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95 lines
3.5 KiB
Markdown
95 lines
3.5 KiB
Markdown
---
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icon: shield-lock
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order: 980
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label: Encryption
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---
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# How is my data encrypted?
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!!!warning
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This document is not a spec, only an explanation, of the encryption process.
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!!!
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## Algorithms & cryptographic library
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1. XChaCha-Poly1305-IETF (for encryption/decryption)
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2. Argon2 (for password hashing & PKDF)
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1. `argon2i` for PKDF
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2. `argon2id` for password hashing
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3. [**libsodium**](https://libsodium.org)
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On all three platforms we use the same exact library for all cryptographic functions. This ensures data integrity across platforms.
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!!!info Fun story
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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?
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!!!
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## Process
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### 1. Sign up & sign in
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When you sign up for an account, the app takes your password and hashes it using Argon2 with a `predictable per user salt`.
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This predictable salt is generated using a `fixed client salt` + `your email`.
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!!!info Your password never leaves your device
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Sending the hash over sending your plain text password ensures that there is no way for us (or anyone else) to get your password.
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!!!
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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.
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This process is repeated every time you sign in.
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### 2. Key generation
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<!-- !!!info Salt generation
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When you create an account, the server generates a cryptographically secure random salt for you. This salt is used for key generation.
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!!! -->
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!!!info
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When you create an account, the server generates a cryptographically secure random salt for you. This salt is used for key generation. This salt is unique for every user, of course.
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!!!
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After you are signed in, the app requests your user data which includes, among other things, your salt.
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You password & salt is then used to derive a strong irreversible key using Argon2 as the password key derivation function (PKDF).
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### 3. Encryption key storage
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+++ Desktop/Web
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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`.
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`CryptoKey` is stored securely by the browser and cannot be exported, viewed, copied except by the app & browser.
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+++ iOS/Android
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On iOS and Android, the encryption key is stored in the phone's keychain.
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+++
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### 4. Data encryption
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Encryption only takes place when you sync. Each item in the database is encrypted seperately using XChaCha-Poly1305-IETF.
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#### How it works
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1. The item is read from the database as JSON object and stringified (i.e. converted to a string).
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2. The string is encrypted using the encryption key generated earlier.
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3. The result is a JSON object which contains:
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1. A base64 encoded `cipher`
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2. A 192-bit nonce (`iv`)
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3. A random `salt`
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4. Algorithm id `alg`
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5. ItemId `id`
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!!!info See the whole process in action [here.](https://notesnook.com/#whynotesnook)
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!!!
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This object is then sent to the server for storage. The server performs no further operation on this data (because it can't).
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<!-- - Hashing is the process of creating a unique, constant length, non-guessable, irreversible representation of a password.
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- For hashing, we use Argon2 with a predictable client salt.
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- The salt used is a combination of some random bytes + your email.
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- This ensures that every time you login the hash remains the same. -->
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