Encryption at rest and in transit

🚚 The armoured van

Say you are moving gold bars, your data, to a bank vault, the cloud.

• In transit, the van. The gold travels in an armoured van, so nobody robs it on the road. That is HTTPS.
• At rest, the vault. The bank puts the gold in a steel vault, so a break-in at night gets nothing. That is disk encryption.
• The catch. The manager has the key to the vault. He can open it, count your gold, look at it, or hand it to whoever asks with the right paperwork.

A third layer changes the picture. You seal the gold in your own box before it goes into the van. The bank stores your box in the vault and cannot open it, manager included.

🚦 In transit

This is the padlock next to the address in your browser.

• What it is. TLS, the successor to SSL.
• What it stops. Somebody on the same café network intercepting your password on the way past.
• Where it ends. At the server's front door. To act on your request, the server decrypts it.

🗄️ At rest

This means the disks in the data centre are encrypted.

• What it is. Usually AES-256, applied by the server.
• What it stops. Somebody physically walking out with a drive.
• Where it ends. The application on that server needs the key in order to work at all, to build a search index for instance. So the data is readable to the application, and to the people who administer it.

🏆 What we add

We use both, and then add the layer that actually decides the question: encryption on your device.

Because your notes are locked before they leave and stay locked afterwards, with a key we do not hold:

• On the wire. Even if the transport layer failed, an eavesdropper sees ciphertext.
• On the disk. Even if our database leaked tomorrow, the file is ciphertext.
• On our own servers. Our own processes cannot read your notes either.

So when you are comparing note apps, encryption at rest is table stakes rather than an answer. The question worth asking is who holds the key.

❓ Questions people ask