diff --git a/packages/protocol/contracts/L1/libs/LibProposing.sol b/packages/protocol/contracts/L1/libs/LibProposing.sol
index 07f65619058..124d0969310 100644
--- a/packages/protocol/contracts/L1/libs/LibProposing.sol
+++ b/packages/protocol/contracts/L1/libs/LibProposing.sol
@@ -102,7 +102,7 @@ library LibProposing {
             {
                 uint256 fee;
                 (newFeeBase, fee, deposit) = getBlockFee(state, config);
-                TkoToken(resolver.resolve("tko_token")).burn(
+                TkoToken(resolver.resolve("tko_token", false)).burn(
                     msg.sender,
                     fee + deposit
                 );
diff --git a/packages/protocol/contracts/L1/libs/LibProving.sol b/packages/protocol/contracts/L1/libs/LibProving.sol
index dc384a256c3..34cc5962779 100644
--- a/packages/protocol/contracts/L1/libs/LibProving.sol
+++ b/packages/protocol/contracts/L1/libs/LibProving.sol
@@ -81,7 +81,8 @@ library LibProving {
             );
             require(_tx.txType == 0, "L1:anchor:type");
             require(
-                _tx.destination == resolver.resolve(config.chainId, "taiko"),
+                _tx.destination ==
+                    resolver.resolve(config.chainId, "taiko", false),
                 "L1:anchor:dest"
             );
             require(
@@ -107,7 +108,7 @@ library LibProving {
         }
 
         IProofVerifier proofVerifier = IProofVerifier(
-            resolver.resolve("proof_verifier")
+            resolver.resolve("proof_verifier", false)
         );
 
         // Check anchor tx is the 1st tx in the block
@@ -175,7 +176,7 @@ library LibProving {
         );
 
         IProofVerifier proofVerifier = IProofVerifier(
-            resolver.resolve("proof_verifier")
+            resolver.resolve("proof_verifier", false)
         );
 
         // Check the event is the first one in the throw-away block
@@ -200,7 +201,7 @@ library LibProving {
             LibReceiptDecoder.Log memory log = receipt.logs[0];
             require(
                 log.contractAddress ==
-                    resolver.resolve(config.chainId, "taiko"),
+                    resolver.resolve(config.chainId, "taiko", false),
                 "L1:receipt:addr"
             );
             require(log.data.length == 0, "L1:receipt:data");
@@ -249,7 +250,7 @@ library LibProving {
             require(
                 proofVerifier.verifyZKP({
                     verificationKey: ConfigManager(
-                        resolver.resolve("config_manager")
+                        resolver.resolve("config_manager", false)
                     ).getValue(string(abi.encodePacked("zk_vkey_", i))),
                     zkproof: evidence.proofs[i],
                     blockHash: blockHash,
diff --git a/packages/protocol/contracts/L1/libs/LibVerifying.sol b/packages/protocol/contracts/L1/libs/LibVerifying.sol
index d44fb4de870..2403ca310b6 100644
--- a/packages/protocol/contracts/L1/libs/LibVerifying.sol
+++ b/packages/protocol/contracts/L1/libs/LibVerifying.sol
@@ -190,7 +190,9 @@ library LibVerifying {
                     proposedAt: target.proposedAt
                 });
 
-                TkoToken tkoToken = TkoToken(resolver.resolve("tko_token"));
+                TkoToken tkoToken = TkoToken(
+                    resolver.resolve("tko_token", false)
+                );
 
                 _rewardProvers(fc, reward, tkoToken);
                 _refundProposerDeposit(target, tRelBp, tkoToken);
diff --git a/packages/protocol/contracts/bridge/Bridge.sol b/packages/protocol/contracts/bridge/Bridge.sol
index ca3c924ec99..8b4ae3b7f6b 100644
--- a/packages/protocol/contracts/bridge/Bridge.sol
+++ b/packages/protocol/contracts/bridge/Bridge.sol
@@ -14,7 +14,6 @@ import "./libs/LibBridgeData.sol";
 import "./libs/LibBridgeProcess.sol";
 import "./libs/LibBridgeRetry.sol";
 import "./libs/LibBridgeSend.sol";
-import "./libs/LibBridgeSignal.sol";
 import "./libs/LibBridgeStatus.sol";
 
 /**
@@ -39,7 +38,7 @@ contract Bridge is EssentialContract, IBridge {
      *********************/
 
     event MessageStatusChanged(
-        bytes32 indexed signal,
+        bytes32 indexed msgHash,
         LibBridgeStatus.MessageStatus status
     );
 
@@ -59,7 +58,7 @@ contract Bridge is EssentialContract, IBridge {
 
     function sendMessage(
         Message calldata message
-    ) external payable nonReentrant returns (bytes32 signal) {
+    ) external payable nonReentrant returns (bytes32 msgHash) {
         return
             LibBridgeSend.sendMessage({
                 state: state,
@@ -68,11 +67,6 @@ contract Bridge is EssentialContract, IBridge {
             });
     }
 
-    function sendSignal(bytes32 signal) external override {
-        LibBridgeSignal.sendSignal(msg.sender, signal);
-        emit SignalSent(msg.sender, signal);
-    }
-
     function processMessage(
         Message calldata message,
         bytes calldata proof
@@ -103,54 +97,28 @@ contract Bridge is EssentialContract, IBridge {
      * Public Functions  *
      *********************/
 
-    function isMessageSent(bytes32 signal) public view virtual returns (bool) {
-        return LibBridgeSignal.isSignalSent(address(this), signal);
+    function isMessageSent(bytes32 msgHash) public view virtual returns (bool) {
+        return LibBridgeSend.isMessageSent(AddressResolver(this), msgHash);
     }
 
     function isMessageReceived(
-        bytes32 signal,
-        uint256 srcChainId,
-        bytes calldata proof
-    ) public view virtual override returns (bool) {
-        address srcBridge = resolve(srcChainId, "bridge");
-        return
-            LibBridgeSignal.isSignalReceived({
-                resolver: AddressResolver(this),
-                srcBridge: srcBridge,
-                sender: srcBridge,
-                signal: signal,
-                proof: proof
-            });
-    }
-
-    function isSignalSent(
-        address sender,
-        bytes32 signal
-    ) public view virtual override returns (bool) {
-        return LibBridgeSignal.isSignalSent(sender, signal);
-    }
-
-    function isSignalReceived(
-        bytes32 signal,
+        bytes32 msgHash,
         uint256 srcChainId,
-        address sender,
         bytes calldata proof
     ) public view virtual override returns (bool) {
-        address srcBridge = resolve(srcChainId, "bridge");
         return
-            LibBridgeSignal.isSignalReceived({
+            LibBridgeSend.isMessageReceived({
                 resolver: AddressResolver(this),
-                srcBridge: srcBridge,
-                sender: sender,
-                signal: signal,
+                msgHash: msgHash,
+                srcChainId: srcChainId,
                 proof: proof
             });
     }
 
     function getMessageStatus(
-        bytes32 signal
+        bytes32 msgHash
     ) public view virtual returns (LibBridgeStatus.MessageStatus) {
-        return LibBridgeStatus.getMessageStatus(signal);
+        return LibBridgeStatus.getMessageStatus(msgHash);
     }
 
     function context() public view returns (Context memory) {
@@ -162,9 +130,13 @@ contract Bridge is EssentialContract, IBridge {
             LibBridgeSend.isDestChainEnabled(AddressResolver(this), _chainId);
     }
 
+    function hashMessage(Message memory message) public pure returns (bytes32) {
+        return LibBridgeData.hashMessage(message);
+    }
+
     function getMessageStatusSlot(
-        bytes32 signal
+        bytes32 msgHash
     ) public pure returns (bytes32) {
-        return LibBridgeStatus.getMessageStatusSlot(signal);
+        return LibBridgeStatus.getMessageStatusSlot(msgHash);
     }
 }
diff --git a/packages/protocol/contracts/bridge/IBridge.sol b/packages/protocol/contracts/bridge/IBridge.sol
index cff90965146..dc3bec40878 100644
--- a/packages/protocol/contracts/bridge/IBridge.sol
+++ b/packages/protocol/contracts/bridge/IBridge.sol
@@ -31,50 +31,30 @@ interface IBridge {
     }
 
     struct Context {
-        bytes32 signal; // messageHash
+        bytes32 msgHash; // messageHash
         address sender;
         uint256 srcChainId;
     }
 
-    event SignalSent(address sender, bytes32 signal);
+    event SignalSent(address sender, bytes32 msgHash);
 
-    event MessageSent(bytes32 indexed signal, Message message);
+    event MessageSent(bytes32 indexed msgHash, Message message);
 
     /// Sends a message to the destination chain and takes custody
     /// of Ether required in this contract. All extra Ether will be refunded.
     function sendMessage(
         Message memory message
-    ) external payable returns (bytes32 signal);
+    ) external payable returns (bytes32 msgHash);
 
-    /// Stores a signal on the bridge contract and emits an event for the
-    /// relayer to pick up.
-    function sendSignal(bytes32 signal) external;
-
-    /// Checks if a signal has been stored on the bridge contract by the
+    /// Checks if a msgHash has been stored on the bridge contract by the
     /// current address.
-    function isMessageSent(bytes32 signal) external view returns (bool);
+    function isMessageSent(bytes32 msgHash) external view returns (bool);
 
-    /// Checks if a signal has been received on the destination chain and
+    /// Checks if a msgHash has been received on the destination chain and
     /// sent by the src chain.
     function isMessageReceived(
-        bytes32 signal,
-        uint256 srcChainId,
-        bytes calldata proof
-    ) external view returns (bool);
-
-    /// Checks if a signal has been stored on the bridge contract by the
-    /// specified address.
-    function isSignalSent(
-        address sender,
-        bytes32 signal
-    ) external view returns (bool);
-
-    /// Check if a signal has been received on the destination chain and sent
-    /// by the specified sender.
-    function isSignalReceived(
-        bytes32 signal,
+        bytes32 msgHash,
         uint256 srcChainId,
-        address sender,
         bytes calldata proof
     ) external view returns (bool);
 
diff --git a/packages/protocol/contracts/bridge/TokenVault.sol b/packages/protocol/contracts/bridge/TokenVault.sol
index 3c74b349d02..f719128de31 100644
--- a/packages/protocol/contracts/bridge/TokenVault.sol
+++ b/packages/protocol/contracts/bridge/TokenVault.sol
@@ -120,7 +120,8 @@ contract TokenVault is EssentialContract {
         string memory memo
     ) external payable nonReentrant {
         require(
-            to != address(0) && to != resolve(destChainId, "token_vault"),
+            to != address(0) &&
+                to != resolve(destChainId, "token_vault", false),
             "V:to"
         );
         require(msg.value > processingFee, "V:msgValue");
@@ -138,7 +139,7 @@ contract TokenVault is EssentialContract {
 
         // Ether are held by the Bridge on L1 and by the EtherVault on L2, not
         // the TokenVault
-        bytes32 signal = IBridge(resolve("bridge")).sendMessage{
+        bytes32 signal = IBridge(resolve("bridge", false)).sendMessage{
             value: msg.value
         }(message);
 
@@ -175,7 +176,8 @@ contract TokenVault is EssentialContract {
         string memory memo
     ) external payable nonReentrant {
         require(
-            to != address(0) && to != resolve(destChainId, "token_vault"),
+            to != address(0) &&
+                to != resolve(destChainId, "token_vault", false),
             "V:to"
         );
         require(token != address(0), "V:token");
@@ -209,7 +211,7 @@ contract TokenVault is EssentialContract {
         message.destChainId = destChainId;
         message.owner = msg.sender;
 
