feat:implement New contract: stealth-address announcement registry

Author: hunter-baddie

contracts/Cargo.lock

@@ -23,6 +23,7 @@ members = [
   "contracts/guardian",
   "contracts/fx-oracle",
   "contracts/payment-splitter",
+  "contracts/stealth-announcement",
   "integration_tests",
 ]
 

contracts/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "stealth-announcement"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+doctest = false
+
+[dependencies]
+soroban-sdk = { workspace = true }
+
+[dev-dependencies]
+soroban-sdk = { workspace = true, features = ["testutils"] }

contracts/contracts/stealth-announcement/Cargo.toml

@@ -0,0 +1,319 @@
+#![no_std]
+//! Stealth Address Announcement Registry.
+//!
+//! # Purpose
+//! Senders of stealth payments publish an **ephemeral pubkey** (R = r·G) alongside
+//! an optional **view tag** on-chain.  Recipients scan announcements with their
+//! view private key and, when the view tag matches, derive the one‑time stealth
+//! address P = spend_pubkey + H(view_privkey · R)·G to detect incoming payments.
+//!
+//! # Privacy (No Linkability)
+//! The contract deliberately stores **no sender identity, no recipient identity,
+//! and no amount or asset**.  Every field is public by the very nature of the
+//! stealth protocol:
+//!
+//! * `ephemeral_pubkey` – already committed in the payment transaction memo.
+//! * `view_tag`           – the first byte of a hash anyone can *try* to match
+//!                          against their own view key.  A single byte leaks
+//!                          at most 1/256 of the search space and is purely a
+//!                          scanning optimisation.
+//! * `announcement_index` – a monotonic counter for pagination.
+//! * `timestamp`          – ledger time, public regardless.
+//!
+//! An observer learns only that *someone* published a stealth announcement;
+//! they cannot tell which recipient it is for, nor link two announcements to
+//! the same recipient without knowledge of that recipient's view private key.
+
+use soroban_sdk::{
+    contract, contracterror, contractevent, contractimpl, contracttype, vec, Address, Bytes, Env,
+    Vec,
+};
+
+// ============================================================================
+// Errors
+// ============================================================================
+
+#[contracterror]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum AnnouncementError {
+    AlreadyInit       = 1,  // contract already initialised
+    EmptyPubkey       = 2,  // ephemeral_pubkey has zero length
+    PubkeyTooLong     = 3,  // ephemeral_pubkey exceeds 128 bytes
+    RangeTooLarge     = 4,  // pagination range exceeds MAX_PAGE_SIZE
+    InvalidRange      = 5,  // start > end
+    NotAdmin          = 6,  // caller is not the admin
+}
+
+/// Maximum number of announcements returned in a single paginated query.
+pub const MAX_PAGE_SIZE: u64 = 100;
+
+/// Maximum acceptable byte length for an ephemeral pubkey.
+/// secp256k1 compressed = 33 bytes; uncompressed = 65 bytes;
+/// we accept up to 128 bytes to leave room for future schemes.
+pub const MAX_PUBKEY_LEN: u32 = 128;
+
+// ============================================================================
+// Types
+// ============================================================================
+
+/// A single on‑chain stealth announcement.
+///
+/// Every field is public information; nothing links the announcement to a
+/// specific recipient or sender.
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct StealthAnnouncement {
+    /// Ephemeral public key R = r·G.  Variable‑length bytes so the registry
+    /// is curve‑agnostic (secp256k1 compressed 33 B, ed25519 32 B, …).
+    pub ephemeral_pubkey: Bytes,
+    /// View tag — low 8 bits of H(ECDH(view_pubkey, R)), stored as u32
+    /// because Soroban does not expose a raw u8 ABI.  Recipients reject
+    /// ~255/256 non‑matching announcements without a full scalar mul.
+    pub view_tag: u32,
+    /// Monotonically increasing index assigned at publish time.  Used as the
+    /// pagination cursor — guarantees order without leaking timing correlation
+    /// beyond the public ledger timestamp.
+    pub announcement_index: u64,
+    /// Ledger timestamp when the announcement was recorded.
+    pub timestamp: u64,
+}
+
+#[contracttype]
+#[derive(Clone)]
+enum DataKey {
+    Admin,
+    AnnouncementCount,
+    Announcement(u64),
+}
+
