diff --git a/node/src/crypto.rs b/node/src/crypto.rs
index 53a570f0..c3d9b08d 100644
--- a/node/src/crypto.rs
+++ b/node/src/crypto.rs
@@ -9,6 +9,8 @@ pub use ed25519::Signature;
 pub trait Signer: 'static {
     /// Return this signer's public/verification key.
     fn public_key(&self) -> &PublicKey;
+    /// Sign a message and return the signature.
+    fn sign(&self, msg: &[u8]) -> Signature;
 }
 
 /// The public/verification key.
diff --git a/node/src/protocol/message.rs b/node/src/protocol/message.rs
index 46b3ce14..6f98fdfc 100644
--- a/node/src/protocol/message.rs
+++ b/node/src/protocol/message.rs
@@ -58,6 +58,14 @@ pub struct NodeAnnouncement {
     addresses: Vec<Address>,
 }
 
+impl NodeAnnouncement {
+    /// Verify a signature on this message.
+    pub fn verify(&self, signature: &crypto::Signature) -> bool {
+        let msg = serde_json::to_vec(self).unwrap();
+        self.id.verify(signature, &msg).is_ok()
+    }
+}
+
 /// Message payload.
 /// These are the messages peers send to each other.
 #[derive(Debug, Serialize, Deserialize, Clone)]
@@ -110,6 +118,16 @@ impl Message {
         }
     }
 
+    pub fn node<S: crypto::Signer>(announcement: NodeAnnouncement, signer: S) -> Self {
+        let msg = serde_json::to_vec(&announcement).unwrap();
+        let signature = signer.sign(&msg);
+
+        Self::Node {
+            signature,
+            announcement,
+        }
+    }
+
     pub fn inventory<S, T, G>(ctx: &mut Context<S, T, G>) -> Result<Self, storage::Error>
     where
         T: storage::ReadStorage,
diff --git a/node/src/protocol/peer.rs b/node/src/protocol/peer.rs
index 807ac683..66ae863d 100644
--- a/node/src/protocol/peer.rs
+++ b/node/src/protocol/peer.rs
@@ -194,7 +194,16 @@ impl Peer {
                     }));
                 }
             }
-            (PeerState::Negotiated { .. }, Message::Node { .. }) => {
+            (
+                PeerState::Negotiated { .. },
+                Message::Node {
+                    announcement,
+                    signature,
+                },
+            ) => {
+                if !announcement.verify(&signature) {
+                    return Err(PeerError::Misbehavior);
+                }
                 todo!();
             }
             (PeerState::Negotiated { .. }, Message::Hello { .. }) => {
diff --git a/node/src/test/crypto.rs b/node/src/test/crypto.rs
index 3577b824..0f624082 100644
--- a/node/src/test/crypto.rs
+++ b/node/src/test/crypto.rs
@@ -1,8 +1,11 @@
+use ed25519_consensus as ed25519;
+
 use crate::crypto::{PublicKey, SecretKey, Signer};
 
 #[derive(Debug)]
 pub struct MockSigner {
-    key: PublicKey,
+    pk: PublicKey,
+    sk: SecretKey,
 }
 
 impl MockSigner {
@@ -15,7 +18,8 @@ impl MockSigner {
         let sk = SecretKey::from(bytes);
 
         Self {
-            key: sk.verification_key().into(),
+            pk: sk.verification_key().into(),
+            sk,
         }
     }
 }
@@ -26,13 +30,18 @@ impl Default for MockSigner {
         let sk = SecretKey::from(bytes);
 
         Self {
-            key: sk.verification_key().into(),
+            pk: sk.verification_key().into(),
+            sk,
         }
     }
 }
 
 impl Signer for MockSigner {
     fn public_key(&self) -> &PublicKey {
-        &self.key
+        &self.pk
+    }
+
+    fn sign(&self, msg: &[u8]) -> ed25519::Signature {
+        self.sk.sign(msg)
     }
 }