Home > Articles > Security > Network Security

This chapter is from the book

Types of Proxies

Proxies can be used for several purposes. The classic use is as a proxy firewall located on the perimeter between the Internet and your private network. Proxies are not limited to this role though. Proxies can be used to accelerate web performance, provide remote access to internal servers, and provide anonymity for network conversations. In this section, we will highlight these other uses that can be made of proxy technology.

Web Proxies

Proxies are not just used to implement firewalls. One of their most popular uses inside a network is increasing web performance. Web conversations make up a large percentage of the traffic on many networks, so making the Web more efficient can have a dramatic impact on network operations. Proxies can help by monitoring web conversations and eliminating redundant requests. Web traffic is often characterized by frequent transmissions of nearly identical information. Some studies have shown that as much as half the requests for information across the Web are duplicates of other recent requests. Caching frequently requested web pages can dramatically speed up web browsing.

Proxy servers that provide web caching are often referred to as proxy caches or web caches. When a proxy cache is used, browsers are directed to make their HTTP requests to the proxy cache instead of directly to the destination web server (see Figure 4.3). The proxy then has the opportunity to determine whether it already has a copy of the requested information or if it needs to request a copy from the destination server. If the HTTP request is new, the proxy will make a TCP connection and HTTP request to the destination server, returning the resulting information to the browser and also storing a copy of the returned result for future use. Whenever any client of the proxy requests the same information, the proxy can reply using its local copy, eliminating the need to make a request from the destination server. This reduces network traffic as well as the load on the web server. However, it can introduce problems.

Caching works best when the information being retrieved does not change rapidly. However, some information is very time sensitive, such as stock quotes. This can cause problems if the client receives old information from the cache, when newer, more relevant data is available on the web server. The term for this is freshness. A file is "fresh" if the version on the cache is the same as the version on the web server. Web servers can specify when a file should no longer be considered fresh by placing an "Expires:" header in the returned request. This tells any caches being used (whether proxy or browser based) when to discard the file and request a new one. Many web servers do not provide good expiration guidance though. Because of this, it is important during the configuration of a proxy cache to establish good freshness policies.

Figure

Figure 4.3 Web caches accelerate performance by eliminating unnecessary server requests.

Freshness policies are normally developed using several values associated with the file. The most important, if supplied by the web server, is the "Expires:" field. This field is part of the HTTP protocol and, if configured by the web administrator, is provided in the server's response to a browser request. It allows the website to provide specific guidance concerning when a file should be disregarded. When this information is not available, though, the web proxy server will need to look at other data to make a freshness decision. One simple method would be to set a fixed time to cache all files that lack "Expires:" headers. The problem with this approach is that many sites with dynamic content that do not support "Expires:" will not work correctly when cached. A better approach is to use the age of the file to determine how long to cache. If a file is received that is seconds old, you might not want to cache it because it is much more likely that it was dynamically generated. A file that is weeks old, though, is much less likely to change while its copy is held in the cache. Even with files that have not been modified for a long time, it is still a good idea to periodically refresh the cached files, so most web proxy servers set a maximum time a file can be considered fresh.

Another benefit that can be gained through web proxies is control over where users can browse. Security and productivity can be increased by limiting access to non-organization-related web browsing. It is not uncommon for viruses, worms, and other types of malicious code to be introduced into a protected network based on files downloaded by users from inappropriate websites. By limiting what sites users can reach, you can decrease the chance that this will happen to your network. Placing restrictions on browsing has also been shown to increase productivity by taking away the temptation to spend excessive time surfing the Web. However, not all organizations will want to or be able to place restrictions on user web behavior. Before considering web filtering, you must examine your site's policies and procedures regarding user web access. Often your Human Resources and Legal departments will need to be involved.

One last item to discuss with web proxies is the logging they can provide. As we showed earlier with RingZero, proxy logging can be very useful in detecting malicious activity on your network. With a web proxy, all the URLs that browsers request can be used for intrusion analysis. Looking for requests that do not appear normal can be a powerful method to discover attacks against your network. Often your proxy logs will contain the first indications that your network is under attack. Things to look for include excessive requests for files that do not exist on your web servers (such as those that return 404 errors). This can indicate that someone is scanning your websites looking for vulnerable software. Also looking for excessively long URL requests, or requests that contain special characters, can indicate that someone is attacking your site. If you do discover that someone has successfully attacked your site, these logs can also be invaluable at discovering what weakness led to the compromise, how extensive the damage is, and (rarely) who is responsible.

Reverse Proxies

Firewalls are frequently thought of as devices that restrict access, not enable it. However, proxy techniques can be used for both. If you have a need to support remote Internet users, reverse proxies can be the answer.

