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// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved. // SPDX-License-Identifier: MIT OR Apache-2.0 //! Tough is a client library for [TUF repositories]. //! //! This client adheres to [TUF version 1.0.0][spec], with the following exceptions: //! //! * Delegated roles (and TAP 3) are not yet supported. //! * TAP 4 (multiple repository consensus) is not yet supported. //! //! [TUF repositories]: https://theupdateframework.github.io/ //! [spec]: https://github.com/theupdateframework/specification/blob/9f148556ca15da2ec5c022c8b3e6f99a028e5fe5/tuf-spec.md //! //! # Testing //! //! Unit tests are run in the usual manner: `cargo test`. //! Integration tests require docker and are disabled by default behind a feature named `integ`. //! To run all tests, including integration tests: `cargo test --all-features` or //! `cargo test --features 'http,integ'`. #![forbid(missing_debug_implementations, missing_copy_implementations)] #![deny(rust_2018_idioms)] // missing_docs is on its own line to make it easy to comment out when making changes. #![deny(missing_docs)] #![warn(clippy::pedantic)] #![allow( clippy::module_name_repetitions, clippy::must_use_candidate, clippy::missing_errors_doc )] mod cache; mod datastore; pub mod editor; pub mod error; mod fetch; #[cfg(feature = "http")] pub mod http; mod io; pub mod key_source; pub mod schema; pub mod sign; mod transport; use crate::datastore::Datastore; use crate::error::Result; use crate::fetch::{fetch_max_size, fetch_sha256}; /// An HTTP transport that includes retries. #[cfg(feature = "http")] pub use crate::http::{HttpTransport, HttpTransportBuilder, RetryRead}; use crate::schema::{DelegatedRole, Delegations}; use crate::schema::{Role, RoleType, Root, Signed, Snapshot, Timestamp}; pub use crate::transport::{ DefaultTransport, FilesystemTransport, Transport, TransportError, TransportErrorKind, }; use chrono::{DateTime, Utc}; use snafu::{ensure, OptionExt, ResultExt}; use std::collections::HashMap; use std::io::Read; use std::path::PathBuf; use url::Url; /// Represents whether a Repository should fail to load when metadata is expired (`Safe`) or whether /// it should ignore expired metadata (`Unsafe`). Only use `Unsafe` if you are sure you need it. #[derive(Debug, Clone, Copy, PartialEq, Eq)] pub enum ExpirationEnforcement { /// Expirations will be enforced. You MUST use this option to get TUF security guarantees. Safe, /// Expirations will not be enforced. This is available for certain offline use cases, does NOT /// provide TUF security guarantees, and should only be used if you are sure that you need it. Unsafe, } /// `ExpirationEnforcement` defaults to `Safe` mode. impl Default for ExpirationEnforcement { fn default() -> Self { ExpirationEnforcement::Safe } } impl From<bool> for ExpirationEnforcement { fn from(b: bool) -> Self { if b { ExpirationEnforcement::Safe } else { ExpirationEnforcement::Unsafe } } } impl From<ExpirationEnforcement> for bool { fn from(ee: ExpirationEnforcement) -> Self { ee == ExpirationEnforcement::Safe } } /// A builder for settings with which to load a [`Repository`]. Required settings are provided in /// the [`RepositoryLoader::new`] function. Optional parameters can be added after calling new. /// Finally, call [`RepositoryLoader::load`] to load the [`Repository`]. /// /// # Examples /// /// ## Basic usage: /// /// ```rust /// # use std::fs::File; /// # use std::path::PathBuf; /// # use tough::RepositoryLoader; /// # use url::Url; /// # let dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests").join("data").join("tuf-reference-impl"); /// # let root = dir.join("metadata").join("1.root.json"); /// # let metadata_base_url = Url::from_file_path(dir.join("metadata")).unwrap(); /// # let targets_base_url = Url::from_file_path(dir.join("targets")).unwrap(); /// /// let repository = RepositoryLoader::new( /// File::open(root).unwrap(), /// metadata_base_url, /// targets_base_url, /// ) /// .load() /// .unwrap(); /// /// ``` /// /// ## With optional settings: /// /// ```rust /// # use std::fs::File; /// # use std::path::PathBuf; /// # use tough::{RepositoryLoader, FilesystemTransport, ExpirationEnforcement}; /// # use url::Url; /// # let dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests").join("data").join("tuf-reference-impl"); /// # let root = dir.join("metadata").join("1.root.json"); /// # let metadata_base_url = Url::from_file_path(dir.join("metadata")).unwrap(); /// # let targets_base_url = Url::from_file_path(dir.join("targets")).unwrap(); /// /// let repository = RepositoryLoader::new( /// File::open(root).unwrap(), /// metadata_base_url, /// targets_base_url, /// ) /// .transport(FilesystemTransport) /// .expiration_enforcement(ExpirationEnforcement::Unsafe) /// .load() /// .unwrap(); /// /// ``` #[derive(Debug, Clone)] pub