With an update in the iOS Security Guide, it was indicated that Apple is using Google’s Cloud Platform for its iCloud storage service. Apple had been using Amazon’s S3 and Microsoft Azure Cloud services for iCloud but now Azure is replaced by Google’s Cloud Platform.
It was reported back in 2016 for the first time that Apple would soon be using Google’s Cloud Platform for its iCloud services but now it is officially confirmed.
Data stored on Google servers may include photos, videos, documents, contacts, calendars, and more. As for the fact that whether the data is accessible by Google or not, Apple is very keen that Google has no way of accessing the stored data on servers.
“Each file is broken into chunks and encrypted by iCloud using AES-128 and a key derived from each chunk’s contents that utilizes SHA-256. The keys and the file’s metadata are stored by Apple in the user’s iCloud account. The encrypted chunks of the file are stored, without any user-identifying information, using third-party storage services, such as S3 and Google Cloud Platform.”
This means that Google would be able to see nothing else than encrypted data with no way to link that data to a particular individual. Apple doesn’t indicate any specificity about the use of third-party servers so, it is very much possible that the user data of one individual may be available across more than one platforms.
But it is safe to that the way Apple handles users data, it definitely would be secure on which platform it is on.