This document is not a spec, only an explanation of the encryption process.
argon2idfor password hashing
On all three platforms we use the same exact library for all cryptographic functions. This ensures data integrity across platforms.
When we first added encryption, we used AES-GCM-256 across platforms but the cross-platform compatbility was abyssmal. That is when I found out about the great libsodium. Written in C, wrappers available for all platforms…what more could I want?
When you sign up for an account, the app takes your password and hashes it using Argon2 with a
predictable per user salt.
This predictable salt is generated using a
fixed client salt +
Your password never leaves your device
Sending the hash over sending your plain text password ensures that there is no way for us (or anyone else) to get your password.
After the hash is generated, it is sent to the server. This hash is used as a
password and is hashed again to mitigate password passthrough attacks.
This process is repeated every time you sign in.
After you are signed in, the app requests your user data which includes, among other things, your salt.
When you create an account, the server generates a cryptographically secure random salt for you. This salt is used for key generation.
You password & salt is then used to derive a strong irreversible key using Argon2 as the password key derivation function (PKDF).
Instead of storing the key as plain text (and allowing anyone to copy/move it), we use browser’s
IndexedDB to store the key as a
CryptoKey is stored securely by the browser and cannot be exported, viewed, copied except by the app & browser.
On iOS and Android, the encryption key is stored in the phone’s keychain.
Encryption only takes place when you sync. Each item in the database is encrypted seperately using XChaCha-Poly1305-IETF.
See the whole process in action here.
This object is then sent to the server for storage. The server performs no further operation on this data (because it can’t).