struct RepositoryLoader<R> where R: Read, { root: R, metadata_base_url: Url, targets_base_url: Url, transport: Option<Box<dyn Transport>>, limits: Option<Limits>, datastore: Option<PathBuf>, expiration_enforcement: Option<ExpirationEnforcement>, } impl<R: Read> RepositoryLoader<R> { /// Create a new `RepositoryLoader`. /// /// `root` is a [`Read`]er for the trusted root metadata file, which you must ship with your /// software using an out-of-band process. It should be a copy of the most recent root.json /// from your repository. (It's okay if it becomes out of date later; the client establishes /// trust up to the most recent root.json file.) /// /// `metadata_base_url` and `targets_base_url` are the base URLs where the client can find /// metadata (such as root.json) and targets (as listed in targets.json). pub fn new(root: R, metadata_base_url: Url, targets_base_url: Url) -> Self { Self { root, metadata_base_url, targets_base_url, transport: None, limits: None, datastore: None, expiration_enforcement: None, } } /// Load and verify TUF repository metadata. pub fn load(self) -> Result<Repository> { Repository::load(self) } /// Set the transport. If no transport has been set, [`DefaultTransport`] will be used. pub fn transport<T: Transport + 'static>(mut self, transport: T) -> Self { self.transport = Some(Box::new(transport)); self } /// Set a the repository [`Limits`]. pub fn limits(mut self, limits: Limits) -> Self { self.limits = Some(limits); self } /// Set a `datastore` directory path. `datastore` is a directory on a persistent filesystem. /// This directory's contents store the most recently fetched timestamp, snapshot, and targets /// metadata files to detect version rollback attacks. /// /// You may chose to provide a [`PathBuf`] to a directory on a persistent filesystem, which must /// exist prior to calling [`RepositoryLoader::load`]. If no datastore is provided, a temporary /// directory will be created and cleaned up for for you. pub fn datastore<P: Into<PathBuf>>(mut self, datastore: P) -> Self { self.datastore = Some(datastore.into()); self } /// Set the [`ExpirationEnforcement`]. /// /// **CAUTION:** TUF metadata expiration dates, particularly `timestamp.json`, are designed to /// limit a replay attack window. By setting `expiration_enforcement` to `Unsafe`, you are /// disabling this feature of TUF. Use `Safe` unless you have a good reason to use `Unsafe`. pub fn expiration_enforcement(mut self, exp: ExpirationEnforcement) -> Self { self.expiration_enforcement = Some(exp); self } } /// Limits used when fetching repository metadata. /// /// These limits are implemented to prevent endless data attacks. Clients must ensure these values /// are set higher than what would reasonably be expected by a repository, but not so high that the /// amount of data could interfere with the system. /// /// `max_root_size` and `max_timestamp_size` are the maximum size for the `root.json` and /// `timestamp.json` files, respectively, downloaded from the repository. These must be /// sufficiently large such that future updates to your repository's key management strategy /// will still be supported, but sufficiently small such that you are protected against an /// endless data attack (defined by TUF as an attacker responding to clients with extremely /// large files that interfere with the client's system). /// /// The [`Default`] implementation sets the following values: /// * `max_root_size`: 1 MiB /// * `max_targets_size`: 10 MiB /// * `max_timestamp_size`: 1 MiB /// * `max_root_updates`: 1024 #[derive(Debug, Clone, Copy)] pub struct Limits { /// The maximum allowable size in bytes for downloaded root.json files. pub max_root_size: u64, /// The maximum allowable size in bytes for downloaded targets.json file **if** the size is not /// listed in snapshots.json. This setting is ignored if the size of targets.json is in the /// signed snapshots.json file. pub max_targets_size: u64, /// The maximum allowable size in bytes for the downloaded timestamp.json file. pub max_timestamp_size: u64, /// The maximum number of updates to root.json to download. pub max_root_updates: u64, } impl Default for Limits { fn default() -> Self { Self { max_root_size: 1024 * 1024, // 1 MiB max_targets_size: 1024 * 1024 * 10, // 10 MiB max_timestamp_size: 1024 * 1024, // 1 MiB max_root_updates: 1024, } } } /// A TUF repository. /// /// You can create a `Repository` using a [`RepositoryLoader`]. #[derive(Debug, Clone)] pub struct Repository { transport: Box<dyn Transport>, consistent_snapshot: bool, datastore: Datastore, earliest_expiration: DateTime<Utc>, earliest_expiration_role: RoleType, root: Signed<Root>, snapshot: Signed<Snapshot>, timestamp: Signed<Timestamp>, targets: Signed<crate::schema::Targets>, limits: Limits, metadata_base_url: Url, targets_base_url: