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    How is my data encrypted?

    Note

    This document is not a spec, only an explanation of the encryption process.

    Algorithms & cryptographic library

    1. XChaCha-Poly1305-IETF (for encryption/decryption)
    2. Argon2 (for password hashing & PKDF)
      1. argon2i for PKDF
      2. argon2id for password hashing
    3. libsodium

    On all three platforms we use the same exact library for all cryptographic functions. This ensures data integrity across platforms.

    Fun story

    When we first added encryption, we used AES-GCM-256 across platforms but the cross-platform compatibility 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?

    Process

    1. Sign up & sign in

    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 email.

    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.

    2. Key generation

    When you first sign up for an account, your client generates two encryption keys. One is a unique data encryption key that encrypts all your notes and other data. The second is your master encryption key, this is derived by your password and predictable salt. This key protects all your encryption keys, like the aforementioned data encryption key. If you change your password, your client will re-encrypt your existing data encryption key with your new master key.

    3. Encryption key storage

    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.

    CryptoKey is stored securely by the browser and cannot be exported, viewed, or copied except by the app & browser.

    On iOS and Android, the encryption key is stored in the phone’s keychain.

    4. Data encryption

    Encryption only takes place when you sync. Each item in the database is encrypted separately using XChaCha-Poly1305-IETF.

    How it works

    1. The item is read from the database as JSON object and stringified (i.e. converted to a string).
    2. The string is encrypted using the data encryption key generated earlier.
    3. The result is a JSON object which contains:
      1. A base64 encoded cipher
      2. A 192-bit nonce (iv)
      3. A random salt
      4. Algorithm id alg
      5. ItemId id

    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).

    Faqs

    I am an old user of Notesnook, I don’t have a data encryption key.

    Your data encryption key will be created when you change your password.

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