+// ============================================================================
+// Events
+// ============================================================================
+
+/// Fired when a new announcement is published.  The index is the only new
+/// piece of data (the rest are also in calldata) — included for event log
+/// consumers that want a short lookup key.
+#[contractevent]
+pub struct AnnouncementPublished {
+    pub announcement_index: u64,
+    pub view_tag: u32,
+}
+
+// ============================================================================
+// Contract
+// ============================================================================
+
+#[contract]
+pub struct StealthAnnouncementContract;
+
+#[contractimpl]
+impl StealthAnnouncementContract {
+    // ------------------------------------------------------------------------
+    // Initialisation
+    // ------------------------------------------------------------------------
+
+    /// Initialise the registry with an optional `admin` address.
+    ///
+    /// The admin has no special powers over announcements (anyone can publish,
+    /// anyone can query) — the role exists purely to allow future upgrades of
+    /// the contract if the workspace adopts the `contract-upgrade` pattern.
+    /// Pass the zero/any address if you want an effectively immutable registry.
+    pub fn init(env: Env, admin: Address) -> Result<(), AnnouncementError> {
+        if env.storage().instance().has(&DataKey::Admin) {
+            return Err(AnnouncementError::AlreadyInit);
+        }
+        env.storage().instance().set(&DataKey::Admin, &admin);
+        env.storage()
+            .instance()
+            .set(&DataKey::AnnouncementCount, &0u64);
+        Ok(())
+    }
+
+    /// Return the admin address, if any.  Exposed for upgrade tooling.
+    pub fn get_admin(env: Env) -> Option<Address> {
+        env.storage().instance().get(&DataKey::Admin)
+    }
+
+    // ------------------------------------------------------------------------
+    // Publish
+    // ------------------------------------------------------------------------
+
+    /// Publish a stealth announcement.
+    ///
+    /// # Arguments
+    /// * `ephemeral_pubkey` – ephemeral public key R.  Variable length; the
+    ///   contract does *not* validate the point (validation is the scanner's
+    ///   responsibility and skipping it keeps the registry lightweight and
+    ///   curve‑agnostic).  However we do reject empty bytes and cap length at
+    ///   `MAX_PUBKEY_LEN` to prevent griefing.
+    /// * `view_tag` – first byte of `H(shared_secret)`.  The contract does
+    ///   **not** verify it (the sender could even lie); recipients do the
+    ///   check off‑chain and simply skip false positives.
+    ///
+    /// # Returns
+    /// The `announcement_index` assigned to this entry.
+    ///
+    /// # Permissions
+    /// **Any** address may call `publish`.  Announcements are inherently
+    /// self‑authenticating via the ECDH that recipients run; spamming costs
+    /// the sender transaction fees and recipients' view‑tag filter discards
+    /// junk at ~1/256 false‑positive rate.
+    pub fn publish(
+        env: Env,
+        ephemeral_pubkey: Bytes,
+        view_tag: u32,
+    ) -> Result<u64, AnnouncementError> {
+        if ephemeral_pubkey.is_empty() {
+            return Err(AnnouncementError::EmptyPubkey);
+        }
+        if ephemeral_pubkey.len() > MAX_PUBKEY_LEN {
+            return Err(AnnouncementError::PubkeyTooLong);
+        }
+        // Mask to the low 8 bits so the stored value is always 0..=255
+        // regardless of what the caller passes.  Scanners only inspect one
+        // byte; keeping the range small makes the on‑chain data uniform and
+        // avoids accidentally leaking a 32‑bit correlate.
+        let view_tag_clamped = view_tag & 0xFF;
+
+        let count: u64 = env
+            .storage()
+            .instance()
+            .get(&DataKey::AnnouncementCount)
+            .unwrap_or(0);
+
+        let index = count
+            .checked_add(1)
+            .expect("announcement index overflow");
+
+        env.storage()
+            .instance()
+            .set(&DataKey::AnnouncementCount, &index);
+
+        let announcement = StealthAnnouncement {
+            ephemeral_pubkey: ephemeral_pubkey.clone(),
+            view_tag: view_tag_clamped,
+            announcement_index: count,