Url, expiration_enforcement: ExpirationEnforcement, } impl Repository { /// Load and verify TUF repository metadata using a [`RepositoryLoader`] for the settings. fn load<R: Read>(loader: RepositoryLoader<R>) -> Result<Self> { let datastore = Datastore::new(loader.datastore)?; let transport = loader .transport .unwrap_or_else(|| Box::new(DefaultTransport::new())); let limits = loader.limits.unwrap_or_default(); let expiration_enforcement = loader.expiration_enforcement.unwrap_or_default(); let metadata_base_url = parse_url(loader.metadata_base_url)?; let targets_base_url = parse_url(loader.targets_base_url)?; // 0. Load the trusted root metadata file + 1. Update the root metadata file let root = load_root( transport.as_ref(), loader.root, &datastore, limits.max_root_size, limits.max_root_updates, &metadata_base_url, expiration_enforcement, )?; // 2. Download the timestamp metadata file let timestamp = load_timestamp( transport.as_ref(), &root, &datastore, limits.max_timestamp_size, &metadata_base_url, expiration_enforcement, )?; // 3. Download the snapshot metadata file let snapshot = load_snapshot( transport.as_ref(), &root, ×tamp, &datastore, &metadata_base_url, expiration_enforcement, )?; // 4. Download the targets metadata file let targets = load_targets( transport.as_ref(), &root, &snapshot, &datastore, limits.max_targets_size, &metadata_base_url, expiration_enforcement, )?; let expires_iter = [ (root.signed.expires, RoleType::Root), (timestamp.signed.expires, RoleType::Timestamp), (snapshot.signed.expires, RoleType::Snapshot), (targets.signed.expires, RoleType::Targets), ]; let (earliest_expiration, earliest_expiration_role) = expires_iter.iter().min_by_key(|tup| tup.0).unwrap(); Ok(Self { transport, consistent_snapshot: root.signed.consistent_snapshot, datastore, earliest_expiration: earliest_expiration.to_owned(), earliest_expiration_role: *earliest_expiration_role, root, snapshot, timestamp, targets, limits, metadata_base_url, targets_base_url, expiration_enforcement, }) } /// Returns the list of targets present in the repository. pub fn targets(&self) -> &Signed<crate::schema::Targets> { &self.targets } /// Returns a reference to the signed root pub fn root(&self) -> &Signed<Root> { &self.root } /// Returns a reference to the signed snapshot pub fn snapshot(&self) -> &Signed<Snapshot> { &self.snapshot } /// Returns a reference to the signed timestamp pub fn timestamp(&self) -> &Signed<Timestamp> { &self.timestamp } ///return a vec of all targets including all target files delegated by targets pub fn all_targets(&self) -> impl Iterator + '_ { self.targets.signed.targets_iter() } /// Fetches a target from the repository. /// /// If the repository metadata is expired or there is an issue making the request, `Err` is /// returned. /// /// If the requested target is not listed in the repository metadata, `Ok(None)` is returned. /// /// Otherwise, a reader is returned, which provides streaming access to the target contents /// before its checksum is validated. If the maximum size is reached or there is a checksum /// mismatch, the reader returns a [`std::io::Error`]. **Consumers of this library must not use /// data from the reader if it returns an error.** pub fn read_target(&self, name: &str) -> Result<Option<impl Read + Send>> { // Check for repository metadata expiration. if self.expiration_enforcement == ExpirationEnforcement::Safe { ensure!( system_time(&self.datastore)? < self.earliest_expiration, error::ExpiredMetadata { role: self.earliest_expiration_role } ); } // 5. Verify the desired target against its targets metadata. // // 5.1. If there is no targets metadata about this target, abort the update cycle and // report that there is no such target. // // 5.2. Otherwise, download the target (up to the number of bytes specified in the targets // metadata), and verify that its hashes match the targets metadata. (We download up to // this number of bytes, because in some cases, the exact number is unknown. This may // happen, for example, if an external program is used to compute the root hash of a tree // of targets files, and this program does not provide the total size of all of these // files.) If consistent snapshots are not used (see Section 7), then the filename used // to download the target file is of the fixed form FILENAME.EXT (e.g., foobar.tar.gz). // Otherwise, the filename is of the form HASH.FILENAME.EXT (e.g., // c14aeb4ac9f4a8fc0d83d12482b9197452f6adf3eb710e3b1e2b79e8d14cb681.foobar.tar.gz), where // HASH is one of the hashes of the targets file listed in the targets metadata file // found earlier in step 4. In either case, the client MUST write the file to // non-volatile storage as FILENAME.EXT. Ok(if let Ok(target) = self.targets.signed.find_target(name) { let (sha256, file) = self.target_digest_and_filename(target, name); Some(self.fetch_target(target, &sha256, file.as_str())?) } else { None }) } /// Return the named `DelegatedRole` if found. pub fn delegated_role(&self, name: &str) -> Option<&DelegatedRole> { self.targets.signed.delegated_role(name).ok() } } /// Ensures that system time has not stepped backward since it was last sampled fn system_time(datastore: &Datastore) -> Result<DateTime<Utc>> { let file = "latest_known_time.json"; // Get 'current' system time let sys_time = Utc::now(); // Load the latest known system time, if it exists if let Some(Ok(latest_known_time)) = datastore .reader(file)? .map(serde_json::from_reader::<_, DateTime<Utc>>) { // Make sure the sampled system time did not go back in time ensure!