# Evaluation and Improvement of Internet Printing Protocol Based on HCPN Model Detection Method
## 6 Discussion  
Table 6 shows the comparison of the results of the state space before and after the improvement. As compared to previous results, before the improvement, the number of transitions and places, as well as the number of state nodes and arcs of the improved model, had increased significantly, which was typical. The reason was explained in Section 4.2. By comparing the definition (8) with the definition (18), we found that the improved scheme only increased the signature step of the client and the verification step of the server. There were the internal data processing steps of the communicating parties, which were not visible to the outside world, and would not affect the external handshake process of the standard protocol. For each authentication, the communication parties still followed the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Before** & **After** \\ \hline Nodes & 875 & 1718 \\ Arcs & 2593 & 5988 \\ Status & Full & Full \\ Nodes(SCC) & 875 & 1718 \\ Arcs(SCC) & 2593 & 5988 \\ Home Markings & 875 * & 1718 * \\ Live Transitions & 0 & 0 \\ Dead Transitions & 875 * & 1718 * \\ \hline \hline \end{tabular}  
* An asterisk represents a terminal state node.  
\end{table} 
Table 6: Comparison of state space before and after improvement. Figure 14: Improved server entity. sequence from MSG1 to MSG8 to complete all the steps. This guaranteed the equivalence and verifiability of the improved scheme, as compared to the standard protocol. After modeling correctly, we used the Sim tool again to observe the end-state of the model and obtained the end-state vector (ED, SESSIONKEY, STATUS) = (\"replay_ED\", NULL, \"Closed\"), as shown in Figure 15. This showed that when the adversary had activated the replay attack and replayed the early data ED multiple times, the server detected the abnormality, did not generate the subsequent session key, and closed the session, which ensured the authentication security. The improved scheme of introducing random number signature enhanced the server's ability to resist multiple replay attacks, which was proved by the experimental results. The reason for the success of this scheme was related to the following two points: First, every time the client used the 0-RTT authentication, it attached a newly generated random number rand and signed it to the early data. This ensured that the random number could only be generated by the client and was different every time. The adversary could only replay but could not tamper or forge the random number because they did not have a client-signing private key. Second, the server cached the random number in the last session resumption request and compared it with the newly decrypted random number. Once the two were equal, it indicated that the early data ED had been replayed, and the handshake should be closed immediately. In general, the optimized protocol only added a signature to the client's session recovery request, which was a very small cost for the processing speed of modern computers and the transmission speed of the network. The return was that it effectively enhanced the server's ability to perceive and identify replay attacks. In addition, the added signature would not affect other messages, especially the finished message sent by the last communication parties. The change introduced by the new scheme was only the following: the  
Figure 15: Improved scheme’s termination state. variable \(c_{\text{8}}\) in Definition (14) was replaced by \(c_{\text{8}}^{\prime}\) in Definition (18). This did not introduce any structural changes to the computing. It should be noted that the signature algorithm used by the optimization protocol was recommended for a fixed algorithm, so that there was no need to add the content of the negotiation parameters in the client-hello message.