P3P

 

P3P是万维网联盟（W3C）公布的一项隐私保护推荐标准，旨在为网上冲浪的 Internet用户提供隐私保护。现在有越来越多的网站在消费者访问时，都会收集一些用户信息。制定P3P标准的出发点就是为了减轻消费者因网站收集个人信息所引发的对于隐私权可能受到侵犯的忧虑。P3P标准的构想是：Web 站点的隐私策略应该告之访问者该站点所收集的信息类型、信息将提供给哪些人、信息将被保留多少时间及其使用信息的方式，如站点应做诸如 “本网站将监测您所访问的页面以提高站点的使用率”或“本网站将尽可能为您提供更合适的广告”等申明。访问支持P3P网站的用户有权查看站点隐私报告，然后决定是否接受cookie或是否使用该网站。

P3P官方文档。http://www.w3.org/TR/P3P/

因为IE 6的增强安全机制，通过<IFRAME>内嵌一个三方网页时，缺省设置不允许使用该第三方的cookie。当然不能通过修改IE配置来解决这个问题，但是通过P3P可以解决这个问题。

P3P常见的几种场景

Scenario 1: Web site basic.example.com uses a variety of images, all of which it hosts. It also includes some forms, which are all submitted directly to the site. This site can declare a single P3P policy for the entire site (or if different privacy policies apply to different parts of the site, it can declare multiple P3P policies). As long as all of the images and form action URIs are in directories covered by the site's P3P policy, user agents will automatically recognize the images and forms as covered by the site's policy.

Scenario 2: Web site busy.example.com uses a content distribution network called cdn.example.com to host its images so as to reduce the load on its servers. Thus, all of the images on the site have URIs at cdn.example.com. CDN acts as an agent to Busy in this situation, and collects no data other than log data. This log data is used only for Web site and system administration in support of providing the services that Busy contracted for. Busy's privacy policy applies to the images hosted by CDN, so Busy uses the HINT element in its policy reference file to point to a suitable policy reference file at CDN, indicating that such images are covered by example.com P3P policy.

Scenario 3: Web site busy.example.com also has a contract with an advertising company called clickads.example.com to provide banner ads on its site. The contract allows Clickads to set cookies so as to make sure each user does not see a given ad more than three times. Clickads collects statistics on how many users view each ad and reports them to the companies whose products are being advertised. But these reports do not reveal information about any individual users. As was the case in Scenario 2, Busy's privacy policies applies to these ads hosted by Clickads, so Busy uses the HINT element in its policy reference file to point to a suitable policy reference file at Clickads, indicating that Busy P3P policy applies to such embedded content served by clickads.example.com. The companies whose products are being advertised need not be mentioned in the Busy privacy policy because the only data they are receiving is aggregate data.

Scenario 4: Web site busy.example.com also has a contract with funchat.example.com to host a chat room for its users. When users enter the chat room they are actually leaving the Busy site. However, the chat room has the Busy logo and is actually covered by the Busy privacy policy. In this instance Funchat is acting as an agent for Busy, but -- unlike the previous examples -- their content is not embedded in the Busy site. Busy can use the HINT element in its policy reference file to point to a suitable Funchat policy reference file, that indicates that Funchat chat room is covered by Busy privacy policy, therefore facilitating a smoother transition to the chat room.

Scenario 5: Web site bigsearch.example.com has a form that allows users to type in a search query and have it performed on their choice of search engines located on other sites. When a user clicks the "submit" button, the search query is actually submitted directly to these search engines -- the action URI is not on bigsearch.example.com but rather on the search engine selected by the user. Bigsearch can declare the privacy policies for these search engines by using the HINTelement to point to their corresponding policy reference files. So when a user clicks the "submit" button, their user agent can check its privacy policy before posting any data. In order to make this search choice mechanism work, Bigsearch might actually have a form with an action URI on its own site, which redirects to the appropriate search engine. In this case, the user agent should check the search engine privacy policy upon receiving the redirect response.

Scenario 6: Web site bigsearch.example.com also has a form that allows users to type in a search query and have it simultaneously performed on ten different search engines. Bigsearch submits the queries, gets back the results from each search engine, removes the duplicates, and presents the results to the user. In this case, the user interacts only with Bigsearch. Thus, the only P3P policy involved is the one that covers the Bigsearch Web site. However, Bigsearch must disclose that it shares the users' search queries with third parties (the search Web sites), unless Bigsearch has a contract with these search engines and they act as agents to Bigsearch.

Scenario 7: Web site bigsearch.example.com also has banner advertisements provided by a company called adnetwork.example.com. Adnetwork uses cookies to develop profiles of users across many different Web sites so that it can provide them with ads better suited to their interests. Because the data about the sites that users are visiting is being used for purposes other than just serving ads on the Bigsearch Web site, Adnetwork cannot be considered an agent in this context. Adnetwork must create its own P3P policy and use its own policy reference file to indicate what content it applies to. In addition, Bigsearch may optionally use the HINT element in its policy reference file to indicate that the Adnetwork P3P policy reference file applies to these advertisements. Bigsearch should only do this if Adnetwork has told it what P3P policy applies to these advertisements and has agreed to notify Bigsearch if the policy reference needs to be changed.

Scenario 8: Web site busy.example.com uses cookies throughout its Web site. It discloses a cookie policy, separate from its regular P3P policy to cover these cookies. It uses the COOKIE-INCLUDE element in its policy reference file to declare the appropriate policy for these cookies. As a performance optimization, it also makes available a compact policy by sending a P3P header that includes this compact policy whenever it sets a cookie.

Scenario 9: Web site config.example.com provides a service in which they optimize various kinds of Web content based on each user's computer and Internet configuration. Users go to the Config Web site and answer questions about their computer, monitor, and Internet connection. Config encodes the responses and stores them in a cookie. Later, when the user is visiting Busy -- a  Web site that has contracted with Config -- whenever the browser requests content that can be optimized (certain images, audio files, etc.), Busy will redirect the user to Config, which will read the user's cookie, and deliver the appropriate content. In this case, Config should declare a privacy policy that describes the kinds of data collected and stored in its cookies, and how that data is used. It should use a COOKIE-INCLUDEelement in its  policy reference file to declare the policy for the cookies. It will probably reference Busy's P3P policy for the actual images or audio files delivered, as it is acting much like CDN acts in scenario 2. Busy will probably also use HINT elements in its policy reference file to reference the policy for the Config-delivered content.