hoặc thời gian để cố gắng trở lại-nếu không có tên và phiên bản của phần mềm ứng dụng của máy chủ Đối với tài liệu HTML, tiêu đề được đưa ra trong HTML Một thông điệp cảnh báo chi tiết hơn so với những gì có trong cụm từ lý do của phản ứng HTTP loại phạm vi mà một máy chủ | In logging these activities be sure to also capture data such as Who performed the action Where the request originated What the resource in question was What the referring page was What time and date the event occurred .and any other information that might be useful in an investigation. Availability It doesn t matter how good your application is if nobody can reach it. Because applications rely on the availability of resources and data it is important to take steps to ensure that these other systems are also available. One way of measuring availability can be expressed by the myth of nines. The saying our system is available of the time can be interpreted to mean the system is down for only minutes a year or minutes a day see Table 2-1 for a matrix measuring availability . Table 2-1. Availability matrix Availability Downtime Year Downtime Month Downtime Week 98 days days hours 99 days days hours days hours minutes hours minutes minutes minutes minutes minutes minutes seconds seconds seconds seconds seconds More often than not availability measurements are expressed this way in marketing documents presumably because it looks impressive. However data such as this is often used in legal contracts and service level agreements so it is worth remembering. Trust Trust is the ability to rely on the integrity of a particular person or thing. For a web application trust most often applies to users. To develop trust with a user we must Ensure proper authentication. Confirm that the user is performing only allowed actions. Validate and inspect all data given. Log and report all significant activity. 36 Chapter 2 Web Security Download at The problem with trust is that it is always a leap of faith. You never really know for sure whether something or someone can be trusted. Risk Analysis What if something goes wrong We