+            timestamp: env.ledger().timestamp(),
+        };
+
+        env.storage()
+            .persistent()
+            .set(&DataKey::Announcement(count), &announcement);
+
+        AnnouncementPublished {
+            announcement_index: count,
+            view_tag: view_tag_clamped,
+        }
+        .publish(&env);
+
+        Ok(count)
+    }
+
+    // ------------------------------------------------------------------------
+    // Query (single)
+    // ------------------------------------------------------------------------
+
+    /// Fetch a single announcement by its monotonic `announcement_index`.
+    pub fn get_announcement(env: Env, announcement_index: u64) -> Option<StealthAnnouncement> {
+        env.storage()
+            .persistent()
+            .get(&DataKey::Announcement(announcement_index))
+    }
+
+    /// Total number of announcements ever published.
+    pub fn get_announcement_count(env: Env) -> u64 {
+        env.storage()
+            .instance()
+            .get(&DataKey::AnnouncementCount)
+            .unwrap_or(0)
+    }
+
+    // ------------------------------------------------------------------------
+    // Query (paginated range)
+    // ------------------------------------------------------------------------
+
+    /// Fetch announcements by inclusive index range: `[start_index, end_index]`.
+    ///
+    /// # Pagination cursors
+    /// The caller uses `announcement_index` as a cursor.  For example:
+    /// * first page: `start = 0, end = min(99, count - 1)`
+    /// * next page:  `start = prev_end + 1, end = min(start + 99, count - 1)`
+    ///
+    /// # Limits
+    /// At most `MAX_PAGE_SIZE` entries are returned per call.  Use multiple
+    /// calls to walk the full set — the monotonic index guarantees you won't
+    /// miss or double‑count entries as new announcements are appended.
+    ///
+    /// Gaps (e.g. if an individual entry were somehow missing) are skipped
+    /// silently — this matches the behaviour of the `subscription_logging`
+    /// contract and keeps iteration simple.
+    pub fn get_announcements_range(
+        env: Env,
+        start_index: u64,
+        end_index: u64,
+    ) -> Result<Vec<StealthAnnouncement>, AnnouncementError> {
+        if end_index < start_index {
+            return Err(AnnouncementError::InvalidRange);
+        }
+        let range_size = end_index - start_index + 1;
+        if range_size > MAX_PAGE_SIZE {
+            return Err(AnnouncementError::RangeTooLarge);
+        }
+
+        let mut results = vec![&env];
+        for idx in start_index..=end_index {
+            if let Some(a) = Self::get_announcement(env.clone(), idx) {
+                results.push_back(a);
+            }
+        }
+        Ok(results)
+    }
+
+    /// Convenience: return the last `limit` announcements (most recent first).
+    ///
+    /// Equivalent to calling `get_announcement_count()` then building a
+    /// range `[count - limit, count - 1]`.  Useful for UI "latest" widgets.
+    ///
+    /// `limit` is capped at `MAX_PAGE_SIZE`.
+    pub fn get_latest_announcements(
+        env: Env,
+        limit: u64,
+    ) -> Result<Vec<StealthAnnouncement>, AnnouncementError> {
+        let count = Self::get_announcement_count(env.clone());
+        if count == 0 {
+            return Ok(vec![&env]);
+        }
+        let effective_limit = if limit > MAX_PAGE_SIZE {
+            MAX_PAGE_SIZE
+        } else {
+            limit
+        };
+        let start = count.saturating_sub(effective_limit);
+        let end = count - 1;
+
+        let page = Self::get_announcements_range(env.clone(), start, end)?;
+        // Reverse so newest is first.
+        let mut reversed = vec![&env];
+        for i in (0..page.len()).rev() {
+            reversed.push_back(page.get_unchecked(i).clone());
+        }
+        Ok(reversed)
+    }
+
+    // ------------------------------------------------------------------------
+    // Admin-only helpers (none of them can censor announcements)
+    // ------------------------------------------------------------------------
+
+    fn require_admin(env: &Env) -> Result<(), AnnouncementError> {
+        let admin: Address = env
+            .storage()
+            .instance()
+            .get(&DataKey::Admin)
+            .ok_or(AnnouncementError::NotAdmin)?;
+        admin.require_auth();
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test;