feat(evm): implement EVM sign transaction handling in client and user agent

protobufs/client.proto

@@ -42,6 +42,7 @@ message ClientRequest {
     AuthChallengeRequest auth_challenge_request = 1;
     AuthChallengeSolution auth_challenge_solution = 2;
     google.protobuf.Empty query_vault_state = 3;
+    arbiter.evm.EvmSignTransactionRequest evm_sign_transaction = 5;
   }
 }
 

protobufs/user_agent.proto

@@ -137,6 +137,11 @@ message SdkClientConnectionResponse {
 
 message SdkClientConnectionCancel {}
 
+message UserAgentEvmSignTransactionRequest {
+  int32 client_id = 1;
+  arbiter.evm.EvmSignTransactionRequest request = 2;
+}
+
 message UserAgentRequest {
   int32 id = 16;
   oneof payload {
@@ -155,6 +160,7 @@ message UserAgentRequest {
     SdkClientRevokeRequest sdk_client_revoke = 13;
     google.protobuf.Empty sdk_client_list = 14;
     BootstrapEncryptedKey bootstrap_encrypted_key = 15;
+    UserAgentEvmSignTransactionRequest evm_sign_transaction = 17;
   }
 }
 message UserAgentResponse {
@@ -175,5 +181,6 @@ message UserAgentResponse {
     SdkClientRevokeResponse sdk_client_revoke_response = 13;
     SdkClientListResponse sdk_client_list_response = 14;
     BootstrapResult bootstrap_result = 15;
+    arbiter.evm.EvmSignTransactionResponse evm_sign_transaction = 17;
   }
 }

server/crates/arbiter-client/src/transport.rs

@@ -1,6 +1,4 @@
-use arbiter_proto::proto::{
-    client::{ClientRequest, ClientResponse},
-};
+use arbiter_proto::proto::client::{ClientRequest, ClientResponse};
 use std::sync::atomic::{AtomicI32, Ordering};
 use tokio::sync::mpsc;
 
@@ -36,9 +34,7 @@ impl ClientTransport {
             .map_err(|_| ClientSignError::ChannelClosed)
     }
 
-    pub(crate) async fn recv(
-        &mut self,
-    ) -> std::result::Result<ClientResponse, ClientSignError> {
+    pub(crate) async fn recv(&mut self) -> std::result::Result<ClientResponse, ClientSignError> {
         match self.receiver.message().await {
             Ok(Some(resp)) => Ok(resp),
             Ok(None) => Err(ClientSignError::ConnectionClosed),

server/crates/arbiter-client/src/wallets/evm.rs

@@ -8,7 +8,15 @@ use async_trait::async_trait;
 use std::sync::Arc;
 use tokio::sync::Mutex;
 
-use crate::transport::ClientTransport;
+use arbiter_proto::proto::{
+    client::{
+        ClientRequest, client_request::Payload as ClientRequestPayload,
+        client_response::Payload as ClientResponsePayload,
+    },
+    evm::evm_sign_transaction_response::Result as EvmSignTransactionResult,
+};
+
+use crate::transport::{ClientTransport, next_request_id};
 
 pub struct ArbiterEvmWallet {
     transport: Arc<Mutex<ClientTransport>>,
@@ -79,11 +87,61 @@ impl TxSigner<Signature> for ArbiterEvmWallet {
         &self,
         tx: &mut dyn SignableTransaction<Signature>,
     ) -> Result<Signature> {
-        let _transport = self.transport.lock().await;
         self.validate_chain_id(tx)?;
 
-        Err(Error::other(
-            "transaction signing is not supported by current arbiter.client protocol",
-        ))
+        let mut transport = self.transport.lock().await;
+        let request_id = next_request_id();
+        let rlp_transaction = tx.encoded_for_signing();
+
+        transport
+            .send(ClientRequest {
+                request_id,
+                payload: Some(ClientRequestPayload::EvmSignTransaction(
+                    arbiter_proto::proto::evm::EvmSignTransactionRequest {
+                        wallet_address: self.address.to_vec(),
+                        rlp_transaction,
+                    },
+                )),
+            })
+            .await
+            .map_err(|_| Error::other("failed to send evm sign transaction request"))?;
+
+        let response = transport
+            .recv()
+            .await
+            .map_err(|_| Error::other("failed to receive evm sign transaction response"))?;
+
+        if response.request_id != Some(request_id) {
+            return Err(Error::other(
+                "received mismatched response id for evm sign transaction",
+            ));
+        }
+
+        let payload = response
+            .payload
+            .ok_or_else(|| Error::other("missing evm sign transaction response payload"))?;
+
+        let ClientResponsePayload::EvmSignTransaction(response) = payload else {
+            return Err(Error::other(
+                "unexpected response payload for evm sign transaction request",
+            ));
+        };
+
+        let result = response
+            .result
+            .ok_or_else(|| Error::other("missing evm sign transaction result"))?;
+
+        match result {
+            EvmSignTransactionResult::Signature(signature) => {
+                Signature::try_from(signature.as_slice())
+                    .map_err(|_| Error::other("invalid signature returned by server"))
+            }
+            EvmSignTransactionResult::EvalError(eval_error) => Err(Error::other(format!(
+                "transaction rejected by policy: {eval_error:?}"
+            ))),
+            EvmSignTransactionResult::Error(code) => Err(Error::other(format!(
+                "server failed to sign transaction with error code {code}"
+            ))),
+        }
     }
 }

