With an unencrypted connection between the MySQL client and the server, someone with access to the network could watch all your traffic and inspect the data being sent or received between client and server.
When you must move information over a network in a secure fashion, an unencrypted connection is unacceptable. To make any kind of data unreadable, use encryption. Encryption algorithms must include security elements to resist many kinds of known attacks such as changing the order of encrypted messages or replaying data twice.
MySQL supports encrypted connections between clients and the server using the TLS (Transport Layer Security) protocol. TLS is sometimes referred to as SSL (Secure Sockets Layer) but MySQL does not actually use the SSL protocol for encrypted connections because its encryption is weak (see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”).
TLS uses encryption algorithms to ensure that data received over a public network can be trusted. It has mechanisms to detect data change, loss, or replay. TLS also incorporates algorithms that provide identity verification using the X.509 standard.
X.509 makes it possible to identify someone on the Internet. In basic terms, there should be some entity called a “Certificate Authority” (or CA) that assigns electronic certificates to anyone who needs them. Certificates rely on asymmetric encryption algorithms that have two encryption keys (a public key and a secret key). A certificate owner can present the certificate to another party as proof of identity. A certificate consists of its owner's public key. Any data encrypted using this public key can be decrypted only using the corresponding secret key, which is held by the owner of the certificate.
MySQL can be compiled for encrypted-connection support using OpenSSL or yaSSL. For a comparison of the two packages, see Section 6.3.4, “SSL Library-Dependent Capabilities” For information about the encryption protocols and ciphers each package supports, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.
It is possible to compile MySQL using yaSSL as an alternative to OpenSSL only prior to MySQL 5.7.28. As of MySQL 5.7.28, support for yaSSL is removed and all MySQL builds use OpenSSL.
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. For information about options that affect use of encrypted connections, see Section 6.3.1, “Configuring MySQL to Use Encrypted Connections” and Command Options for Encrypted Connections.
MySQL performs encryption on a per-connection basis, and use of
encryption for a given user can be optional or mandatory. This
enables you to choose an encrypted or unencrypted connection
according to the requirements of individual applications. For
information on how to require users to use encrypted connections,
see the discussion of the
REQUIRE clause of the
CREATE USER statement in
Section 126.96.36.199, “CREATE USER Syntax”. See also the description of the
variable at Section 5.1.7, “Server System Variables”
Encrypted connections can be used between master and slave replication servers. See Section 16.3.8, “Setting Up Replication to Use Encrypted Connections”.
For information about using encrypted connections from the MySQL C API, see Section 27.8.15, “C API Encrypted Connection Support”.
It is also possible to connect using encryption from within an SSH connection to the MySQL server host. For an example, see Section 6.3.5, “Connecting to MySQL Remotely from Windows with SSH”.
Several improvements were made to encrypted-connection support in MySQL 5.7. The following timeline summarizes the changes:
5.7.3: On the client side, an explicit
--ssloption is no longer advisory but prescriptive. Given a server enabled to support encrypted connections, a client program can require an encrypted connection by specifying only the
--ssloption. (Previously, it was necessary for the client to specify either the
--ssl-caoption, or all three of the
--ssl-certoptions.) The connection attempt fails if an encrypted connection cannot be established. Other
--ssl-options on the client side are advisory in the absence of
--ssl: The client attempts to connect using encryption but falls back to an unencrypted connection if an encrypted connection cannot be established.
5.7.5: The server-side
--ssloption value is enabled by default.
For servers compiled using OpenSSL, the
sha256_password_auto_generate_rsa_keyssystem variables are available to enable autogeneration and autodiscovery of SSL/RSA certificate and key files at startup. For certificate and key autodiscovery, if
--sslis enabled and other
--ssl-options are not given to configure encrypted connections explicitly, the server attempts to enable support for encrypted connections automatically at startup if it discovers the requisite certificate and key files in the data directory.
5.7.6: The mysql_ssl_rsa_setup utility is available to make it easier to manually generate SSL/RSA certificate and key files. Autodiscovery of SSL/RSA files at startup is expanded to apply to all servers, whether compiled using OpenSSL or yaSSL. (This means that
auto_generate_certsneed not be enabled for autodiscovery to occur.)
If the server discovers at startup 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.)
5.7.7: The C client library attempts to establish an encrypted connection by default if the server supports encrypted connections. This affects client programs as follows:
In the absence of an
--ssloption, clients attempt to connect using encryption, falling back to an unencrypted connection if an encrypted connection cannot be established.
This change also affects subsequent releases of MySQL Connectors that are based on the C client library: Connector/C, Connector/C++, and Connector/ODBC.
require_secure_transportsystem variable is available to control whether client connections to the server must use some form of secure transport.
5.7.10: TLS protocol support is extended from TLSv1 to also include TLSv1.1 and TLSv1.2. The
tls_versionsystem variable on the server side and
--tls-versionoption on the client side enable the level of support to be selected. See Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.
5.7.11: MySQL client programs support an
--ssl-modeoption that enables you to specify the security state of the connection to the server. The
--ssl-modeoption comprises the capabilities of the client-side
--ssl-verify-server-certare deprecated, and are removed in MySQL 8.0.
5.7.28: Support for yaSSL was removed. All MySQL builds use OpenSSL.