RE: one-time password (OTP) authentication

[maburns () safenet-inc com]

Regardless of saving the money on a two factor USB token that range from for
$29-$55 I think this approach mentioned is so insecure..." The administrator
prints off a list of one-time passwords and delivers a hard-copy via
physical medium (fax, phone, snail-mail, person-to-person handoff)"

The power of two-factor authentication is that Nothing is written down which
is part of the reason passwords are so insecure

Two-factor authentication is   1) "something physical only the user has" -
like an USB Key which is the same as a ATM card and 2) a "pin # that only
user knows" . This is not difficult to implement there are SDK's available
and users trust their ATM cards so making the jump to a USB token would not
be too difficult

Mary Ann

-----Original Message-----
From: james [mailto:james () tlhenterprises net] 
Sent: Saturday, June 18, 2005 9:16 PM
To: webappsec () securityfocus com
Subject: one-time password (OTP) authentication

Two-factor authentication (authenticating user with something they know AND
something they possess) is becoming more and more popular due to increasing
security requirements and the prevalence of spyware software.  However, in
open source projects, solutions such as RSA securID, smartcards, etc. are
not always feasible because of funding, licensing, or other constraints.
Here is a complete, standards-based, open source, no-hardware solution.
Here is a PHP implementation for generating, challenging, and authenticating
one-time passwords according to RFC 2289.  (go to
http://www.dcphp.com/Developers/files/otp_pub.zip
to download)  Below are two scenarious for OTP use. 

Scenario A: 
Users across an organization need access to corporate resources at home, on
the road, in airplanes, etc.  Users are many (>1000) and geographically
distributed.  A user applies for access and is approved.  The administrator
prints off a list of one-time passwords and delivers a hard-copy via
physical medium (fax, phone, snail-mail, person-to-person handoff). 

Scenario B: 
Users self-register for a commercial (or other) website.  Once successfully
registered, the user is given the option to generate a list of one-time
passwords and use them for authentication in addition to their
username/password (of course, user can ignore OTP from certain trusted
computers, such as the one they registered from, if they trust it).  The
user can generate new OTP's at any time once authenticated. 



When the user logs in, they use their username,password, and a
one-time-password (which one depends on which one they are prompted for by
the server).  The OTP expires immediately upon authentication.  Now, if a
hacker intercepts all three tokens, they are still unable to perform a
replay attack because the third token is already invalidated.  Their is a
race condition if they are watching real-time, but this can be accounted for
via transaction locking in the session handling code. 


--
the brown cow
--