From 3d8cb88d00ecaecff0c3c7368fdb03abb715a349 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 11:43:29 -0500
Subject: [PATCH 1/9] adjust spec_version to proper semver format

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index 9b125e9..d6fa7e6 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -8,7 +8,15 @@ use crate::error::Error;
 use crate::metadata::{self, Metadata};
 use crate::Result;
 
-const SPEC_VERSION: &str = "1.0";
+const SPEC_VERSION: &str = "1.0.0";
+
+// Ensure the given spec version matches our spec version.
+//
+// We also need to handle the literal "1.0" here, despite that fact that it is not a valid version
+// according to the SemVer spec, because it is already baked into some of the old roots.
+fn valid_spec_version(other: &str) -> bool {
+    other == SPEC_VERSION || other == "1.0"
+}
 
 fn parse_datetime(ts: &str) -> Result<DateTime<Utc>> {
     Utc.datetime_from_str(ts, "%FT%TZ")
@@ -70,7 +78,7 @@ impl RootMetadata {
             )));
         }
 
-        if self.spec_version != SPEC_VERSION {
+        if !valid_spec_version(&self.spec_version) {
             return Err(Error::Encoding(format!(
                 "Unknown spec version {}",
                 self.spec_version
@@ -184,7 +192,7 @@ impl TimestampMetadata {
             )));
         }
 
-        if self.spec_version != SPEC_VERSION {
+        if !valid_spec_version(&self.spec_version) {
             return Err(Error::Encoding(format!(
                 "Unknown spec version {}",
                 self.spec_version
@@ -233,7 +241,7 @@ impl SnapshotMetadata {
             )));
         }
 
-        if self.spec_version != SPEC_VERSION {
+        if !valid_spec_version(&self.spec_version) {
             return Err(Error::Encoding(format!(
                 "Unknown spec version {}",
                 self.spec_version
@@ -299,7 +307,7 @@ impl TargetsMetadata {
             )));
         }
 
-        if self.spec_version != SPEC_VERSION {
+        if !valid_spec_version(&self.spec_version) {
             return Err(Error::Encoding(format!(
                 "Unknown spec version {}",
                 self.spec_version

From 4b48acf7612fdc15cac1787958b72aa9837f2a41 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 11:45:03 -0500
Subject: [PATCH 2/9] use RFC3339 functions for datetime handling

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index d6fa7e6..8327f45 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -19,20 +19,13 @@ fn valid_spec_version(other: &str) -> bool {
 }
 
 fn parse_datetime(ts: &str) -> Result<DateTime<Utc>> {
-    Utc.datetime_from_str(ts, "%FT%TZ")
+    DateTime::parse_from_rfc3339(ts)
+        .map(|ts| ts.with_timezone(&Utc))
         .map_err(|e| Error::Encoding(format!("Can't parse DateTime: {:?}", e)))
 }
 
 fn format_datetime(ts: &DateTime<Utc>) -> String {
-    format!(
-        "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}Z",
-        ts.year(),
-        ts.month(),
-        ts.day(),
-        ts.hour(),
-        ts.minute(),
-        ts.second()
-    )
+    ts.to_rfc3339()
 }
 
 #[derive(Debug, Serialize, Deserialize)]

From 70283a78ef6b62e9e72eb0e33ef03cc5c9f7451c Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 11:47:58 -0500
Subject: [PATCH 3/9] add Send bound to repository types

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/mod.rs | 2 +-
 tuf/src/repository.rs      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tuf/src/interchange/mod.rs b/tuf/src/interchange/mod.rs
index e295461..f69b0e5 100644
--- a/tuf/src/interchange/mod.rs
+++ b/tuf/src/interchange/mod.rs
@@ -10,7 +10,7 @@ use std::fmt::Debug;
 use crate::Result;
 
