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Re: Multi-Factor Authentication Concern
From: Mike Lococo <mike.lococo () nyu edu>
Date: Tue, 14 Aug 2007 14:58:40 -0400

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.

Because authentication is, by definition, the process of verifying an
asserted identity (that statement is easy to find references for,
including the wikipedia article on authentication).  An access control
system must authenticate _each_ identity separately, even when several
identities are involved in a single transaction and even if the process
is streamlined to 'feel' as though it's a single action.  As you're
thinking and speaking about this, remember the difference between
identification, authentication, and authorization.

1) Identification:  Your identity is your username in the system.  You
may have to say it, or type it, or it may be inferred from a retinal
scan or whatever.  As a basic access control principle, every individual
must have an identity.  Anytime you're accepting credentials from more
than one individual, you are _by_definition_ performing more than one

2) Authentication:  An identity is authenticated via password, or
voiceprint, or token, or whatever.  If only one type is required, it's
single factor.  If more than one type is required, it's multi-factor.
If more than one type is available (you have a token and a password),
but either is sufficient (you can log in with your password even if you
lost the token), it's still single factor... you just have options.

3) Authorization:  Once you are authenticated, you may or may not be
_authorized_ to access the resource you're interested in.  If a system
requires more than one user to authenticate in order authorize an
action, it implements split-authentication or split-authorization (often
referred to in the context of passwords/pins as split-knowledge).  Each
identity is still authenticated individually, but more than one is
required before any are authorized.

You're talking about multi-factor authentication.  Your friend is
talking about split-knowledge/authentication/authorization.  No
authoritative source on IDM or access-control is going to talk about
whether multi-factor authentication involves multiple identities because
it's well-established that all authentication schemes have as their
basic goal the verification of a single asserted identity.
Authorization schemes exist that require multiple identities to be
involved in a single transaction (nukes and expensive safe-deposit boxes
work this way), but each is always authenticated individually.

Mike Lococo

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