diff --git a/src/connection/authentication.rs b/src/connection/authentication.rs
index 6675291..e505bdc 100644
--- a/src/connection/authentication.rs
+++ b/src/connection/authentication.rs
@@ -9,7 +9,6 @@ use crate::model::authenticated::{Message, MessageHandler};
 
 use super::wrapper::ConnectionState;
 
-
 pub async fn authentication_handle(
     message_type: &str,
     message: &NetworkMessage,
diff --git a/src/connection/repository.rs b/src/connection/repository.rs
index c9a6f2c..87d13ae 100644
--- a/src/connection/repository.rs
+++ b/src/connection/repository.rs
@@ -9,7 +9,7 @@ use crate::{
     model::authenticated::{AuthenticatedUser, Message, MessageHandler, NetworkMessage, State},
 };
 
-use super::{wrapper::ConnectionState};
+use super::wrapper::ConnectionState;
 
 pub async fn repository_handle(
     message_type: &str,
diff --git a/src/connection/user.rs b/src/connection/user.rs
index 7133bc8..fa2fa9e 100644
--- a/src/connection/user.rs
+++ b/src/connection/user.rs
@@ -1,6 +1,5 @@
 use anyhow::Error;
 
-
 use crate::model::authenticated::AuthenticatedUser;
 use crate::model::user::User;
 use crate::{
@@ -11,7 +10,7 @@ use crate::{
     model::authenticated::{Message, MessageHandler, NetworkMessage, State},
 };
 
-use super::{wrapper::ConnectionState};
+use super::wrapper::ConnectionState;
 
 pub async fn user_handle(
     message_type: &str,
diff --git a/src/model/authenticated.rs b/src/model/authenticated.rs
index b865cc3..6248463 100644
--- a/src/model/authenticated.rs
+++ b/src/model/authenticated.rs
@@ -3,6 +3,13 @@ use std::{any::type_name, collections::HashMap, ops::Deref};
 use anyhow::Error;
 use futures_util::Future;
 use jsonwebtoken::{decode, Algorithm, DecodingKey, TokenData, Validation};
+use rsa::{
+    pkcs1::{DecodeRsaPrivateKey, DecodeRsaPublicKey},
+    pss::{Signature, SigningKey, VerifyingKey},
+    sha2::Sha256,
+    signature::{RandomizedSigner, SignatureEncoding, Verifier},
+    RsaPrivateKey, RsaPublicKey,
+};
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use serde_json::Value;
 
@@ -102,11 +109,17 @@ pub struct InstanceAuthenticator<'a> {
 }
 
 impl AuthenticationSourceProvider for InstanceAuthenticator<'_> {
-    fn authenticate(self, _payload: &Vec<u8>) -> AuthenticationSource {
+    fn authenticate(self, payload: &Vec<u8>) -> AuthenticationSource {
+        let mut rng = rand::thread_rng();
+
+        let private_key = RsaPrivateKey::from_pkcs1_pem(self.private_key).unwrap();
+        let signing_key = SigningKey::<Sha256>::new(private_key);
+        let signature = signing_key.sign_with_rng(&mut rng, &payload);
+
         AuthenticationSource::Instance {
             instance: self.instance,
             // TODO: Actually parse signature from private key
-            signature: InstanceSignature(self.private_key.as_bytes().to_vec()),
+            signature: InstanceSignature(signature.to_bytes().into_vec()),
         }
     }
 }
@@ -136,6 +149,12 @@ impl AsRef<str> for UserAuthenticationToken {
 #[derive(Clone, Debug, Hash, PartialEq, Eq, Serialize, Deserialize)]
 pub struct InstanceSignature(Vec<u8>);
 
+impl AsRef<[u8]> for InstanceSignature {
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
 #[derive(Clone, Debug, Hash, PartialEq, Eq, Serialize, Deserialize)]
 pub enum AuthenticationSource {
     User {
@@ -234,12 +253,12 @@ impl FromMessage<ConnectionState> for AuthenticatedUser {
 impl FromMessage<ConnectionState> for AuthenticatedInstance {
     async fn from_message(
         network_message: &NetworkMessage,
-        _state: &ConnectionState,
+        state: &ConnectionState,
     ) -> Result<Self, Error> {
-        let message: Authenticated<HashMap<String, Value>> =
+        let message: Authenticated<Value> =
             serde_json::from_slice(&network_message).map_err(|e| Error::from(e))?;
 
-        let (instance, _signature) = message
+        let (instance, signature) = message
             .source
             .iter()
             .filter_map(|auth| {
@@ -257,9 +276,21 @@ impl FromMessage<ConnectionState> for AuthenticatedInstance {
             // TODO: Instance authentication error
             .ok_or_else(|| UserAuthenticationError::Missing)?;
 
-        // TODO: Actually validate
+        let public_key = public_key(instance).await?;
+        let public_key = RsaPublicKey::from_pkcs1_pem(&public_key).unwrap();
+
+        let verifying_key: VerifyingKey<Sha256> = VerifyingKey::new(public_key);
+
+        let message_json = serde_json::to_vec(&message.message).unwrap();
+
+        verifying_key
+            .verify(
+                &message_json,
+                &Signature::try_from(signature.as_ref()).unwrap(),
+            )
+            .unwrap();
 
-        Ok(Self(instance.clone()))
+        Ok(AuthenticatedInstance(instance.clone()))
     }
 }