fix!: protect evm_wallet integrity and bind key ciphertext to wallet address

Three independent failures allowed an offline attacker with DB write access
to sign transactions using a different wallet's private key:
1. evm_wallet had no HMAC envelope — aead_encrypted_id could be swapped silently.
2. AEAD used a static tag as AAD — any valid ciphertext decrypted as any wallet key.
3. No post-decryption check that the derived address matched the requested wallet.

Fix: sign_entity covers (address, aead_encrypted_id) in a single transaction;
CreateNew/Decrypt take caller-provided AAD (wallet address bytes); after decryption
signer.address() is verified against the requested wallet address.

server/crates/arbiter-server/src/actors/evm/mod.rs

@@ -1,6 +1,6 @@
 use crate::{
     actors::vault::{CreateNew, Decrypt, Vault},
-    crypto::integrity,
+    crypto::integrity::{self, Integrable},
     db::{
         DatabaseError, DatabasePool,
         models::{self},
@@ -25,14 +25,35 @@ use diesel::{
 use diesel_async::RunQueryDsl;
 use kameo::{Actor, actor::ActorRef, messages};
 use rand::{SeedableRng, rng, rngs::StdRng};
+use tracing::error;
 
 pub use crate::evm::safe_signer;
 
+/// Integrity guard that binds a wallet's encrypted key ID to its Ethereum address.
+/// Both fields are included in the HMAC — swapping `aead_encrypted_id` in the DB
+/// invalidates the envelope MAC, and the AEAD ciphertext is also bound to `address`
+/// as AAD, so decryption fails too.
+#[derive(arbiter_macros::Hashable)]
+struct EvmWalletIntegrity {
+    aead_encrypted_id: i32,
+    address: Address,
+}
+
+impl Integrable for EvmWalletIntegrity {
+    const KIND: &'static str = "evm_wallet";
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum SignTransactionError {
     #[error("Wallet not found")]
     WalletNotFound,
 
+    #[error("Decrypted key does not match requested wallet address")]
+    KeyAddressMismatch,
+
+    #[error("Internal signing error")]
+    Internal,
+
     #[error("Database error: {0}")]
     Database(#[from] DatabaseError),
 
@@ -64,6 +85,12 @@ pub enum Error {
     Integrity(#[from] integrity::Error),
 }
 
+impl From<diesel::result::Error> for Error {
+    fn from(e: diesel::result::Error) -> Self {
+        Self::Database(DatabaseError::from(e))
+    }
+}
+
 #[derive(Actor)]
 pub struct EvmActor {
     pub vault: ActorRef<Vault>,
@@ -97,20 +124,39 @@ impl EvmActor {
 
         let aead_id: i32 = self
             .vault
-            .ask(CreateNew { plaintext })
+            .ask(CreateNew {
+                plaintext,
+                aad: address.as_slice().to_vec(),
+            })
             .await
             .map_err(|_| Error::VaultSend)?;
 
         let mut conn = self.db.get().await.map_err(DatabaseError::from)?;
-        let wallet_id = insert_into(schema::evm_wallet::table)
+        let wallet_id = conn
+            .exclusive_transaction(async |conn| {
+                let wallet_id: i32 = insert_into(schema::evm_wallet::table)
                     .values(&models::NewEvmWallet {
                         address: address.as_slice().to_vec(),
                         aead_encrypted_id: aead_id,
                     })
                     .returning(schema::evm_wallet::id)
-            .get_result(&mut conn)
+                    .get_result(conn)
                     .await
-            .map_err(DatabaseError::from)?;
+                    .map_err(DatabaseError::from)
+                    .map_err(Error::Database)?;
+
+                integrity::sign_entity(
+                    conn,
+                    &self.vault,
+                    &EvmWalletIntegrity { address, aead_encrypted_id: aead_id },
+                    wallet_id,
+                )
+                .await
+                .map_err(Error::Integrity)?;
+
+                Ok::<i32, Error>(wallet_id)
+            })
+            .await?;
 
         Ok((wallet_id, address))
     }
@@ -241,16 +287,51 @@ impl EvmActor {
             .ok_or(SignTransactionError::WalletNotFound)?;
         drop(conn);
 
