# Extending the Quality of Secure Service Model to Multi-Hop Networks
## 2 Related Work  
Network architects need methods to quantify the security available in their systems. Ideally, those methods could also help to increase security, without impacting flexibility. Incorporating more security or reliability mechanisms into a system is much easier than it is to quantify the resulting security. By analogy, consider computer performance metrics. To quantify the performance of a computer, it is generally accepted that \"the only consistent and reliable measure of performance is the execution time of real programs, and that all proposed alternatives to time as the metric or to real programs as the items measured have eventually led to misleading claims or even mistakes in computer design\" [5]. With such a clear metric, it is unsurprising that computer performance has steadily improved over several decades. One technique that has demonstrably improved reliability, as well as potentially improved security based on the specific applications, is to fragment and distribute data across communication channels [6, 7]. Signaling System Number 7 (SS7) [8, 9], Redundant Array of Inexpensive Disks (RAID) [5], transmission diversity within 5G cellular networks [10], and Perfectly Secure Message Transmission (PSMT) [11, 12, 13, 14] are all examples of using two or more channels to increase system reliability. Research has also evaluated multiple channels for sensor networks [15]. These examples are inspiration for the multi-channel architecture introduced in conjunction with the QoS model. Directly comparing the security of those respective applications, including an arbitrary multi-channel communication architecture, is challenging without the QoS modeling framework. There are some similarities between the proposed fragmentation of data across multiple communication channels and Multiple-Input Multiple-Output (MIMO) wireless communication architectures as defined by various standards [16]. MIMO exploits multi-path propagation within the radio frequency spectral medium to enhance the performance of a single data signal. The channels referred to in the QoS model can be considered logical channels, as opposed to their physical implementations, because the QoS model resides at a higher layer of the networking stack. With that, the QoS model may utilize any possible physical medium for connectivity to the fragment and spread the data across the multiple connections as a technique to increase the security of the transmissions. To compare the security of one network to another, a set of quantifiable and repeatable metrics that account for the confidentiality, integrity, and availability of the network is essential. Methods already exist for assessing and improving the availability of a network. These are conveyed in traditional QoS metrics [17]. Metrics that measure confidentiality and integrity can be derived using a probabilistic model that considers data leakage and data corruption in place of confidentiality and integrity, and thereby quantify the QoS. As shown in Figure 1, a communication network provides a channel for a user to send data across, and that channel may be comprised of one or multiple channels, which should be transparent to the end-user. The QoS model allows the direct and repeatable quantification of the security, specifically the confidentiality and integrity, available in a single or multi-channel network under static configurations. Authentication, which is based upon and derivative of confidentiality and integrity, has been demonstrated to be feasible using multiple transmission paths [18]. In this approach, the quantification of security is based upon probabilities that attackers, whether they are adversarial listeners or disruptors, are able to gain access to or change the original message. The attackers may also only have access to a portion of the channels within the network. Message fragmentation and duplication across the available channels provide demonstrably improved theoretical performances at the expense of the increased complexity of the network architecture.