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Re: Multi-Factor Authentication Concern
From: Jason Sewell <jsewell () mac com>
Date: Tue, 14 Aug 2007 10:05:14 -0400

I appreciate all of these responses.

The general consensus seems to be:

1) The system that "Bob" has implemented does not reflect multi- factor authentication as it is commonly defined, and 2) there may be some esoteric reason to require different people to provide different authentication factors to protect a single resource, but 3) such a convoluted access control mechanism is not appropriate for protection of our data center, and furthermore
4) accounting and logging are complicated by such a system.

However, what I still have not found yet is an authoritative document that I can point to and say "Bob, you're wrong". He's a hard-headed guy and responses from security experts on a mailing list won't convince him. I looked at all of the suggested links, including the Wikipedia article, and I cannot find anything that explicitly states that the factors in a multi-factor authentication system must all be from the same person.

So, I'll show him these response, and I'll continue to try to find an authoritative source for my assertion (or perhaps I'll edit the wikipedia article).

Thanks again everyone for you help!

On Aug 14, 2007, at 8:58 AM, Kevin Wilcox wrote:

Hash: SHA1

Mngadi, Simphiwe (SS) wrote:

All three are accountable; I don't see the logic in your hypothesis. in anyway authentication should be monitored, and your concern should have
been build-in into the security system.

All three *are* accountable and therein lies the problem - only *one* of
the individuals actually entered the data centre but it appears as if
all three of them entered. Authentication is not only a method for
authorization, it is a method of accounting for who accessed what
resources. Just because all three of them are authorized to be in the
data centre doesn't mean that any one of them should be able to gain
entry using the credentials of the other two. One of the things
multi-factor authentication attempts to address is the scenario where an individual can pass themselves off as someone else - basically ID theft.

Another scenario would be on-line banking. Suppose you and your business
partner have access to the same account. You decide to use web-based
banking. To access the account information you have to login using a
password then enter a PIN. To gain access to the account details you
would not login using your password then enter your partner's PIN - you would use *your* password and *your* PIN. Like the data centre scenario, just because more than one person has access to a resource doesn't mean
you allow authentication credentials from anyone with access - it
destroys the concept of accountability. Instead you require that all of the authentication credentials come from the same person so you know who
to hold accountable if something happens (and because it could be the
law in your vicinity).

That said, there *are* times when group level access may be desired and
a "piece of the key" from each person is acceptable (or required) - if
that is the case then the original question is moot.

I hate relying on hypothetical examples but it really does come down to
"what are you trying to accomplish with your authentication methods?"
and "what are the laws in your area?". If group accountability is your
goal then you can suffice with allowing credentials from anyone at any
stage in the process (just make sure you have other accountability
measures in place). If you want granular accountability at the
individual level then all of the credentials must come from the same

I hope that helps.

Version: GnuPG v1.4.7 (GNU/Linux)


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