server/crates/arbiter-server/src/actors/client/auth.rs

@@ -54,10 +54,19 @@ pub enum Outbound {
     AuthSuccess,
 }
 
+#[derive(Debug, Clone)]
+pub struct AuthenticatedClient {
+    pub pubkey: VerifyingKey,
+    pub client_id: i32,
+}
+
 /// Atomically reads and increments the nonce for a known client.
 /// Returns `None` if the pubkey is not registered.
-async fn get_nonce(db: &db::DatabasePool, pubkey: &VerifyingKey) -> Result<Option<i32>, Error> {
-    let pubkey_bytes = pubkey.as_bytes().to_vec();
+async fn get_nonce(
+    db: &db::DatabasePool,
+    pubkey: &VerifyingKey,
+) -> Result<Option<(/* client_id */ i32, /* nonce */ i32)>, Error> {
+    let pubkey_bytes = pubkey.as_bytes();
 
     let mut conn = db.get().await.map_err(|e| {
         error!(error = ?e, "Database pool error");
@@ -65,7 +74,6 @@ async fn get_nonce(db: &db::DatabasePool, pubkey: &VerifyingKey) -> Result<Optio
     })?;
 
     conn.exclusive_transaction(|conn| {
-        let pubkey_bytes = pubkey_bytes.clone();
         Box::pin(async move {
             let Some((client_id, current_nonce)) = program_client::table
                 .filter(program_client::public_key.eq(&pubkey_bytes))
@@ -83,8 +91,7 @@ async fn get_nonce(db: &db::DatabasePool, pubkey: &VerifyingKey) -> Result<Optio
                 .execute(conn)
                 .await?;
 
-            let _ = client_id;
-            Ok(Some(current_nonce))
+            Ok(Some((client_id, current_nonce)))
         })
     })
     .await
@@ -213,23 +220,25 @@ where
 pub async fn authenticate<T>(
     props: &mut ClientConnection,
     transport: &mut T,
-) -> Result<VerifyingKey, Error>
+) -> Result<AuthenticatedClient, Error>
 where
     T: Bi<Inbound, Result<Outbound, Error>> + Send + ?Sized,
 {
-    let Some(Inbound::AuthChallengeRequest { pubkey }) = transport.recv().await
-    else {
+    let Some(Inbound::AuthChallengeRequest { pubkey }) = transport.recv().await else {
         return Err(Error::Transport);
     };
 
-    let nonce = match get_nonce(&props.db, &pubkey).await? {
-        Some(nonce) => nonce,
+    let (client_id, nonce) = match get_nonce(&props.db, &pubkey).await? {
+        Some(client_nonce) => client_nonce,
         None => {
             approve_new_client(&props.actors, pubkey).await?;
             match insert_client(&props.db, &pubkey).await? {
-                InsertClientResult::Inserted => 0,
+                InsertClientResult::Inserted => match get_nonce(&props.db, &pubkey).await? {
+                    Some((client_id, _)) => (client_id, 0),
+                    None => return Err(Error::DatabaseOperationFailed),
+                },
                 InsertClientResult::AlreadyExists => match get_nonce(&props.db, &pubkey).await? {
-                    Some(nonce) => nonce,
+                    Some((client_id, nonce)) => (client_id, nonce),
                     None => return Err(Error::DatabaseOperationFailed),
                 },
             }
@@ -245,5 +254,5 @@ where
             Error::Transport
         })?;
 
-    Ok(pubkey)
+    Ok(AuthenticatedClient { pubkey, client_id })
 }

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

@@ -10,11 +10,16 @@ use crate::{
 pub struct ClientConnection {
     pub(crate) db: db::DatabasePool,
     pub(crate) actors: GlobalActors,
+    pub(crate) client_id: i32,
 }
 
 impl ClientConnection {
     pub fn new(db: db::DatabasePool, actors: GlobalActors) -> Self {
-        Self { db, actors }
+        Self {
+            db,
+            actors,
+            client_id: 0,
+        }
     }
 }
 
