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// Copyright 2023 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use std::fmt;
use matrix_sdk_base::crypto::{secret_storage::SecretStorageKey, CrossSigningKeyExport};
use ruma::{
events::{
secret::request::SecretName, secret_storage::secret::SecretEventContent,
GlobalAccountDataEventType,
},
serde::Raw,
};
use serde_json::value::to_raw_value;
use tracing::{
error,
field::{debug, display},
info, instrument, warn, Span,
};
use zeroize::Zeroize;
use super::{DecryptionError, Result};
use crate::Client;
#[cfg_attr(doc, aquamarine::aquamarine)]
/// Secure key/value storage for Matrix users.
///
/// The `SecretStore` struct encapsulates the secret storage mechanism for
/// Matrix users, as it is specified in the [Matrix specification].
///
/// This specialized storage is tied to the user's Matrix account and serves as
/// an encrypted key/value store, backed by [account data] residing on the
/// homeserver. Any secrets uploaded to the homeserver using the
/// [`SecretStore::put_secret()`] method are automatically encrypted by the
/// [`SecretStore`].
///
/// [`SecretStore`] enables you to safely manage and access sensitive
/// information while ensuring that it remains protected from unauthorized
/// access. It plays a crucial role in maintaining the privacy and security of a
/// Matrix user's data.
///
/// **Data Flow Overview:**
/// ```mermaid
/// flowchart LR
/// subgraph Client
/// SecretStore
/// end
/// subgraph Homeserver
/// data[Account Data]
/// end
/// SecretStore <== Encrypted ==> data
/// ```
///
/// **Note**: It's important to emphasize that the `SecretStore` should not be
/// used for storing large volumes of data due to its nature as a key/value
/// store for sensitive information.
///
/// # Examples
///
/// ```no_run
/// # use matrix_sdk::Client;
/// # use url::Url;
/// # async {
/// # let homeserver = Url::parse("http://example.com")?;
/// # let client = Client::new(homeserver).await?;
/// use ruma::events::secret::request::SecretName;
///
/// let secret_store = client
/// .encryption()
/// .secret_storage()
/// .open_secret_store("It's a secret to everybody")
/// .await?;
///
/// let my_secret = "Top secret secret";
/// let my_secret_name = SecretName::from("m.treasure");
///
/// secret_store.put_secret(my_secret_name, my_secret);
///
/// # anyhow::Ok(()) };
/// ```
///
/// [Matrix specification]: https://spec.matrix.org/v1.8/client-server-api/#secret-storage
/// [account data]: https://spec.matrix.org/v1.8/client-server-api/#client-config
pub struct SecretStore {
pub(super) client: Client,
pub(super) key: SecretStorageKey,
}
impl SecretStore {
/// Export the [`SecretStorageKey`] of this [`SecretStore`] as a
/// base58-encoded string as defined in the [spec].
///
/// *Note*: This returns a copy of the private key material of the
/// [`SecretStorageKey`] as a string. The caller needs to ensure that this
/// string is zeroized.
///
/// [spec]: https://spec.matrix.org/v1.8/client-server-api/#key-representation
pub fn secret_storage_key(&self) -> String {
self.key.to_base58()
}
/// Retrieve a secret from the homeserver's account data
///
/// This method allows you to retrieve a secret from the account data stored
/// on the Matrix homeserver.
///
/// # Arguments
///
/// - `secret_name`: The name of the secret. The provided `secret_name`
/// serves as the event type for the associated account data event.
///
/// The `retrieve_secret` method enables you to access and decrypt secrets
/// previously stored in the user's account data on the homeserver. You can
/// use the `secret_name` parameter to specify the desired secret to
/// retrieve.
///
/// # Examples
///
/// ```no_run
/// # use matrix_sdk::Client;
/// # use url::Url;
/// # async {
/// # let homeserver = Url::parse("http://example.com")?;
/// # let client = Client::new(homeserver).await?;
/// use ruma::events::secret::request::SecretName;
///
/// let secret_store = client
/// .encryption()
/// .secret_storage()
/// .open_secret_store("It's a secret to everybody")
/// .await?;
///
/// let my_secret_name = SecretName::from("m.treasure");
///
/// let secret = secret_store.get_secret(my_secret_name).await?;
///
/// # anyhow::Ok(()) };
/// ```
pub async fn get_secret(&self, secret_name: impl Into<SecretName>) -> Result<Option<String>> {
let secret_name = secret_name.into();
let event_type = GlobalAccountDataEventType::from(secret_name.to_owned());
if let Some(secret_content) = self.client.account().fetch_account_data(event_type).await? {
let mut secret_content = secret_content.deserialize_as::<SecretEventContent>()?;
// The `SecretEventContent` contains a map from the secret storage key ID to the
// ciphertext. Let's try to find a secret which was encrypted using our
// [`SecretStorageKey`].
if let Some(secret_content) = secret_content.encrypted.remove(self.key.key_id()) {
// We found a secret we should be able to decrypt, let's try to do so.
let decrypted = self
.key
.decrypt(&secret_content.try_into()?, &secret_name)
.map_err(DecryptionError::from)?;
let secret = String::from_utf8(decrypted).map_err(DecryptionError::from)?;
Ok(Some(secret))
} else {
// We did not find a secret which was encrypted using our [`SecretStorageKey`],
// no need to try to decrypt.
