## 3 Risk Assessment-Based Dynamic Access Model
### Request a Risk Assessment
#### 3.1.1 Establishment of Risk Assessment Indicators for Access Requests  
Since risk is an abstract and dynamic concept, to assess risk better and reflect real scenarios, this paper divides risk assessment into three layers, namely the target layer, attribute layer, and the evidence layer, and refines the three attributes layer by layer into the evidence values that the system can directly obtain in the process of requesting access. The target layer is the target we evaluate risk. In terms of the division of the attribute layer, because this paper mainly evaluates the risk that the access may cause to the system, the attribute layer is divided into three main aspects according to the source of the risk: main attribute, resource attribute, and environmental attribute. Below we will analyze in detail the selection of indicators from three aspects: subject, resource, and environment. In terms of subject attributes, the subject here is mainly the initiator of the request, mainly referring to the user, but not limited to the user, but also an application, a virtual machine or a workflow, and so on. The request is the process of the subject requesting the system to operate a certain resource, so the request is embodied as the subject's behavior in the system. On the one hand, the behavior is the specific operation of the subject on the resource request, such as reading, writing, or copying a resource request. These operations have different sensitivity levels. From the perspective of possible risks to the system, the sensitivity level of writing is the highest; On the other hand, the historical preference behavior of the subject is mainly reflected in the common time of the subject initiating the request, the common IP, the historical request success rate, the number of historical login failures, etc. The system maintains the behavior history of each subject for the current request risk assessment. For example, when a subject fails to log in multiple times, the system will determine that the request is a potential attack and has high risk, so it will ask for a verification code when logging in next time; and a subject initiates a written request to the resource. The system query finds that if the historical success rate of the subject's request to write to the resource is high, the subject will accept the request because the risk of this request is low. Regarding resource attributes, resources mainly refer to data in this article. Access control's primary goal is to prevent unauthorized access to system resources. However, data security will also be somewhat impacted by how vulnerable the data is. Here we define  
Figure 1: Dynamic Access Control Model Overall Scheme. the vulnerability of data to refer to various security risks in the data itself or the protection methods of the data. Attackers can relatively easily destroy, obtain, and tamper with the data by exploiting such security risks. First of all, the storage method of data resources is also one of the factors affecting the vulnerability of resources. When data are encrypted and stored in the system, if the decryption key is unavailable, even if the adversary obtains the encrypted data, there is no way to decrypt it. Secondly, the importance of data is also a factor that affects the vulnerability of resources. If the importance of data is high, the risk of accessing requests to operate on it will also increase. In terms of environmental attributes, this paper divides the environmental attributes into two aspects, namely, the environment of the terminal and the environment of the server. The terminal environment is mainly used to measure the security of the user terminal, such as the IP packet loss rate. If the current IP packet loss rate is high, it means that the network connection where the user is located is unstable, which not only reduces the quality of service but also brings viruses to resources.