I'm pretty sure this means that you shouldn't encrypt users data without their consent, or encrypt existing data. There are plenty of 3rd party apps which have

I'm pretty sure this means that you shouldn't encrypt users data without their consent, or encrypt existing data. There are plenty of 3rd party apps which have been approved by Amazon which encrypt your data client side. e.g Arq Backup I know Stablebit Clouddrive (which does client side encryption) have been struggling to get approval from Amazon, but this is due to excessive API requests, not client side encryption.