From 800b9a1099187d61a4413c396e924b59821474c5 Mon Sep 17 00:00:00 2001
From: shreyas-londhe <shreyas_londhe@outlook.com>
Date: Thu, 26 Sep 2024 12:26:28 +0530
Subject: [PATCH] feat: added range checks to RevealSubstring template

---
 .../circuits/helpers/reveal-substring.circom  | 13 ++++++
 .../circuits/tests/reveal-substring.test.ts   | 45 +++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/packages/circuits/helpers/reveal-substring.circom b/packages/circuits/helpers/reveal-substring.circom
index e585d1d1..f3197e71 100644
--- a/packages/circuits/helpers/reveal-substring.circom
+++ b/packages/circuits/helpers/reveal-substring.circom
@@ -19,6 +19,19 @@ template RevealSubstring(maxLength, maxSubstringLength, shouldCheckUniqueness) {
 
     signal output substring[maxSubstringLength];
 
+    // Substring start index should be less than maxLength
+    signal isSubstringStartIndexValid <== LessThan(log2Ceil(maxLength))([substringStartIndex, maxLength]);
+    isSubstringStartIndexValid === 1;
+
+    // Substring length should be less than maxSubstringLength + 1
+    signal isSubstringLengthValid <== LessThan(log2Ceil(maxSubstringLength + 1))([substringLength, maxSubstringLength + 1]);
+    isSubstringLengthValid === 1;
+
+    // substring index + substring length should be less than maxLength + 1
+    signal sum <== substringStartIndex + substringLength;
+    signal isSumValid <== LessThan(log2Ceil(maxLength + 1))([sum, maxLength + 1]);
+    isSumValid === 1;
+
     // Extract the substring
     component selectSubArray = SelectSubArray(maxLength, maxSubstringLength);
     selectSubArray.in <== in;
diff --git a/packages/circuits/tests/reveal-substring.test.ts b/packages/circuits/tests/reveal-substring.test.ts
index ea035184..64861579 100644
--- a/packages/circuits/tests/reveal-substring.test.ts
+++ b/packages/circuits/tests/reveal-substring.test.ts
@@ -143,4 +143,49 @@ describe("RevealSubstring Circuit", () => {
             ...Array(13).fill(0n),
         ]);
     });
+
+    it("should fail when substringStartIndex is equal to maxLength", async () => {
+        const input = {
+            in: Array(256).fill(1),
+            substringStartIndex: 256, // Equal to maxLength
+            substringLength: 1,
+        };
+        await expect(circuit.calculateWitness(input)).rejects.toThrow();
+    });
+
+    it("should fail when substringStartIndex is greater than maxLength", async () => {
+        const input = {
+            in: Array(256).fill(1),
+            substringStartIndex: 257, // Greater than maxLength
+            substringLength: 1,
+        };
+        await expect(circuit.calculateWitness(input)).rejects.toThrow();
+    });
+
+    it("should fail when substringLength is equal to maxSubstringLength", async () => {
+        const input = {
+            in: Array(256).fill(1),
+            substringStartIndex: 0,
+            substringLength: 16, // Equal to maxSubstringLength
+        };
+        await expect(circuit.calculateWitness(input)).rejects.toThrow();
+    });
+
+    it("should fail when substringLength is greater than maxSubstringLength", async () => {
+        const input = {
+            in: Array(256).fill(1),
+            substringStartIndex: 0,
+            substringLength: 17, // Greater than maxSubstringLength
+        };
+        await expect(circuit.calculateWitness(input)).rejects.toThrow();
+    });
+
+    it("should fail when substringStartIndex + substringLength is greater than maxLength", async () => {
+        const input = {
+            in: Array(256).fill(1),
+            substringStartIndex: 250,
+            substringLength: 7, // 250 + 7 > 256
+        };
+        await expect(circuit.calculateWitness(input)).rejects.toThrow();
+    });
 });