 /// The format used for data interchange, serialization, and deserialization.
-pub trait DataInterchange: Debug + PartialEq + Clone {
+pub trait DataInterchange: Debug + PartialEq + Clone + Send {
     /// The type of data that is contained in the `signed` portion of metadata.
     type RawData: Serialize + DeserializeOwned + Clone + PartialEq;
 
diff --git a/tuf/src/repository.rs b/tuf/src/repository.rs
index a23f1bc..3b314a3 100644
--- a/tuf/src/repository.rs
+++ b/tuf/src/repository.rs
@@ -108,7 +108,7 @@ where
 
 /// A writable TUF repository. Most implementors of this trait should also implement
 /// `RepositoryProvider`.
-pub trait RepositoryStorage<D>
+pub trait RepositoryStorage<D>: Send
 where
     D: DataInterchange + Sync,
 {

From c38603b7a22e6ac203e87c76d648cb5f8e97d11d Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 11:48:35 -0500
Subject: [PATCH 4/9] don't consider asterisks illegal in paths

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/metadata.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tuf/src/metadata.rs b/tuf/src/metadata.rs
index d8aa7e3..d8550fb 100644
--- a/tuf/src/metadata.rs
+++ b/tuf/src/metadata.rs
@@ -66,7 +66,6 @@ static PATH_ILLEGAL_STRINGS: &[&str] = &[
     "\"",
     "|",
     "?",
-    "*",
     // control characters, all illegal in FAT
     "\u{000}",
     "\u{001}",

From c1313e133aca9229542b3005cdba16c0b67b65e7 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 15:30:48 -0500
Subject: [PATCH 5/9] back out datetime formatting change since it doesn't
 actually match spec

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index 8327f45..63e6f14 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -25,7 +25,15 @@ fn parse_datetime(ts: &str) -> Result<DateTime<Utc>> {
 }
 
 fn format_datetime(ts: &DateTime<Utc>) -> String {
-    ts.to_rfc3339()
+    format!(
+        "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}Z",
+        ts.year(),
+        ts.month(),
+        ts.day(),
+        ts.hour(),
+        ts.minute(),
+        ts.second()
+    )
 }
 
 #[derive(Debug, Serialize, Deserialize)]

From 4dfc36e2a31cfa35d8701945a9fb04839281919a Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 15:31:28 -0500
Subject: [PATCH 6/9] add tests for datetime parsing, spec_version, and path
 asterisks

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs | 48 ++++++++++++++++++++++++++++++
 tuf/src/metadata.rs                | 18 +++++++++++
 2 files changed, 66 insertions(+)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index 63e6f14..f50d3fb 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -579,3 +579,51 @@ mod deserialize_reject_duplicates {
         })
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::{parse_datetime, valid_spec_version};
+
+    #[test]
+    fn spec_version_validation() {
+        let valid_spec_versions = ["1.0.0", "1.0"];
+
+        for version in valid_spec_versions {
+            assert!(valid_spec_version(version), "{:?} should be valid", version);
+        }
+
+        let invalid_spec_versions = ["1.0.1", "1.1.0", "2.0.0", "3.0"];
+
+        for version in invalid_spec_versions {
+            assert!(
+                !valid_spec_version(version),
+                "{:?} should be invalid",
+                version
+            );
+        }
+    }
+
+    #[test]
+    fn datetime_formats() {
+        // The TUF spec says datetimes should be in ISO8601 format, specifically
+        // "YYYY-MM-DDTHH:MM:SSZ". Since not all TUF clients adhere strictly to that, we choose to
+        // be more lenient here. The following represent the intersection of valid ISO8601
+        // and RFC3339 datetime formats (source: https://ijmacd.github.io/rfc3339-iso8601/).
+        let valid_formats = [
+            "2022-08-30T19:53:55Z",
+            "2022-08-30T19:53:55.7Z",
+            "2022-08-30T19:53:55.77Z",
+            "2022-08-30T19:53:55.775Z",
+            "2022-08-30T19:53:55+00:00",
+            "2022-08-30T19:53:55.7+00:00",
+            "2022-08-30T14:53:55-05:00",
+            "2022-08-30T14:53:55.7-05:00",
+            "2022-08-30T14:53:55.77-05:00",
+            "2022-08-30T14:53:55.775-05:00",
+        ];
+
+        for format in valid_formats {
+            assert!(parse_datetime(format).is_ok(), "should parse {:?}", format);
+        }
+    }
+}
diff --git a/tuf/src/metadata.rs b/tuf/src/metadata.rs
index d8550fb..2f510c8 100644
--- a/tuf/src/metadata.rs
+++ b/tuf/src/metadata.rs
@@ -2313,6 +2313,24 @@ mod test {
         }
     }
 