@@ -26,7 +31,8 @@ where
     T: Bi<auth::Inbound, Result<auth::Outbound, auth::Error>> + Send + ?Sized,
 {
     match auth::authenticate(&mut props, transport).await {
-        Ok(_pubkey) => {
+        Ok(authenticated) => {
+            props.client_id = authenticated.client_id;
             ClientSession::spawn(ClientSession::new(props));
             info!("Client authenticated, session started");
         }

server/crates/arbiter-server/src/actors/client/session.rs

@@ -1,11 +1,18 @@
 use kameo::{Actor, messages};
 use tracing::error;
 
+use alloy::{consensus::TxEip1559, primitives::Address, signers::Signature};
+
 use crate::{
     actors::{
-        GlobalActors, client::ClientConnection, keyholder::KeyHolderState, router::RegisterClient,
+        GlobalActors,
+        client::ClientConnection,
+        evm::{ClientSignTransaction, SignTransactionError},
+        keyholder::KeyHolderState,
+        router::RegisterClient,
     },
     db,
+    evm::VetError,
 };
 
 pub struct ClientSession {
@@ -34,6 +41,34 @@ impl ClientSession {
 
         Ok(vault_state)
     }
+
+    #[message]
+    pub(crate) async fn handle_sign_transaction(
+        &mut self,
+        wallet_address: Address,
+        transaction: TxEip1559,
+    ) -> Result<Signature, SignTransactionRpcError> {
+        match self
+            .props
+            .actors
+            .evm
+            .ask(ClientSignTransaction {
+                client_id: self.props.client_id,
+                wallet_address,
+                transaction,
+            })
+            .await
+        {
+            Ok(signature) => Ok(signature),
+            Err(kameo::error::SendError::HandlerError(SignTransactionError::Vet(vet_error))) => {
+                Err(SignTransactionRpcError::Vet(vet_error))
+            }
+            Err(err) => {
+                error!(?err, "Failed to sign EVM transaction in client session");
+                Err(SignTransactionRpcError::Internal)
+            }
+        }
+    }
 }
 
 impl Actor for ClientSession {
@@ -69,3 +104,12 @@ pub enum Error {
     #[error("Internal error")]
     Internal,
 }
+
+#[derive(Debug, thiserror::Error)]
+pub enum SignTransactionRpcError {
+    #[error("Policy evaluation failed")]
+    Vet(#[from] VetError),
+
+    #[error("Internal error")]
+    Internal,
+}

server/crates/arbiter-server/src/actors/user_agent/session.rs

@@ -36,7 +36,10 @@ impl Error {
 pub struct UserAgentSession {
     props: UserAgentConnection,
     state: UserAgentStateMachine<DummyContext>,
-    #[allow(dead_code, reason = "The session keeps ownership of the outbound transport even before the state-machine flow starts using it directly")]
+    #[allow(
+        dead_code,
+        reason = "The session keeps ownership of the outbound transport even before the state-machine flow starts using it directly"
+    )]
     sender: Box<dyn Sender<OutOfBand>>,
 }
 
@@ -44,8 +47,11 @@ mod connection;
 pub(crate) use connection::{
     BootstrapError, HandleBootstrapEncryptedKey, HandleEvmWalletCreate, HandleEvmWalletList,
     HandleGrantCreate, HandleGrantDelete, HandleGrantList, HandleQueryVaultState,
+    HandleSignTransaction,
+};
+pub use connection::{
+    HandleUnsealEncryptedKey, HandleUnsealRequest, SignTransactionError, UnsealError,
 };
-pub use connection::{HandleUnsealEncryptedKey, HandleUnsealRequest, UnsealError};
 
 impl UserAgentSession {
     pub(crate) fn new(props: UserAgentConnection, sender: Box<dyn Sender<OutOfBand>>) -> Self {

server/crates/arbiter-server/src/actors/user_agent/session/connection.rs

@@ -1,6 +1,6 @@
 use std::sync::Mutex;
 
-use alloy::primitives::Address;
+use alloy::{consensus::TxEip1559, primitives::Address, signers::Signature};
 use chacha20poly1305::{AeadInPlace, XChaCha20Poly1305, XNonce, aead::KeyInit};
 use kameo::error::SendError;
 use kameo::messages;
@@ -14,7 +14,8 @@ use crate::safe_cell::SafeCell;
 use crate::{
     actors::{
         evm::{
-            Generate, ListWallets, UseragentCreateGrant, UseragentDeleteGrant, UseragentListGrants,
+            ClientSignTransaction, Generate, ListWallets, SignTransactionError as EvmSignError,
+            UseragentCreateGrant, UseragentDeleteGrant, UseragentListGrants,
         },
         keyholder::{self, Bootstrap, TryUnseal},
         user_agent::session::{
@@ -103,6 +104,15 @@ pub enum BootstrapError {
     General(#[from] super::Error),
 }
 