( sys_time >= latest_known_time, error::SystemTimeSteppedBackward { sys_time, latest_known_time } ); } // Store the latest known time // Serializes RFC3339 time string and store to datastore datastore.create(file, &sys_time)?; Ok(sys_time) } /// TUF v1.0.16, 5.2.9, 5.3.3, 5.4.5, 5.5.4, The expiration timestamp in the `[metadata]` file MUST /// be higher than the fixed update start time. fn check_expired<T: Role>(datastore: &Datastore, role: &T) -> Result<()> { ensure!( system_time(datastore)? <= role.expires(), error::ExpiredMetadata { role: T::TYPE } ); Ok(()) } /// Checks to see if the `Url` has a trailing slash and adds one if not. Without a trailing slash, /// the last component of a `Url` is considered to be a file. `metadata_url` and `targets_url` /// must refer to a base (i.e. directory), so we need them to end with a slash. fn parse_url(url: Url) -> Result<Url> { if url.as_str().ends_with('/') { Ok(url) } else { let mut s = url.to_string(); s.push('/'); Url::parse(&s).context(error::ParseUrl { url: s }) } } /// Steps 0 and 1 of the client application, which load the current root metadata file based on a /// trusted root metadata file. fn load_root<R: Read>( transport: &dyn Transport, root: R, datastore: &Datastore, max_root_size: u64, max_root_updates: u64, metadata_base_url: &Url, expiration_enforcement: ExpirationEnforcement, ) -> Result<Signed<Root>> { // 0. Load the trusted root metadata file. We assume that a good, trusted copy of this file was // shipped with the package manager or software updater using an out-of-band process. Note // that the expiration of the trusted root metadata file does not matter, because we will // attempt to update it in the next step. let mut root: Signed<Root> = serde_json::from_reader(root).context(error::ParseTrustedMetadata)?; root.signed .verify_role(&root) .context(error::VerifyTrustedMetadata)?; // Used in step 1.2 let original_root_version = root.signed.version.get(); // Used in step 1.9 let original_timestamp_keys = root .signed .keys(RoleType::Timestamp) .cloned() .collect::<Vec<_>>(); let original_snapshot_keys = root .signed .keys(RoleType::Snapshot) .cloned() .collect::<Vec<_>>(); // 1. Update the root metadata file. Since it may now be signed using entirely different keys, // the client must somehow be able to establish a trusted line of continuity to the latest // set of keys. To do so, the client MUST download intermediate root metadata files, until // the latest available one is reached. Therefore, it MUST temporarily turn on consistent // snapshots in order to download versioned root metadata files as described next. loop { // 1.1. Let N denote the version number of the trusted root metadata file. // // 1.2. Try downloading version N+1 of the root metadata file, up to some X number of bytes // (because the size is unknown). The value for X is set by the authors of the // application using TUF. For example, X may be tens of kilobytes. The filename used to // download the root metadata file is of the fixed form VERSION_NUMBER.FILENAME.EXT // (e.g., 42.root.json). If this file is not available, or we have downloaded more than Y // number of root metadata files (because the exact number is as yet unknown), then go to // step 1.8. The value for Y is set by the authors of the application using TUF. For // example, Y may be 2^10. ensure!( root.signed.version.get() < original_root_version + max_root_updates, error::MaxUpdatesExceeded { max_root_updates } ); let path = format!