+    #[test]
+    fn allow_asterisk_in_target_path() {
+        let good_paths = &[
+            "*",
+            "*/some/path",
+            "*/some/path/",
+            "some/*/path",
+            "some/*/path/*",
+        ];
+
+        for path in good_paths.iter() {
+            assert!(safe_path(path).is_ok());
+            assert!(TargetPath::new(path.to_string()).is_ok());
+            assert!(MetadataPath::new(path.to_string()).is_ok());
+            assert!(TargetPath::new(path.to_string()).is_ok());
+        }
+    }
+
     #[test]
     fn path_matches_chain() {
         let test_cases: &[(bool, &str, &[&[&str]])] = &[

From 94ccc7ff72e6f69ce62ac9e9f7a450d9c5619d67 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Tue, 30 Aug 2022 15:33:47 -0500
Subject: [PATCH 7/9] adjust existing tests for new spec_version

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/metadata.rs | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/tuf/src/metadata.rs b/tuf/src/metadata.rs
index 2f510c8..d403629 100644
--- a/tuf/src/metadata.rs
+++ b/tuf/src/metadata.rs
@@ -2479,7 +2479,7 @@ mod test {
 
         let jsn = json!({
             "_type": "root",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "consistent_snapshot": true,
@@ -2546,7 +2546,7 @@ mod test {
     fn jsn_root_metadata_without_keyid_hash_algos() -> serde_json::Value {
         json!({
             "_type": "root",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "consistent_snapshot": false,
@@ -2651,7 +2651,7 @@ mod test {
         let jsn = json!({
             "signatures": [{
                 "keyid": "a9f3ebc9b138762563a9c27b6edd439959e559709babd123e8d449ba2c18c61a",
-                "sig": "c4ba838e0d3f783716393a4d691f568f840733ff488bb79ac68287e97e0b31d63fcef392dbc978e878c2103ba231905af634cc651d6f0e63a35782d051ac6e00"
+                "sig": "1f944e022d0b30c5a9ddc9c210026f396e18a17cc9a4ee92c339a8ee63357608dba8121847a825c3a5c84c1081435436bd784c8086c3103cdd1489e79cff2802"
             }],
             "signed": jsn_root_metadata_without_keyid_hash_algos()
         });
@@ -2676,11 +2676,11 @@ mod test {
         let jsn = json!({
             "signatures": [{
                 "keyid": "a9f3ebc9b138762563a9c27b6edd439959e559709babd123e8d449ba2c18c61a",
-                "sig": "c4ba838e0d3f783716393a4d691f568f840733ff488bb79ac68287e97e0b31d63fcef392dbc978e878c2103ba231905af634cc651d6f0e63a35782d051ac6e00"
+                "sig": "1f944e022d0b30c5a9ddc9c210026f396e18a17cc9a4ee92c339a8ee63357608dba8121847a825c3a5c84c1081435436bd784c8086c3103cdd1489e79cff2802"
             },
             {
                 "keyid": "a9f3ebc9b138762563a9c27b6edd439959e559709babd123e8d449ba2c18c61a",
-                "sig": "c4ba838e0d3f783716393a4d691f568f840733ff488bb79ac68287e97e0b31d63fcef392dbc978e878c2103ba231905af634cc651d6f0e63a35782d051ac6e00"
+                "sig": "1f944e022d0b30c5a9ddc9c210026f396e18a17cc9a4ee92c339a8ee63357608dba8121847a825c3a5c84c1081435436bd784c8086c3103cdd1489e79cff2802"
             }],
             "signed": jsn_root_metadata_without_keyid_hash_algos()
         });
@@ -2688,6 +2688,7 @@ mod test {
         let decoded: SignedMetadata<crate::interchange::cjson::Json, RootMetadata> =
             serde_json::from_value(jsn).unwrap();
         let raw_root = decoded.to_raw().unwrap();
+
         assert_matches!(
             verify_signatures(&MetadataPath::root(), &raw_root, 2, &[root_key.public().clone()]),
             Err(Error::MetadataMissingSignatures {
@@ -2825,7 +2826,7 @@ mod test {
 