+#[derive(Debug, Error)]
+pub enum SignTransactionError {
+    #[error("Policy evaluation failed")]
+    Vet(#[from] crate::evm::VetError),
+
+    #[error("Internal signing error")]
+    Internal,
+}
+
 #[messages]
 impl UserAgentSession {
     #[message]
@@ -351,4 +361,33 @@ impl UserAgentSession {
             }
         }
     }
+
+    #[message]
+    pub(crate) async fn handle_sign_transaction(
+        &mut self,
+        client_id: i32,
+        wallet_address: Address,
+        transaction: TxEip1559,
+    ) -> Result<Signature, SignTransactionError> {
+        match self
+            .props
+            .actors
+            .evm
+            .ask(ClientSignTransaction {
+                client_id,
+                wallet_address,
+                transaction,
+            })
+            .await
+        {
+            Ok(signature) => Ok(signature),
+            Err(SendError::HandlerError(EvmSignError::Vet(vet_error))) => {
+                Err(SignTransactionError::Vet(vet_error))
+            }
+            Err(err) => {
+                error!(?err, "EVM sign transaction failed in user-agent session");
+                Err(SignTransactionError::Internal)
+            }
+        }
+    }
 }

server/crates/arbiter-server/src/evm/policies/ether_transfer/mod.rs

@@ -36,8 +36,8 @@ use super::{DatabaseID, EvalContext, EvalViolation};
 // Plain ether transfer
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Meaning {
-    to: Address,
-    value: U256,
+    pub(crate) to: Address,
+    pub(crate) value: U256,
 }
 impl Display for Meaning {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {

server/crates/arbiter-server/src/evm/policies/token_transfers/mod.rs

@@ -38,9 +38,9 @@ fn grant_join() -> _ {
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Meaning {
-    token: &'static TokenInfo,
-    to: Address,
-    value: U256,
+    pub(crate) token: &'static TokenInfo,
+    pub(crate) to: Address,
+    pub(crate) value: U256,
 }
 impl std::fmt::Display for Meaning {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {

server/crates/arbiter-server/src/grpc/client.rs

@@ -1,4 +1,5 @@
 use arbiter_proto::{
+    google::protobuf::Empty as ProtoEmpty,
     proto::client::{
         ClientRequest, ClientResponse, VaultState as ProtoVaultState,
         client_request::Payload as ClientRequestPayload,
@@ -17,16 +18,135 @@ use crate::{
     actors::{
         client::{
             self, ClientConnection,
-            session::{ClientSession, Error, HandleQueryVaultState},
+            session::{
+                ClientSession, Error, HandleQueryVaultState, HandleSignTransaction,
+                SignTransactionRpcError,
+            },
         },
         keyholder::KeyHolderState,
     },
+    evm::{PolicyError, VetError, policies::EvalViolation},
     grpc::request_tracker::RequestTracker,
     utils::defer,
 };
 
+use alloy::{
+    consensus::TxEip1559,
+    primitives::{Address, U256},
+    rlp::Decodable,
+};
+use arbiter_proto::proto::evm::{
+    EvmError as ProtoEvmError, EvmSignTransactionResponse, EvalViolation as ProtoEvalViolation,
+    GasLimitExceededViolation, NoMatchingGrantError, PolicyViolationsError,
+    SpecificMeaning as ProtoSpecificMeaning, TokenInfo as ProtoTokenInfo,
+    TransactionEvalError,
+    evm_sign_transaction_response::Result as EvmSignTransactionResult,
+    eval_violation::Kind as ProtoEvalViolationKind,
+    specific_meaning::Meaning as ProtoSpecificMeaningKind,
+    transaction_eval_error::Kind as ProtoTransactionEvalErrorKind,
+};
+
 mod auth;
 
