Verify identity root commit signatures

In RIP-2, we specify that identity document root commits must include
the signature of all founding delegates.

This commit adds the required signatures during document creation
and verifies them on load.

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>

radicle/src/identity.rs

@@ -35,14 +35,16 @@ pub enum IdentityError {
     MismatchedRoot(Oid),
     #[error("the document root is missing")]
     MissingRoot,
+    #[error("root commit is missing one or more delegate signatures")]
+    MissingRootSignatures,
     #[error("commit signature for {0} is invalid: {1}")]
     InvalidSignature(PublicKey, crypto::Error),
     #[error("commit message for {0} is invalid")]
     InvalidCommitMessage(Oid),
     #[error("commit trailers for {0} are invalid: {1}")]
     InvalidCommitTrailers(Oid, trailers::Error),
-    #[error("quorum not reached: {0} signatures for a threshold of {1}")]
-    QuorumNotReached(usize, usize),
+    #[error("threshold not reached: {0} signatures for a threshold of {1}")]
+    ThresholdNotReached(usize, usize),
     #[error("identity document error: {0}")]
     Doc(#[from] doc::DocError),
 }
@@ -106,6 +108,27 @@ impl Identity<Untrusted> {
         let trusted = Doc::from_json(root_blob.content())?;
         let revision = history.len() as u32;
 
+        {
+            let root_commit = repo.commit(root_oid)?;
+            let root_msg = root_commit
+                .message_raw()
+                .ok_or(IdentityError::InvalidCommitMessage(root_oid))?;
+            let root_sigs = trailers::parse_signatures(root_msg)
+                .map_err(|e| IdentityError::InvalidCommitTrailers(root_oid, e))?;
+
+            for (pk, sig) in &root_sigs {
+                if let Err(err) = pk.verify(root_blob.content(), sig) {
+                    return Err(IdentityError::InvalidSignature(*pk, err));
+                }
+            }
+            // Every identity founder must have signed the root document.
+            for founder in &trusted.delegates {
+                if !root_sigs.iter().any(|(k, _)| k == &**founder) {
+                    return Err(IdentityError::MissingRootSignatures);
+                }
+            }
+        }
+
         let mut trusted = trusted.verified()?;
         let mut current = root;
         let mut signatures = Vec::new();
@@ -136,7 +159,10 @@ impl Identity<Untrusted> {
                 .filter(|(key, _)| trusted.delegates.iter().any(|d| &**d == key))
                 .count();
             if quorum < trusted.threshold {
-                return Err(IdentityError::QuorumNotReached(quorum, trusted.threshold));
+                return Err(IdentityError::ThresholdNotReached(
+                    quorum,
+                    trusted.threshold,
+                ));
             }
 
             trusted = untrusted;

radicle/src/identity/doc.rs

@@ -167,10 +167,11 @@ impl Doc<Verified> {
     pub fn init(
         doc: &[u8],
         remote: &RemoteId,
+        signatures: &[(&PublicKey, Signature)],
         repo: &git2::Repository,
     ) -> Result<git::Oid, DocError> {
         let tree = git::write_tree(*PATH, doc, repo)?;
-        let oid = Doc::commit(remote, &tree, "Initialize Radicle\n", &[], repo)?;
+        let oid = Doc::commit(remote, &tree, "Initialize Radicle\n", &[], signatures, repo)?;
 
         Ok(oid)
     }
@@ -182,17 +183,11 @@ impl Doc<Verified> {
         signatures: &[(&PublicKey, Signature)],
         repo: &git2::Repository,
     ) -> Result<git::Oid, DocError> {
-        let mut msg = format!("{}\n\n", msg.trim());
-        for (key, sig) in signatures {
-            writeln!(&mut msg, "{}: {key} {sig}", trailers::SIGNATURE_TRAILER)
-                .expect("in-memory writes don't fail");
-        }
-
         let (_, doc) = self.encode()?;
         let tree = git::write_tree(*PATH, doc.as_slice(), repo)?;
         let id_ref = git::refs::storage::id(remote);
         let head = repo.find_reference(&id_ref)?.peel_to_commit()?;
-        let oid = Doc::commit(remote, &tree, &msg, &[&head], repo)?;
+        let oid = Doc::commit(remote, &tree, msg, &[&head], signatures, repo)?;
 
         Ok(oid)
     }
@@ -202,14 +197,21 @@ impl Doc<Verified> {
         tree: &git2::Tree,
         msg: &str,
         parents: &[&git2::Commit],
+        signatures: &[(&PublicKey, Signature)],
         repo: &git2::Repository,
     ) -> Result<git::Oid, DocError> {
         let sig = repo
             .signature()
             .or_else(|_| git2::Signature::now("radicle", remote.to_string().as_str()))?;
 
+        let mut msg = format!("{}\n\n", msg.trim());
+        for (key, sig) in signatures {
+            writeln!(&mut msg, "{}: {key} {sig}", trailers::SIGNATURE_TRAILER)
+                .expect("in-memory writes don't fail");
+        }
+
         let id_ref = git::refs::storage::id(remote);
-        let oid = repo.commit(Some(&id_ref), &sig, &sig, msg, tree, parents)?;
+        let oid = repo.commit(Some(&id_ref), &sig, &sig, &msg, tree, parents)?;
 
         Ok(oid.into())
     }

radicle/src/rad.rs

@@ -65,7 +65,7 @@ pub fn init<G: Signer>(
         default_branch: default_branch.clone(),
     };
     let doc = identity::Doc::initial(proj, delegate).verified()?;
-    let (project, _) = Repository::init(&doc, pk, storage)?;
+    let (project, _) = Repository::init(&doc, pk, storage, signer)?;
     let url = git::Url::from(project.id).with_namespace(*pk);
 
     git::configure_remote(repo, &REMOTE_NAME, &url)?;

radicle/src/storage/git.rs

@@ -213,15 +213,21 @@ impl Repository {
     }
 
     /// Create the repository's identity branch.
-    pub fn init(
+    pub fn init<G: Signer>(
         doc: &Doc<Verified>,
         remote: &RemoteId,
         storage: &Storage,
+        signer: &G,
     ) -> Result<(Self, git::Oid), Error> {
         let (doc_oid, doc) = doc.encode()?;
         let id = Id::from(doc_oid);
         let repo = Self::open(paths::repository(storage, &id), id)?;
-        let oid = Doc::init(doc.as_slice(), remote, repo.raw())?;
+        let oid = Doc::init(
+            doc.as_slice(),
+            remote,
+            &[(signer.public_key(), signer.sign(&doc))],
+            repo.raw(),
+        )?;
 
         Ok((repo, oid))
     }