         let jsn = json!({
             "_type": "timestamp",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -2857,7 +2858,7 @@ mod test {
 
         let jsn = json!({
             "_type": "timestamp",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -2877,7 +2878,7 @@ mod test {
     fn serde_timestamp_metadata_missing_snapshot() {
         let jsn = json!({
             "_type": "timestamp",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {}
@@ -2893,7 +2894,7 @@ mod test {
     fn serde_timestamp_metadata_extra_metadata() {
         let jsn = json!({
             "_type": "timestamp",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -2939,7 +2940,7 @@ mod test {
 
         let jsn = json!({
             "_type": "snapshot",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -2973,7 +2974,7 @@ mod test {
 
         let jsn = json!({
             "_type": "snapshot",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -3034,7 +3035,7 @@ mod test {
 
             let jsn = json!({
                 "_type": "targets",
-                "spec_version": "1.0",
+                "spec_version": "1.0.0",
                 "version": 1,
                 "expires": "2017-01-01T00:00:00Z",
                 "targets": {
@@ -3104,7 +3105,7 @@ mod test {
 
         let jsn = json!({
             "_type": "targets",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "targets": {},
@@ -3162,14 +3163,14 @@ mod test {
             "signatures": [
                 {
                     "keyid": "a9f3ebc9b138762563a9c27b6edd439959e559709babd123e8d449ba2c18c61a",
-                    "sig": "ea48ddc7b3ea614b394e508eb8722100f94ff1a4e3aac3af09d\
-                        a0dada4f878431e8ac26160833405ec239924dfe62edf605fee8294\
-                        c49b4acade55c76e817602",
+                    "sig": "a9b97b2439cd41e9a8c62e4d2f8f73b25a06095e0a994e8631a0\
+                        88977271909af2cc829c68637af98b07ebffeea308cc1a1c83d18fa2\
+                        9ec401493973b3dfa90e",
                 }
             ],
             "signed": {
                 "_type": "snapshot",
-                "spec_version": "1.0",
+                "spec_version": "1.0.0",
                 "version": 1,
                 "expires": "2017-01-01T00:00:00Z",
                 "meta": {
@@ -3329,7 +3330,7 @@ mod test {
     fn deserialize_json_root_duplicate_keys() {
         let root_json = r#"{
             "_type": "root",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "consistent_snapshot": false,
@@ -3515,7 +3516,7 @@ mod test {
     fn deserialize_json_snapshot_duplicate_metadata() {
         let snapshot_json = r#"{
             "_type": "snapshot",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {
@@ -3580,7 +3581,7 @@ mod test {
     fn deserialize_json_timestamp_duplicate_metadata() {
         let timestamp_json = r#"{
             "_type": "timestamp",
-            "spec_version": "1.0",
+            "spec_version": "1.0.0",
             "version": 1,
             "expires": "2017-01-01T00:00:00Z",
             "meta": {

From f941bab771dbd0ae0fb2873bd32bac580a96f581 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Thu, 1 Sep 2022 16:21:40 -0500
Subject: [PATCH 8/9] collect additional fields on TargetsMetadata

