I want to encrypt my server's backups and upload them to cloud storage (e.g. dropbox, google drive).
I understand the basics with symmetric (single passphrase-secured key) and asymmetric (public/private keypair) encryption. But I don't know which would be more appropriate in my specific use case.
I've read many related questions and there seems to be a 50/50 split between people who recommend the one way or the other (for this specific use case) - but I can't find a reason why.
I know that asymmetric is used when one can perform key exchange between parties, and that it is much slower. So symmetric is typically used to encrypt large payloads.
In my case, my daily backups are a few hundred megabytes each, and there is no key exchange because I am both "sender" and "receiver". And these are secondary backups - I will only decrypt them if my primary backups fail.
So I was planning to store on the server a very long (e.g. 100 char) passphrase, and use it for automated backups using
gpg symmetric encryption, which is simple to manage. Is this good enough, or should I rather use asymmetric encryption?