("{}.root.json", root.signed.version.get() + 1); match fetch_max_size( transport, metadata_base_url.join(&path).context(error::JoinUrl { path, url: metadata_base_url.to_owned(), })?, max_root_size, "max_root_size argument", ) { Err(_) => break, // If this file is not available, then go to step 1.8. Ok(reader) => { let new_root: Signed<Root> = serde_json::from_reader(reader).context(error::ParseMetadata { role: RoleType::Root, })?; // 1.3. Check signatures. Version N+1 of the root metadata file MUST have been // signed by: (1) a threshold of keys specified in the trusted root metadata file // (version N), and (2) a threshold of keys specified in the new root metadata // file being validated (version N+1). If version N+1 is not signed as required, // discard it, abort the update cycle, and report the signature failure. On the // next update cycle, begin at step 0 and version N of the root metadata file. root.signed .verify_role(&new_root) .context(error::VerifyMetadata { role: RoleType::Root, })?; new_root .signed .verify_role(&new_root) .context(error::VerifyMetadata { role: RoleType::Root, })?; // 1.4. Check for a rollback attack. The version number of the trusted root // metadata file (version N) must be less than or equal to the version number of // the new root metadata file (version N+1). Effectively, this means checking // that the version number signed in the new root metadata file is indeed N+1. If // the version of the new root metadata file is less than the trusted metadata // file, discard it, abort the update cycle, and report the rollback attack. On // the next update cycle, begin at step 0 and version N of the root metadata // file. ensure!( root.signed.version <= new_root.signed.version, error::OlderMetadata { role: RoleType::Root, current_version: root.signed.version, new_version: new_root.signed.version } ); // Off-spec: 1.4 specifies that the version number of the trusted root metadata // file must be less than or equal to the version number of the new root metadata // file. If they are equal, this will create an infinite loop, so we ignore the new // root metadata file but do not report an error. This could only happen if the // path we built above, referencing N+1, has a filename that doesn't match its // contents, which would have to list version N. if root.signed.version == new_root.signed.version { break; } // 1.5. Note that the expiration of the new (intermediate) root metadata file does // not matter yet, because we will check for it in step 1.8. // // 1.6. Set the trusted root metadata file to the new root metadata file. // // (This is where version N+1 becomes version N.) root = new_root; // 1.7. Repeat steps 1.1 to 1.7. continue; } } } // TUF v1.0.16, 5.2.9. Check for a freeze attack. The expiration timestamp in the trusted root // metadata file MUST be higher than the fixed update start time. If the trusted root metadata // file has expired, abort the update cycle, report the potential freeze attack. On the next // update cycle, begin at step 5.1 and version N of the root metadata file. if expiration_enforcement == ExpirationEnforcement::Safe { check_expired(datastore, &root.signed)?; } // 1.9. If the timestamp and / or snapshot keys have been rotated, then delete the trusted // timestamp and snapshot metadata files. This is done in order to recover from fast-forward // attacks after the repository has been compromised and recovered. A fast-forward attack // happens when attackers arbitrarily increase the version numbers of: (1) the timestamp // metadata, (2) the snapshot metadata, and / or (3) the targets, or a delegated targets, // metadata file in the snapshot metadata. if original_timestamp_keys .iter() .ne(root.signed.keys(RoleType::Timestamp)) || original_snapshot_keys .iter() .ne(root.signed.keys(RoleType::Snapshot)) { let r1 = datastore.remove("timestamp.json"); let r2 = datastore.remove("snapshot.json"); r1.and(r2)?; } // 1.10. Set whether consistent snapshots are used as per the trusted root metadata file (see // Section 4.3). // // (This is done by checking the value of root.signed.consistent_snapshot throughout this // library.) Ok(root) } /// Step 2 of the client application, which loads the timestamp metadata file. fn load_timestamp( transport: &dyn Transport, root: &Signed<Root>, datastore: &Datastore, max_timestamp_size: u64, metadata_base_url: &Url, expiration_enforcement: ExpirationEnforcement, ) -> Result<Signed<Timestamp>> { // 2. Download the timestamp metadata file, up to Y number of bytes (because the size is // unknown.) The value for Y is set by the authors of the application using TUF. For // example, Y may be tens of kilobytes. The filename used to download the timestamp metadata // file is of the fixed form FILENAME.EXT (e.g., timestamp.json). let path = "timestamp.json"; let reader = fetch_max_size( transport, metadata_base_url.join(path).context(error::JoinUrl { path, url: metadata_base_url.to_owned(), })?, max_timestamp_size, "max_timestamp_size argument", )?; let timestamp: Signed<Timestamp> = serde_json::from_reader(reader).context(error::ParseMetadata { role: RoleType::Timestamp, })?; // 2.1. Check signatures. The new timestamp metadata file must have been signed by a threshold // of keys specified in the trusted root metadata file. If the new timestamp metadata file is // not properly signed, discard it, abort the update cycle, and report the signature failure. root.signed .verify_role(×tamp) .context(error::VerifyMetadata { role: RoleType::Timestamp, })?; // 2.2. Check for a rollback attack. The version number of the trusted timestamp metadata file, // if any, must be less than or equal to the version number of the new timestamp metadata // file. If the new timestamp metadata file is older than the trusted timestamp metadata // file, discard it, abort the update cycle, and report the potential rollback attack. if let Some(Ok(old_timestamp)) = datastore .reader("timestamp.json")? .map(serde_json::from_reader::<_, Signed<Timestamp>>) { if root.signed.verify_role(&old_timestamp).is_ok() { ensure!