@@ -591,6 +591,15 @@ jobs:
               bin.install "git-remote-gitlawb"
             end
 
+            def caveats
+              <<~CAVEATS
+                oh-my-zsh's git plugin aliases gl='git pull', which shadows this
+                binary in interactive shells. If \`gl\` prints "fatal: not a git
+                repository", run:
+                  echo 'unalias gl 2>/dev/null' >> ~/.zshrc && source ~/.zshrc
+              CAVEATS
+            end
+
             test do
               assert_match version.to_s, shell_output("#{bin}/gl --version")
             end
 
@@ -13,6 +13,7 @@ path = "src/main.rs"
 [dependencies]
 gitlawb-core = { path = "../gitlawb-core" }
 icaptcha-client = { path = "../icaptcha-client" }
+base64 = { workspace = true }
 tokio = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 
@@ -41,6 +41,16 @@ pub enum CertCmd {
         node: String,
         #[arg(long)]
         dir: Option<PathBuf>,
+        /// Exit non-zero unless the Ed25519 signature verifies AND the
+        /// issuing node matches the queried node (or --expect-node)
+        #[arg(long)]
+        verify: bool,
+        /// Expected issuing node DID for --verify. A valid signature alone
+        /// only proves the cert is internally consistent — signed by whatever
+        /// key it names — so --verify also anchors the issuer to a DID you
+        /// trust: this value when given, else the queried node's DID.
+        #[arg(long, requires = "verify")]
+        expect_node: Option<String>,
     },
 }
 
@@ -52,7 +62,9 @@ pub async fn run(args: CertArgs) -> Result<()> {
             id,
             node,
             dir,
-        } => cmd_show(repo, id, node, dir).await,
+            verify,
+            expect_node,
+        } => cmd_show(repo, id, node, dir, verify, expect_node).await,
     }
 }
 
@@ -114,7 +126,14 @@ async fn cmd_list(repo: String, node: String, dir: Option<PathBuf>) -> Result<()
     Ok(())
 }
 
-async fn cmd_show(repo: String, id: String, node: String, dir: Option<PathBuf>) -> Result<()> {
+async fn cmd_show(
+    repo: String,
+    id: String,
+    node: String,
+    dir: Option<PathBuf>,
+    require_valid: bool,
+    expect_node: Option<String>,
+) -> Result<()> {
     let (owner, name) = resolve_repo(&repo, &node, dir.as_deref()).await?;
 
     let client = signed_client(&node, dir.as_deref());
@@ -148,39 +167,124 @@ async fn cmd_show(repo: String, id: String, node: String, dir: Option<PathBuf>)
     println!("  Signature: {signature}");
     println!();
 
-    // Reconstruct the signing payload and verify
-    // Fetch the node's current public key to verify
-    let info: Value = client
-        .get("/")
-        .await?
-        .json()
-        .await
-        .context("failed to fetch node info")?;
-    let current_node_did = info["did"].as_str().unwrap_or("");
+    // Verify the Ed25519 signature: rebuild the exact canonical payload the
+    // node signed (see gitlawb-node/src/cert.rs::issue_ref_certificate) and
+    // check it against the public key embedded in the certificate's node DID.
+    // This proves the cert is internally authentic — signed by the key it
+    // names; the node-DID comparison below covers *which* node that is.
+    let repo_id = cert["repo_id"].as_str().unwrap_or("");
+    let verdict = verify_signature(
+        repo_id, ref_name, old_sha, new_sha, pusher, node_did, issued_at, signature,
+    );
 
     println!("Signature verification:");
-    println!("  Signing payload would be:");
-    println!("    {{\"repo_id\": ..., \"ref\": \"{ref_name}\", \"old\": \"{old_sha}\",");
-    println!("      \"new\": \"{new_sha}\", \"pusher\": \"{pusher}\",");
-    println!("      \"node\": \"{node_did}\", \"ts\": \"{issued_at}\"}}");
-    println!();
+    match &verdict {
+        Ok(()) => {
+            println!(
+                "  VALID — Ed25519 signature verified against the key the certificate names ({node_did})"
+            );
+        }
+        Err(reason) => {
+            println!("  INVALID — {reason}");
+        }
+    }
 