+fn u256_to_proto_bytes(value: U256) -> Vec<u8> {
+    value.to_be_bytes::<32>().to_vec()
+}
+
+fn meaning_to_proto(meaning: crate::evm::policies::SpecificMeaning) -> ProtoSpecificMeaning {
+    let kind = match meaning {
+        crate::evm::policies::SpecificMeaning::EtherTransfer(meaning) => {
+            ProtoSpecificMeaningKind::EtherTransfer(arbiter_proto::proto::evm::EtherTransferMeaning {
+                to: meaning.to.to_vec(),
+                value: u256_to_proto_bytes(meaning.value),
+            })
+        }
+        crate::evm::policies::SpecificMeaning::TokenTransfer(meaning) => {
+            ProtoSpecificMeaningKind::TokenTransfer(arbiter_proto::proto::evm::TokenTransferMeaning {
+                token: Some(ProtoTokenInfo {
+                    symbol: meaning.token.symbol.to_string(),
+                    address: meaning.token.contract.to_vec(),
+                    chain_id: meaning.token.chain,
+                }),
+                to: meaning.to.to_vec(),
+                value: u256_to_proto_bytes(meaning.value),
+            })
+        }
+    };
+
+    ProtoSpecificMeaning {
+        meaning: Some(kind),
+    }
+}
+
+fn violation_to_proto(violation: EvalViolation) -> ProtoEvalViolation {
+    let kind = match violation {
+        EvalViolation::InvalidTarget { target } => ProtoEvalViolationKind::InvalidTarget(target.to_vec()),
+        EvalViolation::GasLimitExceeded {
+            max_gas_fee_per_gas,
+            max_priority_fee_per_gas,
+        } => ProtoEvalViolationKind::GasLimitExceeded(GasLimitExceededViolation {
+            max_gas_fee_per_gas: max_gas_fee_per_gas.map(u256_to_proto_bytes),
+            max_priority_fee_per_gas: max_priority_fee_per_gas.map(u256_to_proto_bytes),
+        }),
+        EvalViolation::RateLimitExceeded => ProtoEvalViolationKind::RateLimitExceeded(ProtoEmpty {}),
+        EvalViolation::VolumetricLimitExceeded => {
+            ProtoEvalViolationKind::VolumetricLimitExceeded(ProtoEmpty {})
+        }
+        EvalViolation::InvalidTime => ProtoEvalViolationKind::InvalidTime(ProtoEmpty {}),
+        EvalViolation::InvalidTransactionType => {
+            ProtoEvalViolationKind::InvalidTransactionType(ProtoEmpty {})
+        }
+    };
+
+    ProtoEvalViolation { kind: Some(kind) }
+}
+
+fn eval_error_to_proto(err: VetError) -> Option<TransactionEvalError> {
+    let kind = match err {
+        VetError::ContractCreationNotSupported => {
+            ProtoTransactionEvalErrorKind::ContractCreationNotSupported(ProtoEmpty {})
+        }
+        VetError::UnsupportedTransactionType => {
+            ProtoTransactionEvalErrorKind::UnsupportedTransactionType(ProtoEmpty {})
+        }
+        VetError::Evaluated(meaning, policy_error) => match policy_error {
+            PolicyError::NoMatchingGrant => {
+                ProtoTransactionEvalErrorKind::NoMatchingGrant(NoMatchingGrantError {
+                    meaning: Some(meaning_to_proto(meaning)),
+                })
+            }
+            PolicyError::Violations(violations) => {
+                ProtoTransactionEvalErrorKind::PolicyViolations(PolicyViolationsError {
+                    meaning: Some(meaning_to_proto(meaning)),
+                    violations: violations.into_iter().map(violation_to_proto).collect(),
+                })
+            }
+            PolicyError::Pool(_) | PolicyError::Database(_) => {
+                return None;
+            }
+        },
+    };
+
+    Some(TransactionEvalError { kind: Some(kind) })
+}
+
+fn decode_eip1559_transaction(payload: &[u8]) -> Result<TxEip1559, ()> {
+    let mut body = payload;
+    if let Some((prefix, rest)) = payload.split_first()
+        && *prefix == 0x02
+    {
+        body = rest;
+    }
+
+    let mut cursor = body;
+    let transaction = TxEip1559::decode(&mut cursor).map_err(|_| ())?;
+    if !cursor.is_empty() {
+        return Err(());
+    }
+
+    Ok(transaction)
+}
+
 async fn dispatch_loop(
     mut bi: GrpcBi<ClientRequest, ClientResponse>,
     actor: ActorRef<ClientSession>,
@@ -90,6 +210,64 @@ async fn dispatch_conn_message(
             }
             .into(),
         ),
+        ClientRequestPayload::EvmSignTransaction(request) => {
+            let wallet_address = match <[u8; 20]>::try_from(request.wallet_address.as_slice()) {
+                Ok(address) => Address::from(address),
+                Err(_) => {
+                    let _ = bi
+                        .send(Err(Status::invalid_argument("Invalid EVM wallet address")))
+                        .await;
+                    return Err(());
+                }
+            };
+
+            let transaction = match decode_eip1559_transaction(&request.rlp_transaction) {
+                Ok(transaction) => transaction,
+                Err(()) => {
+                    let _ = bi
+                        .send(Err(Status::invalid_argument(
+                            "Invalid EIP-1559 RLP transaction",
+                        )))
+                        .await;
+                    return Err(());
+                }
+            };
+
+            let response = match actor
+                .ask(HandleSignTransaction {
+                    wallet_address,
+                    transaction,
+                })
+                .await
+            {
+                Ok(signature) => EvmSignTransactionResponse {
+                    result: Some(EvmSignTransactionResult::Signature(signature.as_bytes().to_vec())),
+                },
+                Err(kameo::error::SendError::HandlerError(SignTransactionRpcError::Vet(vet_error))) => {
+                    match eval_error_to_proto(vet_error) {
+                        Some(eval_error) => EvmSignTransactionResponse {
+                            result: Some(EvmSignTransactionResult::EvalError(eval_error)),
+                        },
+                        None => EvmSignTransactionResponse {
+                            result: Some(EvmSignTransactionResult::Error(ProtoEvmError::Internal.into())),
+                        },
+                    }
+                }
+                Err(kameo::error::SendError::HandlerError(SignTransactionRpcError::Internal)) => {
+                    EvmSignTransactionResponse {
+                        result: Some(EvmSignTransactionResult::Error(ProtoEvmError::Internal.into())),
+                    }
+                }
+                Err(err) => {
+                    warn!(error = ?err, "Failed to sign EVM transaction");
+                    EvmSignTransactionResponse {
+                        result: Some(EvmSignTransactionResult::Error(ProtoEvmError::Internal.into())),
+                    }
+                }
+            };
+
+            ClientResponsePayload::EvmSignTransaction(response)
+        }
         payload => {
             warn!(?payload, "Unsupported post-auth client request");
             let _ = bi

