Data at rest that is written to the binary log files and relay log files is encrypted from the point in time where encryption is started, using the two tier encryption architecture described above. Existing binary log files and relay log files that were present on the server when you started encryption are not encrypted. You can purge these files when they are no longer needed.

Data in motion in the replication event stream, which is sent to MySQL clients including mysqlbinlog, is decrypted for transmission, and should therefore be protected in transit by the use of connection encryption (see Section 8.3, “Using Encrypted Connections” and Section 19.3.1, “Setting Up Replication to Use Encrypted Connections”).

Data in use that is held in the binary log transaction and statement caches during a transaction is in unencrypted format in the memory buffer that stores the cache. The data is written to a temporary file on disk if it exceeds the space available in the memory buffer. When binary log encryption is active on the server, temporary files used to hold the binary log cache are encrypted using AES-CTR (AES Counter mode) for stream encryption. Because the temporary files are volatile and tied to a single process, they are encrypted using single-tier encryption, using a randomly generated file password and initialization vector that exist only in memory and are never stored on disk or in the keyring. After each transaction is committed, the binary log cache is reset: the memory buffer is cleared, any temporary file used to hold the binary log cache is truncated, and a new file password and initialization vector are randomly generated for use with the next transaction. This reset also takes place when the server is restarted after a normal shutdown or an unexpected halt.