( old_timestamp.signed.version <= timestamp.signed.version, error::OlderMetadata { role: RoleType::Timestamp, current_version: old_timestamp.signed.version, new_version: timestamp.signed.version } ); } } // TUF v1.0.16, 5.3.3. Check for a freeze attack. The expiration timestamp in the new timestamp // metadata file MUST be higher than the fixed update start time. If so, the new timestamp // metadata file becomes the trusted timestamp metadata file. If the new timestamp metadata file // has expired, discard it, abort the update cycle, and report the potential freeze attack. if expiration_enforcement == ExpirationEnforcement::Safe { check_expired(datastore, ×tamp.signed)?; } // Now that everything seems okay, write the timestamp file to the datastore. datastore.create("timestamp.json", ×tamp)?; Ok(timestamp) } /// Step 3 of the client application, which loads the snapshot metadata file. fn load_snapshot( transport: &dyn Transport, root: &Signed<Root>, timestamp: &Signed<Timestamp>, datastore: &Datastore, metadata_base_url: &Url, expiration_enforcement: ExpirationEnforcement, ) -> Result<Signed<Snapshot>> { // 3. Download snapshot metadata file, up to the number of bytes specified in the timestamp // metadata file. If consistent snapshots are not used (see Section 7), then the filename // used to download the snapshot metadata file is of the fixed form FILENAME.EXT (e.g., // snapshot.json). Otherwise, the filename is of the form VERSION_NUMBER.FILENAME.EXT (e.g., // 42.snapshot.json), where VERSION_NUMBER is the version number of the snapshot metadata // file listed in the timestamp metadata file. In either case, the client MUST write the // file to non-volatile storage as FILENAME.EXT. let snapshot_meta = timestamp .signed .meta .get("snapshot.json") .context(error::MetaMissing { file: "snapshot.json", role: RoleType::Timestamp, })?; let path = if root.signed.consistent_snapshot { format!("{}.snapshot.json", snapshot_meta.version) } else { "snapshot.json".to_owned() }; let reader = fetch_sha256( transport, metadata_base_url.join(&path).context(error::JoinUrl { path, url: metadata_base_url.to_owned(), })?, snapshot_meta.length, "timestamp.json", &snapshot_meta.hashes.sha256, )?; let snapshot: Signed<Snapshot> = serde_json::from_reader(reader).context(error::ParseMetadata { role: RoleType::Snapshot, })?; // 3.1. Check against timestamp metadata. The hashes and version number of the new snapshot // metadata file MUST match the hashes and version number listed in timestamp metadata. If // hashes and version do not match, discard the new snapshot metadata, abort the update // cycle, and report the failure. // // (We already checked the hash in `fetch_sha256` above.) ensure!( snapshot.signed.version == snapshot_meta.version, error::VersionMismatch { role: RoleType::Snapshot, fetched: snapshot.signed.version, expected: snapshot_meta.version } ); // 3.2. Check signatures. The new snapshot metadata file MUST have been signed by a threshold // of keys specified in the trusted root metadata file. If the new snapshot metadata file is // not signed as required, discard it, abort the update cycle, and report the signature // failure. root.signed .verify_role(&snapshot) .context(error::VerifyMetadata { role: RoleType::Snapshot, })?; // 3.3. Check for a rollback attack. // // 3.3.1. Note that the trusted snapshot metadata file may be checked for authenticity, but its // expiration does not matter for the following purposes. if let Some(Ok(old_snapshot)) = datastore .reader("snapshot.json")? .map(serde_json::from_reader::<_, Signed<Snapshot>>) { // 3.3.2. The version number of the trusted snapshot metadata file, if any, MUST be less // than or equal to the version number of the new snapshot metadata file. If the new // snapshot metadata file is older than the trusted metadata file, discard it, abort the // update cycle, and report the potential rollback attack. if root.signed.verify_role(&old_snapshot).is_ok() { ensure!