The only reason I'm aware of for rolling a custom crypto would be fighting against automated attacks. Even ridiculously simple protection can prevent a script f

The only reason I'm aware of for rolling a custom crypto would be fighting against automated attacks. Even ridiculously simple protection can prevent a script from automatically collecting the data. If there's a lot of data streams and each requires human interaction to decrypt it, it can significantly raise the cost of breaking such data. In that case it's probably best to make it just an additional layer over some well-tested method.