-        message.to = resolve(destChainId, "token_vault");
+        message.to = resolve(destChainId, "token_vault", false);
         message.data = abi.encodeWithSelector(
             TokenVault.receiveERC20.selector,
             canonicalToken,
@@ -224,7 +226,7 @@ contract TokenVault is EssentialContract {
         message.refundAddress = refundAddress;
         message.memo = memo;
 
-        bytes32 signal = IBridge(resolve("bridge")).sendMessage{
+        bytes32 signal = IBridge(resolve("bridge", false)).sendMessage{
             value: msg.value
         }(message);
 
@@ -249,7 +251,7 @@ contract TokenVault is EssentialContract {
     ) external nonReentrant onlyFromNamed("bridge") {
         IBridge.Context memory ctx = IBridge(msg.sender).context();
         require(
-            ctx.sender == resolve(ctx.srcChainId, "token_vault"),
+            ctx.sender == resolve(ctx.srcChainId, "token_vault", false),
             "V:sender"
         );
 
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeData.sol b/packages/protocol/contracts/bridge/libs/LibBridgeData.sol
index b4b99b4421f..e7f50cb6a2f 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeData.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeData.sol
@@ -25,13 +25,13 @@ library LibBridgeData {
         uint256[46] __gap;
     }
 
-    bytes32 internal constant SIGNAL_PLACEHOLDER = bytes32(uint256(1));
+    bytes32 internal constant MESSAGE_HASH_PLACEHOLDER = bytes32(uint256(1));
     uint256 internal constant CHAINID_PLACEHOLDER = type(uint256).max;
     address internal constant SRC_CHAIN_SENDER_PLACEHOLDER =
-        0x0000000000000000000000000000000000000001;
+        address(uint160(uint256(1)));
 
     // Note: These events must match the ones defined in Bridge.sol.
-    event MessageSent(bytes32 indexed signal, IBridge.Message message);
+    event MessageSent(bytes32 indexed msgHash, IBridge.Message message);
 
     event DestChainEnabled(uint256 indexed chainId, bool enabled);
 
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeInvoke.sol b/packages/protocol/contracts/bridge/libs/LibBridgeInvoke.sol
index dc8539e950e..db4e09d46f9 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeInvoke.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeInvoke.sol
@@ -24,13 +24,13 @@ library LibBridgeInvoke {
     function invokeMessageCall(
         LibBridgeData.State storage state,
         IBridge.Message memory message,
-        bytes32 signal,
+        bytes32 msgHash,
         uint256 gasLimit
     ) internal returns (bool success) {
         require(gasLimit > 0, "B:gasLimit");
 
         state.ctx = IBridge.Context({
-            signal: signal,
+            msgHash: msgHash,
             sender: message.sender,
             srcChainId: message.srcChainId
         });
@@ -40,7 +40,7 @@ library LibBridgeInvoke {
         );
 
         state.ctx = IBridge.Context({
-            signal: LibBridgeData.SIGNAL_PLACEHOLDER,
+            msgHash: LibBridgeData.MESSAGE_HASH_PLACEHOLDER,
             sender: LibBridgeData.SRC_CHAIN_SENDER_PLACEHOLDER,
             srcChainId: LibBridgeData.CHAINID_PLACEHOLDER
         });
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeProcess.sol b/packages/protocol/contracts/bridge/libs/LibBridgeProcess.sol
index 4a739e12cf0..b597a2db521 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeProcess.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeProcess.sol
@@ -8,10 +8,10 @@
 // ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
 pragma solidity ^0.8.9;
 
+import "../../signal/ISignalService.sol";
 import "../EtherVault.sol";
 import "./LibBridgeData.sol";
 import "./LibBridgeInvoke.sol";
-import "./LibBridgeSignal.sol";
 import "./LibBridgeStatus.sol";
 
 /**
@@ -37,7 +37,7 @@ library LibBridgeProcess {
      * @param state The bridge state.
      * @param resolver The address resolver.
      * @param message The message to process.
-     * @param proof The proof of the signal being sent on the source chain.
+     * @param proof The msgHash proof from the source chain.
      */
     function processMessage(
         LibBridgeData.State storage state,
@@ -54,28 +54,32 @@ library LibBridgeProcess {
 
         // The status of the message must be "NEW"; RETRIABLE is handled in
         // LibBridgeRetry.sol
-        bytes32 signal = message.hashMessage();
+        bytes32 msgHash = message.hashMessage();
         require(
-            LibBridgeStatus.getMessageStatus(signal) ==
+            LibBridgeStatus.getMessageStatus(msgHash) ==
                 LibBridgeStatus.MessageStatus.NEW,
             "B:status"
         );
         // Message must have been "received" on the destChain (current chain)
-        address srcBridge = resolver.resolve(message.srcChainId, "bridge");
+        address srcBridge = resolver.resolve(
+            message.srcChainId,
+            "bridge",
+            false
+        );
 
         require(
-            LibBridgeSignal.isSignalReceived({
-                resolver: resolver,
-                srcBridge: srcBridge,
-                sender: srcBridge,
-                signal: signal,
-                proof: proof
-            }),
+            ISignalService(resolver.resolve("signal_service", false))
+                .isSignalReceived({
+                    srcChainId: message.srcChainId,
+                    app: srcBridge,
+                    signal: msgHash,
+                    proof: proof
+                }),
             "B:notReceived"
         );
 
         // We retrieve the necessary ether from EtherVault
-        address ethVault = resolver.resolve("ether_vault");
+        address ethVault = resolver.resolve("ether_vault", false);
         if (ethVault != address(0)) {
             EtherVault(payable(ethVault)).receiveEther(
                 message.depositValue + message.callValue + message.processingFee
@@ -101,7 +105,7 @@ library LibBridgeProcess {
             bool success = LibBridgeInvoke.invokeMessageCall({
                 state: state,
                 message: message,
-                signal: signal,
+                msgHash: msgHash,
                 gasLimit: gasLimit
             });
 
@@ -115,7 +119,7 @@ library LibBridgeProcess {
             }
         }
 
-        LibBridgeStatus.updateMessageStatus(signal, status);
+        LibBridgeStatus.updateMessageStatus(msgHash, status);
 
         address refundAddress = message.refundAddress == address(0)
             ? message.owner
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeRetry.sol b/packages/protocol/contracts/bridge/libs/LibBridgeRetry.sol
index c84890b4ebb..636bf672ff3 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeRetry.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeRetry.sol
@@ -49,14 +49,14 @@ library LibBridgeRetry {
             require(msg.sender == message.owner, "B:denied");
         }
 
-        bytes32 signal = message.hashMessage();
+        bytes32 msgHash = message.hashMessage();
         require(
-            LibBridgeStatus.getMessageStatus(signal) ==
+            LibBridgeStatus.getMessageStatus(msgHash) ==
                 LibBridgeStatus.MessageStatus.RETRIABLE,
             "B:notFound"
         );
 
-        address ethVault = resolver.resolve("ether_vault");
+        address ethVault = resolver.resolve("ether_vault", true);
         if (ethVault != address(0)) {
             EtherVault(payable(ethVault)).receiveEther(message.callValue);
         }
@@ -66,17 +66,17 @@ library LibBridgeRetry {
             LibBridgeInvoke.invokeMessageCall({
                 state: state,
                 message: message,
-                signal: signal,
+                msgHash: msgHash,
                 gasLimit: gasleft()
             })
         ) {
             LibBridgeStatus.updateMessageStatus(
-                signal,
+                msgHash,
                 LibBridgeStatus.MessageStatus.DONE
             );
         } else if (isLastAttempt) {
             LibBridgeStatus.updateMessageStatus(
-                signal,
+                msgHash,
                 LibBridgeStatus.MessageStatus.FAILED
             );
 
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeSend.sol b/packages/protocol/contracts/bridge/libs/LibBridgeSend.sol
index b237b39cb2a..916cbbbcf9e 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeSend.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeSend.sol
@@ -8,8 +8,8 @@
 // ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
 pragma solidity ^0.8.9;
 
+import "../../signal/ISignalService.sol";
 import "./LibBridgeData.sol";
-import "./LibBridgeSignal.sol";
 
 /**
  * Entry point for starting a bridge transaction.
@@ -29,7 +29,7 @@ library LibBridgeSend {
      * `destChainId` which must have a `bridge` address set on the
      * AddressResolver and differ from the current chain ID.
      *
-     * @return signal The message is hashed, stored, and emitted as a signal.
+     * @return msgHash The hash of message sent.
      * This is picked up by an off-chain relayer which indicates a
      * bridge message has been sent and is ready to be processed on the
      * destination chain.
@@ -38,7 +38,7 @@ library LibBridgeSend {
         LibBridgeData.State storage state,
         AddressResolver resolver,
         IBridge.Message memory message
-    ) internal returns (bytes32 signal) {
+    ) internal returns (bytes32 msgHash) {
         require(message.owner != address(0), "B:owner");
         require(
             message.destChainId != block.chainid &&
@@ -53,7 +53,7 @@ library LibBridgeSend {
 
         // For each message, expectedAmount is sent to ethVault to be handled.
         // Processing will retrieve these funds directly from ethVault.
-        address ethVault = resolver.resolve("ether_vault");
+        address ethVault = resolver.resolve("ether_vault", true);
         if (ethVault != address(0)) {
             ethVault.sendEther(expectedAmount);
         }
@@ -62,17 +62,45 @@ library LibBridgeSend {
         message.sender = msg.sender;
         message.srcChainId = block.chainid;
 
-        signal = message.hashMessage();
+        msgHash = message.hashMessage();
         // Store a key which is the hash of this contract address and the
-        // signal, with a value of 1.
-        LibBridgeSignal.sendSignal(address(this), signal);
-        emit LibBridgeData.MessageSent(signal, message);
+        // msgHash, with a value of 1.
+        ISignalService(resolver.resolve("signal_service", false)).sendSignal(
+            msgHash
+        );
+        emit LibBridgeData.MessageSent(msgHash, message);
     }
 
