# New Security Improvements in Next-Generation Passive Optical Networks Stage 2 +
## 6 Conclusions  
In this article, we focused on security problems in next-generation passive optical networks stage 2. We propose four security improvements in the NG-PON2. Our security improvements use physical unclonable functions, correction codes, and robust cryptographic algorithms in the NG-PON2. The first security improvement (SI-NG-PON2) is based on PUFs and correction codes. PUFs bring a higher level of security and reduce cost. PUFs do not need a secured nonvolatile memory for storing authentication/encryption keys. These keys are generated on the fly by PUFs. For this reason, authentication/encryption keys cannot be copied from the nonvolatile memory and an attacker cannot clone a device. The disadvantage of PUFs is a noise in output responses. It is no problem in the simplest scenario, when PUFs are used only for authentication. In this case, the Hamming distance is used for a decision whether a device will be authenticated or not. In our security improvement (SI-NG-PON2) we need that PUFs will generate stable cryptographic keys. For this purpose, we use a correction code (fuzzy extractor) to make stable cryptographic keys from noisy outputs of PUFs. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Security Issue** & **NG-PON2** & **Our Security Improvements** \\ \hline \hline Clone an ONU & **Yes** & **No** \\ \hline Encryption of a XGEM & **No** & **Yes** \\ payload provides & (uses AES-CTR-128) & (uses AES-CMAC-128) \\ integrity of data & & \\ \hline Encryption of the & **No** & **Yes** \\ encryption keys provides & (uses AES-ECB-128) & (uses AES-CMAC-128) \\ integrity of data & & \\ \hline Integrity protection & & \\ and data origin & **Yes** & **No** \\ verification for OMCI & (uses AES-CMAC-32) & (uses AES-CMAC-64) \\ messages enables & & \\ a guessing attack & & \\ \hline Mutual authentication & & \\ between an ONU and & **No** & **Yes** \\ an OLT CT is mandatory & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison between NG-PON2 and our security improvements in selected security issues. The disadvantage of correction codes is that they need some additional memory space. The second security improvement ensures confidentiality and integrity for an XGEM payload and data encryption keys by AES-CMAC-128. The third security improvement ensures integrity protection and data origin verification for OMCI messages by AES-CMAC-64, which is immune against guessing attacks. The last security improvement introduces mandatory mutual authentication between an ONU and OLT CT. So an attacker cannot impersonate an OLT CT. In this article, we showed how PUFs can be implemented in the NG-PON2. We presented advantages of using PUFs in the NG-PON2. The main advantage is that an ONU cannot be cloned. Therefore, an unauthorized ONU cannot be active in the NG-PON2. Our security improvements involve authentication, encryption, integrity protection, and data origin verification methods that ensure a higher level of security in the NG-PON2. Our security improvement SI-NG-PON2 can be compared to biometric cryptographic systems. Responses of PUFs can be compared to biometric information of a person. Just as a biometric cryptographic system must have some database of biometric information, SI-NG-PON2 must has a database of CRP and helper data. This database must handles the overload like a database with biometric information. There is a minimum latency increase in SI-NG-PON2 compared to NG-PON2. There is the same latency like in biometric cryptographic systems. The creation of a response takes roughly the same time like a take of a biometric information. Our security improvement SI-NG-PON2 requires new PLOAM messages, as mentioned in Section 4. The specification of NG-PON2 networks defines several PLOAM messages but there is not full range specification. On the other words, a vendor is able to define own PLOAM message(s) between OLT and ONU. We rely on this fact with our solution, which may add overhead or delay in key establishment between OLT and ONU.