+        let mut conn = self.db.get().await.map_err(DatabaseError::from)?;
+        let attestation = integrity::verify_entity(
+            &mut conn,
+            &self.vault,
+            &EvmWalletIntegrity {
+                address: wallet_address,
+                aead_encrypted_id: wallet.aead_encrypted_id,
+            },
+            wallet.id,
+        )
+        .await
+        .map_err(|e| {
+            error!(?e, wallet_id = wallet.id, "EVM wallet integrity check failed");
+            SignTransactionError::Internal
+        })?;
+        drop(conn);
+
+        if attestation != integrity::AttestationStatus::Attested {
+            error!(
+                wallet_id = wallet.id,
+                "EVM wallet integrity unavailable; refusing to sign"
+            );
+            return Err(SignTransactionError::Internal);
+        }
+
         let raw_key: SafeCell<Vec<u8>> = self
             .vault
             .ask(Decrypt {
                 aead_id: wallet.aead_encrypted_id,
+                aad: wallet.address.clone(),
             })
             .await
             .map_err(|_| SignTransactionError::VaultSend)?;
 
         let signer = safe_signer::SafeSigner::from_cell(raw_key)?;
 
+        if signer.address() != wallet_address {
+            error!(
+                expected = %wallet_address,
+                actual = %signer.address(),
+                "Decrypted private key address does not match requested wallet"
+            );
+            return Err(SignTransactionError::KeyAddressMismatch);
+        }
+
         self.engine
             .evaluate_transaction(wallet_access, transaction.clone(), RunKind::Execution)
             .await?;

server/crates/arbiter-server/src/actors/vault/mod.rs

@@ -298,8 +298,10 @@ impl Vault {
         Ok(())
     }
 
+    /// Decrypts an AEAD entry. The `aad` must match the value used at encryption time;
+    /// a mismatch causes authentication failure, preventing cross-wallet key swaps.
     #[message]
-    pub async fn decrypt(&mut self, aead_id: i32) -> Result<SafeCell<Vec<u8>>, Error> {
+    pub async fn decrypt(&mut self, aead_id: i32, aad: Vec<u8>) -> Result<SafeCell<Vec<u8>>, Error> {
         let Unsealed { root_key, .. } = Self::expect_unsealed(&mut self.state)?;
 
         let row: models::AeadEncrypted = {
@@ -321,13 +323,15 @@ impl Vault {
             Error::BrokenDatabase
         })?;
         let mut output = SafeCell::new(row.ciphertext);
-        root_key.decrypt_in_place(&nonce, v1::TAG, &mut output)?;
+        root_key.decrypt_in_place(&nonce, &aad, &mut output)?;
         Ok(output)
     }
 
+    /// Creates a new `aead_encrypted` entry and returns its ID.
+    /// The `aad` is bound into the ciphertext and must be reproduced exactly at decryption time.
     // Creates new `aead_encrypted` entry in the database and returns it's ID
     #[message]
-    pub async fn create_new(&mut self, mut plaintext: SafeCell<Vec<u8>>) -> Result<i32, Error> {
+    pub async fn create_new(&mut self, mut plaintext: SafeCell<Vec<u8>>, aad: Vec<u8>) -> Result<i32, Error> {
         let Unsealed {
             root_key,
             root_key_history_id,
@@ -339,7 +343,7 @@ impl Vault {
 
         let mut ciphertext_buffer = plaintext.write();
         let ciphertext_buffer: &mut Vec<u8> = ciphertext_buffer.as_mut();
-        root_key.encrypt_in_place(&nonce, v1::TAG, &mut *ciphertext_buffer)?;
+        root_key.encrypt_in_place(&nonce, &aad, &mut *ciphertext_buffer)?;
 
         let ciphertext = std::mem::take(ciphertext_buffer);
 
@@ -474,7 +478,7 @@ mod tests {
         assert_eq!(root_row.data_encryption_nonce, n2.to_vec());
 
         let id = actor
-            .create_new(SafeCell::new(b"post-interleave".to_vec()))
+            .create_new(SafeCell::new(b"post-interleave".to_vec()), b"test-aad".to_vec())
             .await
             .unwrap();
         let row: models::AeadEncrypted = schema::aead_encrypted::table

server/crates/arbiter-server/tests/vault/concurrency.rs

@@ -14,6 +14,8 @@ use kameo::actor::{ActorRef, Spawn as _};
 use std::collections::{HashMap, HashSet};
 use tokio::task::JoinSet;
 
