Restore an encrypted backup image named <image_name> to <restoreDir> on the server with copy-back-and-apply-log, using the encryption key contained in a file named <keyFile> :

mysqlbackup --defaults-file=<my.cnf> --backup-image=<image_name> \
 --backup-dir=<backupTmpDir> --datadir=<restoreDir> --decrypt --key-file=<keyFile> copy-back-and-apply-log

See Section 20.13, “Encryption Options” for more details on backup encryption and decryption.