server/crates/arbiter-server/src/grpc/client/auth.rs

@@ -151,7 +151,9 @@ impl Receiver<auth::Inbound> for AuthTransportAdapter<'_> {
             _ => {
                 let _ = self
                     .bi
-                    .send(Err(Status::invalid_argument("Unsupported client auth request")))
+                    .send(Err(Status::invalid_argument(
+                        "Unsupported client auth request",
+                    )))
                     .await;
                 None
             }
@@ -168,6 +170,7 @@ pub async fn start(
     response_id: &mut Option<i32>,
 ) -> Result<(), auth::Error> {
     let mut transport = AuthTransportAdapter::new(bi, request_tracker, response_id);
-    client::auth::authenticate(conn, &mut transport).await?;
+    let authenticated = client::auth::authenticate(conn, &mut transport).await?;
+    conn.client_id = authenticated.client_id;
     Ok(())
 }

server/crates/arbiter-server/src/grpc/user_agent.rs

@@ -4,17 +4,24 @@ use arbiter_proto::{
     google::protobuf::{Empty as ProtoEmpty, Timestamp as ProtoTimestamp},
     proto::{
         evm::{
-            EtherTransferSettings as ProtoEtherTransferSettings, EvmError as ProtoEvmError,
-            EvmGrantCreateRequest, EvmGrantCreateResponse, EvmGrantDeleteRequest,
-            EvmGrantDeleteResponse, EvmGrantList, EvmGrantListResponse, GrantEntry,
+            EtherTransferSettings as ProtoEtherTransferSettings,
+            EvalViolation as ProtoEvalViolation, EvmError as ProtoEvmError, EvmGrantCreateRequest,
+            EvmGrantCreateResponse, EvmGrantDeleteRequest, EvmGrantDeleteResponse, EvmGrantList,
+            EvmGrantListResponse, EvmSignTransactionResponse, GasLimitExceededViolation,
+            GrantEntry, NoMatchingGrantError, PolicyViolationsError,
             SharedSettings as ProtoSharedSettings, SpecificGrant as ProtoSpecificGrant,
-            TokenTransferSettings as ProtoTokenTransferSettings,
+            SpecificMeaning as ProtoSpecificMeaning, TokenInfo as ProtoTokenInfo,
+            TokenTransferSettings as ProtoTokenTransferSettings, TransactionEvalError,
             TransactionRateLimit as ProtoTransactionRateLimit,
             VolumeRateLimit as ProtoVolumeRateLimit, WalletCreateResponse, WalletEntry, WalletList,
-            WalletListResponse, evm_grant_create_response::Result as EvmGrantCreateResult,
+            WalletListResponse, eval_violation::Kind as ProtoEvalViolationKind,
+            evm_grant_create_response::Result as EvmGrantCreateResult,
             evm_grant_delete_response::Result as EvmGrantDeleteResult,
             evm_grant_list_response::Result as EvmGrantListResult,
+            evm_sign_transaction_response::Result as EvmSignTransactionResult,
             specific_grant::Grant as ProtoSpecificGrantType,
+            specific_meaning::Meaning as ProtoSpecificMeaningKind,
+            transaction_eval_error::Kind as ProtoTransactionEvalErrorKind,
             wallet_create_response::Result as WalletCreateResult,
             wallet_list_response::Result as WalletListResult,
         },
@@ -23,8 +30,8 @@ use arbiter_proto::{
             BootstrapResult as ProtoBootstrapResult,
             SdkClientConnectionResponse as ProtoSdkClientConnectionResponse,
             UnsealEncryptedKey as ProtoUnsealEncryptedKey, UnsealResult as ProtoUnsealResult,
-            UnsealStart, UserAgentRequest, UserAgentResponse, VaultState as ProtoVaultState,
-            user_agent_request::Payload as UserAgentRequestPayload,
+            UnsealStart, UserAgentEvmSignTransactionRequest, UserAgentRequest, UserAgentResponse,
+            VaultState as ProtoVaultState, user_agent_request::Payload as UserAgentRequestPayload,
             user_agent_response::Payload as UserAgentResponsePayload,
         },
     },
@@ -47,7 +54,9 @@ use crate::{
             session::{
                 BootstrapError, Error, HandleBootstrapEncryptedKey, HandleEvmWalletCreate,
                 HandleEvmWalletList, HandleGrantCreate, HandleGrantDelete, HandleGrantList,
-                HandleQueryVaultState, HandleUnsealEncryptedKey, HandleUnsealRequest, UnsealError,
+                HandleQueryVaultState, HandleSignTransaction, HandleUnsealEncryptedKey,
+                HandleUnsealRequest, SignTransactionError as SessionSignTransactionError,
+                UnsealError,
             },
         },
     },
@@ -55,12 +64,124 @@ use crate::{
         Grant, SharedGrantSettings, SpecificGrant, TransactionRateLimit, VolumeRateLimit,
         ether_transfer, token_transfers,
     },
+    evm::{PolicyError, VetError, policies::EvalViolation},
     grpc::request_tracker::RequestTracker,
     utils::defer,
 };
-use alloy::primitives::{Address, U256};
+use alloy::{
+    consensus::TxEip1559,
+    primitives::{Address, U256},
+    rlp::Decodable,
+};
 mod auth;
 