-    if current_node_did == node_did {
-        println!("  Node DID matches current node. Signature is an Ed25519/base64url value.");
-        println!("  To verify offline, use the node's Ed25519 public key derived from:");
-        println!("    did:key → {node_did}");
-    } else {
-        println!("  WARNING: Certificate node DID ({node_did}) does not match");
-        println!("           current node DID ({current_node_did}).");
-        println!("           This certificate was issued by a different node.");
+    // Contextual only — the verdict above stands on its own, so a node-info
+    // hiccup here must not turn a successfully displayed certificate into an
+    // error exit.
+    let current_node_did = match client.get("/").await {
+        Ok(resp) => resp
+            .json::<Value>()
+            .await
+            .ok()
+            .and_then(|info| info["did"].as_str().map(str::to_string)),
+        Err(_) => None,
+    };
+    match current_node_did.as_deref() {
+        Some(current) if current == node_did => {
+            println!("  Issuing node DID matches the node being queried.");
+        }
+        Some(current) => {
+            println!("  WARNING: Certificate node DID ({node_did}) does not match");
+            println!("           current node DID ({current}).");
+            println!("           This certificate was issued by a different node.");
+        }
+        None => {
+            println!("  NOTE: could not fetch current node info — skipping node-DID comparison.");
+        }
     }
 
-    println!();
-    println!("  Signature (base64url): {signature}");
+    if require_valid {
+        if let Err(reason) = verdict {
+            anyhow::bail!("certificate signature did not verify: {reason}");
+        }
+        // A valid signature proves internal consistency only: the payload was
+        // signed by whatever key the certificate itself names. A hostile
+        // source can mint a keypair, put its DID in node_did, and self-sign.
+        // --verify therefore also anchors the issuer to a trusted DID:
+        // --expect-node when given, else the DID of the node being queried.
+        let expected = expect_node.as_deref().or(current_node_did.as_deref());
+        match expected {
+            Some(expected) if expected == node_did => {}
+            Some(expected) => anyhow::bail!(
+                "certificate is signed by {node_did}, but the expected issuer is {expected} — \
+                 a valid signature alone proves internal consistency, not a trusted issuer"
+            ),
+            None => anyhow::bail!(
+                "cannot anchor the issuer: node info is unreachable and no --expect-node was given"
+            ),
+        }
+    }
 
