# A PEKS-Based NDN Strategy for Name Privacy
## 5 Experiments and Results
### Finding the Length of Input for the PEKS Scheme  
In the straight forward construction, the size of encrypted names becomes larger if there are many name components in a name. Encrypting each name component result in a large amount of size in a packet and a remaining space for content becomes smaller. The number of name components also affects the execution time because ciphertext generation and test algorithms are applied to each of the name components. As explained in this section's introduction, the multiple name components encryption construction is expected to provide faster processing and shorter ciphertext size. Therefore, in this section, we examine to find how many name components should be used as an input to the encryption algorithms. To this end, we assume the following setup. A list of names shared by the producer and the consumers is available for determining a suitable number of name components fed into the hash function.  
Compute \(\left\lceil\#C_{j}/\mathrm{d}\right\rceil\) to get the number of component inputs to the PEKS scheme, where divisor \(d\) is a positive integer and \(\#N_{j}\) is the number of name components of a name entry in the name list. The result  
Figure 10: Experimental setup.  
of this division determines the number of PEKS ciphertexts generation operations for the name entry. One can count the number of name entries having the same value for \(\lceil\#C_{j}/\mathrm{d}\rceil\), which is related to the number of PEKS ciphertext generation operations. As shown in Equations (2) and (3), the number of PEKS ciphertext components and that of corresponding trapdoor components are the same. Therefore, one can predict how many times one should execute PEKS ciphertext generation operations. In the same way, one can predict how many times the Test algorithm is run in the network if one can roughly figure out how many operations executed in the intermediate nodes. In our experiment, the producer's prefix is input to the PEKS scheme and we process the following steps:  
1. Each component of a content name without including the producer's prefix is used to generate PEKS ciphertexts and trapdoors.
2. The outputs, PEKS(\(P_{pub}\), \(N_{j}\)) or Trapdoor(\(P_{pub}\), \(N_{j}\)), of the PEKS scheme are concatenated to create interest packet.
3. Consumers send interest packets to retrieve data from the producer.
4. The producer disseminates trapdoors.  
Then \(d\) is increased by one for each experiment and do the same steps described above. These processes continue until there exits only one component in the ciphertext of content name. In these processes, interest packets are sent only by the consumer Con1 in Figure 10. Then we measure download time starting from PEKS ciphertexts creation until the data packet retrieval. In this experiment, consumer Con1 requests all content name listed in \(\mathbb{N}\).  
In general, if the number of PEKS ciphertexts decreases, the number of tests should also decrease. However, in PEKS_Strategy, the test process depends not only on the number of components but also on whether the number of trapdoor components in the trapdoors and PEKS ciphertexts in the interest packet is equal.  
As shown in Figure 11, when we increase the number of input components to the PEKS scheme, the test process executions significantly drop at 3. However, those executions increase again at 5 where several ciphertexts with the same length are required by several interest packets and trapdoor table is to lookup several times for the exact match according to Algorithm 1. It is significant when the whole of the content name is used as input to the PEKS scheme producing only one ciphertext. Figure 11 also shows the average download time for each number \(\mathrm{d}\) of input components to the PEKS scheme. The average number of tests and the average download time behaves in a similar way and the correlation ratio between them is 0.895189. However, these results actually depend on the name list which is shared between the consumers and the producer and also network operations.