Ok(None)
}
} else {
Ok(None)
}
}
/// Store a secret in the homeserver's account data
///
/// This method allows you to securely store a secret on the Matrix
/// homeserver as an encrypted account data event.
///
/// # Arguments
///
/// - `secret_name`: The name of the secret. The provided `secret_name`
/// serves as the event type for the account data event on the homeserver.
///
/// - `secret`: The secret to be stored on the homeserver. The secret is
/// encrypted before being stored, ensuring its confidentiality and
/// integrity.
///
/// # Examples
///
/// ```no_run
/// # use matrix_sdk::Client;
/// # use url::Url;
/// # async {
/// # let homeserver = Url::parse("http://example.com")?;
/// # let client = Client::new(homeserver).await?;
/// use ruma::events::secret::request::SecretName;
///
/// let secret_store = client
/// .encryption()
/// .secret_storage()
/// .open_secret_store("It's a secret to everybody")
/// .await?;
///
/// let my_secret = "Top secret secret";
/// let my_secret_name = SecretName::from("m.treasure");
///
/// secret_store.put_secret(my_secret_name, my_secret);
///
/// # anyhow::Ok(()) };
/// ```
pub async fn put_secret(&self, secret_name: impl Into<SecretName>, secret: &str) -> Result<()> {
// This function does a read/update/store of an account data event stored on the
// homeserver. We first fetch the existing account data event, the event
// contains a map which gets updated by this method, finally we upload the
// modified event.
//
// To prevent multiple calls to this method trying to update a secret at the
// same time, and thus trampling on each other we introduce a lock which
// acts as a semaphore.
//
// Technically there's a low chance of this happening since we're not storing
// many secrets and the bigger problem is that another client might be
// doing this as well and the server doesn't have a mechanism to protect against
// this.
//
// We could make this lock be per `secret_name` but this is not a performance
// critical method.
let _guard = self.client.locks().store_secret_lock.lock().await;
let secret_name = secret_name.into();
let event_type = GlobalAccountDataEventType::from(secret_name.to_owned());
// Get the existing account data event or create a new empty one.
let mut secret_content = if let Some(secret_content) =
self.client.account().fetch_account_data(event_type.to_owned()).await?
{
secret_content
.deserialize_as::<SecretEventContent>()
.unwrap_or_else(|_| SecretEventContent::new(Default::default()))
} else {
SecretEventContent::new(Default::default())
};
// Encrypt the secret.
let secret = secret.as_bytes().to_vec();
let encrypted_secret = self.key.encrypt(secret, &secret_name);
// Insert the encrypted secret into the account data event.
secret_content.encrypted.insert(self.key.key_id().to_owned(), encrypted_secret.into());
let secret_content = Raw::from_json(to_raw_value(&secret_content)?);
// Upload the modified account data event, now that the new secret has been
// inserted.
self.client.account().set_account_data_raw(event_type, secret_content).await?;
Ok(())
}
/// Get all the well-known private parts/keys of the [`OwnUserIdentity`] as
/// a [`CrossSigningKeyExport`].
///
/// The export can be imported into the [`OlmMachine`] using
/// [`OlmMachine::import_cross_signing_keys()`].
async fn get_cross_signing_keys(&self) -> Result<CrossSigningKeyExport> {
let mut export = CrossSigningKeyExport::default();
export.master_key = self.get_secret(SecretName::CrossSigningMasterKey).await?;
export.self_signing_key = self.get_secret(SecretName::CrossSigningSelfSigningKey).await?;
export.user_signing_key = self.get_secret(SecretName::CrossSigningUserSigningKey).await?;
Ok(export)
}
async fn put_cross_signing_keys(&self, export: CrossSigningKeyExport) -> Result<()> {
if let Some(master_key) = &export.master_key {
self.put_secret(SecretName::CrossSigningMasterKey, master_key).await?;
}
if let Some(user_signing_key) = &export.user_signing_key {
self.put_secret(SecretName::CrossSigningUserSigningKey, user_signing_key).await?;
}
if let Some(self_signing_key) = &export.self_signing_key {
self.put_secret(SecretName::CrossSigningSelfSigningKey, self_signing_key).await?;
}
Ok(())
}
async fn maybe_enable_backups(&self) -> Result<()> {
if let Some(mut secret) = self.get_secret(SecretName::RecoveryKey).await? {
let ret = self.client.encryption().backups().maybe_enable_backups(&secret).await;
if let Err(e) = &ret {
warn!("Could not enable backups from secret storage: {e:?}");
}
secret.zeroize();
Ok(ret.map(|_| ())?)