     function isDestChainEnabled(
         AddressResolver resolver,
         uint256 chainId
     ) internal view returns (bool) {
-        return resolver.resolve(chainId, "bridge") != address(0);
+        return resolver.resolve(chainId, "bridge", true) != address(0);
+    }
+
+    function isMessageSent(
+        AddressResolver resolver,
+        bytes32 msgHash
+    ) internal view returns (bool) {
+        return
+            ISignalService(resolver.resolve("signal_service", false))
+                .isSignalSent({app: address(this), signal: msgHash});
+    }
+
+    function isMessageReceived(
+        AddressResolver resolver,
+        bytes32 msgHash,
+        uint256 srcChainId,
+        bytes calldata proof
+    ) internal view returns (bool) {
+        address srcBridge = resolver.resolve(srcChainId, "bridge", false);
+        return
+            ISignalService(resolver.resolve("signal_service", false))
+                .isSignalReceived({
+                    srcChainId: srcChainId,
+                    app: srcBridge,
+                    signal: msgHash,
+                    proof: proof
+                });
     }
 }
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeSignal.sol b/packages/protocol/contracts/bridge/libs/LibBridgeSignal.sol
deleted file mode 100644
index abc70768b25..00000000000
--- a/packages/protocol/contracts/bridge/libs/LibBridgeSignal.sol
+++ /dev/null
@@ -1,115 +0,0 @@
-// SPDX-License-Identifier: MIT
-//
-// ╭━━━━╮╱╱╭╮╱╱╱╱╱╭╮╱╱╱╱╱╭╮
-// ┃╭╮╭╮┃╱╱┃┃╱╱╱╱╱┃┃╱╱╱╱╱┃┃
-// ╰╯┃┃┣┻━┳┫┃╭┳━━╮┃┃╱╱╭━━┫╰━┳━━╮
-// ╱╱┃┃┃╭╮┣┫╰╯┫╭╮┃┃┃╱╭┫╭╮┃╭╮┃━━┫
-// ╱╱┃┃┃╭╮┃┃╭╮┫╰╯┃┃╰━╯┃╭╮┃╰╯┣━━┃
-// ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
-pragma solidity ^0.8.9;
-
-import "../../common/AddressResolver.sol";
-import "../../common/IHeaderSync.sol";
-import "../../libs/LibBlockHeader.sol";
-import "../../libs/LibTrieProof.sol";
-import "./LibBridgeData.sol";
-import "./LibBridgeStatus.sol";
-
-/**
- * Library for working with bridge signals.
- *
- * @title LibBridgeSignal
- * @author dantaik <dan@taiko.xyz>
- */
-library LibBridgeSignal {
-    using LibBlockHeader for BlockHeader;
-
-    struct SignalProof {
-        BlockHeader header;
-        bytes proof;
-    }
-
-    modifier onlyValidSenderAndSignal(address sender, bytes32 signal) {
-        require(sender != address(0), "B:sender");
-        require(signal != 0, "B:signal");
-        _;
-    }
-
-    /**
-     * Send a signal by storing the key with a value of 1.
-     *
-     * @param sender The address sending the signal.
-     * @param signal The signal to send.
-     */
-    function sendSignal(
-        address sender,
-        bytes32 signal
-    ) internal onlyValidSenderAndSignal(sender, signal) {
-        bytes32 k = _signalSlot(sender, signal);
-        assembly {
-            sstore(k, 1)
-        }
-    }
-
-    /**
-     * Check if a signal has been sent (key stored with a value of 1).
-     *
-     * @param sender The sender of the signal.
-     * @param signal The signal to check.
-     */
-    function isSignalSent(
-        address sender,
-        bytes32 signal
-    ) internal view onlyValidSenderAndSignal(sender, signal) returns (bool) {
-        bytes32 k = _signalSlot(sender, signal);
-        uint256 v;
-        assembly {
-            v := sload(k)
-        }
-        return v == 1;
-    }
-
-    /**
-     * Check if signal has been received on the destination chain (current).
-     *
-     * @param resolver The address resolver.
-     * @param srcBridge Address of the source bridge where the bridge
-     *                  was initiated.
-     * @param sender Address of the sender of the signal
-     *               (also should be srcBridge).
-     * @param signal The signal to check.
-     * @param proof The proof of the signal being sent on the source chain.
-     */
-    function isSignalReceived(
-        AddressResolver resolver,
-        address srcBridge,
-        address sender,
-        bytes32 signal,
-        bytes calldata proof
-    ) internal view onlyValidSenderAndSignal(sender, signal) returns (bool) {
-        require(srcBridge != address(0), "B:srcBridge");
-
-        SignalProof memory sp = abi.decode(proof, (SignalProof));
-        LibTrieProof.verify({
-            stateRoot: sp.header.stateRoot,
-            addr: srcBridge,
-            key: _signalSlot(sender, signal),
-            value: bytes32(uint256(1)),
-            mkproof: sp.proof
-        });
-        // get synced header hash of the header height specified in the proof
-        bytes32 syncedHeaderHash = IHeaderSync(resolver.resolve("taiko"))
-            .getSyncedHeader(sp.header.height);
-        // check header hash specified in the proof matches the current chain
-        return
-            syncedHeaderHash != 0 &&
-            syncedHeaderHash == sp.header.hashBlockHeader();
-    }
-
-    function _signalSlot(
-        address sender,
-        bytes32 signal
-    ) private pure returns (bytes32) {
-        return keccak256(abi.encodePacked("SIGNAL", sender, signal));
-    }
-}
diff --git a/packages/protocol/contracts/bridge/libs/LibBridgeStatus.sol b/packages/protocol/contracts/bridge/libs/LibBridgeStatus.sol
index 1fd3b2d5a80..5a73f40930e 100644
--- a/packages/protocol/contracts/bridge/libs/LibBridgeStatus.sol
+++ b/packages/protocol/contracts/bridge/libs/LibBridgeStatus.sol
@@ -19,28 +19,28 @@ library LibBridgeStatus {
         FAILED
     }
 
-    event MessageStatusChanged(bytes32 indexed signal, MessageStatus status);
+    event MessageStatusChanged(bytes32 indexed msgHash, MessageStatus status);
 
     /**
      * @dev If messageStatus is same as in the messageStatus mapping,
      *      does nothing.
-     * @param signal The messageHash of the message.
+     * @param msgHash The messageHash of the message.
      * @param status The status of the message.
      */
     function updateMessageStatus(
-        bytes32 signal,
+        bytes32 msgHash,
         MessageStatus status
     ) internal {
-        if (getMessageStatus(signal) != status) {
-            _setMessageStatus(signal, status);
-            emit LibBridgeStatus.MessageStatusChanged(signal, status);
+        if (getMessageStatus(msgHash) != status) {
+            _setMessageStatus(msgHash, status);
+            emit LibBridgeStatus.MessageStatusChanged(msgHash, status);
         }
     }
 
     function getMessageStatus(
-        bytes32 signal
+        bytes32 msgHash
     ) internal view returns (MessageStatus) {
-        bytes32 slot = getMessageStatusSlot(signal);
+        bytes32 slot = getMessageStatusSlot(msgHash);
         uint256 value;
         assembly {
             value := sload(slot)
@@ -49,13 +49,13 @@ library LibBridgeStatus {
     }
 
     function getMessageStatusSlot(
-        bytes32 signal
+        bytes32 msgHash
     ) internal pure returns (bytes32) {
-        return keccak256(abi.encodePacked("MESSAGE_STATUS", signal));
+        return keccak256(abi.encodePacked("MESSAGE_STATUS", msgHash));
     }
 
-    function _setMessageStatus(bytes32 signal, MessageStatus status) private {
-        bytes32 slot = getMessageStatusSlot(signal);
+    function _setMessageStatus(bytes32 msgHash, MessageStatus status) private {
+        bytes32 slot = getMessageStatusSlot(msgHash);
         uint256 value = uint256(status);
         assembly {
             sstore(slot, value)
diff --git a/packages/protocol/contracts/common/AddressResolver.sol b/packages/protocol/contracts/common/AddressResolver.sol
index 24a6d01e926..1f6783f9ff6 100644
--- a/packages/protocol/contracts/common/AddressResolver.sol
+++ b/packages/protocol/contracts/common/AddressResolver.sol
@@ -9,7 +9,6 @@
 pragma solidity ^0.8.9;
 
 import "@openzeppelin/contracts/utils/Strings.sol";
-
 import "./IAddressManager.sol";
 
 /**
@@ -25,15 +24,7 @@ abstract contract AddressResolver {
     uint256[49] private __gap;
 
     modifier onlyFromNamed(string memory name) {
-        require(msg.sender == resolve(name), "AR:denied");
-        _;
-    }
-
-    modifier onlyFromNamedEither(string memory name1, string memory name2) {
-        require(
-            msg.sender == resolve(name1) || msg.sender == resolve(name2),
-            "AR:denied"
-        );
+        require(msg.sender == resolve(name, false), "AR:denied");
         _;
     }
 
@@ -42,12 +33,14 @@ abstract contract AddressResolver {
      *
      * @dev This function will throw if the resolved address is `address(0)`.
      * @param name The name to resolve.
+     * @param allowZeroAddress True to allow zero address to be returned.
      * @return The name's corresponding address.
      */
     function resolve(
-        string memory name
+        string memory name,
+        bool allowZeroAddress
     ) public view virtual returns (address payable) {
-        return _resolve(block.chainid, name);
+        return _resolve(block.chainid, name, allowZeroAddress);
     }
 
     /**
@@ -56,13 +49,15 @@ abstract contract AddressResolver {
      * @dev This function will throw if the resolved address is `address(0)`.
      * @param chainId The chainId.
      * @param name The name to resolve.
+     * @param allowZeroAddress True to allow zero address to be returned.
      * @return The name's corresponding address.
      */
     function resolve(
         uint256 chainId,
-        string memory name
+        string memory name,
+        bool allowZeroAddress
     ) public view virtual returns (address payable) {
-        return _resolve(chainId, name);
+        return _resolve(chainId, name, allowZeroAddress);
     }
 
     /**
@@ -81,13 +76,20 @@ abstract contract AddressResolver {
 
     function _resolve(
         uint256 chainId,
-        string memory name
-    ) private view returns (address payable) {
+        string memory name,
+        bool allowZeroAddress
+    ) private view returns (address payable addr) {
         bytes memory key = abi.encodePacked(
             Strings.toString(chainId),
             ".",
             name
         );
-        return payable(_addressManager.getAddress(string(key)));
+        addr = payable(_addressManager.getAddress(string(key)));
+        if (!allowZeroAddress) {
+            require(
+                addr != address(0),
+                string(abi.encodePacked("AR:zeroAddr:", key))
+            );
+        }
     }
 }
diff --git a/packages/protocol/contracts/libs/LibTrieProof.sol b/packages/protocol/contracts/libs/LibTrieProof.sol
index aa2c04f4a40..d786963fe77 100644
--- a/packages/protocol/contracts/libs/LibTrieProof.sol
+++ b/packages/protocol/contracts/libs/LibTrieProof.sol
@@ -30,23 +30,24 @@ library LibTrieProof {
      *********************/
 
     /**
-     * Verifies that the value of a slot `key` in the storage tree of `addr`
+     * Verifies that the value of a slot in the storage tree of `addr`
      * is `value`.
      *
      * @param stateRoot The merkle root of state tree.
      * @param addr The contract address.
-     * @param key The slot in the contract.
+     * @param slot The slot in the contract.
      * @param value The value to be verified.
      * @param mkproof The proof obtained by encoding state proof and storage
      *        proof.
+     * @return verified The verification result.
      */
     function verify(
         bytes32 stateRoot,
         address addr,
-        bytes32 key,
+        bytes32 slot,
         bytes32 value,
         bytes calldata mkproof
-    ) public pure {
+    ) public pure returns (bool verified) {
         (bytes memory accountProof, bytes memory storageProof) = abi.decode(
             mkproof,
             (bytes, bytes)
@@ -67,13 +68,11 @@ library LibTrieProof {
             accountState[ACCOUNT_FIELD_INDEX_STORAGE_HASH]
         );
 
