Retrieve query string with character "+"

I have in my controller, a method where I get a Query String , decrypt it and use the data in my query. However, when the encrypted value has a + sign, it is not recovered by Request.QueryString . I soon get an error trying to decrypt.

Follow my controller:

 public ActionResult 
       {

            //Recebe a string Criptografada
            string param = Request.QueryString["param"];// Nesta Parte o sinal de + não é recuperado
            string nome = HttpUtility.UrlDecode(param);

            //Instancia obj da DLL
            Criptografia cr = new Criptografia();
            //Descriptografa a string
            string nomeDescrypt = cr.Decrypt(nome);// recebo o erro

            //Separa a string por meio do "|"
            string[] stringSeparators = new string[] { "|" };
            var result = nomeDescrypt.Split(stringSeparators, StringSplitOptions.None);

            //Converte para o tipo de dado correto
            var matricula = Convert.ToInt32(result[0]);
            var contrato = Convert.ToInt32(result[1]);

            var usuarios = usuarioRepository.Lista.Where(r => r.CdMatricula == matriculaUser && r.SqContrato == contratoUser).FirstOrDefault();

            return View();
        }

What is retrieved: Parameter example passed: ./?param=kmFxK8ID3ç ZdGGbQN9oJA ==

The sign of + disappears, and space is left in place.