} else {
info!("No backup recovery key found.");
Ok(())
}
}
/// Retrieve and store well-known secrets locally
///
/// This method retrieves and stores all well-known secrets from the account
/// data on the Matrix homeserver to enhance local security and identity
/// verification.
///
/// The following secrets are retrieved by this method:
///
/// - `m.cross_signing.master`: The master cross-signing key.
/// - `m.cross_signing.self_signing`: The self-signing cross-signing key.
/// - `m.cross_signing.user_signing`: The user-signing cross-signing key.
/// - `m.megolm_backup.v1`: The backup recovery key.
///
/// If the `m.cross_signing.self_signing` key is successfully imported, it
/// is used to sign our own [`Device`], marking it as verified. This step is
/// establishes trust in your own device's identity.
///
/// By invoking this method, you ensure that your device has access to
/// the necessary secrets for device and identity verification.
///
/// # Examples
///
/// ```no_run
/// # use matrix_sdk::Client;
/// # use url::Url;
/// # async {
/// # let homeserver = Url::parse("http://example.com")?;
/// # let client = Client::new(homeserver).await?;
/// use ruma::events::secret::request::SecretName;
///
/// let secret_store = client
/// .encryption()
/// .secret_storage()
/// .open_secret_store("It's a secret to everybody")
/// .await?;
///
/// secret_store.import_secrets().await?;
///
/// let status = client
/// .encryption()
/// .cross_signing_status()
/// .await
/// .expect("We should be able to check out cross-signing status");
///
/// println!("Cross-signing status {status:?}");
///
/// # anyhow::Ok(()) };
/// ```
///
/// [`Device`]: crate::encryption::identities::Device
#[instrument(fields(user_id, device_id, cross_signing_status))]
pub async fn import_secrets(&self) -> Result<()> {
let olm_machine = self.client.olm_machine().await;
let olm_machine = olm_machine.as_ref().ok_or(crate::Error::NoOlmMachine)?;
Span::current()
.record("user_id", display(olm_machine.user_id()))
.record("device_id", display(olm_machine.device_id()));
info!("Fetching the private cross-signing keys from the secret store");
// Get all our private cross-signing keys from the secret store.
let export = self.get_cross_signing_keys().await?;
info!(cross_signing_keys = ?export, "Received the cross signing keys from the server");
// We need to ensure that we have the public parts of the cross-signing keys,
// those are represented as the `OwnUserIdentity` struct. The public
// parts from the server are compared to the public parts re-derived from the
// private parts. We will only import the private parts of the cross-signing
// keys if they match to the public parts, otherwise we would risk
// importing some stale cross-signing keys leftover in the secret store.
let (request_id, request) = olm_machine.query_keys_for_users([olm_machine.user_id()]);
self.client.keys_query(&request_id, request.device_keys).await?;
// Let's now try to import our private cross-signing keys.
let status = olm_machine.import_cross_signing_keys(export).await?;
Span::current().record("cross_signing_status", debug(&status));
info!("Done importing the cross signing keys");
if status.has_self_signing {
info!("Successfully imported the self-signing key, attempting to sign our own device");
// Now that we successfully imported them, the self-signing key can be used to
// verify our own device so other devices and user identities trust
// it if the trust our user identity.
if let Some(own_device) = self.client.encryption().get_own_device().await? {
own_device.verify().await?;
// Another /keys/query request to ensure that the signatures we uploaded using
// `own_device.verify()` are attached to the `Device` we have in storage.
let (request_id, request) =
olm_machine.query_keys_for_users([olm_machine.user_id()]);
self.client.keys_query(&request_id, request.device_keys).await?;
info!("Successfully signed our own device, the device is now verified");
} else {
error!("Couldn't find our own device in the store");
}
}
self.maybe_enable_backups().await?;
Ok(())
}
pub(super) async fn export_secrets(&self) -> Result<()> {
let olm_machine = self.client.olm_machine().await;
let olm_machine = olm_machine.as_ref().ok_or(crate::Error::NoOlmMachine)?;
if let Some(cross_signing_keys) = olm_machine.export_cross_signing_keys().await? {
self.put_cross_signing_keys(cross_signing_keys).await?;
}
let backup_keys = olm_machine.backup_machine().get_backup_keys().await?;
if let Some(backup_recovery_key) = backup_keys.decryption_key {
let mut key = backup_recovery_key.to_base64();
self.put_secret(SecretName::RecoveryKey, &key).await?;
key.zeroize();
}
Ok(())
}
}
impl fmt::Debug for SecretStore {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SecretStore").field("key", &self.key).finish_non_exhaustive()
}
}