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RE: Multi-Factor Authentication Concern
From: "Mngadi, Simphiwe (SS)" <Simphiwe.Mngadi () sasol com>
Date: Wed, 15 Aug 2007 14:13:04 +0200


-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com]
On Behalf Of Jason Sewell
Sent: 14 August 2007 16:05 PM
To: security-basics () securityfocus com
Subject: Re: Multi-Factor Authentication Concern

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  
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  

Another scenario would be on-line banking. Suppose you and your  
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 -  
would use *your* password and *your* PIN. Like the data centre  
just because more than one person has access to a resource doesn't  
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  
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.

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