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs |  8 ++++++++
 tuf/src/metadata.rs                | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index f50d3fb..71780b9 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -282,6 +282,8 @@ pub struct TargetsMetadata {
     targets: BTreeMap<metadata::TargetPath, metadata::TargetDescription>,
     #[serde(default, skip_serializing_if = "metadata::Delegations::is_empty")]
     delegations: metadata::Delegations,
+    #[serde(flatten)]
+    additional_fields: BTreeMap<String, serde_json::Value>,
 }
 
 impl TargetsMetadata {
@@ -297,6 +299,11 @@ impl TargetsMetadata {
                 .map(|(p, d)| (p.clone(), d.clone()))
                 .collect(),
             delegations: metadata.delegations().clone(),
+            additional_fields: metadata
+                .additional_fields()
+                .iter()
+                .map(|(p, d)| (p.clone(), d.clone()))
+                .collect(),
         })
     }
 
@@ -320,6 +327,7 @@ impl TargetsMetadata {
             parse_datetime(&self.expires)?,
             self.targets.into_iter().collect(),
             self.delegations,
+            self.additional_fields.into_iter().collect(),
         )
     }
 }
diff --git a/tuf/src/metadata.rs b/tuf/src/metadata.rs
index d403629..3d835e5 100644
--- a/tuf/src/metadata.rs
+++ b/tuf/src/metadata.rs
@@ -1841,6 +1841,7 @@ pub struct TargetsMetadata {
     expires: DateTime<Utc>,
     targets: HashMap<TargetPath, TargetDescription>,
     delegations: Delegations,
+    additional_fields: HashMap<String, serde_json::Value>,
 }
 
 impl TargetsMetadata {
@@ -1850,6 +1851,7 @@ impl TargetsMetadata {
         expires: DateTime<Utc>,
         targets: HashMap<TargetPath, TargetDescription>,
         delegations: Delegations,
+        additional_fields: HashMap<String, serde_json::Value>,
     ) -> Result<Self> {
         if version < 1 {
             return Err(Error::IllegalArgument(format!(
@@ -1863,6 +1865,7 @@ impl TargetsMetadata {
             expires,
             targets,
             delegations,
+            additional_fields,
         })
     }
 
@@ -1875,6 +1878,11 @@ impl TargetsMetadata {
     pub fn delegations(&self) -> &Delegations {
         &self.delegations
     }
+
+    /// An immutable reference to any additional fields on the metadata.
+    pub fn additional_fields(&self) -> &HashMap<String, serde_json::Value> {
+        &self.additional_fields
+    }
 }
 
 impl Metadata for TargetsMetadata {
@@ -1991,6 +1999,7 @@ impl TargetsMetadataBuilder {
             self.expires,
             self.targets,
             self.delegations.unwrap_or_default(),
+            Default::default(),
         )
     }
 
@@ -3260,6 +3269,7 @@ mod test {
             Utc.ymd(2038, 1, 1).and_hms(0, 0, 0),
             hashmap!(),
             Delegations::default(),
+            Default::default(),
         )
         .unwrap();
 

From f0d6ca38002ba3e112427b13e4d72387fb49e6c4 Mon Sep 17 00:00:00 2001
From: Luke Steensen <luke.steensen@gmail.com>
Date: Fri, 2 Sep 2022 13:54:24 -0500
Subject: [PATCH 9/9] add additional_fields handling to root, timestamp, and
 snapshot metas

