Triển khai phương thức chứng thực bảo mật mật nhất cho wireless(English)

Triển khai phương thức chứng thực bảo mật mật nhất cho wireless

Takeaway: Enterprise wireless LAN security is a persistent concern for every system administrator and CIO. This article, part of the TechRepublic ultimate guide to enterprise wireless LAN security, describes how to configure Microsoft's IAS RADIUS server, provided free with Windows Server 20003, for wireless authentication.


The complete TechRepublic Ultimate Wireless Security Guide is available as a download in PDF form.

Windows Server 2003 comes bundled with a very capable RADIUS (also known as AAA) server that's extremely stable, secure, and robust. When you search on Internet security databases for Microsoft IAS vulnerabilities, you won't find any. The IAS service just runs for years without the need to patch IAS. If your Windows Server 2003 box is hardened to only accept IAS requests with host-based firewall restrictions on all other ports and you install no other services on a Windows 2003 box, you can literally keep an IAS RADIUS server up for years of zero downtime or reboots.
IAS competitors

One of IAS' biggest competitors in the Enterprise market is Cisco ACS which people often assume they must use if they're using Cisco networking equipment which simply isn't true. Your Cisco network equipment works perfectly fine so long as you avoid proprietary, less-secure harder-to-deploy protocols, like LEAP or EAP-FAST.
Furthermore, the stability of ACS is questionable and there is an endless patch cycle for it since it has been plagued with security vulnerabilities and bugs. I've spent my share of time troubleshooting ACS and many hours on tech support. I have had a lot of hands-on experience with Cisco ACS. The latest version of Cisco ACS 4.x currently has two unpatched security vulnerabilities one of which is critical. Version 3.x and 2.x also have their share of critical vulnerabilities some of which are unpatched as of December 10, 2006.
Cisco ACS also lacks the ability to act as a relay RADIUS server which limits its ability to serve in a more robust multi-tier RADIUS environment. You need that ability to link to multiple Active Directories or other user directories that are not tied to each other. ACS also costs around $8000 per copy whereas Microsoft IAS comes with Windows Server 2003. Two redundant RADIUS servers would add up pretty quickly. Cisco ACS also comes on a dedicated appliance but that's even harder to use in my experience since you don't even get a Windows console graphical interface to work with.
Funk software (acquired by Juniper) has a pretty good solution with Steel-belted RADIUS at around $4000 per copy but that is still a significant cost especially when you need two RADIUS servers for redundancy. Funk is a great solution for companies which don't run a Windows Active Directory environment because IAS is tightly wound in to Microsoft Active Directory and doesn't support non-Microsoft databases.
Linux users have FreeRADIUS available to them. FreeRADIUS has had critical flaws (0.x and 1.x) in the past but they're all patched now unlike Cisco. FreeRADIUS still isn't as clean as the Funk or Microsoft RADIUS solutions but it's completely free if you're rolling your own Linux distribution or you don't need enterprise Linux support. If you're talking about SuSE or Red Hat and you want enterprise support, then the annual support contracts is double the cost of a perpetual Windows Server 2003 license. It all depends on usage model and some people will prefer Linux and some will prefer Microsoft.
Install IAS

Windows Server 2003 doesn't come with any extra services installed by default for security reasons so you'll need to manually install IAS. It's fairly simple if you have the Windows Server 2003 install CD. To install IAS, simply open "Add remove programs" from your control panel and select "Add remove windows components". You will see the following window (Figure OO) so you'll need to scroll down to "Network Services". You don't want to just check it because you don't want all Network Services installed, just highlight it and hit the "Details" button.
Figure OO
Networking services Once you get to the screen shown in Figure PP, scroll down and just check off "Internet Authentication Service" IAS for short.
Figure PP
Internet Authentication Once you've installed IAS, you'll be able to launch IAS from your Administrative Tools either from the control panel or from the start menu. You'll see the following interface. (Figure QQ)
Figure QQ
Service
Set logging policies

