stealth-addresses: Adds announcer implementation

src/stealth-addresses/ERC5564Announcer.sol

@@ -0,0 +1,104 @@
+/*
+
+ ██████ ██████  ██    ██ ███████  ██████  ██
+██      ██   ██  ██  ██  ██      ██    ██ ██
+██      ██████    ████   ███████ ██    ██ ██
+██      ██   ██    ██         ██ ██    ██ ██
+ ██████ ██   ██    ██    ███████  ██████  ███████
+
+*/
+
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.16;
+
+/**
+ * @title IERC5561Announcer
+ *
+ * @notice Interface to announce a tx to an [EIP-5564] stealth address
+ *
+ * @dev Metadata Specification and Recommendations
+ *
+ *      The first byte of the metadata MUST be the view tag. The view tag is a
+ *      probabilistic filter to skip computations when checking announcements.
+ *
+ *      The following recommendations are given in [EIP-5564]:
+ *
+ *      - Tx transferring the native token, eg ETH:
+ *
+ *         Index      |  Description                                  | Length in bytes
+ *        -----------------------------------------------------------------------------
+ *        [0x00]      | View tag                                      |              1
+ *        [0x01:0x04] | `0xeeeeeeee`                                  |              4
+ *        [0x05:0x24] | `0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE`  |             20
+ *        [0x18:0x38] | Amount in wei                                 |             32
+ *
+ *      - Tx involving a contract call with a single argument, eg ERC-20 and ERC-721
+ *        transfers:
+ *
+ *         Index      |  Description                                  | Length in bytes
+ *        -----------------------------------------------------------------------------
+ *        [0x00]      | View tag                                      |              1
+ *        [0x01:0x04] | Solidity function selector                    |              4
+ *        [0x05:0x24] | Contract address                              |             20
+ *        [0x18:0x38] | One word argument, eg token amount in wei     |             32
+ *
+ * @custom:references
+ *      - [EIP-5564]: https://eips.ethereum.org/EIPS/eip-5564
+ *      - [EIP-5564 Scheme Registry]: https://eips.ethereum.org/assets/eip-5564/scheme_ids
+ */
+interface IERC5564Announcer {
+    /// @notice Emitted to announce a tx to a stealth address.
+    ///
+    /// @param schemeId Scheme id based on [EIP-5564 Scheme Registry] registry.
+    /// @param stealthAddress The stealth address.
+    /// @param caller The address announcing the tx.
+    /// @param ephemeralPubKey The ephemeral public key created during the
+    ///                        stealth address generation.
+    /// @param metadata Bytes blob providing the view tag and arbitrary
+    ///                 additional metadata. Note that [EIP-5564] provides
+    ///                 recommendations.
+    event Announcement(
+        uint indexed schemeId,
+        address indexed stealthAddress,
+        address indexed caller,
+        bytes ephemeralPubKey,
+        bytes metadata
+    );
+
+    /// @notice Announces a tx to stealth address `stealthAddress` using scheme
+    ///         `schemeId` and ephemeral public key `ephemeralPubKey`. View tag
+    ///         and additional metadata are provided via `metadata`.
+    ///
+    /// @param schemeId Scheme id based on [EIP-5564 Scheme Registry] registry.
+    /// @param stealthAddress The stealth address.
+    /// @param ephemeralPubKey The ephemeral public key created during the
+    ///                        stealth address generation.
+    /// @param metadata Bytes blob providing the view tag and arbitrary
+    ///                 additional metadata. Note that [EIP-5564] provides
+    ///                 recommendations.
+    function announce(
+        uint schemeId,
+        address stealthAddress,
+        bytes memory ephemeralPubKey,
+        bytes memory metadata
+    ) external;
+}
+
+/**
+ * @title ERC5564Announcer
+ *
+ * @notice Minimal [EIP-5564] stealth address announcement contract
+ */
+contract ERC5564Announcer is IERC5564Announcer {
+    /// @inheritdoc IERC5564Announcer
+    function announce(
+        uint schemeId,
+        address stealthAddress,
+        bytes memory ephemeralPubKey,
+        bytes memory metadata
+    ) external {
+        emit Announcement(
+            schemeId, stealthAddress, msg.sender, ephemeralPubKey, metadata
+        );
+    }
+}