So there are a few cloud storage services such as mega.nz, syn.com and others which state that they use zero knowledge encryption. This would mean that they don't have access to the private keys which are required to decrypt and view the content stored by a user on their cloud storage.
If that is the case, then how is it possible to do the following?
I login to my account and I can view all the content and even stream it (for example, videos can be played directly). Does it mean that all this is decrypted on the fly when I login to the account?
If I generate a download link and share it with another user, how are they able to download the content using that download link even though they don't have the password to my account which would be required to decrypt the content?
Or does mega.nz store the information required to decrypt the content in the link itself? For instance, decryption key is a part of the download link?
I wonder if there is a way to actually verify that these cloud storage services which claim to use zero knowledge encryption are indeed using it? Maybe there is some type of third party audit done to confirm this?