The first thing we'll do is look at and set the logging policies (Figure RR). Right click on "Internet Authentication Service (Local)" and click Properties.
Figure RR
IAS Properties You will now see the screen in Figure SS. If you check off the two checkmarks here, you will force IAS to log successful and reject authentication requests to the Windows Event Viewer. If you're intending to use text or SQL based logging, you don't need to check these unless you want the logs showing up in both places.
Figure SS
Local Properties If you click on the "Ports" tab, you'll see the screen shown in Listing TT. These are the default RADIUS ports and you should generally leave them alone for standardized RADIUS conventions. Microsoft IAS will actually listen on two sets of ports. The lower number ports are the more traditional port numbers, Microsoft applications prefer the higher number ports. You should generally leave this setting alone as is.
Listing TT
Ports This next part lets you set the standalone text and SQL logging capability of Microsoft IAS. You right click on "Local File" under "Remote Access Logging" page and hit "Properties". (Figure UU)
Figure UU
Remote Access Logging The first "settings" tab lets you set what events you want to log. (Figure VV)
Figure VV
Local file properties The "Log File" tab lets you set the file format and the log size limits. (Figure WW)
Figure WW
Log file We won't go in to SQL logging in this article because it gets rather complex to set up a SQL database. You have to manually create the accounts and tables in SQL in order for this to work. Furthermore, IAS under Windows Server 2003 insists on stopping the RADIUS service if logging doesn't work so if the SQL server doesn't respond, all of your RADIUS servers stop working. Unfortunately, Microsoft doesn't give you any way to override this "fail-shut" behavior because they claim customers want it this way because it's more secure but every customer I've talked to wants a choice on this behavior.
There is no security risk because the Authentication and Authorization component of Microsoft IAS is working perfectly fine, it's merely unable to make a record of the transaction. I've spoken with Microsoft and they're telling me they will correct this with Windows Server 2007 (or whatever it's going to be called when it's released next year). Hopefully they'll automate the SQL database creation process with a script too.
Add RADIUS clients

A RADIUS "client" is not what you would typically think of as a "client" as in a user. A RADIUS client is something like a wireless access point, a router, a switch, a firewall, or a VPN concentrator. Any device that provides network access that needs to delegate AAA (Access, Authorization, and Accounting) to a RADIUS server is considered a RADIUS client. For the purpose of this tutorial, we'll set up a single access point as a client.
To start, we'll right click on "RADIUS Clients" and select "New RADIUS Client" as shown in Figure XX.
Figure XX
Radius Client You then get the screen shown in Figure YY where we give the device its name and set the IP address of the access device which in this case is an access point. Be aware that if you're talking about a router or firewall that has multiple IP addresses because it has multiple interfaces, you must configure the IP address that is closes to the RADIUS server. This is because the RADIUS request is seen as coming from the closest interface on a multi-homed access device and if you configure the wrong IP, it will not be able to communicate with the RADIUS server.
Figure YY
New RADIUS client name and IP Then we set the RADIUS type and RADIUS secret. The RADIUS type is almost always set to "RADIUS Standard". Cisco devices are the exception and you must select "Cisco" for the "Client-Vendor" field if you want your Cisco devices to work. There are exceptions like Cisco wireless switches because the switches were acquired from Airespace in 2005.
Airespace wireless switches use "RADIUS Standard" like everyone else in the industry. The "shared secret" is the secret shared between the RADIUS server and the access device (Figure ZZ). Try to make the secret 10 characters or more comprised of random numbers and letters. Avoid spaces and special characters since that might have incompatibilities in some devices and software and you'll have a rough time troubleshooting.
Figure ZZ
Setting the shared secret Click "Finish" to complete. You'll need to repeat this for all of your access devices.
Add remote access policies

Now we need to create a remote access policy to authenticate and authorize the user trying to access our access devices. To do this, right click on "Remote Access Policies" and click "New Remote Access Policy". (Figure AAA)
Figure AAA
New Remote Access Policy Click "Next" to move to the next screen (Figure BBB).
Figure BBB
Policy Wizard Give your policy a name and use the wizard. Hit "Next". (Figure CCC)
Figure CCC
Policy Name Choose "Wireless" and hit "Next". (Figure DDD)
Figure DDD
Wireless Here you'll need to grant access to your users and computers. Hit "Add". (Figure EEE)
Figure EEE
Group Access Here you'll need to adjust the location to your domain. Hit "Locations". (Figure FFF)
Figure FFF
Select Groups Choose the domain you're trying to authenticate to and hit "Ok". Note that the IAS server must be joined to the domain you're authenticating to or a trusted domain. (Figure GGG)
Figure GGG
Select Location Type "Domain Users" and "Domain Computers and separate them with a semicolon. (Figure HHH) Then click on "Check Names" to force it to underline and validate your entries. You may of course restrict access to a smaller group of users and computers since the following option allows all domain users and all domain computers to connect to your wireless LAN. Hit "Ok".
Figure HHH
Enter domain Note that "Domain Computers" is used to authenticate your computer for "machine authentication" which connects your wireless PC before the user even logs in. This is a very useful and unique benefit of the Windows Wireless Client since it emulates the full wired experience for wireless users.
If "machine authentication" isn't implemented, group policies and login scripts won't fire off. Furthermore, only cached users can login to the wireless computer, because users who have never signed on to that PC can't authenticate with the domain. For this reason alone is enough for me to always recommend using the Windows Wireless client for Windows users not to mention the auto-deployment capability.
Now you see the screen shown in Figure III with a summary of the user and computer groups you're allowing access. Note that this is an OR operator between these two group names. Either one true registers a success. Hit "Next".
Figure III
Group access defined Choose "Protected EAP (PEAP)" authentication. Then hit "Configure". (Figure JJJ)
Figure JJJ
Authentication Before you get to this page, you must either have a valid Machine Certificate from a Certificate Authority or you have already self-signed one yourself. Leave the rest of the settings like you see in Figure KKK and click OK.
Figure KKK
PEAP Properties Finalize the remaining dialog box and you're finished making a new wireless authentication profile. Now we'll move on to fine tuning the configuration.
Tweak remote access policies

