# New Security Improvements in Next-Generation Passive Optical Networks Stage 2 +
## 4 Our Proposal of Security Improvements in NG-PON2
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Octet** & **Content** & **Description** \\ \hline
1–2 & ONU-ID & Directed message to one ONU. \\ \hline
3 & Message type ID & 0x1D, “Request\_Registration\_PUF”. \\ \hline
4 & SegNo & Eight-bit unicast PLOAM sequence number. \\ \hline
5–40 & Challenge + helper data & A string of 36 octets that combines a \\  & & & challenge and helper data. The challenge \\  & & & is separated from the helper data by the \\  & & & characters \(\parallel\). Unused byte positions \\  & & & are filled by 0x00 values. \\ \hline
41–48 & MIC & Message integrity check computed using \\  & & & the default PLOAM integrity key. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Content of Request_Registration_PUF message. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Message** & **Message Name** & **Function** & **Trigger** & **Effect of Receipt** \\ \hline
0x1D & Registration \_PUF & To report the \_PUFIn the second step, the ONU sends the Registration_ID_PUF to the OLT CT. If the OLT CT receives the Registration_ID_PUF, then it will compare the received Registration_ID_PUF with the response from its CRP database that creates the CRP pair with the challenge that the OLT CT sent to the ONU at the previous step. If they are equal, the ONU will be authenticated, and the MSK and derived shared keys can be computed by using the Registration_ID_PUF instead of the Registration_ID. The response is called Registration_ID_PUF on the ONU's side in SI-NG-PON2. The process of the calculation and verification of the Registration_ID_PUF by an OLT CT and an ONU using the Request_Registration_PUF (Request_Registration_PUF1 and Request_Registration_PUF2) and Registration_PUF messages is shown in Figure 3.  
There are many PUFs and correction codes that are suitable to use in SI-NG-PON2. We propose using optical PUFs or memory-based PUFs. For example, a photonic PUF [12] is fast, simple, compact, and low-cost, or a DRAM PUF can provide a large number of input challenges and can be used in low-cost identification applications. Next, we propose to use fuzzy extractors [18; 19] for correction of the PUF response or the error correction code [24], which works without any further helper data. In this case, the Request_Registration_PUF message in octets 5-40 contains only the challenge without the helper data. Unused byte positions (originally intended for helper data) are filled by 0 \(\times\) 00 values. Another security threat we recognize in using the encryption algorithms AES-CTR and AES-ECB in NG-PON2 is that these algorithms not provide integrity of the encrypted data. AES-CTR is used for encryption of an XGEM payload, and AES-ECB is used for encryption of the data encryption keys. If an attacker changes the transmitted encrypted XGEM payload or the encrypted data encryption keys (conducts a bit-flipping attack), the receiver cannot recognize the changed data. There are several modes for block ciphers that ensure confidentiality, authenticity and integrity of binary data, for example, the Galois counter mode (GCM) [37], cipher block chaining-message authentication code (CCM) [38], EAX [39], offset codebook (OCB) [40], and the CMAC [28]. We recommend the AES-CMAC algorithm with a 128-bit key for encryption of an XGEM payload and the data encryption keys in NG-PON2. The next security threat we evaluate in using the AES-CMAC-32 algorithm for integrity protection and data origin verification for OMCI messages in NG-PON2 involves the following, according to [41], at least a 64-bit MAC should be used for protection against guessing attacks. The AES-CMAC-64 algorithm is used for integrity protection and data origin verification of PLOAM messages. We propose to also use the AES-CMAC-64 algorithm for integrity protection and data origin verification for OMCI messages to increase security in NG-PON2. The last security threat we discern is the possibility of using only unilateral authentication when an ONU is authenticated to an OLT CT in NG-PON2.