diff --git a/l1-contracts/src/core/libraries/Hash.sol b/l1-contracts/src/core/libraries/Hash.sol
new file mode 100644
index 000000000000..4f3be42a996b
--- /dev/null
+++ b/l1-contracts/src/core/libraries/Hash.sol
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2023 Aztec Labs.
+pragma solidity >=0.8.18;
+
+import {Constants} from "./Constants.sol";
+import {DataStructures} from "./DataStructures.sol";
+
+/**
+ * @title Hash library
+ * @author Aztec
+ * @notice A small library of functions to compute hashes for data structures and convert to field elements
+ */
+library Hash {
+  /**
+   * @notice Computes the sha256 hash of the L1 to L2 message and converts it to a field element
+   * @param _message - The L1 to L2 message to hash
+   * @return The hash of the provided message as a field element
+   */
+  function sha256ToField(DataStructures.L1ToL2Msg memory _message) internal pure returns (bytes32) {
+    return sha256ToField(
+      abi.encode(
+        _message.sender,
+        _message.recipient,
+        _message.content,
+        _message.secretHash,
+        _message.deadline,
+        _message.fee
+      )
+    );
+  }
+
+  /**
+   * @notice Computes the sha256 hash of the L2 to L1 message and converts it to a field element
+   * @param _message - The L2 to L1 message to hash
+   * @return The hash of the provided message as a field element
+   */
+  function sha256ToField(DataStructures.L2ToL1Msg memory _message) internal pure returns (bytes32) {
+    return sha256ToField(abi.encode(_message.sender, _message.recipient, _message.content));
+  }
+
+  /**
+   * @notice Computes the sha256 hash of the provided data and converts it to a field element
+   * @dev Using modulo to convert the hash to a field element.
+   * @param _data - The bytes to hash
+   * @return The hash of the provided data as a field element
+   */
+  function sha256ToField(bytes memory _data) internal pure returns (bytes32) {
+    return bytes32(uint256(sha256(_data)) % Constants.P);
+  }
+}
diff --git a/l1-contracts/src/core/messagebridge/Inbox.sol b/l1-contracts/src/core/messagebridge/Inbox.sol
index bdd311c29543..f80ecf3aed96 100644
--- a/l1-contracts/src/core/messagebridge/Inbox.sol
+++ b/l1-contracts/src/core/messagebridge/Inbox.sol
@@ -3,8 +3,8 @@
 pragma solidity >=0.8.18;
 
 import {IInbox} from "@aztec/core/interfaces/messagebridge/IInbox.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
 import {DataStructures} from "@aztec/core/libraries/DataStructures.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 import {MessageBox} from "@aztec/core/libraries/MessageBox.sol";
 import {Errors} from "@aztec/core/libraries/Errors.sol";
 import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
@@ -16,6 +16,7 @@ import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
  */
 contract Inbox is IInbox {
   using MessageBox for mapping(bytes32 entryKey => DataStructures.Entry entry);
+  using Hash for DataStructures.L1ToL2Msg;
 
   IRegistry immutable REGISTRY;
 
@@ -37,20 +38,7 @@ contract Inbox is IInbox {
    * @return The hash of the message (used as the key of the entry in the set)
    */
   function computeEntryKey(DataStructures.L1ToL2Msg memory _message) public pure returns (bytes32) {
-    return bytes32(
-      uint256(
-        sha256(
-          abi.encode(
-            _message.sender,
-            _message.recipient,
-            _message.content,
-            _message.secretHash,
-            _message.deadline,
-            _message.fee
-          )
-        )
-      ) % Constants.P
-    );
+    return _message.sha256ToField();
   }
 
   /**
@@ -58,7 +46,7 @@ contract Inbox is IInbox {
    * @dev Will emit `MessageAdded` with data for easy access by the sequencer
    * @dev msg.value - The fee provided to sequencer for including the entry
    * @param _recipient - The recipient of the entry
-   * @param _deadline - The deadline to consume a message. Only after it, can a message be cancalled.
+   * @param _deadline - The deadline to consume a message. Only after it, can a message be cancelled.
    * it is uint32 to for slot packing of the Entry struct. Should work until Feb 2106.
    * @param _content - The content of the entry (application specific)
    * @param _secretHash - The secret hash of the entry (make it possible to hide when a specific entry is consumed on L2)
diff --git a/l1-contracts/src/core/messagebridge/Outbox.sol b/l1-contracts/src/core/messagebridge/Outbox.sol
index 4b1d800a7a65..b590adf0fbf6 100644
--- a/l1-contracts/src/core/messagebridge/Outbox.sol
+++ b/l1-contracts/src/core/messagebridge/Outbox.sol
@@ -3,8 +3,8 @@
 pragma solidity >=0.8.18;
 
 import {IOutbox} from "@aztec/core/interfaces/messagebridge/IOutbox.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
 import {DataStructures} from "@aztec/core/libraries/DataStructures.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 import {Errors} from "@aztec/core/libraries/Errors.sol";
 import {MessageBox} from "@aztec/core/libraries/MessageBox.sol";
 import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
@@ -17,6 +17,7 @@ import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
  */
 contract Outbox is IOutbox {
   using MessageBox for mapping(bytes32 entryKey => DataStructures.Entry entry);
+  using Hash for DataStructures.L2ToL1Msg;
 