+fn u256_to_proto_bytes(value: U256) -> Vec<u8> {
+    value.to_be_bytes::<32>().to_vec()
+}
+
+fn meaning_to_proto(meaning: crate::evm::policies::SpecificMeaning) -> ProtoSpecificMeaning {
+    let kind = match meaning {
+        crate::evm::policies::SpecificMeaning::EtherTransfer(meaning) => {
+            ProtoSpecificMeaningKind::EtherTransfer(
+                arbiter_proto::proto::evm::EtherTransferMeaning {
+                    to: meaning.to.to_vec(),
+                    value: u256_to_proto_bytes(meaning.value),
+                },
+            )
+        }
+        crate::evm::policies::SpecificMeaning::TokenTransfer(meaning) => {
+            ProtoSpecificMeaningKind::TokenTransfer(
+                arbiter_proto::proto::evm::TokenTransferMeaning {
+                    token: Some(ProtoTokenInfo {
+                        symbol: meaning.token.symbol.to_string(),
+                        address: meaning.token.contract.to_vec(),
+                        chain_id: meaning.token.chain,
+                    }),
+                    to: meaning.to.to_vec(),
+                    value: u256_to_proto_bytes(meaning.value),
+                },
+            )
+        }
+    };
+
+    ProtoSpecificMeaning {
+        meaning: Some(kind),
+    }
+}
+
+fn violation_to_proto(violation: EvalViolation) -> ProtoEvalViolation {
+    let kind = match violation {
+        EvalViolation::InvalidTarget { target } => {
+            ProtoEvalViolationKind::InvalidTarget(target.to_vec())
+        }
+        EvalViolation::GasLimitExceeded {
+            max_gas_fee_per_gas,
+            max_priority_fee_per_gas,
+        } => ProtoEvalViolationKind::GasLimitExceeded(GasLimitExceededViolation {
+            max_gas_fee_per_gas: max_gas_fee_per_gas.map(u256_to_proto_bytes),
+            max_priority_fee_per_gas: max_priority_fee_per_gas.map(u256_to_proto_bytes),
+        }),
+        EvalViolation::RateLimitExceeded => {
+            ProtoEvalViolationKind::RateLimitExceeded(ProtoEmpty {})
+        }
+        EvalViolation::VolumetricLimitExceeded => {
+            ProtoEvalViolationKind::VolumetricLimitExceeded(ProtoEmpty {})
+        }
+        EvalViolation::InvalidTime => ProtoEvalViolationKind::InvalidTime(ProtoEmpty {}),
+        EvalViolation::InvalidTransactionType => {
+            ProtoEvalViolationKind::InvalidTransactionType(ProtoEmpty {})
+        }
+    };
+
+    ProtoEvalViolation { kind: Some(kind) }
+}
+
+fn eval_error_to_proto(err: VetError) -> Option<TransactionEvalError> {
+    let kind = match err {
+        VetError::ContractCreationNotSupported => {
+            ProtoTransactionEvalErrorKind::ContractCreationNotSupported(ProtoEmpty {})
+        }
+        VetError::UnsupportedTransactionType => {
+            ProtoTransactionEvalErrorKind::UnsupportedTransactionType(ProtoEmpty {})
+        }
+        VetError::Evaluated(meaning, policy_error) => match policy_error {
+            PolicyError::NoMatchingGrant => {
+                ProtoTransactionEvalErrorKind::NoMatchingGrant(NoMatchingGrantError {
+                    meaning: Some(meaning_to_proto(meaning)),
+                })
+            }
+            PolicyError::Violations(violations) => {
+                ProtoTransactionEvalErrorKind::PolicyViolations(PolicyViolationsError {
+                    meaning: Some(meaning_to_proto(meaning)),
+                    violations: violations.into_iter().map(violation_to_proto).collect(),
+                })
+            }
+            PolicyError::Pool(_) | PolicyError::Database(_) => {
+                return None;
+            }
+        },
+    };
+
+    Some(TransactionEvalError { kind: Some(kind) })
+}
+
+fn decode_eip1559_transaction(payload: &[u8]) -> Result<TxEip1559, ()> {
+    let mut body = payload;
+    if let Some((prefix, rest)) = payload.split_first()
+        && *prefix == 0x02
+    {
+        body = rest;
+    }
+
+    let mut cursor = body;
+    let transaction = TxEip1559::decode(&mut cursor).map_err(|_| ())?;
+    if !cursor.is_empty() {
+        return Err(());
+    }
+
+    Ok(transaction)
+}
+
 pub struct OutOfBandAdapter(mpsc::Sender<OutOfBand>);
 