+const TEST_AAD: &[u8] = b"test-aad";
+
 async fn write_concurrently(
     actor: ActorRef<Vault>,
     prefix: &'static str,
@@ -27,6 +29,7 @@ async fn write_concurrently(
             let id = actor
                 .ask(CreateNew {
                     plaintext: SafeCell::new(plaintext.clone()),
+                    aad: TEST_AAD.to_vec(),
                 })
                 .await
                 .unwrap();
@@ -120,7 +123,7 @@ async fn insert_failure_does_not_create_partial_row() {
     drop(conn);
 
     let err = actor
-        .create_new(SafeCell::new(b"should fail".to_vec()))
+        .create_new(SafeCell::new(b"should fail".to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap_err();
     assert!(matches!(err, Error::DatabaseTransaction(_)));
@@ -171,7 +174,7 @@ async fn decrypt_roundtrip_after_high_concurrency() {
         .unwrap();
 
     for (id, plaintext) in expected {
-        let mut decrypted = decryptor.decrypt(id).await.unwrap();
+        let mut decrypted = decryptor.decrypt(id, TEST_AAD.to_vec()).await.unwrap();
         assert_eq!(*decrypted.read(), plaintext);
     }
 }

server/crates/arbiter-server/tests/vault/lifecycle.rs

@@ -12,6 +12,8 @@ use arbiter_server::{
 use diesel::{QueryDsl, SelectableHelper};
 use diesel_async::RunQueryDsl;
 
+const TEST_AAD: &[u8] = b"test-aad";
+
 #[tokio::test]
 #[test_log::test]
 async fn bootstrap() {
@@ -57,7 +59,7 @@ async fn create_new_before_bootstrap_fails() {
         .unwrap();
 
     let err = actor
-        .create_new(SafeCell::new(b"data".to_vec()))
+        .create_new(SafeCell::new(b"data".to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap_err();
     assert!(matches!(err, Error::NotBootstrapped));
@@ -71,7 +73,7 @@ async fn decrypt_before_bootstrap_fails() {
         .await
         .unwrap();
 
-    let err = actor.decrypt(1).await.unwrap_err();
+    let err = actor.decrypt(1, TEST_AAD.to_vec()).await.unwrap_err();
     assert!(matches!(err, Error::NotBootstrapped));
 }
 
@@ -85,7 +87,7 @@ async fn new_restores_sealed_state() {
     let mut actor2 = Vault::new(db, GlobalActors::spawn_message_bus())
         .await
         .unwrap();
-    let err = actor2.decrypt(1).await.unwrap_err();
+    let err = actor2.decrypt(1, TEST_AAD.to_vec()).await.unwrap_err();
     assert!(matches!(err, Error::Sealed));
 }
 
@@ -97,7 +99,7 @@ async fn unseal_correct_password() {
 
     let plaintext = b"survive a restart";
     let aead_id = actor
-        .create_new(SafeCell::new(plaintext.to_vec()))
+        .create_new(SafeCell::new(plaintext.to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
     drop(actor);
@@ -108,7 +110,7 @@ async fn unseal_correct_password() {
     let seal_key = SafeCell::new(b"test-seal-key".to_vec());
     actor.try_unseal(seal_key).await.unwrap();
 
-    let mut decrypted = actor.decrypt(aead_id).await.unwrap();
+    let mut decrypted = actor.decrypt(aead_id, TEST_AAD.to_vec()).await.unwrap();
     assert_eq!(*decrypted.read(), plaintext);
 }
 
@@ -120,7 +122,7 @@ async fn unseal_wrong_then_correct_password() {
 
     let plaintext = b"important data";
     let aead_id = actor
-        .create_new(SafeCell::new(plaintext.to_vec()))
+        .create_new(SafeCell::new(plaintext.to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
     drop(actor);
@@ -136,6 +138,6 @@ async fn unseal_wrong_then_correct_password() {
     let good_key = SafeCell::new(b"test-seal-key".to_vec());
     actor.try_unseal(good_key).await.unwrap();
 