   IRegistry immutable REGISTRY;
 
@@ -37,11 +38,7 @@ contract Outbox is IOutbox {
    * @return The key of the entry in the set
    */
   function computeEntryKey(DataStructures.L2ToL1Msg memory _message) public pure returns (bytes32) {
-    // TODO: Replace mod P later on when we have a better idea of how to handle Fields.
-    return bytes32(
-      uint256(sha256(abi.encode(_message.sender, _message.recipient, _message.content)))
-        % Constants.P
-    );
+    return _message.sha256ToField();
   }
 
   /**
diff --git a/l1-contracts/test/portals/RollupNativeAsset.sol b/l1-contracts/test/portals/RollupNativeAsset.sol
index e86600ca08db..5b7d4217a0d0 100644
--- a/l1-contracts/test/portals/RollupNativeAsset.sol
+++ b/l1-contracts/test/portals/RollupNativeAsset.sol
@@ -4,7 +4,7 @@ pragma solidity >=0.8.18;
 
 import {ERC20} from "@oz/token/ERC20/ERC20.sol";
 import {DataStructures} from "@aztec/core/libraries/DataStructures.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 import {Registry} from "@aztec/core/messagebridge/Registry.sol";
 
 contract RollupNativeAsset is ERC20 {
@@ -19,14 +19,12 @@ contract RollupNativeAsset is ERC20 {
   }
 
   function withdraw(uint256 _amount, address _recipient) external returns (bytes32) {
-    bytes memory contentBytes =
-      abi.encodeWithSignature("withdraw(uint256,address)", _amount, _recipient);
-    bytes32 content = bytes32(uint256(sha256(contentBytes)) % Constants.P);
-
     DataStructures.L2ToL1Msg memory message = DataStructures.L2ToL1Msg({
       sender: DataStructures.L2Actor(aztecAddress, 1),
       recipient: DataStructures.L1Actor(address(this), block.chainid),
-      content: content
+      content: Hash.sha256ToField(
+        abi.encodeWithSignature("withdraw(uint256,address)", _amount, _recipient)
+        )
     });
 
     bytes32 entryKey = registry.getOutbox().consume(message);
diff --git a/l1-contracts/test/portals/TokenPortal.sol b/l1-contracts/test/portals/TokenPortal.sol
index 187b56da38bc..11d43a21c71e 100644
--- a/l1-contracts/test/portals/TokenPortal.sol
+++ b/l1-contracts/test/portals/TokenPortal.sol
@@ -7,7 +7,7 @@ import {SafeERC20} from "@oz/token/ERC20/utils/SafeERC20.sol";
 import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
 import {IInbox} from "@aztec/core/interfaces/messagebridge/IInbox.sol";
 import {DataStructures} from "@aztec/core/libraries/DataStructures.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 
 contract TokenPortal {
   using SafeERC20 for IERC20;
@@ -40,8 +40,8 @@ contract TokenPortal {
     DataStructures.L2Actor memory actor = DataStructures.L2Actor(l2TokenAddress, 1);
 
     // Hash the message content to be reconstructed in the receiving contract
-    bytes memory content = abi.encodeWithSignature("mint(uint256,bytes32)", _amount, _to);
-    bytes32 contentHash = bytes32(uint256(sha256(content)) % Constants.P);
+    bytes32 contentHash =
+      Hash.sha256ToField(abi.encodeWithSignature("mint(uint256,bytes32)", _amount, _to));
 
     // Hold the tokens in the portal
     underlying.safeTransferFrom(msg.sender, address(this), _amount);
diff --git a/l1-contracts/test/portals/TokenPortal.t.sol b/l1-contracts/test/portals/TokenPortal.t.sol
index 6852bc20e8f1..620e6d9802a8 100644
--- a/l1-contracts/test/portals/TokenPortal.t.sol
+++ b/l1-contracts/test/portals/TokenPortal.t.sol
@@ -8,7 +8,7 @@ import {Inbox} from "@aztec/core/messagebridge/Inbox.sol";
 import {Registry} from "@aztec/core/messagebridge/Registry.sol";
 import {Outbox} from "@aztec/core/messagebridge/Outbox.sol";
 import {DataStructures} from "@aztec/core/libraries/DataStructures.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 
 // Interfaces
 import {IRegistry} from "@aztec/core/interfaces/messagebridge/IRegistry.sol";
@@ -71,9 +71,7 @@ contract TokenPortalTest is Test {
     DataStructures.L1ToL2Msg memory expectedMessage = DataStructures.L1ToL2Msg({
       sender: DataStructures.L1Actor(address(tokenPortal), 1),
       recipient: DataStructures.L2Actor(l2TokenAddress, 1),
-      content: bytes32(
-        uint256(sha256(abi.encodeWithSignature("mint(uint256,bytes32)", amount, to))) % Constants.P
-        ),
+      content: Hash.sha256ToField(abi.encodeWithSignature("mint(uint256,bytes32)", amount, to)),
       secretHash: secretHash,
       deadline: deadline,
       fee: bid