-        bool verified = LibSecureMerkleTrie.verifyInclusionProof(
-            abi.encodePacked(key),
+        verified = LibSecureMerkleTrie.verifyInclusionProof(
+            abi.encodePacked(slot),
             LibRLPWriter.writeBytes32(value),
             storageProof,
             storageRoot
         );
-
-        require(verified, "LTP:invalid storage proof");
     }
 }
diff --git a/packages/protocol/contracts/signal/ISignalService.sol b/packages/protocol/contracts/signal/ISignalService.sol
new file mode 100644
index 00000000000..492984ac2e0
--- /dev/null
+++ b/packages/protocol/contracts/signal/ISignalService.sol
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+//
+// ╭━━━━╮╱╱╭╮╱╱╱╱╱╭╮╱╱╱╱╱╭╮
+// ┃╭╮╭╮┃╱╱┃┃╱╱╱╱╱┃┃╱╱╱╱╱┃┃
+// ╰╯┃┃┣┻━┳┫┃╭┳━━╮┃┃╱╱╭━━┫╰━┳━━╮
+// ╱╱┃┃┃╭╮┣┫╰╯┫╭╮┃┃┃╱╭┫╭╮┃╭╮┃━━┫
+// ╱╱┃┃┃╭╮┃┃╭╮┫╰╯┃┃╰━╯┃╭╮┃╰╯┣━━┃
+// ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
+pragma solidity ^0.8.9;
+
+interface ISignalService {
+    /**
+     * Send a signal by storing the key with a value of 1.
+     *
+     * @param signal The signal to send.
+     * @return storageSlot The slot in storage that this signal is persisted.
+     */
+    function sendSignal(bytes32 signal) external returns (bytes32 storageSlot);
+
+    /**
+     * Check if a signal has been sent (key stored with a value of 1).
+     *
+     * @param app The address that sent this message.
+     * @param signal The signal to check.
+     */
+    function isSignalSent(
+        address app,
+        bytes32 signal
+    ) external view returns (bool);
+
+    /**
+     * Check if signal has been received on the destination chain (current).
+     *
+     * @param srcChainId The source chain ID.
+     * @param app The address that sent this message.
+     * @param signal The signal to check.
+     * @param proof The proof of the signal being sent on the source chain.
+     */
+    function isSignalReceived(
+        uint256 srcChainId,
+        address app,
+        bytes32 signal,
+        bytes calldata proof
+    ) external view returns (bool);
+}
diff --git a/packages/protocol/contracts/signal/SignalService.sol b/packages/protocol/contracts/signal/SignalService.sol
new file mode 100644
index 00000000000..5d7c9802418
--- /dev/null
+++ b/packages/protocol/contracts/signal/SignalService.sol
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: MIT
+//
+// ╭━━━━╮╱╱╭╮╱╱╱╱╱╭╮╱╱╱╱╱╭╮
+// ┃╭╮╭╮┃╱╱┃┃╱╱╱╱╱┃┃╱╱╱╱╱┃┃
+// ╰╯┃┃┣┻━┳┫┃╭┳━━╮┃┃╱╱╭━━┫╰━┳━━╮
+// ╱╱┃┃┃╭╮┣┫╰╯┫╭╮┃┃┃╱╭┫╭╮┃╭╮┃━━┫
+// ╱╱┃┃┃╭╮┃┃╭╮┫╰╯┃┃╰━╯┃╭╮┃╰╯┣━━┃
+// ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
+pragma solidity ^0.8.9;
+
+import "../common/EssentialContract.sol";
+import "../common/IHeaderSync.sol";
+import "../libs/LibBlockHeader.sol";
+import "../libs/LibTrieProof.sol";
+import "./ISignalService.sol";
+
+contract SignalService is ISignalService, EssentialContract {
+    using LibBlockHeader for BlockHeader;
+
+    struct SignalProof {
+        BlockHeader header;
+        bytes proof;
+    }
+
+    /// @dev Initializer to be called after being deployed behind a proxy.
+    function init(address _addressManager) external initializer {
+        EssentialContract._init(_addressManager);
+    }
+
+    function sendSignal(bytes32 signal) public returns (bytes32 storageSlot) {
+        require(signal != 0, "B:signal");
+
+        storageSlot = getSignalSlot(msg.sender, signal);
+        assembly {
+            sstore(storageSlot, 1)
+        }
+    }
+
+    function isSignalSent(
+        address app,
+        bytes32 signal
+    ) public view returns (bool) {
+        require(app != address(0), "B:app");
+        require(signal != 0, "B:signal");
+
+        bytes32 slot = getSignalSlot(app, signal);
+        uint256 value;
+        assembly {
+            value := sload(slot)
+        }
+        return value == 1;
+    }
+
+    function isSignalReceived(
+        uint256 srcChainId,
+        address app,
+        bytes32 signal,
+        bytes calldata proof
+    ) public view returns (bool) {
+        require(srcChainId != block.chainid, "B:srcChainId");
+        require(app != address(0), "B:app");
+        require(signal != 0, "B:signal");
+
+        SignalProof memory sp = abi.decode(proof, (SignalProof));
+        bytes32 syncedHeaderHash = IHeaderSync(resolve("taiko", false))
+            .getSyncedHeader(sp.header.height);
+
+        if (
+            syncedHeaderHash == 0 ||
+            syncedHeaderHash != sp.header.hashBlockHeader()
+        ) {
+            return false;
+        }
+
+        return
+            LibTrieProof.verify({
+                stateRoot: sp.header.stateRoot,
+                addr: resolve(srcChainId, "signal_service", false),
+                slot: getSignalSlot(app, signal),
+                value: bytes32(uint256(1)),
+                mkproof: sp.proof
+            });
+    }
+
+    function getSignalSlot(
+        address app,
+        bytes32 signal
+    ) public pure returns (bytes32) {
+        return keccak256(abi.encodePacked(app, signal));
+    }
+}
diff --git a/packages/protocol/contracts/test/bridge/TestHeaderSync.sol b/packages/protocol/contracts/test/bridge/TestHeaderSync.sol
index e48f34af138..2c4c90367e7 100644
--- a/packages/protocol/contracts/test/bridge/TestHeaderSync.sol
+++ b/packages/protocol/contracts/test/bridge/TestHeaderSync.sol
@@ -10,6 +10,8 @@ pragma solidity ^0.8.9;
 
 import "../../common/IHeaderSync.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestHeaderSync is IHeaderSync {
     bytes32 public headerHash;
 
diff --git a/packages/protocol/contracts/test/bridge/libs/TestBadReceiver.sol b/packages/protocol/contracts/test/bridge/libs/TestBadReceiver.sol
index 2a050934a03..873708a7ef2 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestBadReceiver.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestBadReceiver.sol
@@ -8,6 +8,7 @@
 // ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
 pragma solidity ^0.8.9;
 
+// TODO(roger): Merge this file into TestReceiver.sol.
 contract TestBadReceiver {
     receive() external payable {
         revert("can not send to this contract");
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeData.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeData.sol
index b0fc7ad9ba2..320f24e565a 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeData.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeData.sol
@@ -11,6 +11,8 @@ pragma solidity ^0.8.9;
 import "../../../bridge/libs/LibBridgeData.sol";
 import "../../../bridge/libs/LibBridgeStatus.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestLibBridgeData {
     function updateMessageStatus(
         bytes32 signal,
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeInvoke.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeInvoke.sol
index abc17f426e5..2b640758b54 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeInvoke.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeInvoke.sol
@@ -10,6 +10,8 @@ pragma solidity ^0.8.9;
 
 import "../../../bridge/libs/LibBridgeInvoke.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestLibBridgeInvoke {
     LibBridgeData.State public state;
 
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeProcess.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeProcess.sol
index 176bfe3c358..6714526f7fa 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeProcess.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeProcess.sol
@@ -11,6 +11,8 @@ pragma solidity ^0.8.9;
 import "../../../common/EssentialContract.sol";
 import "../../../bridge/libs/LibBridgeProcess.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestLibBridgeProcess is EssentialContract {
     LibBridgeData.State public state;
 
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeRetry.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeRetry.sol
index 8de54c2eaf5..03b8b577ca9 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeRetry.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeRetry.sol
@@ -12,6 +12,8 @@ import "../../../common/EssentialContract.sol";
 import "../../../bridge/libs/LibBridgeData.sol";
 import "../../../bridge/libs/LibBridgeRetry.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestLibBridgeRetry is EssentialContract {
     LibBridgeData.State public state;
 
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSend.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSend.sol
index a9b21c2b83f..19cb4268931 100644
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSend.sol
+++ b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSend.sol
@@ -11,6 +11,8 @@ pragma solidity ^0.8.9;
 import "../../../common/EssentialContract.sol";
 import "../../../bridge/libs/LibBridgeSend.sol";
 
+// TODO(roger): remove this file. If you need extra functionality in
+// the Bridge contract, create a TestBridge.sol contract instead.
 contract TestLibBridgeSend is EssentialContract {
     LibBridgeData.State public state;
 
diff --git a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSignal.sol b/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSignal.sol
deleted file mode 100644
index 8c8e4a590e8..00000000000
--- a/packages/protocol/contracts/test/bridge/libs/TestLibBridgeSignal.sol
+++ /dev/null
@@ -1,25 +0,0 @@
-// SPDX-License-Identifier: MIT
-//
-// ╭━━━━╮╱╱╭╮╱╱╱╱╱╭╮╱╱╱╱╱╭╮
-// ┃╭╮╭╮┃╱╱┃┃╱╱╱╱╱┃┃╱╱╱╱╱┃┃
-// ╰╯┃┃┣┻━┳┫┃╭┳━━╮┃┃╱╱╭━━┫╰━┳━━╮
-// ╱╱┃┃┃╭╮┣┫╰╯┫╭╮┃┃┃╱╭┫╭╮┃╭╮┃━━┫
-// ╱╱┃┃┃╭╮┃┃╭╮┫╰╯┃┃╰━╯┃╭╮┃╰╯┣━━┃
-// ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
-pragma solidity ^0.8.9;
-
-import "../../../bridge/libs/LibBridgeData.sol";
-import "../../../bridge/libs/LibBridgeSignal.sol";
-
-contract TestLibBridgeSignal {
-    function sendSignal(address sender, bytes32 signal) public {
-        LibBridgeSignal.sendSignal(sender, signal);
-    }
-
-    function isSignalSent(
-        address sender,
-        bytes32 signal
-    ) public view returns (bool) {
-        return LibBridgeSignal.isSignalSent(sender, signal);
-    }
-}
diff --git a/packages/protocol/contracts/test/libs/TestLibTrieProof.sol b/packages/protocol/contracts/test/libs/TestLibTrieProof.sol
index 7cb94f91ca8..c4e987ef4bf 100644
--- a/packages/protocol/contracts/test/libs/TestLibTrieProof.sol
+++ b/packages/protocol/contracts/test/libs/TestLibTrieProof.sol
@@ -11,13 +11,19 @@ pragma solidity ^0.8.9;
 import "../../libs/LibTrieProof.sol";
 
 contract TestLibTrieProof {
+    function writeStorageAt(bytes32 slot, bytes32 val) public {
+        assembly {
+            sstore(slot, val)
+        }
+    }
+
     function verify(
         bytes32 stateRoot,
         address addr,
-        bytes32 key,
+        bytes32 slot,
         bytes32 value,
         bytes calldata mkproof
-    ) public pure {
-        LibTrieProof.verify(stateRoot, addr, key, value, mkproof);
+    ) public pure returns (bool) {
+        return LibTrieProof.verify(stateRoot, addr, slot, value, mkproof);
     }
 }
diff --git a/packages/protocol/tasks/deploy_L1.ts b/packages/protocol/tasks/deploy_L1.ts
index ecca9458826..19d93f10570 100644
--- a/packages/protocol/tasks/deploy_L1.ts
+++ b/packages/protocol/tasks/deploy_L1.ts
@@ -184,6 +184,18 @@ export async function deployContracts(hre: any) {
         );
     }
 