Reverse proxies are used to provide controlled access for external (normally Internet-based) users to internal servers. They act as a trusted intermediary that external users must use to gain access to internal servers that would not normally be Internet accessible. An external user attempting to gain access to an internal server first connects and authenticates to the reverse proxy. Normally this is done over a Secure Sockets Layer (SSL) connection to provide confidentiality and integrity for the session. If authentication is successful, the proxy will check its policy to see whether the user is allowed to access the requested server. If so, it will begin proxying the connection for the user.

The type of internal servers that can be accessed using a reverse proxy vary depending on the sophistication of the proxy. Simple reverse proxies can only support web-based services. These products are basically normal web proxies that have been enhanced to support user authentication. In many cases, they are sufficient because many sites provide a significant amount of their network content using web systems. If you are trying to grant access to other applications that do not have a web interface, you may need to work harder.

One approach is placing a web interface on top of the application you are trying to proxy. Once the application is web enabled, normal reverse proxy techniques can be used to grant remote access. An example of this is Microsoft's Outlook Web Access (OWA). OWA is part of Microsoft Exchange and provides a web version of the Outlook mail and calendaring application. Any clients who can make a web connection to the OWA application will be able to use most Outlook functions. In fact, it can be difficult to recognize that you're accessing Outlook through a browser because the interface you are interacting with inside the browser so closely resembles the desktop version of Outlook. OWA combined with a reverse proxy provides a secure mail and calendaring solution for remote users.

Alternatively, you can roll the web-enabling technology together with a reverse proxy. This is the approach taken by Citrix MetaFrame. Citrix allows common desktop and server applications to be accessed by web browsers, including applications such as Microsoft Word and Adobe Acrobat. In fact, Citrix can proxy an entire user desktop through a browser, giving a user experience that is highly similar to sitting in front of the actual computer. Citrix also provides extensive management controls, including role-based access to internal applications. Although a capable product, it is not necessarily cheap and simple to implement. If you're considering technologies such as Citrix, make sure to include acquisition and operational costs in your analysis. In some cases, though, Citrix-like products can actually save you money by allowing shared access to products too expensive to place on every user's desktop.

Anonymizing Proxies

Privacy can be an important security service but can be a hard commodity to come by on the Internet. Almost all actions taken on a computer leave a digital trail. If you don't want someone else following that digital trail back to you, an anonymizing proxy may be the answer.

Anonymizing proxies work exactly like normal proxies, but are used for the purpose of protecting your identity while you use services across the Internet. Your requests are forwarded to the anonymizing proxy (usually over an SSL connection), which hides your identifying details (such as IP address) by making the request on your behalf. The destination server you are using only learns about the proxy's information and does not learn who actually made the request. This assumes that you do not pass anything identifying in the actual request.

Also assumed is that no one is monitoring the anonymizing proxy. If they were, they might be able to match incoming requests to outgoing requests, breaching an important aspect of the connection's privacy. This is especially easy to do if the proxy is not busy. If yours is the only IP address connected to the proxy, it's not terribly hard to guess who it is making requests through the proxy!

Various approaches have been used to solve this problem. One of the most popular is proxy chaining. Tools such as SocksChain (http://www.ufasoft.com/socks) can be used to build connections through multiple anonymizing proxies. An observer at the first proxy in the chain will only see that you are sending a request to the anonymizer, but will not learn the destination because the next hop will only be another anonymizer. In this way, the ultimate destination of your request is hidden from any outside observers (see Figure 4.4). Another approach along the same lines is Onion routing (http://www.onion-router.net), which combines proxy chaining with multiple layers of encryption to ensure that a conversation cannot be followed through the proxy nodes.

Figure

Figure 4.4 Proxy chains allow private communications by hiding the true source and destination of a packet from network eavesdroppers.

If you are in need of an anonymizer service, but do not want to set your own up, preexisting services are available on the Internet. Searching on Google for "anonymizers" will return many sites offering this privacy service. However, caveat emptor: You should trust that they maintain your privacy slightly less than you trust them.

A perfect case in point is the Java Anonymous Proxy (JAP). JAP is a anonymizer service run as a joint effort of the Dresden University of Berlin, the Free University of Berlin, and the Independent Centre for Privacy Protection, Schleswig-Holstein, Germain. It is available at http://anon.inf.tu-dresden.de/index_en.html. Back in July of 2003, it was discovered that they had, as a result of a court order, added code to JAP that was designed to monitor access to certain IP addresses. Whenever a user of the service accessed one of these forbidden sites, a message was generated recording the who, what, and when and sent to the police. This hidden behavior was uncovered several days later by an observant user of the service, but until this discovery was made, users of the JAP service were getting less privacy than they thought. For the record, the current version of JAP is supposed to be free of any tattle-tail code.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020