use IndexView + check for length of signature + add invalid tests

src/math/src/ed25519.cairo

@@ -291,13 +291,17 @@ fn check_group_equation(
 }
 
 fn verify_signature(msg: Span<u8>, signature: Span<u256>, pub_key: u256) -> bool {
-    let r: u256 = *signature.get(0).unwrap().unbox();
+    if (signature.len() != 2) {
+        return false;
+    }
+
+    let r: u256 = *signature[0];
     let r_point: Option<Point> = r.try_into();
     if (r_point.is_none()) {
         return false;
     }
 
-    let s: u256 = *signature.get(1).unwrap().unbox();
+    let s: u256 = *signature[1];
     let s_span: Span<u8> = s.into();
     let reversed_s_span = s_span.reverse();
     let s: u256 = reversed_s_span.span().into();

src/math/src/tests/ed25519_test.cairo

@@ -1,4 +1,4 @@
-use alexandria_math::ed25519::{p, Point, verify_signature};
+use alexandria_math::ed25519::verify_signature;
 
 // Public keys and signatures were generated with JS library Noble (https://github.com/paulmillr/noble-ed25519)
 
@@ -71,3 +71,17 @@ fn verify_signature_invalid() {
 
     assert!(!verify_signature(msg, signature.span(), pub_key), "Invalid signature");
 }
+
+#[test]
+#[available_gas(3200000000)]
+fn verify_signature_invalid_2() {
+    let pub_key: u256 = 0x040369a47bcee3ae0cb373037ec0d2e36cae4a3762e388ff0682962aef49f444;
+
+    let msg: Span<u8> = array![0x0].span();
+
+    let r_sign: u256 = 0xc71970448f7368c295d11cd64bb4fc7bb8899c830d9055832b6686b3f606b76d;
+    let s_sign: u256 = 0x68e015fa8775659d1f40a01e1f69b8af4409046f4dc8ff02cdb04fdc3585eb0d;
+    let signature = array![r_sign, s_sign];
+
+    assert!(!verify_signature(msg, signature.span(), pub_key), "Invalid signature");
+}