( old_snapshot.signed.version <= snapshot.signed.version, error::OlderMetadata { role: RoleType::Snapshot, current_version: old_snapshot.signed.version, new_version: snapshot.signed.version } ); // 3.3.3. The version number of the targets metadata file, and all delegated targets // metadata files (if any), in the trusted snapshot metadata file, if any, MUST be // less than or equal to its version number in the new snapshot metadata file. // Furthermore, any targets metadata filename that was listed in the trusted snapshot // metadata file, if any, MUST continue to be listed in the new snapshot metadata // file. If any of these conditions are not met, discard the new snaphot metadadata // file, abort the update cycle, and report the failure. if let Some(old_targets_meta) = old_snapshot.signed.meta.get("targets.json") { let targets_meta = snapshot .signed .meta .get("targets.json") .context(error::MetaMissing { file: "targets.json", role: RoleType::Snapshot, })?; ensure!( old_targets_meta.version <= targets_meta.version, error::OlderMetadata { role: RoleType::Targets, current_version: old_targets_meta.version, new_version: targets_meta.version, } ); } } } // TUF v1.0.16, 5.4.5. Check for a freeze attack. The expiration timestamp in the new snapshot // metadata file MUST be higher than the fixed update start time. If so, the new snapshot // metadata file becomes the trusted snapshot metadata file. If the new snapshot metadata file // is expired, discard it, abort the update cycle, and report the potential freeze attack. if expiration_enforcement == ExpirationEnforcement::Safe { check_expired(datastore, &snapshot.signed)?; } // Now that everything seems okay, write the snapshot file to the datastore. datastore.create("snapshot.json", &snapshot)?; Ok(snapshot) } /// Step 4 of the client application, which loads the targets metadata file. fn load_targets( transport: &dyn Transport, root: &Signed<Root>, snapshot: &Signed<Snapshot>, datastore: &Datastore, max_targets_size: u64, metadata_base_url: &Url, expiration_enforcement: ExpirationEnforcement, ) -> Result<Signed<crate::schema::Targets>> { // 4. Download the top-level targets metadata file, up to either the number of bytes specified // in the snapshot metadata file, or some Z number of bytes. The value for Z is set by the // authors of the application using TUF. For example, Z may be tens of kilobytes. If // consistent snapshots are not used (see Section 7), then the filename used to download the // targets metadata file is of the fixed form FILENAME.EXT (e.g., targets.json). Otherwise, // the filename is of the form VERSION_NUMBER.FILENAME.EXT (e.g., 42.targets.json), where // VERSION_NUMBER is the version number of the targets metadata file listed in the snapshot // metadata file. In either case, the client MUST write the file to non-volatile storage as // FILENAME.EXT. let targets_meta = snapshot .signed .meta .get("targets.json") .context(error::MetaMissing { file: "targets.json", role: RoleType::Timestamp, })?; let path = if root.signed.consistent_snapshot { format!("{}.targets.json", targets_meta.version) } else { "targets.json".to_owned() }; let targets_url = metadata_base_url.join(&path).context(error::JoinUrl { path, url: metadata_base_url.to_owned(), })?; let (max_targets_size, specifier) = match targets_meta.length { Some(length) => (length, "snapshot.json"), None => (max_targets_size, "max_targets_size parameter"), }; let reader = if let Some(hashes) = &targets_meta.hashes { Box::new(fetch_sha256( transport, targets_url, max_targets_size, specifier, &hashes.sha256, )?) as Box<dyn Read> } else { Box::new(fetch_max_size( transport, targets_url, max_targets_size, specifier, )?) }; let mut targets: Signed<crate::schema::Targets> = serde_json::from_reader(reader).context(error::ParseMetadata { role: RoleType::Targets, })?; // 4.1. Check against snapshot metadata. The hashes (if any), and version number of the new // targets metadata file MUST match the trusted snapshot metadata. This is done, in part, to // prevent a mix-and-match attack by man-in-the-middle attackers. If the new targets metadata // file does not match, discard it, abort the update cycle, and report the failure. // // (We already checked the hash in `fetch_sha256` above.) ensure!( targets.signed.version == targets_meta.version, error::VersionMismatch { role: RoleType::Targets, fetched: targets.signed.version, expected: targets_meta.version } ); // 4.2. Check for an arbitrary software attack. The new targets metadata file MUST have been // signed by a threshold of keys specified in the trusted root metadata file. If the new // targets metadata file is not signed as required, discard it, abort the update cycle, and // report the failure. root.signed .verify_role(&targets) .context(error::VerifyMetadata { role: RoleType::Targets, })?; // 4.3. Check for a rollback attack. The version number of the trusted targets metadata file, // if any, MUST be less than or equal to the version number of the new targets metadata file. // If the new targets metadata file is older than the trusted targets metadata file, discard // it, abort the update cycle, and report the potential rollback attack. if let Some(Ok(old_targets)) = datastore .reader("targets.json")? .map(serde_json::from_reader::<_, Signed<crate::schema::Targets>>) { if root.signed.verify_role(&old_targets).is_ok() { ensure!