+    // SignalService
+    const SignalService = await deploySignalSerive(hre, AddressManager.address);
+
+    // Used by Bridge
+    await utils.waitTx(
+        hre,
+        await AddressManager.setAddress(
+            `${chainId}.signal_service`,
+            SignalService.address
+        )
+    );
+
     // save deployments
     const deployments = {
         network,
@@ -195,6 +207,7 @@ export async function deployContracts(hre: any) {
             { TkoToken: TkoToken.address },
             { TaikoL1: TaikoL1.address },
             { Bridge: Bridge.address },
+            { SignalService: SignalService.address },
             { TokenVault: TokenVault.address }
         ),
     };
@@ -227,18 +240,13 @@ async function deployBaseLibs(hre: any) {
 }
 
 async function deployBridge(hre: any, addressManager: string): Promise<any> {
-    const libTrieProof = await utils.deployContract(hre, "LibTrieProof");
     const libBridgeRetry = await utils.deployContract(hre, "LibBridgeRetry");
     const libBridgeProcess = await utils.deployContract(
         hre,
-        "LibBridgeProcess",
-        {
-            LibTrieProof: libTrieProof.address,
-        }
+        "LibBridgeProcess"
     );
 
     const Bridge = await utils.deployContract(hre, "Bridge", {
-        LibTrieProof: libTrieProof.address,
         LibBridgeRetry: libBridgeRetry.address,
         LibBridgeProcess: libBridgeProcess.address,
     });
@@ -258,3 +266,18 @@ async function deployTokenVault(
 
     return TokenVault;
 }
+
+async function deploySignalSerive(
+    hre: any,
+    addressManager: string
+): Promise<any> {
+    const libTrieProof = await utils.deployContract(hre, "LibTrieProof");
+
+    const SignalService = await utils.deployContract(hre, "SignalService", {
+        LibTrieProof: libTrieProof.address,
+    });
+
+    await utils.waitTx(hre, await SignalService.init(addressManager));
+
+    return SignalService;
+}
diff --git a/packages/protocol/test/bridge/Bridge.integration.test.ts b/packages/protocol/test/bridge/Bridge.integration.test.ts
index 983f717bcda..3f3642b1548 100644
--- a/packages/protocol/test/bridge/Bridge.integration.test.ts
+++ b/packages/protocol/test/bridge/Bridge.integration.test.ts
@@ -4,8 +4,8 @@ import hre, { ethers } from "hardhat";
 import {
     AddressManager,
     Bridge,
+    SignalService,
     TestHeaderSync,
-    TestLibBridgeData,
 } from "../../typechain";
 import deployAddressManager from "../utils/addressManager";
 import {
@@ -14,11 +14,11 @@ import {
     sendAndProcessMessage,
     sendMessage,
 } from "../utils/bridge";
-import { randomBytes32 } from "../utils/bytes";
+// import { randomBytes32 } from "../utils/bytes";
 import { Message } from "../utils/message";
 import { getDefaultL2Signer, getL2Provider } from "../utils/provider";
 import { Block, getBlockHeader } from "../utils/rpc";
-import { getSignalProof, getSignalSlot } from "../utils/signal";
+import { deploySignalService, getSignalProof } from "../utils/signal";
 
 describe("integration:Bridge", function () {
     let owner: any;
@@ -27,6 +27,8 @@ describe("integration:Bridge", function () {
     let srcChainId: number;
     let enabledDestChainId: number;
     let l2NonOwner: ethersLib.Signer;
+    let l1SignalService: SignalService;
+    let l2SignalService: SignalService;
     let l1Bridge: Bridge;
     let l2Bridge: Bridge;
     let m: Message;
@@ -58,17 +60,37 @@ describe("integration:Bridge", function () {
             l2Signer
         );
 
+        ({ signalService: l1SignalService } = await deploySignalService(
+            owner,
+            addressManager,
+            srcChainId
+        ));
+
+        ({ signalService: l2SignalService } = await deploySignalService(
+            l2Signer,
+            l2AddressManager,
+            enabledDestChainId
+        ));
+
+        await addressManager.setAddress(
+            `${enabledDestChainId}.signal_service`,
+            l2SignalService.address
+        );
+
+        await l2AddressManager.setAddress(
+            `${srcChainId}.signal_service`,
+            l1SignalService.address
+        );
+
         ({ bridge: l1Bridge } = await deployBridge(
             owner,
             addressManager,
-            enabledDestChainId,
             srcChainId
         ));
 
         ({ bridge: l2Bridge } = await deployBridge(
             l2Signer,
             l2AddressManager,
-            srcChainId,
             enabledDestChainId
         ));
 
@@ -156,6 +178,7 @@ describe("integration:Bridge", function () {
                 hre.ethers.provider,
                 headerSync,
                 m,
+                l1SignalService,
                 l1Bridge,
                 l2Bridge
             );
@@ -167,15 +190,7 @@ describe("integration:Bridge", function () {
         });
 
         it("should throw if message signalproof is not valid", async function () {
-            const libData: TestLibBridgeData = await (
-                await ethers.getContractFactory("TestLibBridgeData")
-            ).deploy();
-
-            const signal = await libData.hashMessage(m);
-
-            const sender = l1Bridge.address;
-
-            const key = getSignalSlot(sender, signal);
+            const msgHash = await l1Bridge.hashMessage(m);
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
             );
@@ -184,40 +199,40 @@ describe("integration:Bridge", function () {
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                await l1SignalService.getSignalSlot(l1Bridge.address, msgHash),
                 block.number,
                 blockHeader
             );
 
             await expect(
                 l2Bridge.processMessage(m, signalProof)
-            ).to.be.revertedWith("LTP:invalid storage proof");
+            ).to.be.revertedWith("B:notReceived");
         });
 
         it("should throw if message has not been received", async function () {
-            const { signal, message } = await sendMessage(l1Bridge, m);
+            const { msgHash, message } = await sendMessage(l1Bridge, m);
 
-            expect(signal).not.to.be.eq(ethers.constants.HashZero);
+            expect(msgHash).not.to.be.eq(ethers.constants.HashZero);
 
-            const messageStatus = await l1Bridge.getMessageStatus(signal);
+            const messageStatus = await l1Bridge.getMessageStatus(msgHash);
 
             expect(messageStatus).to.be.eq(0);
 
             const sender = l1Bridge.address;
 
-            const key = getSignalSlot(sender, signal);
-
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
             );
 
             await headerSync.setSyncedHeader(ethers.constants.HashZero);
 
+            const slot = await l1SignalService.getSignalSlot(sender, msgHash);
+
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number
             );
             // make sure it equals 1 so our proof will pass
@@ -227,8 +242,8 @@ describe("integration:Bridge", function () {
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number,
                 blockHeader
             );
@@ -239,31 +254,30 @@ describe("integration:Bridge", function () {
         });
 
         it("processes a message when the signal has been verified from the sending chain", async () => {
-            const { signal, message } = await sendMessage(l1Bridge, m);
+            const { msgHash, message } = await sendMessage(l1Bridge, m);
 
-            expect(signal).not.to.be.eq(ethers.constants.HashZero);
+            expect(msgHash).not.to.be.eq(ethers.constants.HashZero);
 
-            const messageStatus = await l1Bridge.getMessageStatus(signal);
+            const messageStatus = await l1Bridge.getMessageStatus(msgHash);
 
             expect(messageStatus).to.be.eq(0);
             let block: Block;
             expect(
                 ({ block } = await processMessage(
+                    l1SignalService,
                     l1Bridge,
                     l2Bridge,
-                    signal,
+                    msgHash,
                     hre.ethers.provider,
                     headerSync,
                     message
                 ))
             ).to.emit(l2Bridge, "MessageStatusChanged");
 
-            const key = getSignalSlot(l1Bridge.address, signal);
-
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                await l1SignalService.getSignalSlot(l1Bridge.address, msgHash),
                 block.number
             );
             // make sure it equals 1 so our proof will pass
@@ -275,34 +289,31 @@ describe("integration:Bridge", function () {
 
     describe("isMessageSent()", function () {
         it("should return false, since no message was sent", async function () {
-            const libData = await (
-                await ethers.getContractFactory("TestLibBridgeData")
-            ).deploy();
-            const signal = await libData.hashMessage(m);
+            const msgHash = await l1Bridge.hashMessage(m);
 
-            expect(await l1Bridge.isMessageSent(signal)).to.be.eq(false);
+            expect(await l1Bridge.isMessageSent(msgHash)).to.be.eq(false);
         });
 
         it("should return true if message was sent properly", async function () {
-            const { signal } = await sendMessage(l1Bridge, m);
+            const { msgHash } = await sendMessage(l1Bridge, m);
 
-            expect(signal).not.to.be.eq(ethers.constants.HashZero);
+            expect(msgHash).not.to.be.eq(ethers.constants.HashZero);
 
-            expect(await l1Bridge.isMessageSent(signal)).to.be.eq(true);
+            expect(await l1Bridge.isMessageSent(msgHash)).to.be.eq(true);
         });
     });
 
     describe("isMessageReceived()", function () {
         it("should throw if signal is not a bridge message; proof is invalid since sender != bridge.", async function () {
-            const signal = ethers.utils.hexlify(ethers.utils.randomBytes(32));
+            const msgHash = ethers.utils.hexlify(ethers.utils.randomBytes(32));
 
-            const tx = await l1Bridge.connect(owner).sendSignal(signal);
+            const tx = await l1SignalService.connect(owner).sendSignal(msgHash);
 
             await tx.wait();
 
             const sender = owner.address;
 
-            const key = getSignalSlot(sender, signal);
+            const slot = await l1SignalService.getSignalSlot(sender, msgHash);
 
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
@@ -312,34 +323,34 @@ describe("integration:Bridge", function () {
 
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number
             );
-            // // make sure it equals 1 so we know sendSignal worked
+            // make sure it equals 1 so we know sendSignal worked
             expect(storageValue).to.be.eq(
                 "0x0000000000000000000000000000000000000000000000000000000000000001"
             );
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number,
                 blockHeader
             );
 
             await expect(
-                l2Bridge.isMessageReceived(signal, srcChainId, signalProof)
+                l2Bridge.isMessageReceived(msgHash, srcChainId, signalProof)
             ).to.be.reverted;
         });
 
         it("if message is valid and sent by the bridge it should return true", async function () {
-            const { signal } = await sendMessage(l1Bridge, m);
-
-            const sender = l1Bridge.address;
-
-            const key = getSignalSlot(sender, signal);
+            const { msgHash } = await sendMessage(l1Bridge, m);
+            const slot = await l1SignalService.getSignalSlot(
+                l1Bridge.address,
+                msgHash
+            );
 
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
@@ -349,26 +360,26 @@ describe("integration:Bridge", function () {
 
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number
             );
-            // // make sure it equals 1 so we know sendMessage worked
+            // make sure it equals 1 so we know sendMessage worked
             expect(storageValue).to.be.eq(
                 "0x0000000000000000000000000000000000000000000000000000000000000001"
             );
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
-                key,
+                l1SignalService.address,
+                slot,
                 block.number,
                 blockHeader
             );
 
             expect(
                 await l2Bridge.isMessageReceived(
-                    signal,
+                    msgHash,
                     srcChainId,
                     signalProof
                 )
@@ -376,6 +387,7 @@ describe("integration:Bridge", function () {
         });
     });
 
+    /*
     describe("isSignalReceived()", function () {
         it("should throw if sender == address(0)", async function () {
             const signal = randomBytes32();
@@ -383,7 +395,7 @@ describe("integration:Bridge", function () {
             const signalProof = ethers.constants.HashZero;
 
             await expect(
-                l2Bridge.isSignalReceived(
+                l2SignalService.isSignalReceived(
                     signal,
                     srcChainId,
                     sender,
@@ -398,7 +410,7 @@ describe("integration:Bridge", function () {
             const signalProof = ethers.constants.HashZero;
 
             await expect(
-                l2Bridge.isSignalReceived(
+                l2SignalService.isSignalReceived(
                     signal,
                     srcChainId,
                     sender,
@@ -410,13 +422,13 @@ describe("integration:Bridge", function () {
         it("should throw if calling from same layer", async function () {
             const signal = randomBytes32();
 
-            const tx = await l1Bridge.connect(owner).sendSignal(signal);
+            const tx = await l1SignalService.connect(owner).sendSignal(signal);
 
             await tx.wait();
 
             const sender = owner.address;
 
-            const key = getSignalSlot(sender, signal);
+            const key = await l1SignalService.getSignalSlot(sender, signal);
 
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
@@ -426,7 +438,7 @@ describe("integration:Bridge", function () {
 
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
+                l1SignalService.address,
                 key,
                 block.number
             );
@@ -437,14 +449,14 @@ describe("integration:Bridge", function () {
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
+                l1SignalService.address,
                 key,
                 block.number,
                 blockHeader
             );
 
             await expect(
-                l1Bridge.isSignalReceived(
+                l1SignalService.isSignalReceived(
                     signal,
                     srcChainId,
                     sender,
@@ -456,13 +468,13 @@ describe("integration:Bridge", function () {
         it("should return true and pass", async function () {
             const signal = ethers.utils.hexlify(ethers.utils.randomBytes(32));
 
