5d716f969d
* Use `IndexeddbSerializer` more widely in test code
reuse `IndexeddbSerializer::maybe_encrypt_value` instead of re-inventing it.
* Rewrite `StoreCipher::decrypt_value_base64_typed`
Instead of un-base64-ing and calling `decrypt_value_typed` (which deserializes
the result`), call `decrypt_value_base64_data` (which un-base64s before
decrypting but does not deserialize the result), then deserialize.
This makes it more symmetrical with `encrypt_value_base64_typed`, and helps me
get rid of `decrypt_value_typed` (which is barely used.)
* Fix docs on `StoreCipher::encrypt_value_base64_typed`
looks like they got C&Ped from `encrypt_value_typed`.
* Inline `StoreCipher::{encrypt,decrypt}_value_typed`
Each of these are quite simple, are only used in two places, and their
existence melts my brain.
* Rewrite `IndexeddbSerializer::maybe_{encrypt,decrypt}_value`
... to use `en/decrypt_value_base64_data` instead of
`en/decrypt_value_base64_typed`.
We have to have the de/serialization code for the unencrypted case anyway, so
using the higher-level method isn't helping us much.
* Remove unused `StoreCipher::{en,de}crypt_value_base64_typed`
Outside of tests, these things are totally unused.
A general purpose encryption scheme for key/value stores.
Usage
use matrix_sdk_store_encryption::StoreCipher;
use serde_json::{json, value::Value};
fn main() -> anyhow::Result<()> {
let store_cipher = StoreCipher::new()?;
// Export the store cipher and persist it in your key/value store
let export = store_cipher.export("secret-passphrase")?;
let value = json!({
"some": "data",
});
let encrypted = store_cipher.encrypt_value(&value)?;
let decrypted: Value = store_cipher.decrypt_value(&encrypted)?;
assert_eq!(value, decrypted);
let key = "bulbasaur";
// Hash the key so people don't know which pokemon we have collected.
let hashed_key = store_cipher.hash_key("list-of-pokemon", key.as_ref());
let another_table = store_cipher.hash_key("my-starter", key.as_ref());
let same_key = store_cipher.hash_key("my-starter", key.as_ref());
assert_ne!(key.as_ref(), hashed_key);
assert_ne!(hashed_key, another_table);
assert_eq!(another_table, same_key);
Ok(())
}
⚠️ Security Warning: Hazmat!
This crate only implements the low-level block cipher function, to be used only as a building block for higher-level constructions. It is NOT intended for direct use in applications.
USE AT YOUR OWN RISK!
Encryption scheme
The central component of the encryption scheme is the StoreCipher type, used
for both obfuscating keys and encrypting values of the key/value store.
A StoreCipher object consists of two randomly-generated 32 byte secrets.
The first secret is used to encrypt values. XChaCha20Poly1305 with a random nonce is used to encrypt each value. The nonce is saved with the ciphertext.
The second secret is used as a seed to derive table-specific keys, used to key a keyed hash construction, which is in turn used to hash table data. Currently we use blake3 as the keyed hash construction.
┌───────────────────────────────────────┐
│ StoreCipher │
│ Encryption key | Hash key seed │
│ [u8; 32] | [u8; 32] │
└───────────────────────────────────────┘
The StoreCipher has some Matrix-specific assumptions built in, which ensure that
the limits of the cryptographic primitives are not exceeded. If this crate is
used for non-Matrix data, users need to ensure:
- That individual values are chunked, otherwise decryption might be susceptible to a DOS attack.
- The
StoreCipheris periodically rotated/rekeyed.
WASM support
This crate relies on the random and getrandom crates which don't support
WASM automatically.
Either turn the js feature on directly on this crate or depend on getrandom
with the js feature turned on. More info can be found in the getrandom
docs.