feat: adding time check contract

Nargo.toml

@@ -1,4 +1,5 @@
 [workspace]
 members = [
-"src/token_contract"
+"src/token_contract",
+"src/time_check_contract"
 ]

src/time_check_contract/Nargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "time_check_contract"
+authors = [""]
+compiler_version = ">=1.0.0"
+type = "contract"
+
+[dependencies]
+aztec = { git = "https://github.com/AztecProtocol/aztec-packages/", tag = "aztec-packages-v0.72.1", directory = "noir-projects/aztec-nr/aztec" }

src/time_check_contract/README.md

@@ -0,0 +1,20 @@
+# Timestamp verification in private circuits
+
+## Overview
+
+In private circuits, timestamps are challenging to use since circuits are timeless, and proofs cannot depend on when they are generated. Aztec’s PrivateContext does not include a timestamp variable due to the transaction lifecycle: proving → broadcasting → inclusion on-chain.
+
+However, many DeFi applications require time-based logic, such as vesting schedules. The usual alternative block numbers may not be suitable in all cases.
+
+## Solution
+
+To verify timestamps privately:
+
+- Users optimistically input the timestamp in the circuit.
+- A call to a public function is enqueued to check its validity against the execution timestamp.
+- If incorrect, the transaction and state changes (private and public) revert.
+- To prevent privacy leaks, this intermediary contract TimeCheck is used:
+  - Instead of `ContractA(private)` → `ContractA(public)`,
+  - Transaction flows as `ContractA(private)` → `TimeCheck(private)` → `TimeCheck(public)`.
+
+This prevents observers from linking the timestamp check to a specific contract, ensuring confidentiality.

src/time_check_contract/src/main.nr

@@ -0,0 +1,54 @@
+use dep::aztec::macros::aztec;
+
+#[aztec]
+// Timestamp validation in private circuits, for secure and anonymous time-based logic execution.
+contract TimeCheck {
+
+    /** ==========================================================
+     * ========================= IMPORTS =========================
+     * ======================================================== */
+
+    use dep::aztec::macros::functions::{internal, private, public};
+
+    /** ==========================================================
+     * ==================== PRIVATE ENTRYPOINTS ==================
+     * ======================================================== */
+
+    #[private]
+    fn timestamp_gt(t: u64) {
+        TimeCheck::at(context.this_address()).assert_timestamp_gt(t).enqueue(&mut context);
+    }
+
+    #[private]
+    fn timestamp_lt(t: u64) {
+        TimeCheck::at(context.this_address()).assert_timestamp_lt(t).enqueue(&mut context);
+    }
+
+    /** ==========================================================
+     * ===================== PUBLIC ENTRYPOINTS ==================
+     * ======================================================== */
+
+    #[public]
+    #[internal] // TODO: is internal needed here?
+    fn assert_timestamp_gt(t: u64) {
+        let current_t = context.timestamp();
+        // TODO: define if = should pass or not
+        assert(current_t >= t, "Timestamp not greater than current");
+    }
+
+    #[public]
+    #[internal] // TODO: is internal needed here?
+    fn assert_timestamp_lt(t: u64) {
+        let current_t = context.timestamp();
+        // TODO: define if = should pass or not
+        assert(current_t <= t, "Timestamp not lesser than current");
+    }
+
+    // NOTE: assert_timestamp_eq has no actual application (prone to fail)
+    /* TODO:
+     * Implement:
+     * - timestamp_gt_by_delta(t:64, delta: 64)
+     * - timestamp_lt_by_delta(t:64, delta: 64)
+     */
+}
+