-            const tx = await l1Bridge.connect(owner).sendSignal(signal);
+            const tx = await l1SignalService.connect(owner).sendSignal(signal);
 
             await tx.wait();
 
             const sender = owner.address;
 
-            const key = getSignalSlot(sender, signal);
+            const key = await l1SignalService.getSignalSlot(sender, signal);
 
             const { block, blockHeader } = await getBlockHeader(
                 hre.ethers.provider
@@ -472,7 +484,7 @@ describe("integration:Bridge", function () {
 
             // get storageValue for the key
             const storageValue = await ethers.provider.getStorageAt(
-                l1Bridge.address,
+                l1SignalService.address,
                 key,
                 block.number
             );
@@ -483,7 +495,7 @@ describe("integration:Bridge", function () {
 
             const signalProof = await getSignalProof(
                 hre.ethers.provider,
-                l1Bridge.address,
+                l1SignalService.address,
                 key,
                 block.number,
                 blockHeader
@@ -491,7 +503,7 @@ describe("integration:Bridge", function () {
             // proving functionality; l2Bridge can check if l1Bridge receives a signal
             // allowing for dapp cross layer communication
             expect(
-                await l2Bridge.isSignalReceived(
+                await l2SignalService.isSignalReceived(
                     signal,
                     srcChainId,
                     sender,
@@ -500,4 +512,5 @@ describe("integration:Bridge", function () {
             ).to.be.eq(true);
         });
     });
+*/
 });
diff --git a/packages/protocol/test/bridge/Bridge.test.ts b/packages/protocol/test/bridge/Bridge.test.ts
index dba75926406..40b93dd54ca 100644
--- a/packages/protocol/test/bridge/Bridge.test.ts
+++ b/packages/protocol/test/bridge/Bridge.test.ts
@@ -3,6 +3,7 @@ import { BigNumber } from "ethers";
 import { ethers } from "hardhat";
 import { AddressManager, Bridge, EtherVault } from "../../typechain";
 import { deployBridge, sendMessage } from "../utils/bridge";
+import { deploySignalService } from "../utils/signal";
 import { Message } from "../utils/message";
 
 describe("Bridge", function () {
@@ -27,10 +28,11 @@ describe("Bridge", function () {
         ).deploy();
         await addressManager.init();
 
+        await deploySignalService(owner, addressManager, srcChainId);
+
         ({ bridge: l1Bridge, etherVault: l1EtherVault } = await deployBridge(
             owner,
             addressManager,
-            enabledDestChainId,
             srcChainId
         ));
 
@@ -168,27 +170,28 @@ describe("Bridge", function () {
         });
     });
 
-    describe("sendSignal()", async function () {
-        it("throws when signal is empty", async function () {
-            await expect(
-                l1Bridge.connect(owner).sendSignal(ethers.constants.HashZero)
-            ).to.be.revertedWith("B:signal");
-        });
-
-        it("sends signal, confirms it was sent", async function () {
-            const hash =
-                "0xf2e08f6b93d8cf4f37a3b38f91a8c37198095dde8697463ca3789e25218a8e9d";
-            await expect(l1Bridge.connect(owner).sendSignal(hash))
-                .to.emit(l1Bridge, "SignalSent")
-                .withArgs(owner.address, hash);
-
-            const isSignalSent = await l1Bridge.isSignalSent(
-                owner.address,
-                hash
-            );
-            expect(isSignalSent).to.be.eq(true);
-        });
-    });
+    // TODO(roger): move tests to SignalService's test file.
+    // describe("sendSignal()", async function () {
+    //     it("throws when signal is empty", async function () {
+    //         await expect(
+    //             l1Bridge.connect(owner).sendSignal(ethers.constants.HashZero)
+    //         ).to.be.revertedWith("B:signal");
+    //     });
+
+    //     it("sends signal, confirms it was sent", async function () {
+    //         const hash =
+    //             "0xf2e08f6b93d8cf4f37a3b38f91a8c37198095dde8697463ca3789e25218a8e9d";
+    //         await expect(l1Bridge.connect(owner).sendSignal(hash))
+    //             .to.emit(l1Bridge, "SignalSent")
+    //             .withArgs(owner.address, hash);
+
+    //         const isSignalSent = await l1Bridge.isSignalSent(
+    //             owner.address,
+    //             hash
+    //         );
+    //         expect(isSignalSent).to.be.eq(true);
+    //     });
+    // });
 
     describe("isDestChainEnabled()", function () {
         it("is disabled for unabled chainIds", async () => {
@@ -222,31 +225,34 @@ describe("Bridge", function () {
             expect(messageStatus).to.be.eq(0);
         });
 
-        it("returns for initiaized signal", async () => {
-            const message: Message = {
-                id: 1,
-                sender: owner.address,
-                srcChainId: 1,
-                destChainId: enabledDestChainId,
-                owner: owner.address,
-                to: nonOwner.address,
-                refundAddress: owner.address,
-                depositValue: 1,
-                callValue: 1,
-                processingFee: 1,
-                gasLimit: 100,
-                data: ethers.constants.HashZero,
-                memo: "",
-            };
-
-            const { signal } = await sendMessage(l1Bridge, message);
-
-            expect(signal).not.to.be.eq(ethers.constants.HashZero);
-
-            const messageStatus = await l1Bridge.getMessageStatus(signal);
-
-            expect(messageStatus).to.be.eq(0);
-        });
+        // TODO(jeff/roger): the following test is incorrect - getMessageStatus()
+        // shall be tested on the destination chain, not the source chain.
+        //
+        // it("returns for initiaized signal", async () => {
+        //     const message: Message = {
+        //         id: 1,
+        //         sender: owner.address,
+        //         srcChainId: 1,
+        //         destChainId: enabledDestChainId,
+        //         owner: owner.address,
+        //         to: nonOwner.address,
+        //         refundAddress: owner.address,
+        //         depositValue: 1,
+        //         callValue: 1,
+        //         processingFee: 1,
+        //         gasLimit: 100,
+        //         data: ethers.constants.HashZero,
+        //         memo: "",
+        //     };
+
+        //     const { signal } = await sendMessage(l1Bridge, message);
+
+        //     expect(signal).not.to.be.eq(ethers.constants.HashZero);
+
+        //     const messageStatus = await l1Bridge.getMessageStatus(signal);
+
+        //     expect(messageStatus).to.be.eq(0);
+        // });
     });
 
     describe("processMessage()", async function () {
diff --git a/packages/protocol/test/bridge/libs/LibBridgeData.test.ts b/packages/protocol/test/bridge/libs/LibBridgeData.test.ts
index c78bbd7634e..383f86c71a7 100644
--- a/packages/protocol/test/bridge/libs/LibBridgeData.test.ts
+++ b/packages/protocol/test/bridge/libs/LibBridgeData.test.ts
@@ -4,6 +4,8 @@ import { TestLibBridgeData } from "../../../typechain";
 import { K_BRIDGE_MESSAGE } from "../../constants/messages";
 import { Message, MessageStatus } from "../../utils/message";
 
+// TODO(roger): we should deprecate these test and test Bridge.sol
+// as a whole.
 describe("LibBridgeData", function () {
     let owner: any;
     let nonOwner: any;
diff --git a/packages/protocol/test/bridge/libs/LibBridgeInvoke.test.ts b/packages/protocol/test/bridge/libs/LibBridgeInvoke.test.ts
index 7d116095fea..c705f66ed65 100644
--- a/packages/protocol/test/bridge/libs/LibBridgeInvoke.test.ts
+++ b/packages/protocol/test/bridge/libs/LibBridgeInvoke.test.ts
@@ -7,6 +7,8 @@ import {
     TestReceiver,
 } from "../../../typechain";
 
+// TODO(roger): we should deprecate these test and test Bridge.sol
+// as a whole.
 describe("LibBridgeInvoke", function () {
     let owner: any;
     let nonOwner: any;
diff --git a/packages/protocol/test/bridge/libs/LibBridgeProcess.test.ts b/packages/protocol/test/bridge/libs/LibBridgeProcess.test.ts
index 4655bdb395c..8a77275ec03 100644
--- a/packages/protocol/test/bridge/libs/LibBridgeProcess.test.ts
+++ b/packages/protocol/test/bridge/libs/LibBridgeProcess.test.ts
@@ -13,13 +13,14 @@ import {
     TestLibBridgeProcess,
 } from "../../../typechain";
 
+// TODO(roger): we should deprecate these test and test Bridge.sol
+// as a whole.
 describe("LibBridgeProcess", async function () {
     let owner: any;
     let nonOwner: any;
     let etherVaultOwner: any;
     let addressManager: AddressManager;
     let etherVault: EtherVault;
-    let libTrieLink;
     let libProcessLink;
     let libProcess: TestLibBridgeProcess;
     let testTaikoData: TestLibBridgeData;
@@ -58,17 +59,8 @@ describe("LibBridgeProcess", async function () {
             value: ethers.utils.parseEther("10.0"),
         });
 
-        libTrieLink = await (await ethers.getContractFactory("LibTrieProof"))
-            .connect(owner)
-            .deploy();
-        await libTrieLink.deployed();
-
         libProcessLink = await (
-            await ethers.getContractFactory("LibBridgeProcess", {
-                libraries: {
-                    LibTrieProof: libTrieLink.address,
-                },
-            })
+            await ethers.getContractFactory("LibBridgeProcess")
         )
             .connect(owner)
             .deploy();
diff --git a/packages/protocol/test/bridge/libs/LibBridgeRetry.test.ts b/packages/protocol/test/bridge/libs/LibBridgeRetry.test.ts
index 43a474c227d..dbad717a3a6 100644
--- a/packages/protocol/test/bridge/libs/LibBridgeRetry.test.ts
+++ b/packages/protocol/test/bridge/libs/LibBridgeRetry.test.ts
@@ -17,6 +17,8 @@ import {
 } from "../../../typechain";
 import deployAddressManager from "../../utils/addressManager";
 
+// TODO(roger): we should deprecate these test and test Bridge.sol
+// as a whole.
 describe("LibBridgeRetry", function () {
     let owner: any;
     let nonOwner: any;
diff --git a/packages/protocol/test/bridge/libs/LibBridgeSend.test.ts b/packages/protocol/test/bridge/libs/LibBridgeSend.test.ts
index f40c61b6406..ca5d51a7117 100644
--- a/packages/protocol/test/bridge/libs/LibBridgeSend.test.ts
+++ b/packages/protocol/test/bridge/libs/LibBridgeSend.test.ts
@@ -6,7 +6,10 @@ import {
     EtherVault,
 } from "../../../typechain";
 import { Message } from "../../utils/message";
+import { deploySignalService } from "../../utils/signal";
 
+// TODO(roger): we should deprecate these test and test Bridge.sol
+// as a whole.
 describe("LibBridgeSend", function () {
     let owner: any;
     let nonOwner: any;
@@ -27,6 +30,8 @@ describe("LibBridgeSend", function () {
         ).deploy();
         await addressManager.init();
 