 #[async_trait]
@@ -271,6 +392,92 @@ async fn dispatch_conn_message(
                 actor.ask(HandleGrantDelete { grant_id }).await,
             ))
         }
+        UserAgentRequestPayload::EvmSignTransaction(UserAgentEvmSignTransactionRequest {
+            client_id,
+            request,
+        }) => {
+            if client_id <= 0 {
+                let _ = bi
+                    .send(Err(Status::invalid_argument("Invalid SDK client id")))
+                    .await;
+                return Err(());
+            }
+
+            let Some(request) = request else {
+                let _ = bi
+                    .send(Err(Status::invalid_argument(
+                        "Missing EVM sign transaction payload",
+                    )))
+                    .await;
+                return Err(());
+            };
+
+            let wallet_address = match <[u8; 20]>::try_from(request.wallet_address.as_slice()) {
+                Ok(address) => Address::from(address),
+                Err(_) => {
+                    let _ = bi
+                        .send(Err(Status::invalid_argument("Invalid EVM wallet address")))
+                        .await;
+                    return Err(());
+                }
+            };
+
+            let transaction = match decode_eip1559_transaction(&request.rlp_transaction) {
+                Ok(transaction) => transaction,
+                Err(()) => {
+                    let _ = bi
+                        .send(Err(Status::invalid_argument(
+                            "Invalid EIP-1559 RLP transaction",
+                        )))
+                        .await;
+                    return Err(());
+                }
+            };
+
+            let response = match actor
+                .ask(HandleSignTransaction {
+                    client_id,
+                    wallet_address,
+                    transaction,
+                })
+                .await
+            {
+                Ok(signature) => EvmSignTransactionResponse {
+                    result: Some(EvmSignTransactionResult::Signature(
+                        signature.as_bytes().to_vec(),
+                    )),
+                },
+                Err(SendError::HandlerError(SessionSignTransactionError::Vet(vet_error))) => {
+                    match eval_error_to_proto(vet_error) {
+                        Some(eval_error) => EvmSignTransactionResponse {
+                            result: Some(EvmSignTransactionResult::EvalError(eval_error)),
+                        },
+                        None => EvmSignTransactionResponse {
+                            result: Some(EvmSignTransactionResult::Error(
+                                ProtoEvmError::Internal.into(),
+                            )),
+                        },
+                    }
+                }
+                Err(SendError::HandlerError(SessionSignTransactionError::Internal)) => {
+                    EvmSignTransactionResponse {
+                        result: Some(EvmSignTransactionResult::Error(
+                            ProtoEvmError::Internal.into(),
+                        )),
+                    }
+                }
+                Err(err) => {
+                    warn!(error = ?err, "Failed to sign EVM transaction via user-agent");
+                    EvmSignTransactionResponse {
+                        result: Some(EvmSignTransactionResult::Error(
+                            ProtoEvmError::Internal.into(),
+                        )),
+                    }
+                }
+            };
+
+            UserAgentResponsePayload::EvmSignTransaction(response)
+        }
         payload => {
             warn!(?payload, "Unsupported post-auth user agent request");
             let _ = bi