## 4 Innovation-Decision Model  
The adoption process of innovations (such as identifying, choosing, and implementing one security control over another, like CL-PKC over traditional PKI) can be described as  
Figure 1: Conceptual system architecture of a CL-PKC setup with a KGC and two users ID\({}_{A}\) and ID\({}_{B}\). To generate a secret key, the user needs to make a collaborative computation with the KGC, i.e., generating and combining \(sk_{1}\) and \(sk_{2}\). proposed by the five-phased Innovation-Decision Model [16]. This model can help shed light upon what stage and under what conditions an innovation was first discovered by an individual (e.g., a decision maker on security controls), and how decisions to either adopt or reject that innovation was made, as well as potential reinforcements of that decision. Note that innovation with regard to the Innovation-Decision Model does not necessarily mean a new invention. Indeed, the innovation might have been known for many years. Rather, it refers to a technology, process, method, etc., that is previously unknown to a particular individual (read 'decision maker'). This individual can, faced with this innovation and in contrast to current best-practices, norms, and knowledge, decide to either adopt or reject this (new) solution [33]. The Innovation-Decision Model five phases are: knowledge, persuasion, decision, implementation, and confirmation. Each one of these phases is depicted in Figure 2 and further described below. Knowledge --This phase of the model occurs when an individual first learns about the existence of an innovation (e.g., an idea, method, or practice) [16]. Some limited understanding of how the innovation works is gained in this phase which can be divided into three knowledge types. First, the innovation must not be new per se; it can have been invented a long time ago, but is perceived as new to the individual. This type of knowledge is known as 'awareness-knowledge', and can motivate individuals to learn more about the innovation [33]. For example, by gaining 'how-to-knowledge'--which is the next knowledge type--in which additional practical knowledge is sought to better understand the innovation and its uses. Last is 'principles-knowledge', where the individual not only knows how an innovation works, but also why it works, which increases the chances of effective use and adoption [33]. Persuasion--At the persuasion phase, the individual forms a favorable or unfavorable attitude towards the innovation [16]. That is to say, knowing how and why an innovation work does not necessarily mean an individual will or will not adopt it. Other, external, and more feeling-centered factors may affect the decision [33]. For example, social influences from peers and colleagues can affect the attitude towards and opinion about the innovation. The persuasion phase follows the knowledge phase, as individuals shape their attitude towards the innovation after they know about it [33]. Decision--The decision phase is where the individual engages in activities that lead to a decision being made on whether to adopt or reject the innovation [16]. While the decision to adopt or reject the innovation can be made at any point in the innovation-decision process (see step 'a' in Figure 2), this phase also captures two types of rejection as being either active or passive [33]. An active rejection means the individual has tried the innovation and considered adopting it but later decides not to (see step 'b' and 'd' in Figure 2), while a passive rejection means the individual never considered adopting the innovation in the first place (see step 'c' in Figure 2) [33]. Implementation--If the innovation is decided for adoption, this phase captures the innovation put into practice and the potential consequences thereof (see step 'b' in Figure 2) [16,33]. Confirmation--The last step of the process is the confirmation phase, in which the individual seeks reinforcement of an adoption or rejection decision already made [16].