From 06bc1c0d2bbeee8a20055148d5872dd2b08e3f89 Mon Sep 17 00:00:00 2001
From: Mathieu <60658558+enitrat@users.noreply.github.com>
Date: Wed, 18 Sep 2024 20:19:51 +0200
Subject: [PATCH] fix: ec_recover when point at infinity (#958)

* fix: y parity in ec_recover

* fix: ecrecover point at infinity
---
 crates/evm/src/precompiles/ec_recover.cairo | 29 +++++++++++++++------
 crates/utils/src/traits.cairo               |  7 +++++
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/crates/evm/src/precompiles/ec_recover.cairo b/crates/evm/src/precompiles/ec_recover.cairo
index 0262cd3d5..b18264568 100644
--- a/crates/evm/src/precompiles/ec_recover.cairo
+++ b/crates/evm/src/precompiles/ec_recover.cairo
@@ -1,13 +1,18 @@
-use core::starknet::secp256_trait::{recover_public_key, Signature};
+use core::starknet::secp256_trait::{
+    Signature, recover_public_key, Secp256PointTrait, is_valid_signature
+};
+use core::starknet::secp256_trait::{Secp256Trait};
 use core::starknet::{
-    EthAddress, eth_signature::{public_key_point_to_eth_address}, secp256k1::{Secp256k1Point}
+    EthAddress, eth_signature::{public_key_point_to_eth_address}, secp256k1::{Secp256k1Point},
+    SyscallResultTrait
 };
 use core::traits::Into;
 use evm::errors::EVMError;
 use evm::precompiles::Precompile;
+use utils::helpers::U8SpanExTrait;
 use utils::helpers::{ToBytes, FromBytes};
-use utils::traits::BoolIntoNumeric;
 use utils::traits::EthAddressIntoU256;
+use utils::traits::{NumericIntoBool, BoolIntoNumeric};
 
 const EC_RECOVER_PRECOMPILE_GAS_COST: u64 = 3000;
 
@@ -20,6 +25,8 @@ pub impl EcRecover of Precompile {
     fn exec(input: Span<u8>) -> Result<(u64, Span<u8>), EVMError> {
         let gas = EC_RECOVER_PRECOMPILE_GAS_COST;
 
+        // Pad the input to 128 bytes to avoid out-of-bounds accesses
+        let input = input.pad_right_with_zeroes(128);
         let message_hash = input.slice(0, 32);
         let message_hash = match message_hash.from_be_bytes() {
             Option::Some(message_hash) => message_hash,
@@ -29,12 +36,11 @@ pub impl EcRecover of Precompile {
         let v: Option<u256> = input.slice(32, 32).from_be_bytes();
         let y_parity = match v {
             Option::Some(v) => {
-                let y_parity = v - 27;
-                if (y_parity == 0 || y_parity == 1) {
-                    y_parity == 1
-                } else {
+                if !(v == 27 || v == 28) {
                     return Result::Ok((gas, [].span()));
                 }
+                let y_parity = v - 27; //won't overflow because v is 27 or 28
+                y_parity.into()
             },
             Option::None => { return Result::Ok((gas, [].span())); }
         };
@@ -55,7 +61,14 @@ pub impl EcRecover of Precompile {
 
         let recovered_public_key =
             match recover_public_key::<Secp256k1Point>(message_hash, signature) {
-            Option::Some(public_key_point) => public_key_point,
+            Option::Some(public_key_point) => {
+                // EVM spec requires that the public key is not the point at infinity
+                let (x, y) = public_key_point.get_coordinates().unwrap_syscall();
+                if (x == 0 && y == 0) {
+                    return Result::Ok((gas, [].span()));
+                }
+                public_key_point
+            },
             Option::None => { return Result::Ok((gas, [].span())); }
         };
 
diff --git a/crates/utils/src/traits.cairo b/crates/utils/src/traits.cairo
index 202a9f0d8..e325f72cf 100644
--- a/crates/utils/src/traits.cairo
+++ b/crates/utils/src/traits.cairo
@@ -45,6 +45,13 @@ pub impl BoolIntoNumeric<T, +Zero<T>, +One<T>> of Into<bool, T> {
     }
 }
 
+pub impl NumericIntoBool<T, +Drop<T>, +Zero<T>, +One<T>, +PartialEq<T>> of Into<T, bool> {
+    #[inline(always)]
+    fn into(self: T) -> bool {
+        self != Zero::<T>::zero()
+    }
+}
+
 pub impl EthAddressIntoU256 of Into<EthAddress, u256> {
     fn into(self: EthAddress) -> u256 {
         let intermediate: felt252 = self.into();