Many model checking methods have been developed and applied to analyze cryptographic protocols. Most of them can analyze only one attack trace of a found attack. In this paper, we propose a very simple but practical model checking methodology for the analysis of cryptographic protocols. Our methodology offers an efficient analysis of all attack traces for each found attack, and is independent to model checking tools. It contains two novel techniques which are on-the-fly trace generation and textual trace analysis. In addition, we apply our method to two case studies which are TMN authenticated key exchanged protocol and Micali's contract signing protocol. Surprisingly, it turns out that our simple method is very efficient when the numbers of traces and states are large. Also, we found many new attacks in those protocols.