I own a Synology NAS which i synchronised with Google Drive using the 'Cloud Sync' feature. For security reasons, i used the Synology built-in feature to encrypt the files on the NAS before sending them to the cloud. However now, i can't read them in the cloud, much less use the bidirectionnal sync feature while keeping files encrypted. Their is over 1TB of data which i can't store on my own HDD. I was thinking of mounting the NAS files as network drives and encrypt them with an indépendant software solutions such as VeraCrypt which i can then decrypt on the synced googled drive folder. What do you think ? Will it take to much time to decrypt/encrypt to allow regular use in sync (1TB..) ?
I would use something like Boxcryptor. It allows you to encrypt your files and upload them to the Google Drive. Or use any 3rd party security solution for Google Drive. https://www.boxcryptor.com/en/google-drive
You have 1TB of data that you are syncing, encrypted by the NAS, to Google Drive. You are right: the data in Google Drive is unusable. The Synology Cloud Sync feature with encrypting is meant to BACKUP data on your NAS to cloud providers.
You mentioned that you have 1TB of data that you "can't store on your own HDD". Can't store on your the harddisk of your own workstation because of security reasons or because of space considerations? Are you accessing the Google Drive files from your web browser, or do you sync this data with the Google Drive program to your workstation?
I don't think VeraCypt is a direction to go to. VeraCrypt creates an encrypted container file ('drive') to store files in. That would mean an encrypted container file of more than 1TB in size that you would to download to your workstation. It's like moving the entire bakery to your house when you ordered only a sandwich, every time you want to access a file.
Synology Cloud Storage: Did you know that Synology NAS is 'Cloud storage' (a kind of Google Drive web site) on its own? When you enable your Synology NAS to be connected from internet from your browser, you can use Synology FileStation (a program on your NAS) to access your files. These files only exist on your NAS, until you download them for use on your workstation.
Synology QuickConnect is one way to do that: "How to make Synology NAS accessible over the Internet". QuickConnect is a DDNS solution where you don't have to forward ports on your internet router to your NAS. I prefer using my own domain name to access my NAS from internet where I bought a domain name, created DNS entries, forwarded ports on my router and configured Synology DSM to handle this domain name.
You can also use Synology CloudStation Server on your NAS and Synology CloudStation Drive on your workstation, creating a dedicated file synchronization between your NAS and workstation. See Sync files between Synology NAS and your computer using Cloud Station
Yes, your data that is on Google Drive is encrypted, even though the filenames are not. Use the "Synology Cloud Sync Decryption Tool" you can download from here to decrypt your files after you download them from Drive: https://www.synology.com/en-us/support/download
You will need to use the same encryption password that you used in Cloud Sync, or you will need the private.pem file from the key.zip file that it offered to let you download when you set up the encryption on Cloud Sync on your Synology NAS.