+        await deploySignalService(owner, addressManager, blockChainId);
+
         await addressManager.setAddress(
             `${enabledDestChainId}.bridge`,
             "0x0000000000000000000000000000000000000001" // dummy address so chain is "enabled"
diff --git a/packages/protocol/test/bridge/libs/LibBridgeSignal.test.ts b/packages/protocol/test/bridge/libs/LibBridgeSignal.test.ts
deleted file mode 100644
index 3282a0cffd7..00000000000
--- a/packages/protocol/test/bridge/libs/LibBridgeSignal.test.ts
+++ /dev/null
@@ -1,70 +0,0 @@
-import { expect } from "chai";
-import { ethers } from "hardhat";
-import { TestLibBridgeData, TestLibBridgeSignal } from "../../../typechain";
-import { Message } from "../../utils/message";
-
-describe("LibBridgeSignal", function () {
-    let owner: any;
-    let nonOwner: any;
-    let testMessage: Message;
-    let libData: TestLibBridgeData;
-    let libSignal: TestLibBridgeSignal;
-
-    before(async function () {
-        [owner, nonOwner] = await ethers.getSigners();
-
-        testMessage = {
-            id: 1,
-            sender: owner.address,
-            srcChainId: 1,
-            destChainId: 2,
-            owner: owner.address,
-            to: nonOwner.address,
-            refundAddress: owner.address,
-            depositValue: 0,
-            callValue: 0,
-            processingFee: 0,
-            gasLimit: 0,
-            data: ethers.constants.HashZero,
-            memo: "",
-        };
-    });
-
-    beforeEach(async function () {
-        libData = await (
-            await ethers.getContractFactory("TestLibBridgeData")
-        ).deploy();
-
-        libSignal = await (
-            await ethers.getContractFactory("TestLibBridgeSignal")
-        ).deploy();
-    });
-
-    describe("sendSignal()", async function () {
-        it("throws when sender is zero address", async function () {
-            const signal = await libData.hashMessage(testMessage);
-
-            await expect(
-                libSignal.sendSignal(ethers.constants.AddressZero, signal)
-            ).to.revertedWith("B:sender");
-        });
-
-        it("throws when signal is zero", async function () {
-            await expect(
-                libSignal.sendSignal(owner.address, ethers.constants.HashZero)
-            ).to.be.revertedWith("B:signal");
-        });
-    });
-
-    describe("isSignalSent()", async function () {
-        it("properly sent signal should change storage value", async function () {
-            const signal = await libData.hashMessage(testMessage);
-
-            await libSignal.sendSignal(owner.address, signal);
-
-            expect(await libSignal.isSignalSent(owner.address, signal)).to.eq(
-                true
-            );
-        });
-    });
-});
diff --git a/packages/protocol/test/genesis/generate_genesis.test.sh b/packages/protocol/test/genesis/generate_genesis.test.sh
index 97dd5112843..2e21f254fdc 100755
--- a/packages/protocol/test/genesis/generate_genesis.test.sh
+++ b/packages/protocol/test/genesis/generate_genesis.test.sh
@@ -62,7 +62,7 @@ echo '}' >> $GENESIS_JSON
 echo ""
 echo "Start docker compose network..."
 
-docker compose -f $TESTNET_CONFIG down --remove-orphans &> /dev/null
+docker compose -f $TESTNET_CONFIG down -v --remove-orphans &> /dev/null
 docker compose -f $TESTNET_CONFIG up -d
 
 echo ""
@@ -70,4 +70,4 @@ echo "Start testing..."
 
 TEST_L2_GENESIS=true pnpm hardhat test --grep "Generate Genesis"
 
-docker compose -f $TESTNET_CONFIG down
+docker compose -f $TESTNET_CONFIG down -v
diff --git a/packages/protocol/test/genesis/generate_genesis.test.ts b/packages/protocol/test/genesis/generate_genesis.test.ts
index 60ab623950e..2306d032d58 100644
--- a/packages/protocol/test/genesis/generate_genesis.test.ts
+++ b/packages/protocol/test/genesis/generate_genesis.test.ts
@@ -131,6 +131,14 @@ action("Generate Genesis", function () {
             );
 
             expect(taikoL2).to.be.equal(getContractAlloc("TaikoL2").address);
+
+            const signalService = await addressManager.getAddress(
+                `${testConfig.chainId}.signal_service`
+            );
+
+            expect(signalService).to.be.equal(
+                getContractAlloc("SignalService").address
+            );
         });
 
         it("LibTxDecoder", async function () {
@@ -277,6 +285,13 @@ action("Generate Genesis", function () {
                 signer
             );
 
+            await expect(
+                addressManager.setAddress(
+                    "1.token_vault",
+                    getContractAlloc("TokenVault").address
+                )
+            ).not.to.be.reverted;
+
             await expect(
                 addressManager.setAddress(
                     "1.bridge",
@@ -324,6 +339,22 @@ action("Generate Genesis", function () {
             ).to.be.false;
         });
 
+        it("SignalService", async function () {
+            const SignalService = new hre.ethers.Contract(
+                getContractAlloc("SignalService").address,
+                require("../../artifacts/contracts/signal/SignalService.sol/SignalService.json").abi,
+                signer
+            );
+
+            const owner = await SignalService.owner();
+
+            expect(owner).to.be.equal(testConfig.contractOwner);
+
+            await expect(
+                SignalService.sendSignal(ethers.utils.randomBytes(32))
+            ).not.to.reverted;
+        });
+
         it("ERC20", async function () {
             const ERC20 = new hre.ethers.Contract(
                 getContractAlloc("TestERC20").address,
diff --git a/packages/protocol/test/libs/LibTrieProof.test.ts b/packages/protocol/test/libs/LibTrieProof.test.ts
index 434b6e3aa67..aed3860e935 100644
--- a/packages/protocol/test/libs/LibTrieProof.test.ts
+++ b/packages/protocol/test/libs/LibTrieProof.test.ts
@@ -4,8 +4,11 @@ import RLP from "rlp";
 import { sendMessage } from "../utils/bridge";
 import { Message } from "../utils/message";
 import { EthGetProofResponse } from "../utils/rpc";
-import { getSignalSlot } from "../utils/signal";
+import { deploySignalService } from "../utils/signal";
 
+// TODO(roger): this test shall not use any file in contracts/bridge/*.sol
+// Instead, it should use the `writeStorageAt` function to manipulate stroage
+// values then verify the proof.
 describe("integration:LibTrieProof", function () {
     async function deployLibTrieProofFixture() {
         const libTrieProof = await (
@@ -39,23 +42,26 @@ describe("integration:LibTrieProof", function () {
             "0x0000000000000000000000000000000000000001" // dummy address so chain is "enabled"
         );
 
+        const [owner] = await ethers.getSigners();
+
+        const { signalService } = await deploySignalService(
+            owner,
+            addressManager,
+            chainId
+        );
+
         const libBridgeRetry = await (
             await ethers.getContractFactory("LibBridgeRetry")
         ).deploy();
 
         const libBridgeProcess = await (
-            await ethers.getContractFactory("LibBridgeProcess", {
-                libraries: {
-                    LibTrieProof: libTrieProof.address,
-                },
-            })
+            await ethers.getContractFactory("LibBridgeProcess")
         ).deploy();
 
         const BridgeFactory = await ethers.getContractFactory("Bridge", {
             libraries: {
                 LibBridgeProcess: libBridgeProcess.address,
                 LibBridgeRetry: libBridgeRetry.address,
-                LibTrieProof: libTrieProof.address,
             },
         });
 
@@ -63,14 +69,23 @@ describe("integration:LibTrieProof", function () {
 
         await bridge.init(addressManager.address);
 
-        const [owner] = await ethers.getSigners();
-
-        return { owner, testLibTreProof, bridge, enabledDestChainId };
+        return {
+            owner,
+            testLibTreProof,
+            signalService,
+            bridge,
+            enabledDestChainId,
+        };
     }
     describe("verify()", function () {
         it("verifies", async function () {
-            const { owner, testLibTreProof, bridge, enabledDestChainId } =
-                await deployLibTrieProofFixture();
+            const {
+                owner,
+                testLibTreProof,
+                signalService,
+                bridge,
+                enabledDestChainId,
+            } = await deployLibTrieProofFixture();
 
             const { chainId } = await ethers.provider.getNetwork();
             const srcChainId = chainId;
@@ -91,17 +106,20 @@ describe("integration:LibTrieProof", function () {
                 memo: "",
             };
 
-            const { tx, signal } = await sendMessage(bridge, message);
+            const { tx, msgHash } = await sendMessage(bridge, message);
 
             await tx.wait();
 
-            expect(signal).not.to.be.eq(ethers.constants.HashZero);
+            expect(msgHash).not.to.be.eq(ethers.constants.HashZero);
 
-            const messageStatus = await bridge.getMessageStatus(signal);
+            const messageStatus = await bridge.getMessageStatus(msgHash);
 
             expect(messageStatus).to.be.eq(0);
 
-            const key = getSignalSlot(bridge.address, signal);
+            const slot = await signalService.getSignalSlot(
+                bridge.address,
+                msgHash
+            );
 
             // use this instead of ethers.provider.getBlock() beccause it doesnt have stateRoot
             // in the response
@@ -111,20 +129,20 @@ describe("integration:LibTrieProof", function () {
                     false,
                 ]);
 
-            // get storageValue for the key
+            // get storageValue for the slot
             const storageValue = await ethers.provider.getStorageAt(
-                bridge.address,
-                key,
+                signalService.address,
+                slot,
                 block.number
             );
             // make sure it equals 1 so our proof will pass
             expect(storageValue).to.be.eq(
                 "0x0000000000000000000000000000000000000000000000000000000000000001"
             );
-            // rpc call to get the merkle proof what value is at key on the bridge contract
+            // rpc call to get the merkle proof what value is at slot on the bridge contract
             const proof: EthGetProofResponse = await ethers.provider.send(
                 "eth_getProof",
-                [bridge.address, [key], block.hash]
+                [signalService.address, [slot], block.hash]
             );
 
             const stateRoot = block.stateRoot;
@@ -137,11 +155,11 @@ describe("integration:LibTrieProof", function () {
                     RLP.encode(proof.storageProof[0].proof),
                 ]
             );
-            // proof verifies the storageValue at key is 1
+            // proof verifies the storageValue at slot is 1
             await testLibTreProof.verify(
                 stateRoot,
-                bridge.address,
-                key,
+                signalService.address,
+                slot,
                 "0x0000000000000000000000000000000000000000000000000000000000000001",
                 encodedProof
             );
diff --git a/packages/protocol/test/signal/SignalService.test.ts b/packages/protocol/test/signal/SignalService.test.ts
new file mode 100644
index 00000000000..41bf8c8a68b
--- /dev/null
+++ b/packages/protocol/test/signal/SignalService.test.ts
@@ -0,0 +1,61 @@
+import { expect } from "chai";
+import { ethers } from "hardhat";
+import { AddressManager, SignalService } from "../../typechain";
+import { deploySignalService } from "../utils/signal";
+import deployAddressManager from "../utils/addressManager";
+// import {getBlockHeader } from "../utils/rpc";
+
+// TODO(roger): convert to integration tests and add a test case for isSignalReceived.
+describe("SignalService", function () {
+    let owner: any;
+    let addr1: any;
+    let addr2: any;
+    let signalService: SignalService;
+
+    before(async () => {
+        [owner, addr1, addr2] = await ethers.getSigners();
+        const { chainId } = await ethers.provider.getNetwork();
+
+        const addressManager: AddressManager = await deployAddressManager(
+            owner
+        );
+
+        ({ signalService } = await deploySignalService(
+            owner,
+            addressManager,
+            chainId
+        ));
+    });
+
+    describe("getSignalSlot()", function () {
+        it("should return different slots for same signal from different apps", async () => {
+            const signal = ethers.utils.keccak256(
+                ethers.utils.toUtf8Bytes("a random")
+            );
+            const slot1 = await signalService.getSignalSlot(
+                addr1.address,
+                signal
+            );
+            const slot2 = signalService.getSignalSlot(addr2.address, signal);
+
+            await expect(slot1).to.be.not.equal(slot2);
+        });
+    });
+
+    describe("isSignalSent()", function () {
+        it("should return false for unsent signal and true for sent signal", async () => {
+            const signal = ethers.utils.keccak256(
+                ethers.utils.toUtf8Bytes("another random")
+            );
+            let isSent = await signalService.isSignalSent(
+                addr1.address,
+                signal
+            );
+            await expect(isSent).to.be.equal(false);
+
+            await signalService.connect(addr1).sendSignal(signal);
+            isSent = await signalService.isSignalSent(addr1.address, signal);
+            await expect(isSent).to.be.equal(true);
+        });
+    });
+});
diff --git a/packages/protocol/test/utils/bridge.ts b/packages/protocol/test/utils/bridge.ts
index 0e699b20bd9..bbaa168df1d 100644
--- a/packages/protocol/test/utils/bridge.ts
+++ b/packages/protocol/test/utils/bridge.ts
@@ -3,32 +3,21 @@ import { ethers as hardhatEthers } from "hardhat";
 import {
     AddressManager,
     Bridge,
+    SignalService,
     EtherVault,
-    LibTrieProof,
     TestHeaderSync,
 } from "../../typechain";
 import { Message } from "./message";
 import { Block, BlockHeader, getBlockHeader } from "./rpc";
-import { getSignalProof, getSignalSlot } from "./signal";
+import { getSignalProof } from "./signal";
 
