Letting The Telecommuters Into The Network
Date: Dec 23, 2004
Locking down the network and patrolling the perimeter is a never-ending job. Still, it feels good to get through another shift on the Forbidden Planet without an invisible force penetrating your shield and setting off alarms. But there's a change: now, other humans want to work from their home worlds -- but by mind alone, over the computer screen. It's up to you to create for them a safe passage (one that won't have Robby the Robot all stirred up and carrying Anne Francis around like a rag doll) and to make sure the Krell don't come sneaking in, under the fence, behind the newcomers.
In other words, you need to let the right people into your network -- telecommuters and other people working remotely -- while continuing to protect the company from criminals. What to do?
The Number One Answer: A Sit-Down VPN
The answer that helps administrators sleep most securely is a fixed Virtual Private Network (VPN). A VPN uses end-to-end encryption to carve out a private tunnel over the public network.
The most secure VPN is the traditional arrangement with the telecommuter coming from a fixed site, ideally using a managed, corporate device, and terminating in a secure, private network on either side. Quite a bit of effort can go into setting up this arrangement; you need to see that hardware, software, and settings, as well as authentication, are set up perfectly and maintained on both ends, despite user changes to software, firmware, and hardware, but the security can be worth the trouble.
Don't let this next bit scare you away: After the act with all the acronyms, you'll have the secret of the monster sneaking past the alarms, and everything lightens up.
Let's throw out some protocols -- literally. There are three or four at this end of the pool. Only one from this group is secure enough to take seriously: IPSec, especially in conjunction with L2TP.
Sit-Down VPNs: IPSec
IPSec is the standard to buy; it encrypts at the packet level. PPTP has weak encryption keys, weak password hashing, and unauthenticated control traffic. L2TP traffic can be read by network sniffers, however, combined with IPSec for encryption, L2TP becomes unreadable, and offers IPSec authenticated access for multiple protocols. Just be sure the device you buy supports the combined IPSec and L2TP standard.
NOTE
For more on planning and troubleshooting a hardcore VPN -- the kind with special rigging on both ends -- take a look at two additional articles: Introductory VPNs: Mapping LANs and Lines for Fewer Landmines, and VPNs: Dial 'T' for Troubleshooting. (You didn't think we were going to spoil the secret of the monster from "Forbidden Planet," did you? No -- it's only the remote access that gets easier from here on out.)
VPNs-a-Go-Go: SSL
Maybe you have mobile employees without fixed access, who want to come in from a variety of sites. Salespeople are the typical example, as they may need to connect to your network from a hotel room or a customer site.
Things may actually be easier for them, depending on how much trust they request from your network. In recent years, Secure Sockets Layer (SSL) VPN appliances, such as those sold by Aventail and Juniper, have sprung onto the planet, and ask nothing of the visitor except an SSL-enabled browser: No software installation, no matching hardware. Remote users can come into the VPN from anyplace that has an SSL browser or kiosk.
The administrator manages access rights and authentication rites in advance, setting up different rules based on who the user is, how secure a "neighborhood" he's calling from, and so on. If he phones into the office from an airport kiosk, the user may not see those medical records he would get if he were calling from an approved device at home -- at least not if the administrator set things up correctly. You don't want the good doctor looking at your record from the airport, because he can forget to log out. "Hey, look at this, man." "Is this thing on?" Talk about letting in the rabble.
And therein lies the first of the security concerns with SSL VPNs. Another concern with SSL VPNs is the recent discovery that local desktop search engines cache and index SSL VPN sessions, even though the VPNs have tools to wipe their own caches. Some SSL VPN vendor tools are available to combat this new threat.
Microsoft Terminal Services
Microsoft Terminal Services lets users work on applications in thin client fashion from a remote location. Terminal Services, part of Windows' NT Server 4.0 Terminal Services Edition, Windows 2000, and .NET Server, is a time-honored institution at many shops with ID badges and telecommuters who sport authentication token fobs. They get a new password number each 30 seconds and type it, along with their login, whenever they need to get in. (That's just one way to authenticate, of course.)
When initially released, "Term Server," like its parent, Citrix WinFrame, from Citrix Systems, Inc., became an enticing way for many shops to let employees access applications remotely, and it remains so to this day. With the addition of Citrix' Secure ICA Services' 128-bit, end-to-end encryption, (not included) Term Server traffic becomes more secure. You have to think about what happens after that secure log-in.
It's Not the Aliens: Remote Control
Perhaps the easiest to set up, lowest-budget solution for telecommuter access is remote control software, such as Symantec's PC Anywhere. These packages allow the remote user to literally control the machine back at the office. VNC is an open source selection that runs on Windows, Mac, Linux, and other platforms; it can be more trouble and additional skills are required, but you only pay if it works.
Some remote control software, such as Netopia's Timbuktu Version 7, use non-standard encryption when sending copies of your screen over the Internet. Currently, Timbuktu uses a proprietary method to scramble bits and randomize parts of the screen. Experts advise against using home-grown encryption, as even well-known methods often fail to pass muster once put under scrutiny and, with a proprietary cipher, you're getting what Gramma called "a pig in a poke." (Netopia says it plans to employ an as-yet unannounced form of standard encryption in its next version of Timbuktu.)
Meanwhile, Altiris Inc.'s Carbon Copy uses 128-bit MD5 encryption during authentication only, and the MD5 collision weakness that came to light in 2004 shouldn't be a problem for Carbon Copy. However, Carbon Copy's data stream is guarded by a 64-bit proprietary encryption key for each packet sent. Users may define any key for authentication of the data stream -- presumably if they provide the key.
Symantec Corporation just announced PC Anywhere 11.5 with AES encryption (up to 256-bit cipher strength) for both authentication and the data stream. The new version of pcAnywhere also offers host address blocking, 13 different methods of authentication (including RSA SecurID authentication), the ability to specify TCP/IP addresses and subnets that are allowed to connect, and the option to hide pcAnywhere hosts from TCP/IP browse lists.
Check security specs before you buy, because these things change. Go to BugTraq and check the product name (in date order) for security reports.
Also, make sure you can blank the screen in the office so telecommuters don't have an audience watching what they're doing from home.
The Important Things
Before you open the gates of your compound to your fellow humans, here are some final words of advice on keeping out the slathering monsters beyond the walls:
The lamest dual-mode authentication beats the slickest new trick. So take back the link to the national nose-print database if it isn't integrated with strong password protection.
If your troops are going to work on the road, talk to them about physical notebook security.
If your users are working at home, put something in the six-month memo about the safest place for storing passwords: in their heads! They are guardians of your network now.