End-to-end encryption
To better understand what end-to-end encryption, let's use an analogy, comparing it to other "secure" sites...
Analogy
Imagine if the mayor of your Town/City had a master key which could unlock every house in the town/city, and that key was stored in the Town/City Hall.
Sounds unsettling right? Isn't it redundant with your own personal key? Could it introduce additional risks were the Town/City themselves want to go into your house, or if a thief got a hold of the Town/City's key? Well...
Existing sites
...this is exactly how Google Drive, Dropbox and other "secure" portals work. There is a centralized key that while preventing your Average Joe from downloading your files, the companies routinely share your data with third parties, by taking their master key and unlocking your house (documents) and letting other people walk around! Take a look at the below, which is taken straight from Dropbox's own website:
So not only does Dropbox share your documents and data with other companies, but if a hacker were to get access to the servers and the "master key", then all of the data could be leaked
Everyone has a different risk tolerance, and so each individual should evaluate whether or not they are comfortable with all of these companies having access to your documents and personal information. I for one enjoy having guests over my house, but prefer that Eric Adams, the Mayor of New York City, can't just walk in whenever he pleases.
So then what's end-to-end encryption?
To reuse the analogy from the beginning of this article, instead of the Town Hall having a master key that unlocks each house in the down, each individual person has their own key to their house, so therefore only they can access it. End-to-end encryption is the same way, where only you and your client can view the documents, not even LegalFiler! We couldn't access them even if we tried.