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
---
 tuf/src/interchange/cjson/shims.rs | 12 +++++++++++
 tuf/src/metadata.rs                | 34 ++++++++++++++++++++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/tuf/src/interchange/cjson/shims.rs b/tuf/src/interchange/cjson/shims.rs
index 71780b9..f9a502d 100644
--- a/tuf/src/interchange/cjson/shims.rs
+++ b/tuf/src/interchange/cjson/shims.rs
@@ -47,6 +47,8 @@ pub struct RootMetadata {
     #[serde(deserialize_with = "deserialize_reject_duplicates::deserialize")]
     keys: BTreeMap<crypto::KeyId, crypto::PublicKey>,
     roles: RoleDefinitions,
+    #[serde(flatten)]
+    additional_fields: BTreeMap<String, serde_json::Value>,
 }
 
 impl RootMetadata {
@@ -68,6 +70,7 @@ impl RootMetadata {
                 targets: meta.targets().clone(),
                 timestamp: meta.timestamp().clone(),
             },
+            additional_fields: meta.additional_fields().clone().into_iter().collect(),
         })
     }
 
@@ -104,6 +107,7 @@ impl RootMetadata {
             self.roles.snapshot,
             self.roles.targets,
             self.roles.timestamp,
+            self.additional_fields.into_iter().collect(),
         )
     }
 }
@@ -163,6 +167,8 @@ pub struct TimestampMetadata {
     version: u32,
     expires: String,
     meta: TimestampMeta,
+    #[serde(flatten)]
+    additional_fields: BTreeMap<String, serde_json::Value>,
 }
 
 #[derive(Serialize, Deserialize)]
@@ -182,6 +188,7 @@ impl TimestampMetadata {
             meta: TimestampMeta {
                 snapshot: metadata.snapshot().clone(),
             },
+            additional_fields: metadata.additional_fields().clone().into_iter().collect(),
         })
     }
 
@@ -204,6 +211,7 @@ impl TimestampMetadata {
             self.version,
             parse_datetime(&self.expires)?,
             self.meta.snapshot,
+            self.additional_fields.into_iter().collect(),
         )
     }
 }
@@ -217,6 +225,8 @@ pub struct SnapshotMetadata {
     expires: String,
     #[serde(deserialize_with = "deserialize_reject_duplicates::deserialize")]
     meta: BTreeMap<String, metadata::MetadataDescription>,
+    #[serde(flatten)]
+    additional_fields: BTreeMap<String, serde_json::Value>,
 }
 
 impl SnapshotMetadata {
@@ -231,6 +241,7 @@ impl SnapshotMetadata {
                 .iter()
                 .map(|(p, d)| (format!("{}.json", p), d.clone()))
                 .collect(),
+            additional_fields: metadata.additional_fields().clone().into_iter().collect(),
         })
     }
 
@@ -268,6 +279,7 @@ impl SnapshotMetadata {
                     Ok((p, d))
                 })
                 .collect::<Result<_>>()?,
+            self.additional_fields.into_iter().collect(),
         )
     }
 }
diff --git a/tuf/src/metadata.rs b/tuf/src/metadata.rs
index 3d835e5..df82a2e 100644
--- a/tuf/src/metadata.rs
+++ b/tuf/src/metadata.rs
@@ -718,6 +718,7 @@ impl RootMetadataBuilder {
             RoleDefinition::new(self.snapshot_threshold, self.snapshot_key_ids)?,
             RoleDefinition::new(self.targets_threshold, self.targets_key_ids)?,
             RoleDefinition::new(self.timestamp_threshold, self.timestamp_key_ids)?,
+            Default::default(),
         )
     }
 
@@ -766,6 +767,7 @@ pub struct RootMetadata {
     snapshot: RoleDefinition,
     targets: RoleDefinition,
     timestamp: RoleDefinition,
+    additional_fields: HashMap<String, serde_json::Value>,
 }
 
 impl RootMetadata {
@@ -779,6 +781,7 @@ impl RootMetadata {
         snapshot: RoleDefinition,
         targets: RoleDefinition,
         timestamp: RoleDefinition,
+        additional_fields: HashMap<String, serde_json::Value>,
     ) -> Result<Self> {
         if version < 1 {
             return Err(Error::IllegalArgument(format!(
@@ -796,6 +799,7 @@ impl RootMetadata {
             snapshot,
             targets,
             timestamp,
+            additional_fields,
         })
     }
 
