The test: who holds the keys?
"Encrypted" alone says little. Nearly every service encrypts data in transit and on its disks, but it also holds the keys, so it can read your data, and so can anyone who breaks in or compels it. In end to end encryption, the keys exist only on your devices and the server gets only ciphertext.
A quick check: can the company reset your password and give you back your data? If yes, it can read your data, or has a way to. A true end to end design means that losing both your password and your recovery key loses the data.
The same test applies to the tool that holds your server logins: an SSH key manager with an encrypted vault should pass it.
What the server can still see
Encryption hides content. It cannot hide everything, because the server still has to run an account and deliver data:
- Your email and plan, and often your device names.
- Activity dates, and your IP address when you connect.
- How many encrypted items you have and roughly how large they are. Padding can blur the size but not remove it.
The server can also delete or block your data. End to end encryption protects secrecy, and it does not guarantee availability, so keep your own copy of what you cannot lose.
What it does not protect against
- A weak password. If your keys come from your password, whoever steals the database can guess offline, with no rate limit. See Argon2id explained.
- A malicious update. The app holds your keys, so whoever controls what the app does can read them. Signing limits who can ship an update, but you still trust the vendor and its signing key.
- A compromised device. Malware on an unlocked device can read what you can read.
- An unlocked device in the wrong hands, if the app has no lock of its own.
- Code delivered by the server. A web app loaded from the server on each visit can be swapped by whoever controls that server, and it could steal your password as you type it.
Questions to ask any vendor
- Where is the encryption done, and are keys ever sent to you, even wrapped?
- How is the password turned into a key, and is a second secret, such as a key made on my device, needed too?
- Exactly what metadata do you store? Are item names and types encrypted?
- What happens if I forget my password? Any answer other than a recovery key I hold needs an explanation.
- Does a website or web app ever see my password?
Questions
Is end to end encryption the same as zero knowledge?
In practice, yes. Zero knowledge is a marketing name for the same idea: the provider stores your data without the keys to read it.
Can an end to end encrypted service recover my data if I forget my password?
Only with a recovery key or kit that you hold. If the company can restore your data after an email reset alone, it has a key to it, and the data is not end to end encrypted.
Does end to end encryption hide my metadata?
No. The server still sees your email, activity dates and the number and rough size of your items. Only the content is hidden.