( old_targets.signed.version <= targets.signed.version, error::OlderMetadata { role: RoleType::Targets, current_version: old_targets.signed.version, new_version: targets.signed.version } ); } } // TUF v1.0.16, 5.5.4. Check for a freeze attack. The expiration timestamp in the new targets // metadata file MUST be higher than the fixed update start time. If so, the new targets // metadata file becomes the trusted targets metadata file. If the new targets metadata file is // expired, discard it, abort the update cycle, and report the potential freeze attack. if expiration_enforcement == ExpirationEnforcement::Safe { check_expired(datastore, &targets.signed)?; } // Now that everything seems okay, write the targets file to the datastore. datastore.create("targets.json", &targets)?; // 4.5. Perform a preorder depth-first search for metadata about the desired target, beginning // with the top-level targets role. if let Some(delegations) = &mut targets.signed.delegations { load_delegations( transport, snapshot, root.signed.consistent_snapshot, metadata_base_url, max_targets_size, delegations, &datastore, )?; } Ok(targets) } // Follow the paths of delegations starting with the top level targets.json delegation fn load_delegations( transport: &dyn Transport, snapshot: &Signed<Snapshot>, consistent_snapshot: bool, metadata_base_url: &Url, max_targets_size: u64, delegation: &mut Delegations, datastore: &Datastore, ) -> Result<()> { let mut delegated_roles: HashMap<String, Option<Signed<crate::schema::Targets>>> = HashMap::new(); for delegated_role in &delegation.roles { // find the role file metadata let role_meta = snapshot .signed .meta .get(&format!("{}.json", &delegated_role.name)) .context(error::RoleNotInMeta { name: delegated_role.name.clone(), })?; let path = if consistent_snapshot { format!("{}.{}.json", &role_meta.version, &delegated_role.name) } else { format!("{}.json", &delegated_role.name) }; let role_url = metadata_base_url.join(&path).context(error::JoinUrl { path: path.clone(), url: metadata_base_url.to_owned(), })?; let specifier = "max_targets_size parameter"; // load the role json file let reader = Box::new(fetch_max_size( transport, role_url, max_targets_size, specifier, )?); // since each role is a targets, we load them as such let role: Signed<crate::schema::Targets> = serde_json::from_reader(reader).context(error::ParseMetadata { role: RoleType::Targets, })?; // verify each role with the delegation delegation .verify_role(&role, &delegated_role.name) .context(error::VerifyMetadata { role: RoleType::Targets, })?; ensure!( role.signed.version == role_meta.version, error::VersionMismatch { role: RoleType::Targets, fetched: role.signed.version, expected: role_meta.version } ); { if let Some(delegations) = role.signed.delegations.as_ref() { delegations.verify_paths().context(error::InvalidPath {})? } } datastore.create(&path, &role)?; delegated_roles.insert(delegated_role.name.clone(), Some(role)); } // load all roles delegated by this role for delegated_role in &mut delegation.roles { delegated_role.targets = delegated_roles.remove(&delegated_role.name).context( error::DelegatedRolesNotConsistent { name: delegated_role.name.clone(), }, )?; if let Some(targets) = &mut delegated_role.targets { if let Some(delegations) = &mut targets.signed.delegations { load_delegations( transport, snapshot, consistent_snapshot, metadata_base_url, max_targets_size, delegations, datastore, )?; } } } Ok(()) } #[cfg(test)] mod tests { use super::*; // Check if a url with a trailing slash and one without trailing slash can both be parsed #[test] fn url_missing_trailing_slash() { let parsed_url_without_trailing_slash = parse_url(Url::parse("https://example.org/a/b/c").unwrap()).unwrap(); let parsed_url_with_trailing_slash = parse_url(Url::parse("https://example.org/a/b/c/").unwrap()).unwrap(); assert_eq!( parsed_url_without_trailing_slash, parsed_url_with_trailing_slash ) } // Ensure that the `ExpirationEnforcement` traits are not changed by mistake. #[test] fn expiration_enforcement_traits() { let enforce = true; let safe: ExpirationEnforcement = enforce.into(); assert_eq!(safe, ExpirationEnforcement::Safe); let not_enforce = false; let not_safe: ExpirationEnforcement = not_enforce.into(); assert_eq!(not_safe, ExpirationEnforcement::Unsafe); let enforcing: bool = ExpirationEnforcement::Safe.into(); assert!(enforcing); let non_enforcing: bool = ExpirationEnforcement::Unsafe.into(); assert!(!non_enforcing); let default = ExpirationEnforcement::default(); assert_eq!(default, ExpirationEnforcement::Safe); } }