Make EncryptedCVCs an UNLOGGED TABLE to prevent encrypted CVC data being written to the WAL-files. Also update implementation guide and instruct user to do a VACUUM FULL to make sure deleted CVC data is purged from disk permanently.
Temporarily store encrypted CVC in memcached instead of PostgreSQL to prevent the data ever being written to disk. The data in memcached is set to expire automatically after 10 minutes, or deleted immediately when the CVC code is decrypted and used in the authorise request.