Allowing inifinity point in deserialization

src/secp256k1/include/GroupElement.h

@@ -77,6 +77,8 @@ class GroupElement final {
   static constexpr size_t memoryRequired() { return serialize_size; }
   unsigned char* serialize() const;
   unsigned char* serialize(unsigned char* buffer) const;
+  // The function deserializes the GroupElement and checks the validity,
+  // it accepts infinity point, handle it based on your use case
   unsigned const char* deserialize(unsigned const char* buffer);
 
   // These functions are for READWRITE() in serialize.h

src/secp256k1/src/cpp/GroupElement.cpp

@@ -530,7 +530,7 @@ const unsigned char* GroupElement::deserialize(const unsigned char* buffer) {
 
     secp256k1_gej_set_ge(reinterpret_cast<secp256k1_gej *>(g_), &result);
 
-    if (!secp256k1_ge_is_valid_var(&result)) {
+    if (!secp256k1_ge_is_valid_var(&result) && !result.infinity) {
         throw std::runtime_error("GroupElement: deserialize failed");
     }
     return buffer + memoryRequired();

src/sigma/test/serialize_test.cpp

@@ -31,20 +31,22 @@ BOOST_AUTO_TEST_CASE(group_element_invalid)
     buffer[0] = std::rand();
     buffer[1] = std::rand();
 
+    // Making the point not infinity as it is allowed in deserialization
+    buffer[33] = 0;
+
     secp_primitives::GroupElement resulted;
     BOOST_CHECK_THROW(resulted.deserialize(buffer), std::exception);
 }
 
-//This test is not valid already, as infinity point is invalid in check secp256k1_ge_is_valid_var, GroupElement.cpp:533
-//BOOST_AUTO_TEST_CASE(group_element_serialize_infinity)
-//{
-//    secp_primitives::GroupElement initial;
-//    unsigned char buffer [initial.memoryRequired()];
-//    initial.serialize(buffer);
-//    secp_primitives::GroupElement resulted;
-//    resulted.deserialize(buffer);
-//    BOOST_CHECK(initial == resulted);
-//}
+BOOST_AUTO_TEST_CASE(group_element_serialize_infinity)
+{
+    secp_primitives::GroupElement initial;
+    unsigned char buffer [initial.memoryRequired()];
+    initial.serialize(buffer);
+    secp_primitives::GroupElement resulted;
+    resulted.deserialize(buffer);
+    BOOST_CHECK(initial == resulted);
+}
 
 BOOST_AUTO_TEST_CASE(scalar_serialize)
 {