-    let mut decrypted = actor.decrypt(aead_id).await.unwrap();
+    let mut decrypted = actor.decrypt(aead_id, TEST_AAD.to_vec()).await.unwrap();
     assert_eq!(*decrypted.read(), plaintext);
 }

server/crates/arbiter-server/tests/vault/storage.rs

@@ -10,6 +10,8 @@ use diesel::{ExpressionMethods as _, QueryDsl, SelectableHelper, dsl::update};
 use diesel_async::RunQueryDsl;
 use std::collections::HashSet;
 
+const TEST_AAD: &[u8] = b"test-aad";
+
 #[tokio::test]
 #[test_log::test]
 async fn create_decrypt_roundtrip() {
@@ -18,11 +20,11 @@ async fn create_decrypt_roundtrip() {
 
     let plaintext = b"hello arbiter";
     let aead_id = actor
-        .create_new(SafeCell::new(plaintext.to_vec()))
+        .create_new(SafeCell::new(plaintext.to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
 
-    let mut decrypted = actor.decrypt(aead_id).await.unwrap();
+    let mut decrypted = actor.decrypt(aead_id, TEST_AAD.to_vec()).await.unwrap();
     assert_eq!(*decrypted.read(), plaintext);
 }
 
@@ -32,7 +34,7 @@ async fn decrypt_nonexistent_returns_not_found() {
     let db = db::create_test_pool().await;
     let mut actor = common::bootstrapped_vault(&db).await;
 
-    let err = actor.decrypt(9999).await.unwrap_err();
+    let err = actor.decrypt(9999, TEST_AAD.to_vec()).await.unwrap_err();
     assert!(matches!(err, Error::NotFound));
 }
 
@@ -44,11 +46,11 @@ async fn ciphertext_differs_across_entries() {
 
     let plaintext = b"same content";
     let id1 = actor
-        .create_new(SafeCell::new(plaintext.to_vec()))
+        .create_new(SafeCell::new(plaintext.to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
     let id2 = actor
-        .create_new(SafeCell::new(plaintext.to_vec()))
+        .create_new(SafeCell::new(plaintext.to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
 
@@ -68,8 +70,8 @@ async fn ciphertext_differs_across_entries() {
 
     assert_ne!(row1.ciphertext, row2.ciphertext);
 
-    let mut d1 = actor.decrypt(id1).await.unwrap();
+    let mut d1 = actor.decrypt(id1, TEST_AAD.to_vec()).await.unwrap();
-    let mut d2 = actor.decrypt(id2).await.unwrap();
+    let mut d2 = actor.decrypt(id2, TEST_AAD.to_vec()).await.unwrap();
     assert_eq!(*d1.read(), plaintext);
     assert_eq!(*d2.read(), plaintext);
 }
@@ -83,7 +85,7 @@ async fn nonce_never_reused() {
     let n = 5;
     for i in 0..n {
         actor
-            .create_new(SafeCell::new(format!("secret {i}").into_bytes()))
+            .create_new(SafeCell::new(format!("secret {i}").into_bytes()), TEST_AAD.to_vec())
             .await
             .unwrap();
     }
@@ -137,7 +139,7 @@ async fn broken_db_nonce_format_fails_closed() {
     drop(conn);
 
     let err = actor
-        .create_new(SafeCell::new(b"must fail".to_vec()))
+        .create_new(SafeCell::new(b"must fail".to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap_err();
     assert!(matches!(err, Error::BrokenDatabase));
@@ -145,7 +147,7 @@ async fn broken_db_nonce_format_fails_closed() {
     let db = db::create_test_pool().await;
     let mut actor = common::bootstrapped_vault(&db).await;
     let id = actor
-        .create_new(SafeCell::new(b"decrypt target".to_vec()))
+        .create_new(SafeCell::new(b"decrypt target".to_vec()), TEST_AAD.to_vec())
         .await
         .unwrap();
     let mut conn = db.get().await.unwrap();
@@ -156,6 +158,6 @@ async fn broken_db_nonce_format_fails_closed() {
         .unwrap();
     drop(conn);
 
-    let err = actor.decrypt(id).await.unwrap_err();
+    let err = actor.decrypt(id, TEST_AAD.to_vec()).await.unwrap_err();
     assert!(matches!(err, Error::BrokenDatabase));
 }