Oh, there is no good solution. You need to do something using ORAM. There some clever tricks you can use that might be efficient (e.g this paper does some very

Oh, there is no good solution. You need to do something using ORAM. There some clever tricks you can use that might be efficient (e.g this paper does some very interesting things: https://www.internetsociety.org/doc/oblivisync-practical-oblivious-file-backup-and-synchronization https://www.internetsociety.org/doc/oblivisync-practical-obl...), but I wouldn't realistically expect Spider Oak to cover it. What I would expect them to do is clearly state what they don't cover. Metadata is a thing people understand.