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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 #![forbid(missing_debug_implementations, missing_copy_implementations)] #![deny(rust_2018_idioms)] #![warn(clippy::pedantic)] #![allow(clippy::module_name_repetitions)] mod datastore; pub mod error; mod fetch; mod io; pub mod schema; mod transport; #[cfg(feature = "http")] pub use crate::transport::HttpTransport; pub use crate::transport::{FilesystemTransport, Transport}; use crate::datastore::Datastore; use crate::error::Result; use crate::fetch::{fetch_max_size, fetch_sha256}; use crate::schema::{Role, RoleType, Root, Signed, Snapshot, Timestamp}; use chrono::{DateTime, Utc}; use snafu::{ensure, OptionExt, ResultExt}; use std::borrow::Cow; use std::io::Read; use std::path::Path; use url::Url; /// Repository fetch settings, provided to [`Repository::load`]. #[derive(Debug, Clone)] pub struct Settings<'a, R: Read> { /// A [`Read`]er to the trusted root metadata file, which you must ship with your software /// using an out-of-band-process. /// /// This 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 (It's okay if it /// becomes out of date later; the client establishes trust up to the most recent root.json /// file.) pub root: R, /// A [`Path`] to a directory on a persistent filesystem. Tough stores the most recently /// fetched timestamp, snapshot, and targets metadata files here to detect version rollback /// attacks. The directory must exist prior to calling [`Repository::load`]. pub datastore: &'a Path, /// The URL base for TUF metadata (such as timestamp.json). pub metadata_base_url: &'a str, /// The URL base for targets. pub target_base_url: &'a str, /// Limits used when fetching repository metadata. /// /// This parameter implements [`Default`]; see its documentation for details. pub limits: Limits, } /// 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. /// /// 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 the `load` method. #[derive(Debug, Clone)] pub struct Repository<'a, T: Transport> { transport: &'a T, consistent_snapshot: bool, datastore: Datastore<'a>, earliest_expiration: DateTime<Utc>, earliest_expiration_role: RoleType, root: Signed<Root>, snapshot: Signed<Snapshot>, timestamp: Signed<Timestamp>, targets: Signed<crate::schema::Targets>, target_base_url: Url, } impl<'a, T: Transport> Repository<'a, T> { /// Load and verify TUF repository metadata. /// /// `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.) /// /// `datastore` is a [`Path`] to a directory on a persistent filesystem. This directory's /// contents store the most recently fetched timestamp, snapshot, and targets metadata files. /// The directory must exist prior to calling this method. /// /// `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). /// /// `metadata_base_url` and `target_base_url` are the HTTP(S) base URLs for where the client /// can find metadata (such as root.json) and targets (as listed in targets.json). pub fn load<R: Read>(transport: &'a T, settings: Settings<'a, R>) -> Result<Self> { let metadata_base_url = parse_url(settings.metadata_base_url)?; let target_base_url = parse_url(settings.target_base_url)?; let datastore = Datastore::new(settings.datastore); // 0. Load the trusted root metadata file + 1. Update the root metadata file let root = load_root( transport, settings.root, &datastore, settings.limits.max_root_size, settings.limits.max_root_updates, &metadata_base_url, )?; // 2. Download the timestamp metadata file let timestamp = load_timestamp( transport, &root, &datastore, settings.limits.max_timestamp_size, &metadata_base_url, )?; // 3. Download the snapshot metadata file let snapshot = load_snapshot(transport, &root, ×tamp, &datastore, &metadata_base_url)?; // 4. Download the targets metadata file let targets = load_targets( transport, &root, &snapshot, &datastore, settings.limits.max_targets_size, &metadata_base_url, )?; 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, target_base_url, }) } /// 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 } /// 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>> { // Check for repository metadata expiration. 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. let targets = &self.targets.signed.targets; Ok(if let Some(target) = targets.get(name) { let sha256 = &target.hashes.sha256.clone().into_vec(); let file = if self.consistent_snapshot { format!("{}.{}", hex::encode(sha256), name) } else { name.to_owned() }; Some(fetch_sha256( self.transport, self.target_base_url.join(&file).context(error::JoinUrl { path: file, url: self.target_base_url.to_owned(), })?, target.length, "targets.json", sha256, )?) } else { None }) } } /// 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) } fn check_expired<T: Role>(datastore: &Datastore<'_>, role: &T) -> Result<()> { ensure!( system_time(datastore)? < role.expires(), error::ExpiredMetadata { role: T::TYPE } ); Ok(()) } fn parse_url(url: &str) -> Result<Url> { let mut url = Cow::from(url); if !url.ends_with('/') { url.to_mut().push('/'); } Url::parse(&url).context(error::ParseUrl { url }) } /// 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, T: Transport>( transport: &T, root: R, datastore: &Datastore<'_>, max_root_size: u64, max_root_updates: u64, metadata_base_url: &Url, ) -> 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; } } } // 1.8. Check for a freeze attack. The latest known time should be lower than the expiration // timestamp in the trusted root metadata file (version N). 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 0 and version N of the root metadata file. 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<T: Transport>( transport: &T, root: &Signed<Root>, datastore: &Datastore<'_>, max_timestamp_size: u64, metadata_base_url: &Url, ) -> 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 } ); } } // 2.3. Check for a freeze attack. The latest known time should be lower than the expiration // timestamp in the new timestamp metadata file. 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. 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<T: Transport>( transport: &T, root: &Signed<Root>, timestamp: &Signed<Timestamp>, datastore: &Datastore<'_>, metadata_base_url: &Url, ) -> 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, } ); } } } // 3.4. Check for a freeze attack. The latest known time should be lower than the expiration // timestamp in the new snapshot metadata file. 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. 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<T: Transport>( transport: &T, root: &Signed<Root>, snapshot: &Signed<Snapshot>, datastore: &Datastore<'_>, max_targets_size: u64, metadata_base_url: &Url, ) -> 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 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 } ); } } // 4.4. Check for a freeze attack. The latest known time should be lower than the expiration // timestamp in the new targets metadata file. 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. check_expired(datastore, &targets.signed)?; // 4.5. Perform a preorder depth-first search for metadata about the desired target, beginning // with the top-level targets role. // // (This library does not yet handle delegated roles, so we just use the parsed targets from // targets.json.) // Now that everything seems okay, write the targets file to the datastore. datastore.create("targets.json", &targets)?; Ok(targets) } #[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("https://example.org/a/b/c").unwrap(); let parsed_url_with_trailing_slash = parse_url("https://example.org/a/b/c/").unwrap(); assert_eq!( parsed_url_without_trailing_slash, parsed_url_with_trailing_slash ) } }