I can see a number of problems with using mobile phones as a second channel for authentication:
1. It begs the question of tamper resistant hardware. Unless the phone contains a tamper resistant serial number or key, it is relatively easy to clone. And cell phones are merging with PDAs. If you have secure storage, why not implement a local solution on the PDA side? 2. Even if the phone is tamperproof, SMS messages can be intercepted. I can imagine a man-in-the-middle attack where the attacker cuts the user off after getting the SMS message, before the user has a chance to enter their code. 3. Cell phones don't work everywhere. Geographic coverage is limited. Most U.S. phones don't work overseas. Reception can fail inside buildings and cell phone use is prohibited on commercial airplanes in-flight (the airlines are planning to offer Internet access in the near future). And what happens if I choose to TEMPEST shield my facility? 4. The cell phone network can get clogged in times of high stress, e.g. a snow storm at rush hour, a natural disaster or a terrorist incident. Presumably some people who use two factor authentication have important work to do. Do you want them to be locked out of their computers at such critical times? 5. Cell phones are vulnerable to denial of service attacks. A simple RF jammer could prevent an individual or an entire building from accessing their computers. 6. People are generally cavalier about their cell phones. They wear them on belt pouches, leave them in cars and gym lockers, let strangers borrow them. I left mine in a coat pocket that I checked at a restaurant and ended up with a $40 long distance bill. Habits like that are hard to change. On the other hand, a token that goes on a key chain or is worn as jewelry taps into more security conscious cultural behavior. Human factors are usually the weak link in security, so such considerations are important. 7. It's a tax on logins. SMS messages aren't free. 8. If I lose my token, I can use my cell phone to report it promptly. If I lose my cell phone... 9. Improved technology should make authentication tokens even more attractive. For one thing they can be made very small and waterproof. Connection modes like USB and Bluetooth can eliminate the need to type in a code, or allow the PIN to be entered directly into the token (my preference). 10. There is room for more innovative tokens. Imagine a finger ring that detects body heat and pulse and knows if it has removed. It could then refuse to work, emit a distress code when next used or simply require an additional authentication step to be reactivated. Even implants are feasible. Arnold Reinhold At 8:56 AM -0700 10/9/02, Ed Gerck wrote: >Tamper-resistant hardware is out, second channel with remote source is in. >Trust can be induced this way too, and better. There is no need for >PRNG in plain >view, no seed value known. Delay time of 60 seconds (or more) is fine because >each one-time code applies only to one page served. > >Please take a look at: >http://www.rsasecurity.com/products/mobile/datasheets/SIDMOB_DS_0802.pdf > >and http://nma.com/zsentry/ > >Microsoft's move is good, RSA gets a good ride too, and the door may open >for a standards-based two-channel authentication method. > >Cheers, >Ed Gerck > >"Roy M.Silvernail" wrote: > >> On Tuesday 08 October 2002 10:11 pm, it was said: >> >> > Microsoft marries RSA Security to Windows >> > http://www.theregister.co.uk/content/55/27499.html >> >> [...] >> >> > The first initiatives will centre on Microsoft's licensing of RSA SecurID >> > two-factor authentication software and RSA Security's >>development of an RSA >> > SecurID Software Token for Pocket PC. >> >> And here, I thought that a portion of the security embodied in a SecurID >> token was the fact that it was a tamper-resistant, independent piece of >> hardware. Now M$ wants to put the PRNG out in plain view, along with its > > seed value. This cherry is just begging to be picked by some blackhat, > > probably exploiting a hole in Pocket Outlook. >> > --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