     Ok(())
 }
 
+/// Rebuild the node's canonical signing payload (field order must match
+/// gitlawb-node/src/cert.rs::issue_ref_certificate exactly) and verify the
+/// certificate's Ed25519 signature against the key embedded in `node_did`.
+#[allow(clippy::too_many_arguments)]
+fn verify_signature(
+    repo_id: &str,
+    ref_name: &str,
+    old_sha: &str,
+    new_sha: &str,
+    pusher: &str,
+    node_did: &str,
+    issued_at: &str,
+    signature_b64: &str,
+) -> std::result::Result<(), String> {
+    use base64::{engine::general_purpose::URL_SAFE_NO_PAD, Engine};
+    use std::str::FromStr;
+
+    let payload = serde_json::json!({
+        "repo_id": repo_id,
+        "ref":     ref_name,
+        "old":     old_sha,
+        "new":     new_sha,
+        "pusher":  pusher,
+        "node":    node_did,
+        "ts":      issued_at,
+    });
+    let payload_bytes =
+        serde_json::to_vec(&payload).map_err(|e| format!("could not serialize payload: {e}"))?;
+
+    let did =
+        gitlawb_core::did::Did::from_str(node_did).map_err(|e| format!("bad node DID: {e}"))?;
+    let verifying_key = did
+        .to_verifying_key()
+        .map_err(|e| format!("cannot derive a public key from {node_did}: {e}"))?;
+
+    let sig_vec = URL_SAFE_NO_PAD
+        .decode(signature_b64)
+        .map_err(|e| format!("signature is not valid base64url: {e}"))?;
+    let sig_bytes: [u8; 64] = sig_vec
+        .try_into()
+        .map_err(|_| "signature is not 64 bytes".to_string())?;
+
+    gitlawb_core::identity::verify(&verifying_key, &payload_bytes, &sig_bytes)
+        .map_err(|_| "Ed25519 signature does not match the signed payload".to_string())
+}
+
 async fn resolve_cert_id(client: &NodeClient, owner: &str, name: &str, id: &str) -> Result<String> {
     if id.len() >= 36 {
         return Ok(id.to_string());
@@ -209,3 +313,88 @@ async fn resolve_cert_id(client: &NodeClient, owner: &str, name: &str, id: &str)
         _ => anyhow::bail!("certificate prefix {id} matches multiple certificates"),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Pins gl's payload reconstruction to the frozen canonical byte form the
+    /// node signs (default serde_json maps = alphabetically ordered keys). If
+    /// serialization drifts — a field added, or a preserve_order feature
+    /// landing anywhere in the workspace (feature unification flips every
+    /// crate at once) — this literal stops matching and the test fails,
+    /// instead of every real certificate silently rendering INVALID.
+    #[test]
+    fn payload_serialization_matches_frozen_canonical_form() {
+        let payload = serde_json::json!({
+            "repo_id": "repo-1",
+            "ref":     "refs/heads/main",
+            "old":     "oldsha",
+            "new":     "newsha",
+            "pusher":  "did:key:z6MkPusher",
+            "node":    "did:key:z6MkNode",
+            "ts":      "2026-07-22T00:00:00+00:00",
+        });
+        let frozen = concat!(
+            r#"{"new":"newsha","node":"did:key:z6MkNode","old":"oldsha","#,
+            r#""pusher":"did:key:z6MkPusher","ref":"refs/heads/main","#,
+            r#""repo_id":"repo-1","ts":"2026-07-22T00:00:00+00:00"}"#,
+        );
+        assert_eq!(serde_json::to_string(&payload).unwrap(), frozen);
+    }
+
+    /// Signing exactly as the node does must round-trip through
+    /// verify_signature; any field tampering must fail it.
+    #[test]
+    fn verify_signature_round_trip_and_tamper() {
+        let kp = gitlawb_core::identity::Keypair::generate();
+        let node_did = kp.did().as_str().to_string();
+
+        let payload = serde_json::json!({
+            "repo_id": "repo-1",
+            "ref":     "refs/heads/main",
+            "old":     "0".repeat(40),
+            "new":     "a".repeat(40),
+            "pusher":  "did:key:z6MkPusher",
+            "node":    node_did,
+            "ts":      "2026-07-22T00:00:00+00:00",
+        });
+        let sig = kp.sign_b64(&serde_json::to_vec(&payload).unwrap());
+
+        let ok = verify_signature(
+            "repo-1",
+            "refs/heads/main",
+            &"0".repeat(40),
+            &"a".repeat(40),
+            "did:key:z6MkPusher",
+            &node_did,
+            "2026-07-22T00:00:00+00:00",
+            &sig,
+        );
+        assert!(ok.is_ok(), "expected valid signature, got: {ok:?}");
+
+        let tampered = verify_signature(
+            "repo-1",
+            "refs/heads/main",
+            &"0".repeat(40),
+            &"b".repeat(40), // new_sha changed after signing
+            "did:key:z6MkPusher",
+            &node_did,
+            "2026-07-22T00:00:00+00:00",
+            &sig,
+        );
+        assert!(tampered.is_err(), "tampered payload must not verify");
+
+        let garbage = verify_signature(
+            "repo-1",
+            "refs/heads/main",
+            &"0".repeat(40),
+            &"a".repeat(40),
+            "did:key:z6MkPusher",
+            &node_did,
+            "2026-07-22T00:00:00+00:00",
+            "not-base64url!!!",
+        );
+        assert!(garbage.is_err(), "malformed signature must not verify");
+    }
+}