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 secure (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 secure connections because it provides weak encryption (see Section 6.4.3, “Secure Connection 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 X509 standard.

X509 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 secure-connection support using OpenSSL or yaSSL. For a comparison of the two packages, see Section 6.4.1, “OpenSSL Versus yaSSL” For information about the encryption protocols and ciphers each package supports, see Section 6.4.3, “Secure Connection Protocols and Ciphers”.

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 13.7.1.3, “CREATE USER Syntax”. See also the description of the require_secure_transport system variable at Section 5.1.5, “Server System Variables”

Secure connections are available through the MySQL C API using the mysql_ssl_set() and mysql_options() functions. See Section 27.7.7.75, “mysql_ssl_set()”, and Section 27.7.7.50, “mysql_options()”.

Replication uses the C API, so secure connections can be used between master and slave servers. See Section 18.3.9, “Setting Up Replication to Use Secure Connections”.

It is also possible to connect securely from within an SSH connection to the MySQL server host. For an example, see Section 6.4.7, “Connecting to MySQL Remotely from Windows with SSH”.