17.3.2.2 Binary Log Encryption Keys

The binary log encryption keys used to encrypt the file passwords for the log files are 256-bit keys that are generated specifically for each MySQL server instance using MySQL Server's keyring service (see Section 6.4.4, “The MySQL Keyring”). The keyring service handles the creation, retrieval, and deletion of the binary log encryption keys. A server instance only creates and removes keys generated for itself, but it can read keys generated for other instances if they are stored in the keyring, as in the case of a server instance that has been cloned by file copying.

The format of binary log encryption keys in the keyring is as follows:

MySQLReplicationKey_{UUID}_{SEQ_NO}

For example:

MySQLReplicationKey_00508583-b5ce-11e8-a6a5-0010e0734796_1

{UUID} is the true UUID generated by the MySQL server (the value of the server_uuid system variable). {SEQ_NO} is the sequence number for the binary log encryption key, which is incremented by 1 for each new key that is generated on the server.

The binary log encryption key that is currently in use on the server is called the binary log master key. The sequence number for the current binary log master key is stored in the keyring. The binary log master key is used to encrypt each new log file's file password, which is a randomly generated 32-byte file password specific to the log file that is used to encrypt the file data. The file password is encrypted using AES-CBC (AES Cipher Block Chaining mode) with the 256-bit binary log encryption key and a random initialization vector (IV), and is stored in the log file's file header. The file data is encrypted using AES-CTR (AES Counter mode) with a 256-bit key generated from the file password and a nonce also generated from the file password. It is technically possible to decrypt an encrypted file offline, if the binary log encryption key used to encrypt the file password is known, by using tools available in the OpenSSL cryptography toolkit.

If you use file copying to clone a MySQL server instance that has encryption active so its binary log files and relay log files are encrypted, ensure that the keyring is also copied, so that the clone server can read the binary log encryption keys from the source server. When encryption is activated on the clone server (either at startup or subsequently), the clone server recognizes that the binary log encryption keys used with the copied files include the generated UUID of the source server. It automatically generates a new binary log encryption key using its own generated UUID, and uses this to encrypt the file passwords for subsequent binary log files and relay log files. The copied files continue to be read using the source server's keys.