@@ -861,6 +865,11 @@ impl RootMetadata {
     pub fn timestamp(&self) -> &RoleDefinition {
         &self.timestamp
     }
+
+    /// An immutable reference to any additional fields on the metadata.
+    pub fn additional_fields(&self) -> &HashMap<String, serde_json::Value> {
+        &self.additional_fields
+    }
 }
 
 impl Metadata for RootMetadata {
@@ -1127,7 +1136,12 @@ impl TimestampMetadataBuilder {
 
     /// Construct a new `TimestampMetadata`.
     pub fn build(self) -> Result<TimestampMetadata> {
-        TimestampMetadata::new(self.version, self.expires, self.snapshot)
+        TimestampMetadata::new(
+            self.version,
+            self.expires,
+            self.snapshot,
+            Default::default(),
+        )
     }
 
     /// Construct a new `SignedMetadata<D, TimestampMetadata>`.
@@ -1148,6 +1162,7 @@ pub struct TimestampMetadata {
     version: u32,
     expires: DateTime<Utc>,
     snapshot: MetadataDescription,
+    additional_fields: HashMap<String, serde_json::Value>,
 }
 
 impl TimestampMetadata {
@@ -1156,6 +1171,7 @@ impl TimestampMetadata {
         version: u32,
         expires: DateTime<Utc>,
         snapshot: MetadataDescription,
+        additional_fields: HashMap<String, serde_json::Value>,
     ) -> Result<Self> {
         if version < 1 {
             return Err(Error::IllegalArgument(format!(
@@ -1168,6 +1184,7 @@ impl TimestampMetadata {
             version,
             expires,
             snapshot,
+            additional_fields,
         })
     }
 
@@ -1175,6 +1192,11 @@ impl TimestampMetadata {
     pub fn snapshot(&self) -> &MetadataDescription {
         &self.snapshot
     }
+
+    /// An immutable reference to any additional fields on the metadata.
+    pub fn additional_fields(&self) -> &HashMap<String, serde_json::Value> {
+        &self.additional_fields
+    }
 }
 
 impl Metadata for TimestampMetadata {
@@ -1379,7 +1401,7 @@ impl SnapshotMetadataBuilder {
 
     /// Construct a new `SnapshotMetadata`.
     pub fn build(self) -> Result<SnapshotMetadata> {
-        SnapshotMetadata::new(self.version, self.expires, self.meta)
+        SnapshotMetadata::new(self.version, self.expires, self.meta, Default::default())
     }
 
     /// Construct a new `SignedMetadata<D, SnapshotMetadata>`.
@@ -1416,6 +1438,7 @@ pub struct SnapshotMetadata {
     version: u32,
     expires: DateTime<Utc>,
     meta: HashMap<MetadataPath, MetadataDescription>,
+    additional_fields: HashMap<String, serde_json::Value>,
 }
 
 impl SnapshotMetadata {
@@ -1424,6 +1447,7 @@ impl SnapshotMetadata {
         version: u32,
         expires: DateTime<Utc>,
         meta: HashMap<MetadataPath, MetadataDescription>,
+        additional_fields: HashMap<String, serde_json::Value>,
     ) -> Result<Self> {
         if version < 1 {
             return Err(Error::IllegalArgument(format!(
@@ -1436,6 +1460,7 @@ impl SnapshotMetadata {
             version,
             expires,
             meta,
+            additional_fields,
         })
     }
 
@@ -1443,6 +1468,11 @@ impl SnapshotMetadata {
     pub fn meta(&self) -> &HashMap<MetadataPath, MetadataDescription> {
         &self.meta
     }
+
+    /// An immutable reference to any additional fields on the metadata.
+    pub fn additional_fields(&self) -> &HashMap<String, serde_json::Value> {
+        &self.additional_fields
+    }
 }
 
 impl Metadata for SnapshotMetadata {