Once you complete the previous steps, you'll see a new Remote Access Policy called whatever name you gave it. The two default policies you see in Figure LLL the one we created are just there as samples and are disabled by default. We'll right click on it and hit "Properties".
Figure LLL
Remote Access Properties You'll notice there are two "Policy conditions" shown in Figure MMM. Note that there is an AND operator operating between the two conditions. That means both conditions must be true or else the policy spits out a rejection and it moves on to the next "Remote Access Policy". The first policy forces "Wi-Fi Policy" to only permit users coming in from 802.11 connections. The second policy is the permissible user or computer groups we set earlier. Click on "Edit Profile" to continue.
Figure MMM
WiFi Policy Properties The "Dial-in Constraints" tab lets you set the dial-in and session limit restrictions (Figure NNN). It also lets you restrict the times people are allowed to log in.
Figure NNN
Dial-in Profile The "Encryption" tab is important for security (Figure OOO). You must uncheck the three insecure checkmarks to enforce maximum strength encryption.
Figure OOO
Encryption The "Advanced" tab (Figure PPP) is something we won't go in to now, but note that this is a very powerful tab for advanced features. With special RADIUS attributes configured on this page, you can do things like tell your Cisco VPN concentrator what user group a user belongs to so that the concentrator will set VLAN and firewall policies on that user matching their group rights. You can also do things like set VLANs or group association for an Aruba wireless switch which has a built-in firewall. We'll leave the details for a future advanced RADIUS configuration article.
Figure PPP
Advanced tab Under the "Authentication" tab, you can tweak the EAP methods (Figure QQQ). For wireless LAN PEAP authentication, you actually leave all the checkmarks alone. These settings are for more traditional RADIUS applications like a modem dialup service provider that proxies to your RADIUS server. Let's click on the "EAP Methods" button to see what it has.
Figure QQQ
Authentication Here you can edit the PEAP configuration. (Figure RRR) We already set these settings during the initial policy wizard. Click "OK".
Figure RRR
EAP Providers You'll need to click OK one more time to get out of the Dial-in profile window.
This final section in the IAS interface is something we won't do in this article. (Figure SSS) I just wanted to give you a preview of what it does. The "Connection Request Processing" section lets you set advanced RADIUS relaying features. You have granular control of what kind of RADIUS requests you want to relay off to a different RADIUS server and which RADIUS requests you want to handle in the local "Remote Access Policy" engine.
You can even configure groups of RADIUS servers that you want to forward to. This allows IAS to participate in a multi-tier RADIUS environment. For example, if you have a user that isn't in your domain belonging to a business partner's network that needs guest access to your environment, you can forward to the RADIUS request to your business partner for them to process. There are even Universities that honor each other's students and staff by allowing a student to securely log in to any campus participating in the network.
Figure SSS
Connection Request Backup and restore IAS policy

Finally, after all this work we want to be able to backup our RADIUS configuration and maybe even restore it on to a redundant RADIUS server. Microsoft gives you a simple command line tool for exporting and importing the RADIUS configuration.
To perform the backup operation, simply run the following command.
netsh aaaa show config c:\IAS.txt Note that you can use any name for the file. You can use that file locally if you ever screw up the IAS configuration and you want to rapidly recover or if you want to copy the IAS setting to another IAS RADIUS server. To restore the IAS settings from the text file you created, simply run the following command assuming the correct path and file name.
netsh exec c:\IAS.txt This makes it easy to rapidly deploy multiple redundant IAS RADIUS servers and it also gives you the peace of mind to rapidly repair an IAS server.


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