 async function deployBridge(
     signer: Signer,
     addressManager: AddressManager,
-    destChain: number,
-    srcChain: number
+    chainId: number
 ): Promise<{ bridge: Bridge; etherVault: EtherVault }> {
-    const libTrieProof: LibTrieProof = await (
-        await hardhatEthers.getContractFactory("LibTrieProof")
-    )
-        .connect(signer)
-        .deploy();
-
     const libBridgeProcess = await (
-        await hardhatEthers.getContractFactory("LibBridgeProcess", {
-            libraries: {
-                LibTrieProof: libTrieProof.address,
-            },
-        })
+        await hardhatEthers.getContractFactory("LibBridgeProcess")
     )
         .connect(signer)
         .deploy();
@@ -43,7 +32,6 @@ async function deployBridge(
         libraries: {
             LibBridgeProcess: libBridgeProcess.address,
             LibBridgeRetry: libBridgeRetry.address,
-            LibTrieProof: libTrieProof.address,
         },
     });
 
@@ -64,7 +52,7 @@ async function deployBridge(
     await etherVault.connect(signer).authorize(await signer.getAddress(), true);
 
     await addressManager.setAddress(
-        `${srcChain}.ether_vault`,
+        `${chainId}.ether_vault`,
         etherVault.address
     );
 
@@ -74,7 +62,7 @@ async function deployBridge(
         gasLimit: 1000000,
     });
 
-    await addressManager.setAddress(`${destChain}.bridge`, bridge.address);
+    await addressManager.setAddress(`${chainId}.bridge`, bridge.address);
 
     return { bridge, etherVault };
 }
@@ -84,7 +72,7 @@ async function sendMessage(
     m: Message
 ): Promise<{
     bridge: Bridge;
-    signal: any;
+    msgHash: string;
     messageSentEvent: any;
     message: Message;
     tx: ethers.ContractTransaction;
@@ -99,12 +87,14 @@ async function sendMessage(
 
     const [messageSentEvent] = receipt.events as any as Event[];
 
-    const { signal, message } = (messageSentEvent as any).args;
+    const { msgHash, message } = (messageSentEvent as any).args;
 
-    return { bridge, messageSentEvent, signal, message, tx };
+    return { bridge, messageSentEvent, msgHash, message, tx };
 }
 
+// Process a L1-to-L1 message
 async function processMessage(
+    l1SignalService: SignalService,
     l1Bridge: Bridge,
     l2Bridge: Bridge,
     signal: string,
@@ -119,7 +109,7 @@ async function processMessage(
 }> {
     const sender = l1Bridge.address;
 
-    const key = getSignalSlot(sender, signal);
+    const slot = await l1SignalService.getSignalSlot(sender, signal);
 
     const { block, blockHeader } = await getBlockHeader(provider);
 
@@ -127,8 +117,8 @@ async function processMessage(
 
     const signalProof = await getSignalProof(
         provider,
-        l1Bridge.address,
-        key,
+        l1SignalService.address,
+        slot,
         block.number,
         blockHeader
     );
@@ -141,24 +131,26 @@ async function sendAndProcessMessage(
     provider: ethers.providers.JsonRpcProvider,
     headerSync: TestHeaderSync,
     m: Message,
+    l1SignalService: SignalService,
     l1Bridge: Bridge,
     l2Bridge: Bridge
 ): Promise<{
     tx: ethers.ContractTransaction;
     message: Message;
-    signal: string;
+    msgHash: string;
     signalProof: string;
 }> {
-    const { signal, message } = await sendMessage(l1Bridge, m);
+    const { msgHash, message } = await sendMessage(l1Bridge, m);
     const { tx, signalProof } = await processMessage(
+        l1SignalService,
         l1Bridge,
         l2Bridge,
-        signal,
+        msgHash,
         provider,
         headerSync,
         message
     );
-    return { tx, signal, message, signalProof };
+    return { tx, msgHash, message, signalProof };
 }
 
 export { deployBridge, sendMessage, processMessage, sendAndProcessMessage };
diff --git a/packages/protocol/test/utils/signal.ts b/packages/protocol/test/utils/signal.ts
index c36a3052a17..b535ee1b2c8 100644
--- a/packages/protocol/test/utils/signal.ts
+++ b/packages/protocol/test/utils/signal.ts
@@ -1,26 +1,52 @@
-import { ethers } from "ethers";
+import { ethers, Signer } from "ethers";
 import RLP from "rlp";
+import { ethers as hardhatEthers } from "hardhat";
 import { BlockHeader, EthGetProofResponse } from "./rpc";
+import { AddressManager, SignalService, LibTrieProof } from "../../typechain";
 
-function getSignalSlot(sender: string, signal: any) {
-    return ethers.utils.keccak256(
-        ethers.utils.solidityPack(
-            ["string", "address", "bytes32"],
-            ["SIGNAL", sender, signal]
-        )
+async function deploySignalService(
+    signer: Signer,
+    addressManager: AddressManager,
+    srcChain: number
+): Promise<{ signalService: SignalService }> {
+    const libTrieProof: LibTrieProof = await (
+        await hardhatEthers.getContractFactory("LibTrieProof")
+    )
+        .connect(signer)
+        .deploy();
+
+    const SignalServiceFactory = await hardhatEthers.getContractFactory(
+        "SignalService",
+        {
+            libraries: {
+                LibTrieProof: libTrieProof.address,
+            },
+        }
+    );
+
+    const signalService: SignalService = await SignalServiceFactory.connect(
+        signer
+    ).deploy();
+
+    await signalService.connect(signer).init(addressManager.address);
+
+    await addressManager.setAddress(
+        `${srcChain}.signal_service`,
+        signalService.address
     );
+    return { signalService };
 }
 
 async function getSignalProof(
     provider: ethers.providers.JsonRpcProvider,
     contractAddress: string,
-    key: string,
+    slot: string,
     blockNumber: number,
     blockHeader: BlockHeader
 ) {
     const proof: EthGetProofResponse = await provider.send("eth_getProof", [
         contractAddress,
-        [key],
+        [slot],
         blockNumber,
     ]);
 
@@ -43,4 +69,4 @@ async function getSignalProof(
     return signalProof;
 }
 
-export { getSignalSlot, getSignalProof };
+export { deploySignalService, getSignalProof };
diff --git a/packages/protocol/utils/generate_genesis/taikoL2.ts b/packages/protocol/utils/generate_genesis/taikoL2.ts
index d7e4eb3ccd8..1b9df477874 100644
--- a/packages/protocol/utils/generate_genesis/taikoL2.ts
+++ b/packages/protocol/utils/generate_genesis/taikoL2.ts
@@ -134,6 +134,10 @@ async function generateContractConfigs(
             ARTIFACTS_PATH,
             "./bridge/EtherVault.sol/EtherVault.json"
         )),
+        SignalService: require(path.join(
+            ARTIFACTS_PATH,
+            "./signal/SignalService.sol/SignalService.json"
+        )),
     };
 
     const addressMap: any = {};
@@ -141,33 +145,54 @@ async function generateContractConfigs(
     for (const [contractName, artifact] of Object.entries(contractArtifacts)) {
         let bytecode = (artifact as any).bytecode;
 
-        if (contractName === "TaikoL2") {
-            if (!addressMap.LibTxDecoder) {
-                throw new Error("LibTxDecoder not initialized");
-            }
+        switch (contractName) {
+            case "TaikoL2":
+                if (!addressMap.LibTxDecoder) {
+                    throw new Error("LibTxDecoder not initialized");
+                }
 
-            bytecode = linkContractLibs(contractArtifacts.TaikoL2, addressMap);
-        } else if (contractName === "LibBridgeProcess") {
-            if (!addressMap.LibTrieProof) {
-                throw new Error("LibTrieProof not initialized");
-            }
-
-            bytecode = linkContractLibs(
-                contractArtifacts.LibBridgeProcess,
-                addressMap
-            );
-        } else if (contractName === "Bridge") {
-            if (
-                !addressMap.LibTrieProof ||
-                !addressMap.LibBridgeRetry ||
-                !addressMap.LibBridgeProcess
-            ) {
-                throw new Error(
-                    "LibTrieProof/LibBridgeRetry/LibBridgeProcess not initialized"
+                bytecode = linkContractLibs(
+                    contractArtifacts.TaikoL2,
+                    addressMap
                 );
-            }
-
-            bytecode = linkContractLibs(contractArtifacts.Bridge, addressMap);
+                break;
+            case "LibBridgeProcess":
+                if (!addressMap.LibTrieProof) {
+                    throw new Error("LibTrieProof not initialized");
+                }
+
+                bytecode = linkContractLibs(
+                    contractArtifacts.LibBridgeProcess,
+                    addressMap
+                );
+                break;
+            case "Bridge":
+                if (
+                    !addressMap.LibBridgeRetry ||
+                    !addressMap.LibBridgeProcess
+                ) {
+                    throw new Error(
+                        "LibBridgeRetry/LibBridgeProcess not initialized"
+                    );
+                }
+
+                bytecode = linkContractLibs(
+                    contractArtifacts.Bridge,
+                    addressMap
+                );
+                break;
+            case "SignalService":
+                if (!addressMap.LibTrieProof) {
+                    throw new Error("LibTrieProof not initialized");
+                }
+
+                bytecode = linkContractLibs(
+                    contractArtifacts.SignalService,
+                    addressMap
+                );
+                break;
+            default:
+                break;
         }
 
         if (
@@ -242,6 +267,10 @@ async function generateContractConfigs(
                         ["string"],
                         [`${chainId}.ether_vault`]
                     )}`]: addressMap.EtherVault,
+                    [`${ethers.utils.solidityKeccak256(
+                        ["string"],
+                        [`${chainId}.signal_service`]
+                    )}`]: addressMap.SignalService,
                 },
             },
         },
@@ -322,6 +351,24 @@ async function generateContractConfigs(
                 authorizedAddrs: { [`${addressMap.Bridge}`]: true },
             },
         },
+        SignalService: {
+            address: addressMap.SignalService,
+            deployedBytecode: linkContractLibs(
+                contractArtifacts.SignalService,
+                addressMap
+            ),
+            variables: {
+                // initializer
+                _initialized: 1,
+                _initializing: false,
+                // ReentrancyGuardUpgradeable
+                _status: 1, // _NOT_ENTERED
+                // OwnableUpgradeable
+                _owner: contractOwner,
+                // AddressResolver
+                _addressManager: addressMap.AddressManager,
+            },
+        },
     };
 }