificate files.

  • MYSQL_OPT_SSL_CERT: The path name of the client public key certificate file.

  • MYSQL_OPT_SSL_CIPHER: The list of permissible ciphers for SSL encryption.

  • MYSQL_OPT_SSL_CRL: The path name of the file containing certificate revocation lists.

  • MYSQL_OPT_SSL_CRLPATH: The path name of the directory that contains certificate revocation list files.

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

  • MYSQL_OPT_SSL_MODE: The connection security state.

  • MYSQL_OPT_SSL_VERIFY_SERVER_CERT: Whether to perform host name identity verification of the server certificate Common Name value.

  • MYSQL_OPT_TLS_VERSION: The encryption protocols the client permits.

mysql_ssl_set() can be used as a convenience routine that is equivalent to a set of mysql_options() calls that specify certificate and key files, encryption ciphers, and so forth. See Section 5.4.75, “mysql_ssl_set()”.

Enforcing an Encrypted Connection

mysql_options() options for information such as SSL certificate and key files are used to establish an encrypted connection if such connections are available, but do not enforce any requirement that the connection obtained be encrypted. To require an encrypted connection, use the following technique:

  1. Call mysql_options() as necessary supply the appropriate SSL parameters (certificate and key files, encryption ciphers, and so forth).

  2. Call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_REQUIRED or one of the more-restrictive option values.

  3. Call mysql_real_connect() to connect to the server. The call fails if an encrypted connection cannot be obtained; exit with an error.

Improving Security of Encrypted Connections

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:

  • To specify the CA certificate, call mysql_options() to pass the MYSQL_OPT_SSL_CA (or MYSQL_OPT_SSL_CAPATH) option, and call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_VERIFY_CA.

  • To enable host name identity verification as well, call mysql_options() to pass the MYSQL_OPT_SSL_MODE option with a value of SSL_MODE_VERIFY_IDENTITY rather than SSL_MODE_VERIFY_CA.


Host name identity verification with SSL_MODE_VERIFY_IDENTITY does not work with self-signed certificates created automatically by the server, or manually using mysql_ssl_rsa_setup (see 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.